Air Tractor Maintenance Page 2-i

AT-802/802A June 21, 2018

TABLE OF CONTENTS
SECTION 2 – MAINTENANCE
Page No.

INTRODUCTION .............................................................................................................................2-1

AMSAFE AIRBAG SYSTEM ...........................................................................................................2-1

AILERONS AND FLAPS .................................................................................................................2-1

Ailerons..................................................................................................................................2-1

Aileron Boost Tab Trim and Rigging .....................................................................................2-2

Flaps .....................................................................................................................................2-3

Flap Removal ..............................................................................................................2-3

Flap Installation ...........................................................................................................2-4

Aileron and Flap Rigging .......................................................................................................2-4

Rudder-Aileron Interconnect System Rigging .......................................................................2-4

Aileron and Flap Bellcranks and Supports ............................................................................2-7

Flap-Elevator Interconnect System Rigging ..........................................................................2-8

Flap Actuator .......................................................................................................................2-10

Flap Actuator Troubleshooting ............................................................................................2-11

Flap Motor Troubleshooting ................................................................................................2-11

Flap Actuator Removal Instructions ....................................................................................2-12

Flap Actuator Installation Instructions .................................................................................2-13

Flap Relay Troubleshooting ................................................................................................2-13

ENGINE DRIVEN AIR CONDITIONER ........................................................................................2-15

Cautionary Information ........................................................................................................2-16

R134a Information ...............................................................................................................2-16

Application Specifications....................................................................................................2-18

Diagnosis Confirmation of Compressor Failure ..................................................................2-18

Compressor Repair .............................................................................................................2-22

Compressor Replacement...................................................................................................2-26

Service Procedures .............................................................................................................2-27

Common Causes of Compressor Failure ............................................................................2-32

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TABLE OF CONTENTS
SECTION 2 - MAINTENANCE
(Continued)
Page No.

AVIONICS ...................................................................................................................................2-33

BATTERIES ..................................................................................................................................2-33

Battery Removal and Replacement ....................................................................................2-34

Checking the Batteries ........................................................................................................2-34

Installing a New Gill Dry-Charged Battery ...........................................................................2-35

BRAKES ...................................................................................................................................2-36

Brake Removal and Installation ..........................................................................................2-36

Brake Discs .........................................................................................................................2-37

Brake Linings .......................................................................................................................2-37

Brake Master-Cylinders .......................................................................................................2-37

Brake Bleeding ....................................................................................................................2-37

Parking Brakes ....................................................................................................................2-38

COCKPIT CONTROLS .................................................................................................................2-39

ELECTRICAL SYSTEM ................................................................................................................2-40

General ................................................................................................................................2-40

Starter/Generator ................................................................................................................2-40

Voltage Regulator ................................................................................................................2-40

Engine Instruments .............................................................................................................2-40

Voltmeter .............................................................................................................................2-41

Low-Voltage Warning Light .................................................................................................2-41

Engine Overspeed Solenoid................................................................................................2-41

Boost Pump .........................................................................................................................2-41

Fuel Gauging .......................................................................................................................2-41

Wing Flaps ..........................................................................................................................2-42

Stall-Warning Horn ..............................................................................................................2-42

Windshield Washer .............................................................................................................2-42

Windshield Wiper ................................................................................................................2-42

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TABLE OF CONTENTS
SECTION 2 - MAINTENANCE
(Continued)
Page No.

Cockpit Lighting ...................................................................................................................2-42

Flap Light .............................................................................................................................2-42

Position and Strobe Lighting ...............................................................................................2-42

Taxi Lights ...........................................................................................................................2-43

Night Working Lights ...........................................................................................................2-43

Lighting System Troubleshooting ........................................................................................2-43

Electronic Instrument Light Dimmer ....................................................................2-43

Troubleshooting ..................................................................................................2-43

Hopper Quantity Gauges.....................................................................................................2-44

Oil Cooler Blower ................................................................................................................2-45

Air Conditioner - Engine Powered .......................................................................................2-45

ELECTRONIC STARTING AND CHARGING SYSTEM THEORY OF OPERATION ..................2-46

Generator Mode ..................................................................................................................2-46

Line Contact Relay (LCR) Control .......................................................................................2-46

Reverse Current Protection .................................................................................................2-46

Overvoltage (OV) Protection ...............................................................................................2-46

Charging System Troubleshooting Guide ...........................................................................2-46

General Considerations .............................................................................................2-46

Equipment..................................................................................................................2-47

Troubleshooting Procedures .....................................................................................2-47

ENGINE MAINTENANCE .............................................................................................................2-49

Cleaning Engine Exterior.....................................................................................................2-50

Fuel Requirements ..............................................................................................................2-50

Fuel Filter Cleaning .............................................................................................................2-51

Fuel Header Tank Sump Draining .......................................................................................2-51

Negative Fuel Pressure Warning ........................................................................................2-51

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TABLE OF CONTENTS
SECTION 2 - MAINTENANCE
(Continued)
Page No.

Fuel Nozzle Cleaning ..........................................................................................................2-51

Oil Requirements .................................................................................................................2-52

Oil Filter ...............................................................................................................................2-53

Chip Detector ......................................................................................................................2-53

Air Filters .............................................................................................................................2-53

Engine-Control Cables ........................................................................................................2-54

Engine Rigging Procedures ................................................................................................2-54

Power Lever ..............................................................................................................2-54

Propeller Lever ..........................................................................................................2-55

Start Control ..............................................................................................................2-55

Compressor Washes ...........................................................................................................2-55

Engine Starting Procedures ................................................................................................2-56

Ground Run Procedures .....................................................................................................2-57

FIN AND RUDDER .......................................................................................................................2-58

Vertical Fin ..........................................................................................................................2-58

Rudder .................................................................................................................................2-58

Rudder Controls ..................................................................................................................2-59

Rudder Trim Tab .................................................................................................................2-59

Rudder Trim Controls ..........................................................................................................2-60

FIRE RETARDANT DISPERSAL SYSTEM (FRDS) ....................................................................2-60

FUEL SYSTEM .............................................................................................................................2-60

Fuel Tanks ...........................................................................................................................2-60

Fuel Tank Sealing ...............................................................................................................2-60

Fuel Tank Senders ..............................................................................................................2-61

Fuel Tank Receiver .............................................................................................................2-62

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TABLE OF CONTENTS
SECTION 2 - MAINTENANCE
(Continued)
Page No.

Fuel System Drains .............................................................................................................2-62

Fuel System Screens and Filters ........................................................................................2-62

Airframe Fuel Pump ............................................................................................................2-63

FUSELAGE ...................................................................................................................................2-63

Fuselage Removable Skins.................................................................................................2-63

Fuselage Fixed Skins ..........................................................................................................2-64

Fuselage Cockpit Skins .......................................................................................................2-64

Fuselage Frame ..................................................................................................................2-64

Windshield ...........................................................................................................................2-64

Canopy Doors .....................................................................................................................2-65

Seat ...................................................................................................................................2-66

HOPPERS AND DISPERSAL EQUIPMENT ................................................................................2-66

Hopper Tanks ......................................................................................................................2-66

Hopper Gate Box and Adapter ............................................................................................2-67

Hopper Lid ...........................................................................................................................2-67

Gate Box Controls ...............................................................................................................2-68

Spray Lever Controls ...........................................................................................................2-68

Spray Pump .........................................................................................................................2-69

Spray Plumbing ...................................................................................................................2-70

Bottom- Load Plumbing .......................................................................................................2-70

Spray Nozzles .....................................................................................................................2-70

Filling the Hopper Tanks .....................................................................................................2-71

HORIZONTAL STABILIZERS AND ELEVATORS .......................................................................2-72

Horizontal Stabilizers ...........................................................................................................2-72

Stabilizer Struts ...................................................................................................................2-72

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TABLE OF CONTENTS
SECTION 2 - MAINTENANCE
(Continued)
Page No.

Stabilizer Rigging ................................................................................................................2-73

Elevators..............................................................................................................................2-73

Elevator Controls .................................................................................................................2-74

Elevator Trim Tabs ..............................................................................................................2-74

Elevator Trim Tab Controls .................................................................................................2-75

HYDRAULIC SYSTEM - FIRE GATE ...........................................................................................2-75

ITT INSTRUMENT CALIBRATION CHECK .................................................................................2-75

Description ..........................................................................................................................2-75

Procedure ............................................................................................................................2-76

LEVELING ............................................................................................................................2-78

LIFTING AND JACKING ...............................................................................................................2-78

MAIN AND TAIL GEAR ATTACH BOLTS ....................................................................................2-79

MAIN LANDING GEAR .................................................................................................................2-79

Main Wheels ........................................................................................................................2-79

Main Wheel Alignment ........................................................................................................2-80

Main Gear Spring ................................................................................................................2-80

TIE DOWN INSTRUCTIONS ........................................................................................................2-81

PROPELLER MAINTENANCE .....................................................................................................2-82

ROUTINE MAINTENANCE INSPECTION....................................................................................2-83

STATIC SYSTEM ..........................................................................................................................2-84

STORAGE ............................................................................................................................2-84

STRIPPING AND REPAINTING ...................................................................................................2-84

Stripping and Repainting Aluminum Parts ..........................................................................2-84

Priming Aluminum Parts with Chromated Alkyd Primer ......................................................2-86

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TABLE OF CONTENTS
SECTION 2 - MAINTENANCE
(Continued)
Page No.

Stripping and Repainting Steel Parts ..................................................................................2-86

Materials Used for Stripping, Painting, and Preservation ...................................................2-86

TAIL LANDING GEAR ..................................................................................................................2-87

Tail Wheel ...........................................................................................................................2-87

Tail Wheel Fork ...................................................................................................................2-87

Tail Wheel Fork Housing .....................................................................................................2-87

Tail Wheel Lock Pin and Housing .......................................................................................2-88

Tail Gear Spring ..................................................................................................................2-88

TIME LIMITED PARTS .................................................................................................................2-89

Main and Tail Gear Attach Bolts .........................................................................................2-89

Tail Spring ...........................................................................................................................2-89

Main Gear Spring ................................................................................................................2-89

AmSafe Airbag System (if installed) ....................................................................................2-89

TIRE INFLATION ..........................................................................................................................2-90

TORQUE VALUES FOR SHOP USE ...........................................................................................2-90

TOWING .......................................................................................................................................2-90

WEIGHT AND BALANCE .............................................................................................................2-91

WINGS ..........................................................................................................................................2-91

Wing Attachment to Fuselage .............................................................................................2-92

Wing Center Splice Connection ..........................................................................................2-92

Wing Walk ...........................................................................................................................2-93

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INTRODUCTION

This section is presented to describe maintenance functions that are applicable to the AT-802 airplane.
Airframe maintenance items that are not specifically covered in this section are addressed in FAA Advisory
Circular (AC) 43-13. Additional maintenance functions for the engine, propeller, and other accessories can be
found in the specific manufacturer’s maintenance documentation.

AMSAFE AIRBAG SYSTEM

The AmSafe Airbag system consists of a lap belt and crotch strap attached to the seat frame, a shoulder
harness with integrated airbags, two compressed gas inflators, and an electronics module and cabling. All
maintenance on the system must be performed by an AmSafe Authorized Service Center per AmSafe
Aviation Document Number E510500.

The maintenance requirements of the system include an annual inspection and functional test of the system.
The electronics module must be returned to AmSafe for refurbishment after a period of seven years from
month of manufacture and must be taken out of service after a period of 14 years from month of manufacture.
The inflators must be removed and replaced after a period of 10 years from the month of manufacture.

Any time any component of the AmSafe Airbag system is disconnected or removed from the aircraft, the
system requires a functional test performed by an AmSafe Authorized Service Center.

AILERONS AND FLAPS

Ailerons

The ailerons are all-metal and require very little maintenance. The lead counterweight will sometimes loosen
on the long AN3-35A bolt through the lead and the support tube. If the counterweight is loose, remove the
counterweight and support tube and drill and ream them for a larger bolt. To do this, remove the aileron from
the aircraft by removing the nuts from the three hinge fittings, removing the four screws in the inspection plate
where the push-rod attaches to the wing bellcrank, and removing the nut from the bolt through the bellcrank
and push-rod. Note that there is a spacer washer between the aluminum hinge and the support arm bearing,
and that there is an AN970-4 large washer on the outboard side of the bearing under the bolt head.

With the AN4-12A bolts pointing inboard, the correct order of parts would be a AN970-4 washer under the bolt
head, then a AN960-416L washer, then the bearing, then a AN960-416 washer, then the aluminum aileron
hinge, then a AN960-416 washer, then a AN365-428 nut. The steel inboard hinge uses an AN4-25A bolt, with
an AN960-416 washer under the head, then an AN970-4 washer, then the bearing, then the steel hinge, then
an AN960-416 washer, then an AN365-428 nut. Leave the push-rod attached to the aileron and reach through
the inspection plate opening and remove the bolt attaching the push-rod to the wing bellcrank. Be sure to
have someone holding up on the aileron trailing edge, and the control stick lock should be in place. Then
remove the center hinge bolt, with someone at each end of the aileron, remove the two outboard bolts, lift up
on the push-rod to keep it from dragging, and remove the aileron from the aircraft. A diagram showing
procedure to remove and install the aileron is shown in Figure 24.

The counterweight support tube in p/n 20279-2 and can be removed from the aileron by removing the two
plug buttons on the upper and lower side of the aileron nose skin and removing the AN3-12A bolt that
attaches the support tube to the support structure that is riveted to the aileron. The counterweight and support
tube can then be taken to the workbench where the long AN3-35A bolt is removed. Leaving the parts
together, clamp the counterweight to the base of the drill-press, using a long 3/16 “ drill bit chucked in the drill
press align the spindle with the 3/16 hole through the counterweight and support tube. Then change to a 7/32”
drill bit and enlarge the hole. Then ream .248 through both parts. Grease the new AN4-35A bolt and install.
Re-install the counterweight and support tube on the aileron and check for a snug fit. When installing the
counterweight on the aileron use PR1422A2 to bond the weight to the aileron in addition to the AN4-35A bolt.
The AN3 bolts have a torque of 100 inch-pounds applied at the head. Re-install the aileron in the reverse
order as removed, taking care that the washer arrangement is correct. The bolt through the push rod and wing
bellcrank is an AN4-12A with an AN960-416 washer under the head and one under the AN365-428A nut.
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While the aileron is removed, check the aluminum hinges for secure attachment to the spar, and check the
steel hinge for signs of corrosion, or loose rivets, or cracks in the welded areas. Inspect both ends of the
push-rods for cracks in the threads, check the rod-end bearing (Fafnir RE4F6-2) for condition and lubrication,
and be sure the check nut against the bearing is snug.

After the aileron has been re-installed an inspection of all connections has been made, reach through the
inspection plate opening and check to see if the push-rod is free to rotate slightly as the aileron is moved
through the full range of travel. After being sure the bolt through the push-rod and wing bellcrank has been
torqued, re-install the inspection plate with the four screws.

The bearings in the aileron support arms are Fafnir KP4 and make a press-fit into the 3/8” thick aluminum
arm. These are staked on both sides. These bearings are sealed, require no lubrication, and rarely require
replacement in service.

Aileron Boost Tab Trim and Rigging

Initial Rigging Instructions:

The initial rigging of the Aileron Boost Tabs is performed as follows:

1) Lock the flight control stick in the neutral position using the cockpit control lock. Confirm that the
ailerons are in the neutral position and rigged in accordance with the aircraft Owner’s Manual.

2) Using a straight edged tool approximately 6 inches in length, check that the lower surface of the
boost tab is in line with the lower surface of the aileron. Make this check within 4 inches of the
boost tab control horn.

3) If necessary, adjust the pushrod length to align boost tab per step 2. Ensure that the pushrod
threads are visible in the “witness holes” on the rod end bearings and that the checknuts are tight
against the bearings.

4) Ensure that all hardware is tight and properly installed.

5) Repeat for both sides of the aircraft.

Additional Adjustments:

The aileron boost tabs can be adjusted to tailor the roll handling of the aircraft. The total adjustment for each
boost tab is limited to one full turn of any rod end bearing from the initial rigged position.

With the boost tabs set to their initial rigging positions as described above, perform a test flight of the aircraft
with the electric aileron trim in the neutral position. Note any rolling tendencies and adjust the fixed aluminum
trim tab on the right aileron to correct the rolling tendencies: bending the tab up will raise the right wing and
bending the tab down will drop the right wing.

Repeat the test flight and trim tab bending as necessary to allow the aircraft to fly straight and level. The
electric aileron trim can be used for small trim corrections.

If adjustment of the bendable aileron trim tab is not sufficient to trim the aircraft for level flight, then the boost
tabs may be used for additional trimming. One tab may be deflected upward and the other downward by
identical amounts. Adjusting the trailing edge of the tab upwards will cause that wing to rise.

Additionally, adjusting both tabs upward or downward together will affect the amount of stick force the pilot
experiences in roll. Adjusting the trailing edge of both tabs upward (lengthening the pushrod) will increase the
stick force required and will make the airplane stable in roll. Adjusting the trailing edge of both tabs downward
(shortening the pushrod) will decrease the stick force required and will make the airplane less stable in roll.
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WARNING:
These adjustments should be made with much care. Small changes in the
rigging of the aileron boost tabs can have significant effects on the handling
qualities of the aircraft. Incorrect adjustment of the tabs could lead to aircraft
loss of control and an accident. Adjustments should be made in increments of
½ turn per boost tab, with test flights conducted in between, until the flying
qualities are acceptable within safe limits.

Reducing the aileron control stick forces will reduce the roll stability of the
aircraft. This should only be done if the control forces are objectionable and
require adjustment.

Final Check:

1) Ensue that the total adjustment for each boost tab has not exceeded one full turn of any rod end
bearing from the initial rigged position. If additional adjustment is required, contact the Air Tractor
factory for assistance.

2) Ensure that the pushrod threads are visible in the “witness hole” on each rodend bearing, that
each checknut is tight against the bearings, and that all hardware is tight and properly installed.

Flaps

The flaps are attached to the 1/2” thick aluminum mid and inboard flap arms with AN4-12A bolts and to the
outboard arm with an AN4-24A bolt. The order of washers and parts with the bolt pointing inboard is a AN970-
4 large washer under the bolt head, then the bearing (Fafnir KP4), then the steel flap arm, then a AN960-416
washer, then a AN365-428A nut.

The flap push-rod is attached to the flap with an AN4-12A bolt, which is pointing outboard, and the order of
parts is AN960-416 washer under the nut. The push-rod has an adjustable Fafnir RE4F6-2 bearing with an
AN316-6 check nut. Be sure that the bearing is positioned to allow the push-rod to be rotated slightly from
side to side.

During annual inspections, the AN4-12A bolt through the push-rod should be checked for straightness, and if
bent, both the bolt and bearing should be replaced immediately. At 100 hour intervals, remove the lower
fuselage side skins under the cockpit and while the flaps are being cycled through the full range of travel,
check to see if the push-rods drag on any fuselage parts. With the flaps full down, and then full up, move the
ailerons through the full range of travel and check clearance.

Details showing flap removal and installation are shown in Figure 25. The procedures for these operations are
shown below

Flap Removal

1. Remove fuselage side-skin immediately inboard of the flap’s leading edge.

2. Partially extend the flap to gain easy access to the bolt that attaches the flap push-rod to the
flap.

3. While holding up the trailing edge of the flap, remove the AN4 bolt that attaches the flap
push-rod to the flap.

4. Allow the trailing edge of the flap to rest on the boom hangers.
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5. Remove the nuts from the AN4 bolts that connect the flaps to the flap-support bracket
bearings.

6. Remove the washers and bolt from the center flap-support bearing.

7. With assistance in supporting the flap at both ends, remove the remaining washers and the
inboard and outboard bolts.

8. Carefully lift the flap clear of the airplane.

Flap Installation

The flap is installed by reversing the procedures listed under FLAP REMOVAL.

Aileron and Flap Rigging

When rigging the ailerons, set the control lock and adjust the two 70554-1 Idlers lean inboard 3-1/2 °, which
will position the Idler 90° to the aileron push tube inside the wing.

With the flap actuator in the UP position, the flap push-rods are adjusted so that the lower side of the flaps
form a straight line with the lower side of the fuel tank at station 109.0. Flap travel from this point is then set at
30° +/- 1.5°. Flap markings on the flap are located opposite the wing flap bay upper skin so that the pilot will
view the markings at 10°, 20°, and at full travel.

The ailerons are rigged with the trailing edge 1/8” to 3/16” below the flap trailing edge so that flight loads will
bring the trailing edge up approximately even with the flap trailing edge. Aileron travel (with flaps up) is 17° up
(+/- 1°) and 13° down (+/- 1°). Aileron control stops are located under the cockpit floor on each side of the
control stick torque tube horn. Additional up-aileron stops are located in the wing at the aileron bellcrank. The
adjustment consists of tightening or loosening the bolts that compress a stack of 4 to 6 neoprene washers
(p/n 70067-1). The neoprene washers act as shock absorbers for the control system, but sometimes split and
fall out, so it is advisable to inspect the stops and replace the neoprene washers as necessary during annual
inspections.

Rudder-Aileron Interconnect System Rigging

Reference:

Drawing 70523 Sheet 1 (for AT-802 with dual flight controls).

Drawing 70523 Sheet 2 (for AT-802 and AT 802A with single flight controls).
Drawing 70831.

Rigging Instructions:

Complete these instructions on both sides of the aircraft simultaneously.

1) Lock the flight control stick in the neutral position using the cockpit control lock. Confirm the
ailerons are in the neutral position.

2) Check the position of the clamp that supports the two idler arms. This clamp should be 10.0 (+/-
½) inches from the interface of the longeron and diagonal tube. See figure 1. If necessary,
loosen the clamp, adjust it within this range, and retighten hardware.

3) Check the position of each centering spring. Ensue that the Adel clamp anchoring each spring is
located at a position of 8-3/4 (+/- 1/16) inches from the center of the clamp. See figure 1. Adjust
the position of the Adel clamps if necessary.
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AT-802/802A June 21, 2018

4) Ensure that the lower centering spring is connected to the inboard idler arm and the upper
centering spring is connected to the outboard idler arm.

5) Ensure that the 70814-4 interconnect spring is connected to the top hole of the outboard idler
arm.

6) Ensure that the 70525 interconnect cable is connected to the inboard idler arm. The position of
this cable attachment varies with the serial number of the aircraft. See figure 1.

For serial Numbers -0001 thru -0073, -0075, and -0076: the cable should attach to the top hole in
the inboard idler arm (approx. 3/8 from the end).

For Serial Numbers -0074, and -0077 & subsequent: the cable should attach to the second hole
in the inboard idler arm (approx. 1 3/8 from the end).

7) Manually center the rudder and hold in place.

8) Visually ensure that the rudder pedals are even in the cockpit. Adjust if needed.

9) Measure the horizontal spread of the idler arms as shown in figure 1. This dimension should
measure between 1-3/4 and 1-7/8 inches. In addition, both sides must match within 1/16 inches.

10) If necessary to match the dimension stated in Step 9, adjust the turnbuckles on the cables. See
Figure 2. After adjusting, safety the turnbuckles with MS20995C32 wire (Reference: FAA
Advisory Circular 43.13-1B).

11) Check the cable routing for pulleys that are out of alignment and for cable contact with any
structure. Check the cables for any damage or wear that would necessitate replacement
(Reference: FAA Advisory Circular 43.13-1B).

12) Ensure that all hardware is tight and properly installed.

13) Unlock the controls and move the rudder pedals and aileron controls through their full range of
motion. Check for any binding or sticking of controls. Applying full righthand rudder input should
result in a tendency for the righthand aileron to rise and applying full lefthand rudder input should
result in a tendency for the lefthand aileron to rise.
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Figure 1 – Rudder-Aileron Interconnect Arms

Figure 2 – Rudder-Aileron Interconnect Turnbuckles (under cockpit looking forward)

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Aileron and Flap Bellcranks and Supports

The Aileron Idler under the cockpit floor is p/n 70510-1 and is interchangeable right to left. These bellcranks
have Fafnir KP6A bearings installed with a 70081-2 stainless spacer that allows the AN43B-24A eyebolt that
connect the bellcrank to the support frame assembly to be fully torqued (100 inch-pounds at the nut).

The KP6A bearings are sealed and require no lubrication. Some end play will develop due to tolerance
accumulation, but up to .040” is acceptable.

The aileron bellcranks in the wings are attached to a welded structure with an AN4-46A bolt. These have a
p/n 70081-3 stainless spacer to allow full bolt torque. Bearings are Fafnir KP6A. The wing bellcranks are p/n
700511-1 (L/H) and 70511-2 (R/H). Maximum end play of the wing bellcrank is .03”. The bolt attaching the
wing bellcranks may be reached by removing the plug buttons (11/16) on the top and bottom wing skins. To
remove the bellcrank from the wing it is necessary to remove some rivets attaching the lower wing skin.
Remove only rivets that can be easily reached with a bucking bar for re-installation.

The lower aileron torque tube beneath the cockpit floor is p/n 70509-1 and is supported on each end by p/n
70721-1 housings, which contain the B1212 Torrington needle bearings. There is a grease fitting on each end
of the torque tube to allow greasing the Torrington bearings with General Purpose grease. Pushrods from the
lower torque tube to the Idlers are p/n 70554-1 and have Fafnir RE4F6-2 bearings that may be adjusted on
each end. The two centering springs are p/n 40044-1.

The flap torque tube is attached to the fuselage frame with two AN4-10A bolts. The bearings, which are
pressed into the torque tube fittings and staked, are NMB p/n MS14104-4. These are spherical bearings with
a stainless ball and a Teflon lining. As this type of bearing has some drag, be sure the AN4-10A attach bolts
are fully torqued to 100 inch-pounds at the nut. These bearings do not require lubrication. The 2.5” diameter
flap torque tube consists of the welded assembly and bearings only. At the extreme end of each side of the
torque tube is a 3/8” thick aluminum arm (p/n 70027-4), which also has a NMB p/n MS14104-4 bearing
installed. The two flap push-rods attach to the bearings with AN4-11A bolts and should be torqued to 100
inch-pounds at the nut.

With the AN4-12A bolts pointing inboard, the correct order of parts would be a AN970-4 washer under the bolt
head, then a AN960-416L washer, then the bearing, then a AN960-416 washer, then the aluminum aileron
hinge, then a AN960-416 washer, then a AN365-428 nut. The steel inboard hinge uses a AN4-25A bolt, with a
AN960-416 bolt, with a AN960-416 washer under the head, then a AN970-4 washer, then the bearing, then
the steel hinge, then a AN9670-416 washer, then a AN365-428 nut. Leave the push-rod attached to the
aileron and reach through the inspection plate opening and remove the bolt attaching the push-rod to the wing
bellcrank. Be sure to have someone holding up on the aileron trailing edge, and the control stick lock should
be in place. Then remove the center hinge bolt, with someone at each end of the aileron, remove the two
outboard bolts, lift up on the push-rod to keep it from dragging, and remove the aileron from the aircraft.

The counterweight support tube is p/n 20279-2 and can be removed from the aileron by removing the two
plug buttons on the upper and lower side of the aileron nose skin and removing the AN3-12A bolt that
attaches the support tube to the support structure that is riveted to the aileron. The counterweight and support
tube can then be taken to the workbench where the long AN3-35A bolt is removed. Leaving the parts
together, clamp the counterweight to the base of the drill-press, using a long 3/16” drill bit chucked in the drill
press align the spindle with the 3/16 hole through the counterweight and support tube. Then change to a 7/32”
drill bit and enlarge the hole. Then ream .248 through both parts. Grease the new AN4-35A bolt and install.
Re-install the counterweight and support tube on the aileron and check for a snug fit. As you install the
counterweight, bond it to the leading edge of the aileron with PR1422A2. The AN3 bolts have a torque of
Page 2-8 Maintenance Air Tractor
June 21, 2018 AT-802/802A

60 inch-pounds applied at the nut, the AN4 bolts have a torque of 100 inch-pounds applied at the nut. Re-
install the aileron in the reverse orders as removed, taking care that the washer arrangement is correct. The
bolt through the push rod and wing bellcrank is an AN4-12A with an AN960-416 washer under the head and
one under the AN365-428A nut.

While the aileron is removed, check the aluminum hinges for secure attachment to the spar, and check the
steel hinge for signs of corrosion, of loose rivets, or cracks in the welded areas. Inspect both ends of the
push-rods for cracks in the threads, check the rod-end bearing (Fafnir RE4F6-2) for condition and lubrication,
and be sure the check nut against the bearing is snug.

After the aileron has been re-installed and an inspection of all connections has been made, reach through the
inspection plate opening and check to see if the push rod is free to rotate slightly as the aileron is moved
through the full range of travel. After being sure the bolt through the push-rod and wing bellcrank has been
torqued, re-install the inspection plate with the four screws.

The bearings in the aileron support arms are Fafnir KP4 and make a press-fit into the 3/8” aluminum arm, and
are staked on both sides. These bearings are sealed, require no lubrication, and should not require
replacement in service.

Flap-Elevator Interconnect System Rigging

Note: This procedure does not cover aircraft with a loader seat installation.

Reference:

Drawing 70518 Sheet 1 (for AT-802 with dual flight controls).

Drawing 70518 Sheet 2 (for AT-802 and AT-802A with single flight controls).
Drawing 70518 Sheet 3 (for all AT-802/802A aircraft).

Rigging Instructions

1) Completely retract the flaps to the 0° position.

2) Disconnect the elevator down spring (p/n 70814-1 for single controls, p/n 70814-3 for dual
controls) where it connects to the aft elevator controls idler. This can be done with the flight
control stick in the full forward position.

3) After the spring is disconnected, lock the flight control stick in the neutral position using the
cockpit control lock. Conform the elevators are in the neutral position.

4) Check the hole-to-hole length of the 70796-1 pushrod that connects the flap torque tube to the
70788-1 cable tensioner assembly. This length should be 10-1/2 (+/-1/8) inches.

5) Check the lateral placement of the 70788-1 cable tensioner assembly and the 70784-1 clamp
arm. The center of both of these assemblies should be 5-5/8 (+/- 1/16) inches to the left of the
aircraft centerline. Note that the lower aileron torque tube is centered on the aircraft centerline
and can be used as the centerline reference for this measurement. If required, adjust the
tensioner assembly and the clamp arm to this dimension.
Air Tractor Maintenance Page 2-9
AT-802/802A June 21, 2018

6) Tighten the clamp bolts for the tensioner assembly to secure it in place. Leave the clamp bolts on
the 70784-1 clamp arm loose for now.

7) Ensure the 70796-1 pushrod is installed, connecting the tensioner assembly and the clamp arm
as shown above.

8) Rotate the tensioner assembly to the 60° nominal angle shown below. Note that the holes in the
tensioner bearing can be used to “eyeball” this angle. Allow the 70784-1 clamp arm to rotate on
the flap torque tube as necessary. When the tensioner is at the 60° angle, tighten the clamp arm
bolts to secure the clamp arm to the flap torque tube.
Page 2-10 Maintenance Air Tractor
June 21, 2018 AT-802/802A

9) Reconnect the elevator control downspring to the aft elevator control idler. With the flaps
retracted and elevators neutral, the length of the downspring (excluding the hooks) should
measure 20.0 (+/- 1/8) inches. To adjust this length, adjust the length of the 70796-1 pushrod.

10) After the initial downspring length is set, check the cable routing for pulleys that are out of
alignment, cable contact with any structure.

11) Ensure that all hardware is tight and all rodend checknuts are properly tightened.

12) Actuate the flaps through their full range of motion and watch the cable tensioner and pushrod for
any interference or binding.

Flap Actuator

The flap actuator assembly is either an Air Tractor p/n 71112-1 or a Commercial Aircraft Products p/n
C100168-4. To determine which actuator is installed, check the size of the ball screw shaft with the actuator
deflected. The C100168-4 actuator has a shaft diameter of approximately 9/16”. The 71112-1 actuator has a
shaft diameter of approximately 1.0”. Details of the flap actuator are shown in Figure 26 (C100168-4 actuator
shown, 71112-1 actuator similar). The flap system uses micro-switches to limit the down and up travel of the
flaps. The micro-switches are p/n BZ2R5551-A2 and the arm with the roller attached that actuates the micro-
switch is an AN3169-1 arm.

Commercial Aircraft Products C100168-4 Actuator:

The actuator assembly has a threaded collar. This collar is threaded internally to match the
threads on the worm drive threads of the actuator, and it is threaded externally to match the
threads of the Air Tractor Tee assembly, which is p/n 70037-1. The Tee assembly is attached
to the two 1/4” thick aluminum 70581-1 arm assemblies that are bolted to the flap torque tube
assembly. The Tee assembly has a steel grease shield and cap attached. The shield is p/n
70039-2 and is attached to the Tee with two AN500A5-3 screws. Be sure the lock washers
are under the head of the AN500A5-3 screws. The cap is a 1 1/8 SC Caplug attached to the
shield with a TY-525 Tyrap.

The Tee assembly that screws into the Threaded collar has a AN5675 D6H4 set screw that is
located on the top surface of the Tee. The threaded collar has a large diameter rounded
surface and just forward is a smaller diameter part on the collar that is to be used for
tightening the collar against the Tee. Whenever it is necessary to remove the flap actuator,
the factory practice is to be first loosen the set screw in the Tee assembly with a small Allen
wrench, then place a soft rag or duct tape on the small diameter of the threaded collar so as
not to scratch the finish and with a pair of water-pump pliers or vise-grips, break loose the
connection between the threaded collar and the Tee assembly. Then the threaded collar can
be screwed by hand from the Tee. Be careful not to dent or scratch the finish of the ball nut
as small dents will interfere with the action of the balls inside.

Air Tractor 71112-1 Actuator:

The actuator assembly attaches to the fuselage frame via a clamp. The actuator is attached
to this clamp with an AN4-14A bolt. At this connection there is also a 70026-3 spacer
bushing and a Bunting P37-8 bronze bushing. If the actuator is replaced or removed, be sure
both bushings are in place.
Air Tractor Maintenance Page 2-11
AT-802/802A June 21, 2018

The actuator assembly has a 1-inch diameter ball screw shaft. A ball nut moves along this
shaft. The 71149-1 yoke (tee) assembly is fitted on the ball nut and held in place with the
71152-1 yoke nut assembly. This yoke nut includes a steel grease shield and is secured on
the ball nut with two 90289A338 set screws. The yoke assembly is attached to two 1/4” thick
aluminum 70032-1 arm assemblies that are bolted with four AN4-7A bolts to the flap torque
tube assembly. See Figures 27A and 27B.

CAUTION
Have someone hold up on the flap
trailing edge so the flaps will not fall
down against the boom hangers

See the section on FLAP ACTUATOR TROUBLESHOOTING for a step-by-step procedure for removing the
actuator assembly from the aircraft.

All wires from the flap actuator assembly have Wristlock connections so that it is not necessary to cut or
splice wires when the actuator is removed. Also, it is possible to replace the motor without removing the
actuator assembly.

All wires from the flap actuator assembly have Wristlock connections so that it is not necessary to cut or
splice wires when the actuator is removed. Also, it is possible to replace the motor without removing the
actuator assembly.

Flap Actuator Troubleshooting

If any trouble develops, first check both the flap circuit breaker and flap switch circuit breaker on the panel. If
this does not produce any results, a visual inspection of the micro-switches and micro-switch arms should be
made. Enter the fuselage and inspect the micro-switches for broken actuator arms or loose wires. Inspect the
relays for broken or loose wires.

If the flaps are up but won’t go down, chances are there is something wrong with the down micro-switch, or
down relay. If the flaps are down but won’t go up, look for trouble with the up micro-switch, or up relay. If it is
necessary to keep flying and make repairs later, the flaps can be retracted by rotating, by hand, the rubber
coupling at the motor shaft. This is slow, but the flaps can be raised this way.

If the flap goes down past the 30° mark, check the down micro-switch. Have someone cycle the flaps and see
if the roller on the micro-switch arm lifts properly on the striker plate and pushes in the micro-switch plunger to
stop the travel. If there is any doubt, push the plunger in with the flap midway through the stroke. If the switch
is working, the flap will stop. In this case, the down micro-switch needs to be re-positioned to activate the
micro-switch.

Check the micro-switches with an Ohmmeter. Check continuity between the C pin and the N.C. pin on both
switches. Activate the switch by pushing the plunger in and check continuity between the C pin and the N.O.
pin. If these checks are positive, the micro switches are OK and do not need to be changed. If a switch is bad,
change it.

Flap Motor Troubleshooting

If the micro-switches appear OK the flap motor may be checked as follows:

1. Slide the conduit down from the wire splice (Wristlock) where the red and black wires go into
the wire bundle.

2. Note which wires the black wire from the motor connects to.
Page 2-12 Maintenance Air Tractor
June 21, 2018 AT-802/802A

3. Use an outside source of power (24 volts) protected with a circuit breaker. Attach the
negative power source to the red wire and attach the positive wire through the circuit breaker
to the black wire. The motor should run in one direction. Attach the positive wire through the
circuit breaker to the red motor wire and the negative wire to the black motor wire. The motor
should run in the other direction.

4. If the motor on a C100168-4 actuator does not respond as described above, it is faulty and
should be replaced. It is attached to the actuator by two 1032 nuts. Be sure rubber coupling
is in good condition

Flap Actuator Removal Instructions

1. Disconnect the motor wires at Wristlock connections in wire harness and identify wires for re-
assembly.

2. Remove the nut and washer from the AN4 bolt attaching the actuator assembly to the
fuselage frame.

3. Remove the AN4 bolt, paying close attention to the spacer bushing inside the bronze
bushing, and lower the flaps to rest on boom hangers.

CAUTION
Have someone hold up on the flap trailing
edge before the last bolt is removed.

4. Remove the AN4 bolts that attach the aluminum arms on the flap Tee to the torque tube.

5. Check rubber coupling on motor shaft for excessive backlash. (Commercial A/C Actuator
only)

With the complete actuator on the workbench, if it is desired to change the actuator itself,
perform the following:

(For commercial aircraft actuator only)

1. Remove the two screws that hold the dust shield to the lower end of the assembly.

2. Use open-end wrench to remove down over-ride stop from end of jackscrew. CAUTION:
This stop is left-hand threads.

3. Loosen the setscrew in the top of the Tee assembly with a small Allen wrench.

4. With water-pump pliers or vise-grips, break loose the ball nut from the Tee assembly.

5. Unscrew striker by hand out of Tee assembly.

To install new actuator, use the reverse procedure, but apply a few drops of Locktite to end of jackscrew
threads before attaching the left-hand threaded stop. When all parts are installed, the complete unit is ready
to be installed in aircraft.
Air Tractor Maintenance Page 2-13
AT-802/802A June 21, 2018

Flap Actuator Installation Instructions

The details for flap actuator installation are shown in Figure 27 and Figure 27A, 27B, and 27C (71112-1
Actuator).

1. Re-install actuator in aircraft in reverse order as removal.

2. Raise flaps to full up position with flap switch in cockpit. Check position of flaps relative to
wing (See Flap and Aileron Rigging Section of this manual).

3. With flaps properly positioned with respect to the lower side of the wing, there should be a
gap 1/16” to 1/8” between the ball nut and the actuator grease case. If the gap is not within
the proper range, use the flap switch in the cockpit to provide the proper gap. It will then be
necessary to set the flap position with respect to the lower wing surface by adjusting the flap
pushrods.

4. Then loosen the two screws holding the UP micro-switch and adjust the micro-switch until a
click is heard. Tighten the two screws and once more use the flap switch to lower and then
raise the flaps to the full UP position. Again check the gap between the ball nut and end of
the UP travel for 1/16” to 1/8” travel. Check the position of the flaps with respect to the lower
wing surface. If all is in order, proceed to set the DOWN micro-switches.

5 Extend the flaps to 30° and adjust the micro-switch until a click is heard. Re-cycle the flaps
and check DOWN travel again.

6. Re-check the position of the UP micro-switch two ways: Raise the flaps all the way with the
flap switch. After the flaps are fully retracted, continue to hold the flap switch up and observe
the Voltmeter. If the Voltmeter shows excessive voltage drop, the micro-switch has not turned
OFF the current. If this check is OK, then check the distance between the striker and the
end of the UP travel, which should be 1/16” to 1/8” as, mentioned in steps 3 and 4.

Flap Relay Troubleshooting

If the micro-switches and the flap motor appear OK then the trouble may be in the relays. Details of the flap
relays are shown in Figure 28.

With the master switch on use of a voltmeter to check that there is power to the relays at the -299 and -235
wires. If there is battery voltage there, have someone attempt to extend and retract the flaps with the flap
switch while checking for battery voltage at the relay coils, wire -236 and -238 for down and up respectively. If
there is no battery voltage when the flap switch is activated check the micro-switches and the flap switch. If
there is battery voltage at the respective relay coils when the flap switch is activated you should hear the relay
“click” and the flap motor should operate. If the relay “clicks” and the flap motor does not operate, check for
battery voltage at the motor. If there is not battery voltage at the motor when the relay clicks the relay contacts
are probably bad and the relay should be replaced. If the relay does not click turn off the master switch,
remove one of the coil wires and check the coil with an Ohmmeter. The relay coil terminals are the two
smaller studs (# 10) on the relay case. The resistance through the 70-317224-5-relay coil should be about 59
ohms. Use the Ohmmeter to check that the relay coil is not shorted to ground. If the coil is bad replace the
relay.
Page 2-14 Maintenance Air Tractor
June 21, 2018 AT-802/802A

FLAP ACTUATOR (71112-1) OVERHAUL

The flap actuator should be replaced or overhauled after 1500 hours of service to assure trouble free
operation. If it is to be overhauled order a kit of parts from your dealer. The Overhaul kit part no. is 71112-1-
500 and consists of the following parts:

Qty P/N Description

2 03-057 Replacement Motor Brushes (Specialty Motors)
1 MS28775-016 O-Ring
1 MS35333-39 O-Ring
1 MS24665-283 Cotter Pin
1 MS24665-132 Cotter Pin
2 PS3KDD Bearing (Alt. is S3KDD)
1 00050 Bearing- Cone (Timken)
1 00150 Bearing-Cup (Timken)
1 RA4Z Bearing
1 7410 Seal
1 CR 3725 Seal
1 WHM-87 Retaining Ring

The 71112-1 flap actuator should be replaced or overhauled at the factory or in a factory approved facility
after 1500 hours of service to assure trouble free operation. If the actuator stops functioning, first check to
ensure that there is no binding or seized parts in the entire flap system. Also, ensure the limit switches are
functioning and set properly.

Second, inspect the gearbox for correct operation. To do this, first remove the flap motor from the actuator
gearbox by removing two nuts from the end of the motor closest to the actuator gearbox. Then turn the
gearbox input shaft by hand and ensure that the gearbox and the ballscrew shaft turns without binding or
roughness. If there is any binding or roughness, then the gearbox needs to be replaced or factory-overhauled.

Next, check the motor for proper operation by having someone operate the flap switch in the cockpit. Try the
switch in both directions (Note that if the flaps are in the full up or full down position, the motor will not turn in
both directions because a limit switch will be depressed).

If it is determined that the motor is not functioning properly, remove and inspect the spring loaded motor
brushes for excessive wear. Excessive wear is defined as a brush that has worn down to a length of 1/8” or
less. If this is the case, P/N 03-057 replacement brushes can be purchased from your dealer (2 required for
each motor). For a replacement motor, order P/N 90-1026 from your dealer.

ACTUATOR OVERHAUL STEPS

1. Save and reuse all hardware unless otherwise specified.

2. Remove and inspect the 90-1026 flap motor. Replace on condition. Replace the motor brushes with
P/N 03-057 replacement brushes from Specialty Motors.

3. Inspect flap actuator attach arms (Item 12 on Dwg 71112). Replace on condition.

4. Remove 4 screws and endcap from gearbox. Drain gearbox oil through a strainer. Check for metal
particles. Specifically check for brass particles that might indicate excessive worm gear wear.

5. Remove 8 screws and carefully remove the 71147-1 actuator shaft form the gearbox. Remove the
cotter pin and bolt from the end of the shaft and remove all parts from the shaft (when removing the
ball screw; thread it off of the shaft and onto a cardboard shipping tube to prevent the loss of the ball
bearings). Discard the ball bearing (PS3KDD), the roller bearing (00050 and 00150), and the seal
(7410), and the O-Ring MS35333-39). Clean and inspect the remaining parts.
Air Tractor Maintenance Page 2-15
AT-802/802A June 21, 2018

6. Check the 71118-1 worm gear for any gouging or excessive wear on the teeth. Check the 71154-1
bronze bearing for excessive wear (excessive wear is defined as the bearing being thinner than .040”
at the center.) Check the 71117-1 ballscrew shaft dimensions. Replace all discarded parts with new
parts to accurately set the shaft dimensions. Inspect.

7. Rebuild the 71147-1 actuator shaft per Drawing 71147. Use the T71147-1 and T71147-2 tooling to
accurately set the shaft dimensions. Replace all discarded parts with new parts. Inspect.

8. Remove the half of the 71130-1 spider coupling that is attached to the worm shaft. Inspect all three
pieces of the spider coupling and replace any unserviceable parts. Using the SK655-1 seal pulling
tool, remove and discard the CR3725 seal from the gearbox. Remove and discard the WHM-87
retaining ring. Remove the worm shaft from the gearbox. Remove all parts from the shaft. Discard the
cotter pin (MS24665-132) and bearings (PS3KDD and RA4Z). Clean and inspect the remaining parts.
Check the GLUH worm for any gouging or excessive wear. Discard unserviceable parts.

9. Rebuild the 71148-1 worm shaft per Drawing 71148, replacing all discarded parts with new parts.
Inspect.

10. Inspect the 71125-1 gearbox and P37-8 bushing for serviceability. Discard and replace unserviceable
parts.

11. Rebuild the actuator per Drawing 71112, replacing all discarded parts with new parts.

ENGINE DRIVEN AIR CONDITIONER

All Air Tractor aircraft use a gas-cycle air conditioning system for climate control. The air conditioning system
lets the pilot select ram air from outside, re-circulate cockpit air, or a mix of the two. The ram-air control
handle location is on the aft-cockpit wall on the RH side of the pilot.

The 53126-X compressor has five reciprocating pistons driven by a rotating wobble-plate. It uses reed-type
valves to control flow at the suction and pressure ports. Mechanical power to drive the compressor comes
from an engine accessory drive pad. Gears in the engine drive are a splined-quill shaft that turns a small poly
“V” groove pulley that drives the flywheel pulley with a serpentine belt. The flywheel pulley is connected to the
compressor shaft by an electromagnetic clutch.

The 53126-X compressor is factory-charged to the correct level with Sanden SP-15 oil. The initial oil charge is
210 cc. It is not necessary to check the compressor’s oil level as routine maintenance. The oil level must be
checked when a system component has been replaced or if you think there is an oil leak. All refrigerant must
be removed from the system (depressurized) before the oil is checked.

The air conditioner fans, blowers, and compressor clutch are powered by the aircraft bus. All control switches
for the air conditioning system are located on the Instrument Panel. The pilot can use the switches to turn the
system on or off and to control the cockpit-blower speed as HIGH, MED, or LOW.

A Freon Recycling Unit (FRU) that reclaims the R-134a refrigerant is recommended when refrigerant is added
or removed.

Servicing procedures for the air conditioner are generally the same as those for comparable automotive units.
Most servicing is accomplished by adding or removing Refrigerant R-134a at the servicing ports. These ports
are located beneath the upper right-hand side skin immediately aft of the cockpit.
Page 2-16 Maintenance Air Tractor
June 21, 2018 AT-802/802A

1. Cautionary Information

A. Pressure Release
• Before disconnecting any lines or removing the oil plug, always make sure refrigerant has
been removed from the air conditioning system by recovering it with the appropriate
recovery equipment.
• When working on compressors, separate from the system, always be sure to relieve internal
pressure first. Internal compressor pressure can be relieved by removing shipping caps /
pads from both ports.

B. Recovery of Refrigerant
• Never discharge refrigerant to the atmosphere. Always use approved refrigerant recovery /
recycling equipment to capture refrigerant which is removed from the air conditioning
system. Do not mix refrigerants in the same piece of equipment; one should be designated
for R-12 and another for R-134a.

C. Handling of Refrigerant
• Always wear eye and hand protection when working on an air conditioning system or
compressor. Liquid refrigerant can cause frostbite and / or blindness.

D. Ventilation
• Keep refrigerants and oils away from open flames. Refrigerants can produce poisonous
gasses in the presence of a flame. Work in a well-ventilated area.

E. Avoid Use of Compressed Air

• Do not introduce compressed air into an air conditioning system due to the danger of
contamination.

Note:
Recycling machines must be validated to the appropriate SAE standard and by Underwriters
Laboratories. Recycled refrigerant from other sources must meet the appropriate ARI standards.
Failure to comply with these provisions may void any warranty on the compressor.

2. R134a Information

A. R134a / PAG Oil Handling Precautions

This manual focuses on service information for Sanden compressors intended for use with R134a and
PAG oils.

a) Always follow safety precautions

b) Do not discharge R134a into the atmosphere. Even though its ozone depletion potential is
zero, it does have global warming potential. Recovery and recycling are mandated by the
Clean Air Act. Use recovery equipment designated only for R134a. Never introduce another
refrigerant into the R134a equipment.
c) Never mix R134a with other refrigerants or air conditioning systems failure may to occur.
Air Tractor Maintenance Page 2-17
AT-802/802A June 21, 2018

d) Use only Sanden specified PAG lubricants for R134a systems using Sanden compressors. If
other lubricants are used, air conditioning system failure is likely to occur.
e) The Sanden specified PAG oils used in R134a systems absorb atmospheric moisture very
quickly. Moisture in the air conditioning system can cause major damage or failure.
• Never leave PAG oil exposed to air for a prolonged time. Tightly reseal the oil container
immediately after each use.
• During air conditioning system repair, cap all fittings as soon as opened and leave capped
until just before they are reconnected.
• If a repair is performed on an R134a compressor or system, evacuate the system for at
least 30 minutes before recharging to ensure the removal of moisture which may have
been absorbed by the PAG oil in the compressor and system.

B. Table of Saturation Temperatures and Pressures (R134a)

Temp. (F) Pressure Temp. (F) Pressure Temp. (F) Pressure

(psig) (psig) (psig)
-40 -7.2 in. Hg 25 22 105 135
-30 -4.8 in. Hg 30 26 110 147
-20 -1.7 in. Hg 40 35 115 159
-15 0 50 45 120 172
-10 2 60 57 130 200
-5 4 70 71 140 231
0 6 80 85 150 264
5 9 85 95 160 301
10 12 90 104 180 386
15 15 95 114 200 485
20 18 100 124 210 549

C. System Requirements

AT 802/802A System Requirements

Single Condenser System Dual Condenser System

Oil 10.5 oz (310 cc) 11.8 oz (349 cc)
Refrigerant 3 lbs (1.36 kg) 3 lbs 3 oz (1.45 kg)
Page 2-18 Maintenance Air Tractor
June 21, 2018 AT-802/802A

3. Application Specifications

A. Oil Flow Theory

• Compressor lubrication occurs as the oil which circulates with the refrigerant passes
through the compressor crankcase during operation. The Sanden SD series compressor
achieves optimal durability and cooling performance when oil circulates through the
system at a ratio of 3.3% to 8% oil to refrigerant. Excess oil can act as an insulator limiting
heat transfer in the evaporator and condenser, while too little oil can negatively affect
durability.
• Oil will collect in low pressure cool components (evaporator, accumulator and suction
hose) of the refrigerant loop. For example a long suction hose which sags can collect
several ounces thus reducing overall oil circulation ratio.

B. Oil Charging

a) For a new compressor to be used in this

type of system, subtract the delivered
oil amount from the desired total oil
charge to determine how much oil
should be added to the compressor
and system. (For total system Delivered Oil Amount
required oil amount, see Section 2C
System Requirements).
b) Remove the oil filler plug and charge the compressor with the amount of additional oil
determined in step a). Use only new oil of the correct type as shown on the compressor
label. If calculated amount is greater than 300cc (10oz) oil can be added to other system
components.
c) Re-install oil plug. Seat and O-ring must be clean and not damaged. Torque to 11-18 ft•lb (15-
25 N•m, 150-200 kgf•cm).

4. Diagnosis Confirmation of Compressor Failure

• The compressor is the most expensive component in the air conditioning system loop.
Steps A through D should be used to determine if the compressor is functioning correctly
or not and prevent removal of a good compressor.

A. Compressor Rotation Test

• Most internal compressor failures can be

quickly identified by performing a shaft
rotation test. Normal rotation of the
compressor shaft should be smooth
without catching or binding.
• Compressors which bind or hang during
the shaft rotation test have an internal
part which is broken or contamination
preventing compressor operation. This
compressor should be removed and
replaced with a new unit.
Air Tractor Maintenance Page 2-19
AT-802/802A June 21, 2018

B. Clutch Inspection

a) Voltage Check
• Confirm that the clutch is receiving at a
minimum11.5 V or 23 V for 12 V and 24 V 12 Volts
systems respectively. If voltage is not being
received at the clutch run a diagnostic on the
vehicle electrical system. (Note: perform test
with power applied to coil to fully load the
circuit)
• Pulley or Rotor Spin Check
• With clutch disengage the pulley should spin
freely with no wobbling or
roughness/vibration

b) Air Gap Check

• Air gaps exceeding 0.051” (1.3 mm) can
prevent engagement. This often is noticed after
the clutch and compressor temperature is
heated through normal use.

c) Resistance Check
• Field coils with internal shorts can be tested by 3.2 Ohms
measuring resistance across the field coil.
Resistance should fall within these values.
¾ 12 Volt coil resistance should measure
between2.8 Ω and 4.4 Ω @ room
temperature
¾ 24 Volt coil resistance should measure
between 14 Ω and 18.2 Ω @ room
temperature
Page 2-20 Maintenance Air Tractor
June 21, 2018 AT-802/802A

C. Pressure or Pumping Test

• Compressors cause refrigerant to flow through the system by creating a pressure

differential, high and low pressures. If the compressor can be forced to produce a high
pressure in excess of 350 psig it is a good compressor.

Important: This test must be performed with a full system charge! Confirm the system is
charged per Air Tractor requirements in this section before proceeding.

a) Disconnect electric cooling fan. The condenser can also be blocked with sheet of card board.
The purpose is to limit heat removal from the system and build compressor discharge
pressure.
b) Start engine and engage clutch
c) Compressors operating within specification should be capable of reaching 350 psig.

Important: This test should only be run for a short time period. Shut the system down
immediately once 350 psig is achieved

D. Leak Checking

a) Visual Inspection
Although oil seepage does not necessarily indicate leakage of refrigerant, it should be
considered a sign that a leak may exist. Look for the following items:
• Oil seepage in shaft seal area (between clutch and compressor) - repairable.
• Pinching or extrusion of front housing O-ring – non-repairable.
• Oil around cylinder head (gaskets, service valves, fittings) - repairable.
• Oil around oil plug - repairable.
• Stripped threads – non-repairable.
• Oil around crack in compressor body – non-repairable.

b) Soap Bubble Detection

• Soap bubbles are a means to detect gross leaks. In general one very small bubble
released per second is equal to 40 oz of refrigerant loss per year. Finding leaks smaller
than 40 ounces per year requires an electronic detector.

c) Shop Type Electronic Detectors

• Ensure that the detector being used is sensitive to R134a refrigerant. Many leak detectors
intended for R-12 cannot detect R134a leaks. Use the leak detector in accordance with
the manufacturer's instructions. The leak rate at any portion of the compressor should not
exceed 1.0 oz./yr. Make sure that a suspected leak is an actual flow of refrigerant, not a
small pocket of refrigerant trapped in a recess. Cleaning the suspect area with soap and
water (never a solvent) or blowing off the area with compressed air can help confirm a
suspected leak.
Air Tractor Maintenance Page 2-21
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d) Leak Detection Dyes

• Leak detection dyes are to be used in accordance with the manufactures instructions
• Leak detection dyes work by staining the system oil. So when adding dye to a system
which did not initially contain dye the system will need to operate for some time to allow
all the oil to become stained and arrive at the leak.

E. Noise

a) Unusual Noise Not due to Compressor

Unusual noises may be caused by components other than the compressor
Compressor Mounting - Check for:
• Loose belt - see belt tension specifications.
• Broken bracket or compressor mounting ear. Replace broken component.
• Missing, broken, or loose mounting bolts. Replace, reinstall, or tighten.
• Drive pad shaft or bearing problem. Inspect drive pad bearing and shaft condition.

b) Unusual Noises Due to Compressor

• Suction pressure less than about 6 psig can cause unusual noise. Charge refrigerant to
proper amount and test by applying heat to evaporator to increase suction pressure.
• Clutch bearing
• Oil level--insufficient oil can cause unusual noise.
• Compressor suction or discharge valve breakage will cause a clacking sound at idle.
• If head gasket failure occurs, discharge pressure will be low and suction pressure will be
high at idle.
Page 2-22 Maintenance Air Tractor
June 21, 2018 AT-802/802A

5. Compressor Repair

Clutch Components

2.
6.
1. 8.
4. 10.
3. 5. 7. 9.
2.
1.
6.

1. Armature dust 7. Pulley & Bearing

4. Armature plate 10. Field Coil
cover screw Snap Ring
2. Armature dust 8. Pulley & Bearing
5. Clutch Shims
cover Assembly
6. Rotor Bearing 9. Field Coil Snap
3. Shaft nut
Dust Cover Ring

A. Clutch Removal
a) Armature Nut-Removal
• If armature dust cover is present, remove the 3 or 6
bolts holding it in place and remove cover. If auxiliary
sheet metal pulley is present, remove the screws
holding it in place, then remove pulley.
• Insert pins of armature plate spanner into threaded
holes of armature assembly.
• Hold armature assembly stationary while removing
retaining nut with 3/4", 19mm or 14mm socket wrench,
as appropriate.

b) Key Shaft Armature-Removal

• Remove armature plate assembly using puller. Thread 3
puller bolts into the threaded holes in the armature
assembly. Turn center screw clockwise until armature
assembly comes loose.
Air Tractor Maintenance Page 2-23
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OR b) Spline Shaft Armature-Removal

• The spline shaft armature will not have threaded holes
to accept the armature puller
• Lift off armature plate with fingers. If armature does not
come off easily, spray an anti seizes oil into shaft to
loosen. Armature plate can also be loosened by
gently prying between rotor and armature plate
with two flat screwdrivers.

c) Remove Clutch Accessories

• Bearing Dust Cover (if applicable)
• Shaft Key (if applicable)
• Shims

d) Rotor Pulley Assembly Removal

• Remove rotor snap ring.
• Insert the lip of the jaws into the snap ring groove.
• Place rotor pulley shaft protector (Puller set) over the exposed
shaft.
• Align thumb screws to puller jaws and finger tighten
• Turn puller center bolt clockwise using a socket wrench until
rotor pulley is free.

e) Field Coil Assembly Removal

• Loosen lead wire clamp screw with #2 Phillips screw
driver until wire(s) can be slipped out from under clamp.
• Undo any wire connections on the compressor which
would prevent removal of the field coil assembly.
• Remove field coil snap ring
• Remove the field coil assembly
Page 2-24 Maintenance Air Tractor
June 21, 2018 AT-802/802A

B. Clutch Replacement

a) Field Coil Assembly Installation

• Reverse the steps of the previous section. Protrusion on
underside of coil ring must match hole in front housing to prevent
movement and correctly locate lead wire(s).

b) Rotor Assembly Installation

• Place compressor on support stand, supported at rear end of
compressor. If the compressor must be clamped in a vise, clamp
only on the mounting ears, never on the body of the compressor.
• Set rotor squarely over the front housing boss.
• Place the rotor installer ring into the bearing bore. Ensure that the
edge rests only on the inner race of the bearing, not on the seal,
pulley, or outer race of the bearing.
• Place the driver into the ring and drive the rotor down onto the front
housing with a hammer or arbor press. Drive the rotor against the
front housing step. A distinct change of sound can be heard when
using the hammer to install the rotor.
• Reinstall rotor retaining snap ring with external snap ring pliers. If a
bevel is present on the snap ring, it should face up (away from the body of the
compressor).
• Reinstall rotor bearing dust cover (if present) by gently tapping it into place.

c) Armature Assembly Installation

• Install clutch shims. NOTE: Clutch air
gap is determined by shim thickness.
When installing a clutch on a used
compressor, try the original shims
first. When installing a clutch on a Shims
compressor that has not had a clutch
installed before, first try 0.04", 0.02",
and 0.004" (1.0, 0.5, 0.1 mm) shims.

1. Keyed Shaft Only

• Install shaft key with pliers.
• Align keyway in armature assembly to shaft key.
Using driver and a hammer or arbor press, drive
the armature assembly down over the shaft until
it bottoms on the shims. A distinct sound
change will be noted if driving with a hammer.
Air Tractor Maintenance Page 2-25
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2. Spline Shaft Only

• Align slot in armature with locator tooth on shaft. Press
armature towards rotor with hand until armature rests against
the shims.

d) Armature Retaining Nut

• Replace retaining nut and torque to specification. 1/2-20: 20-
25 ft•lb (27-34 N•m, 270-350 kg•cm) M8: 11-15 ft•lb (15-21
N•m, 150-210 kgf•cm)

e) Air Gap Conformation

• Check air gap with feeler gauge. Specification is 0.016" -
0.031" (0.4 - 0.8mm). If gap is not even around the clutch,
gently tap down at the high spots.
• If the overall gap is out of spec., remove the armature
assembly and change the shims as necessary.
• Replace armature dust cover (if used) and torque 3 or 6 bolts
to specification below.
· 1/4-20 bolts (SD-5): 2-4 ft•lb (2-5 N•m, 25-50 kgf•cm)
· M5 bolts (SD-7): 5-8 ft•lb (7-11 N•m, 70-110 kgf•cm)

*Note: Over torque of SD508/SH14 dust cover bolts will cause air gap to become out of spec.

C. Removing and Replacing the Compressor

To remove the compressor, these steps should be followed:

• Remove all refrigerant from the system using a Freon Recovery Unit (FRU).
• Remove the hose fittings at the rear of the compressor by first removing the bolt and
strap that hold the T-head clamp in place. The hose fittings can now be removed from the
compressor’s head without tools.
• Separate the wrist-lock connector in the wire that powers the clutch.
• Loosen the nuts on the two AN5 pivot bolts that secure the compressor to the drive-shaft
housing.
• Remove safety wire and loosen the belt-tension turnbuckle and remove belts.
• Remove the bolt that connects the belt-adjustment turnbuckle to the compressor case.
Page 2-26 Maintenance Air Tractor
June 21, 2018 AT-802/802A

• Support the compressor and remove the AN5 bolts and nuts that secure the compressor
to the drive-shaft housing. This also releases the turnbuckle that serves as a side brace.
• Gently lift the compressor from the engine compartment.

To replace the compressor, the previous steps should be followed in the reverse order. The belts for the R12
system should be tensioned to 10 lbs using a Deco densitometer or equivalent. Tension the flat serpentine
belt of the R134a system as described in Service Letter #159.
Use compatible refrigeration oil on the O-rings at the compressor-hose fitting before reconnecting to
compressor. Follow evacuation and refrigerant charging instructions spelled out in this section of this manual.

6. Compressor Replacement

x It’s critical for successful compressor replacement that the new compressor is installed in
a clean system with a correct oil charge. Contamination remaining in the system will be
pulled into the new compressor and lodge under the valves and in bearings causing quick
failure of the new compressor. Also it’s important to maintain the original oil charge
amount when replacing the compressor.

A. Contamination Inspection
• Contamination from foreign material can be found by looking at the oil drained from either
the compressor or the suction and discharge lines. Contamination can also be seen
collecting in the orifice tube or expansion valve.

Clean oil is clear

or translucent
Overheated oil is dark
Contaminated oil with
and will require flushing
metal particles will
require system flushing

• To illustrate how contamination will quickly wreck a good

compressor, the photo to the right shows a small metal
shaving lodged under the discharge valve. The valve will
open and close against the metal shaving resulting in a
fatigue break of the valve. The broken valve is now free to
travel inside the compressor causing additional internal
failures. Eventually the compressor will stop pumping and over heat.
Air Tractor Maintenance Page 2-27
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B. Oil Amount (Flushed System or New Systems)

• Systems which have no oil in them due to flushing or the system is being built from new
components will require oil amounts in accordance with the oil charging section
requirements in this manual.
Note:
• The factory oil charge for the compressor can be found on
the compressor label. For total system required oil
amount, see Section 2C, System Requirements. Also see
oil charging section of this manual for additional
information. Delivered Oil

C. Oil Amount (Compressor swap, no flushing)

• The goal of this procedure is to measure the oil amount in
the failed compressor and adjust the amount in the new
compressor to equal that of the failed

a) Remove the oil plug from the failed compressor and drain as
much oil as possible into a suitable container.
b) Drain oil from the suction and discharge ports into a suitable
container while turning the shaft clockwise only with a socket
wrench on the armature retaining nut.
c) Measure and record the amount of oil drained from the
compressor.
d) Drain oil from the new compressor following steps a) and b).
e) Add oil back into the new compressor in an amount equal
measurement taken in step c).
f) Re-install oil plug. Seal and O-ring must be clean and not
damaged. Torque to 11-15 ft•lb (15-20 N•m, 150-200
kgf•cm). Be careful not to cross thread the oil plug.

7. Service Procedures

A. Flushing

a) Equipment types
• Refrigerant recovery recycle machines which contain a flushing circulating pump to
solvent- clean using R134a.
• A closed loop flushing machine in which the circulated flushing fluid is returned to a
reservoir for filtering and continued circulation. Most of these machines provide a pulsing
action to dislodge particles that are stuck in small passageways.
• A pressurized flush gun with a pulsating spray can also be used. To use this technique,
block one end of a air conditioning system component being flushed in order to build
pressure inside the component, and then quickly release the blockage to pulse the
flushing solvent out.
Page 2-28 Maintenance Air Tractor
June 21, 2018 AT-802/802A

b) Safety
• Do not use flammable fluids.
• Protect eyes with safety goggles.
• Wear chemical resistant gloves.
• Use approved fluids. CFCs R-11,113 or 115 and Methyl Chloroform also known as 1,1,1,
Trichloroethane are not acceptable per the Clean Air Act.

c) Acceptable Flushing Fluids

• Fluids designated for air conditioning flushing should be used and
may be either solvent or lubricant based. Fluids used to flush the system should meet SAE
specification J2670 to insure compatibility with refrigerant, oil and any materials used in
the air conditioning system.

d) Components to Flush
• Flush hoses, hard lines and heat exchangers. DO NOT flush the compressor, accumulator
or receiver drier, refrigerant lines with mufflers, thermal expansion valve or orifice tube
because residual flushing fluid cannot be removed from these components and they
restrict the flow of flushing agent through other components.

e) Why Suction Side Flushing Is Important

• When the off-cycle pressure equalizes in the backwards direction through damaged
compressor valves, debris may be forced back up the suction hose. If it is not removed,
this debris will travel into the replacement compressor and be circulated throughout the air
conditioning system, causing subsequent failures.

f) Flushing Rear Evaporator Lines

x Debris is distributed throughout the entire air conditioning system so it is important to flush
the rear lines. The rear expansion valve can be gutted or drilled out and remounted so
that the rear evaporator and hoses can be back flushed as an assembly. After blowing out
the flushing fluid and fumes a new thermal expansion valve should be mounted.

g) Importance Of Flushing Direction

• “Back flush”, or flushing in the reverse direction to normal flow, is the most effective. The
plate fin evaporators used on many front and rear evaporators have many small passages
which are difficult to clean without a strong pulsating reverse flow.

h) How long do I flush?

• Closed loop procedure, flush until the flushing fluid leaving the air conditioning
components are clean. Manual pressurized gun method requires a minimum of three
times, but more if exiting fluid is not clean.

i) Removal of Residual Flushing Fluid before Evacuation and Charge

• The primary vacuum pump should be protected from flushing fluid and fumes. Purging of
flushing solvent is necessary before connecting the recovery recycle machine to evacuate
and charge the air conditioning system. The best method is to allow Nitrogen to flow
through the components. If Nitrogen is not available, clean and dried compressed air can
be blown through the flushed components until the flush liquid is evaporated.
Air Tractor Maintenance Page 2-29
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B. Evacuation
x Evacuation is the process of removing air and moisture from the refrigeration system
before charging the system with refrigerant. Air or moisture remaining in the system
before and during the refrigerant charge process will cause increased pressures during
operation resulting in reduced or poor cooling and greatly reduce the compressor life.

a) Explanation of Evacuation Water Boils Under a Vacuum

x As vacuum is increased the temperature at
System Vacuum Boiling Point
which water boils drops. As the water/moisture
Inches Mercury Degrees F
boils its vapor can be drawn out of the system
by the vacuum pump. It is recommended to 24.04” 140 Fº
perform the evacuation process in a warm area. 26.45” 120 Fº
The vehicle engine can also be run in order to 27.99’ 100 Fº
warm up the components of the air conditioning 28.89” 80 Fº
system to enhance the evacuation process. 29.40” 60 Fº
29.71” 40 Fº
x Allow the vacuum pump to run for 30 minutes
29.82” 20 Fº
drawing down near to 30” Hg. After 30 minutes
of evacuation close the service valves and turn 29.87” 5 Fº
off the pump. Let the system sit for 10 minutes, if vacuum loss of 2” or greater occurs
there is probably a leak.
o Other reasons a vacuum cannot be held for 10 minutes after shut off.
▪ Flush was not completely removed from system before evacuation started.
▪ Refrigerant is trapped in refrigerant oil from previous charge.

b) Vacuum Pump Service

x Vacuum pumps not receiving regular service will be unable to
draw an adequate vacuum. In most cases simple changing the pumps oil will
correct the problem. Be sure to follow the manufacturer’s recommendations for
any maintenance on your evacuation pump. Change the oil after use while the oil
is still hot, because contaminants are still in suspension and will be removed with
the oil. If contaminants cool, solidify and stay in the pump, they lower vacuum
efficiency. In extreme cases, the oil stops lubricating and the pump seizes. The
only way to determine oil condition is to test vacuum pulled with an electronic
vacuum gauge. Contamination cannot be determined by oil color.

C. Charging the Air Conditioning System

a) Charging systems
• Electronic weight scales
• Charging stations

Safety Note
Never open the high side service valve with the system running! This can damage equipment
and cause bodily injury.
Page 2-30 Maintenance Air Tractor
June 21, 2018 AT-802/802A

b) Two ways to charge the system

1. Through the high side with air conditioning system off.

x Charge systems that heat the refrigerant will force the correct charge amount into the
system. Once the full charge has been dispensed the service valve must be closed and
the air conditioning system can be started.
x
2. Through the low side with the system running.
x With the engine running at flight-idle speed (approximately 75 percent Ng) with the
propeller in the feathered position. The air conditioner master switch is turned ON. The
blower switch is turned ON HIGH, and the service gauges are monitored to see that the
reading on the high-pressure gauge is increasing while the reading on the low-pressure
gauge is decreasing. If the gauges fail to behave as specified, turn the air conditioner
master switch OFF, stop the engine, and investigate the cause of the compressor’s
failure to engage. If the gauges behave properly, then charging can continue.

x Refrigerant is introduced into the low-pressure service valve while the compressor is
operating. The low pressure manifold valve should be opened to allow slow increases in
pressure in both the high- and -low pressure sides of the system. This filling should
continue until the low-pressure side of the system stabilizes at 28 to 32 psi and the high
pressure side is between 200 and 250 psi. The sight-glass on top of the receiver/dryer
should show clear liquid flow without bubbles.

D. System Oil Balance

a) Oil Flow
x Compressor lubrication occurs as the oil which circulates with the refrigerant passes
through the compressor crankcase during operation. The Sanden SD series compressor
achieves optimal durability and cooling performance when oil circulates through the
system at a ratio of 3.3% to 8% oil to refrigerant. Excess oil can act as an insulator limiting
heat transfer in the evaporator and condenser, while too little oil can negatively affect
durability.

b) Oil Checking Is Not Required Under Normal Conditions

x The mobile refrigeration system is a closed loop system, hence it is not necessary to
check or change oil in systems functioning normally and not in need of repair. The system
isolates the oil and refrigerant from moisture and contaminants, while normal operating
temperatures will be well below a point that will cause oil degradation.

c) When Oil Addition or Balancing is required

x Compressor or component replacement
x Loss of refrigerant and oil mixture
x Adding oil to the system is required when refrigerant loss occurs due to leakage at any
system component. Since oil is held in suspension with the refrigerant, oil will be lost with
the escaping refrigerant gas. Oil will need to be inspected for contamination during repairs
to determine if flushing is required
Air Tractor Maintenance Page 2-31
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d) Oil Addition When Replacing System Components

x
Air conditioning systems are designed to have a given oil charge so during component
replacement the goal should be to maintain the initial factory oil charge. It is understood
that system oil balance resulting from service activities is not an exact process, however
using these guidelines should roughly maintain the OEM system oil charge.
x Operating conditions at the time of system shut down will determine where and how much
oil settles in any given component in the air conditioning system. Therefore the exact
amount of oil removed during refrigerant loss or component replacement can only be
estimated in a shop environment. Sanden recommends adding SP-15 oil using these
guidelines.
e) System Oil Amount
x Oil circulates with the refrigerant during operation. During off periods oil will settle in all
system components with more collecting in cool components like evaporators,
accumulator and suction lines.

Evaporator

Drier

During shut down oil settles throughout the system collecting in all components

f) Oil Replacement Amount During Service

x When replacing a system component the goal is to restore to the original factory oil
amount. Use the chart below as a guide for restoring oil quantities when replacing system
components.

Typical Oil Amount Typical Oil Amount

Component Dual Cond Single Cond
fl. oz. cc fl. oz. cc
Major System Leak
3 88 1.5 44
Suction Line To Evaporator

Condenser
2 60 1 30
Evaporator
Receiver Drier
Minor System Leak 1 30 .5 15
Other Hoses or Hard Lines
Compressor Equal to amount drained from old compressor
Page 2-32 Maintenance Air Tractor
June 21, 2018 AT-802/802A

Example
A large system with no leak requires new compressor, suction hose Note: New compressors are
and drier. delivered with full oil charge. It
will be necessary to add or
Drain oil from old compressor = 3 oz subtract from the delivered oil
Oil remaining in old compressor = .5 oz (see note below) amount so the total in the
Oil lost from old suction hose = 1oz (from table) compressor equals the amount
Oil remaining in old drier = 1oz (from table) to be added.
Amount to be added 5.5 oz

Example—If the new compressor contains 8 oz (240 cc) you must drain
2.5 oz so the total in the compressor is 5.5 oz.

Note: When draining the old compressor roughly .5oz will remain in the compressor as film coating
all internal surfaces.

8. Common Causes of Compressor Failure

A. Compressor Overheated
x Overheating is most often caused by loss of refrigerant charge. Cool suction side
refrigerant returning from the evaporator provides cooling for the compressor. Once the
refrigerant charge is lost there is no refrigerant entering the compressor, hence no
compressor cooling. Blockages in the system will also prevent cool refrigerant flow to the
compressor.

B. Compressor Contaminated
There are several types of contamination. The most
common types are:
x Foreign material like metal chips, dirt and
desiccant. Resulting in broken internal
compressor components eventually locking up
the compressor
x Moisture from improper evacuation or hose
permeation. Moisture will corrode internal parts
resulting in failure. Moisture will create higher
system pressures or freeze in the expansion
device and blocking refrigerant flow.
x Air Conditioning system flush
Air Tractor Maintenance Page 2-33
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C. Clutch Slippage
x The compressor clutch is simply two friction
surfaces forced together, like a set of brakes.
Each time the clutch is engaged some amount
heat is generated. If the engagements occur
rapidly or the system voltage is to low, excessive
heat created will cause failure of bearing seals
and or melting of the field coil epoxy.

D. Handling or Impact Damage

x Striking, dropping or over torque will result in these types of damage:

AVIONICS

Optional radio equipment may include those listed in drawing 60616. Removal or replacement of any of the
radios requires removal of applicable fasteners in accordance with their corresponding installation drawing as
indicated on drawing 60616. All fasteners must be routinely inspected for tightness. Antennas must be
routinely inspected for secure attachment to the aircraft and structural integrity. Routine cleaning of the
avionics box and its components may be done by wiping with a damp cloth. Ventilation openings in
equipment housings should be open and free from obstructing lint and dust. For further information on
testing, adjustment, troubleshooting and repairs of the electronic equipment and systems, refer to the
manufacturer’s maintenance instructions, manuals and the applicable Federal Aviation Regulations.
Additional avionics maintenance information is found in FAA AC 43.13-1B Chapter 11, 12 and 15.

Electrical power to the radios is controlled by a circuit breaker switch located on the radio box. Power is then
distributed to each avionics component which is protected by an adequately rated circuit breaker located on
the radio box or in the lower panel. Wiring schematics specific to each avionics component may be obtained
from manufacturer’s data. These schematics are found in the figures section of the manual.

BATTERIES

Access to the batteries is shown in Figure 31. The batteries on your turbine will require REGULAR servicing.
Your batteries will last longer if you maintain the proper water level and the proper voltage on the voltage
regulator. Too high a voltage on the regulator will boil the batteries. Most operators use a digital voltmeter to
set the regulator to a measured voltage of 27.5.

One of the hardest things on your batteries is neglect in the off-season. Air Tractors with Crophawk flow
meters or anything else wired direct to the battery should be disconnected during the off-season so as not to
drain the battery. Periodic checks should be made during the off-season to insure that the batteries stay
charged. You may turn on the master switch and read battery voltage on the voltmeter. Batteries below 22
volts should be put on the charger and charged back to full strength. If you will keep them serviced during the
season and give them a little maintenance in the off-season, their longevity will increase. Don’t forget to drain
the battery acid sump at regular intervals as described in Figure 31. Keep the batteries clean. Dirt and acid on
the outside of the battery provide a path for a slight flow of electricity. This will discharge a battery in time.
Page 2-34 Maintenance Air Tractor
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Battery Removal and Replacement

A battery may be removed by following these steps:

1. Remove the side skins immediately forward of the firewall on both sides of the airplane.

2. Release the spring latches and remove covers from all three of the battery boxes.

3. Remove the ground cables from their terminal posts on all three batteries and secure them
well clear of the batteries.

4. Remove the positive cable from the battery or batteries that are desired to be removed.

5. If possible, lift the battery(s) vertically out of the battery box and remove from the right-hand
side of the airplane. If this is not practical, pass a long, sturdy rod through the engine mount,
tie close to the battery with suitable rope or cord, then lift from both sides of the airplane to
clear the battery box and pass out through the right-hand side of the airplane.

Replacement of the batteries may be accomplished by reversing the steps for removal listed above.

DANGER
All of the batteries are connected in parallel. The positive lead from any
battery is HOT even if it and its associated ground lead are disconnected
from their battery. It is vital that all ground leads are disconnected first
and re-connected last when batteries are removed and replaced. Fire,
explosion, and personal injury are possible if this precaution is not
observed.

Checking the Batteries

Always wear protective clothing, rubber gloves, and a face shield when servicing batteries. The batteries are
checked by determining the level of the electrolyte in each cell. First of all the battery caps are removed. Then
each cell is inspected individually. Using a light if necessary, the electrolyte level should be observed at or
slightly above the plastic split-ring that is visible through the filling hole.

Battery Cutout
Air Tractor Maintenance Page 2-35
AT-802/802A June 21, 2018

If the electrolyte fluid level is low and adding fluid is necessary, the electrolyte level can be raised by adding
distilled water. The battery should not be overfilled. The electrolyte level should not be more than one-quarter
inch above the split ring.

When a battery seems weak or will not hold a charge after charging, replacing the battery may be necessary.
The charge capacity of individual cells may be determined by checking the specific-gravity of the electrolyte in
those cells.

The specific-gravity check can be done with the use of a hydrometer constructed of acid-resistant materials.
The specific-gravity should range from 1.1 for a fully-discharged cell to 1.3 for a fully-charged cell. a specific-
gravity of 1.260 or more is considered an adequate charge. A specific-gravity of less than 1.260 indicates
charging is required. A variance of specific-gravity more than 0.1 from other cells in the battery is an indication
of a weak cell and the battery should be replaced. A specific-gravity reading of 1.285 to 1.295 indicates a fully
charged cell.

Commercial battery hydrometers are normally used for specific-gravity checks. These hydrometers may
display specific-gravity readings or might have red and green bands. Depending on the state of charge, the
specific-gravity readings should not be interpreted as absolute but as comparative readings with other cells in
the battery. A single cell whose specific-gravity reading is at wide variances with other cells in the battery
suggests a dead cell requiring replacement of the battery.

To check a G-246 (G-246AT) battery, first disconnect it from the other batteries and make sure that it is fully
charged. Connect a 38-amp load to the battery and monitor the battery voltage. A 38 amp load can be
obtained by connecting two 240 watt, GE 4580, lamps in parallel. If after 24 minutes the battery voltage is at
least 21 Volts or more, the battery is serviceable. While the battery is loaded, monitor the electrolyte in the
cells. Electrolyte boiling in a cell indicates a bad cell. Replace the battery if it fails to meet this requirement. If
the battery passes this test, recharge it before returning it to service.

Installing a New Gill Dry-Charged Battery

When a new Gill G-246 (G-246AT) battery is installed in the airplane, certain procedures must be observed to
ensure the satisfactory service of the battery.

CAUTION
Do not remove seals or vent plugs until ready
to fill with electrolyte.

The procedure for charging the battery is shown below.

1. Remove seals from cells.

2. On INITIAL WET DOWN, fill each cell with 1.235 specific gravity sulfuric acid to a level JUST
ABOVE THE SEPARATORS.

3. Rock battery from side to side to release any trapped air. Readjust electrolyte level as per
Step #2 above.

4. Let battery stand for one hour.

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5. Check electrolyte level and readjust if necessary to a level JUST ABOVE THE
SEPARATORS (Electrolyte level will generally expand or rise due to the gassing experienced
during the charging process outlined below).

6. INSTALL VENT PLUGS TIGHTLY INTO EACH CELL.

7. Prior to charging, clean and neutralize any spilled acid on the battery using a solution of
baking soda and water. Rinse with clean water.

8. Charge battery at an initial charge rate of 3 Amps until all cells are gassing freely and the
charge voltage and specific gravity of electrolytes are constant, or the voltage drops, over
three successive readings taken at one hour intervals (This procedure may take 18-24 hours
with a constant current charger). The charge rate is reduced to 1.5 Amps when the cells start
gassing. The fully-charged battery’s electrolyte level should be at the bottom of the split ring
with the charger still on.

During the period of charging, the electrolyte temperatures shall be maintained between 60°
F and 110° F (15.6° C and 43.3° C).

9. When battery is completely charged, the specific gravity should be greater than 1.275.
Readings should be taken with an aircraft battery hydrometer making sure to take the
readings as outlined on the hydrometer instructions.

10. After the battery is FULLY CHARGED, AND WITH CHARGER STILL ON, ADJUST
ELECTROLYTE LEVEL TO THE BOTTOM OF THE SPLIT RING and continue to charge for
one hour. Clean and neutralize any spilled acid prior to installing in aircraft.

For more detailed instructions call 1-800-456-0070 and ask for your free “GILL” service manual.

BRAKES

The wheel brake units are Cleveland 30-210A. The brake unit consists of the wheel cylinder assembly and
the torque plate, which is attached to the gear leg with the five axle bolts. The torque plates are
interchangeable from right to left, but the cylinder assembly can be converted to a R/H or a L/H by moving the
elbow to the fluid entry port.

Appendix 2 has additional information from Cleveland on brake system servicing.

Brake Removal and Installation

Brake details are shown in Figure 32.

Brake fluid used is red Mil-H-5606A petroleum-base fluid, which is used in most light aircraft. Do not use
automotive brake fluid as this will swell the O-rings.

The wheel units can be removed by using a wrench to remove the twelve bolts attaching the two halves of
each brake assembly. The brake line may be left connected if only the linings are to be charged. Linings are
Cleveland p/n 66-131 and are attached with Cleveland p/n 105-67 rivets. There are 32 linings and 64 rivets
per aircraft.

Each brake assembly has four pistons, which are Cleveland p/n 062-09301. The O-ring installed in the
cylinder is a Cleveland p/n 101-05200.

To remove the pistons in order to change O-rings, remove the brake line and install a 1/4X28 bolt in the
piston. Pull the piston from the caliper housing. The pistons are aluminum and should be checked for wear, or
burrs that could cut the O-ring. Check the bore in the housing at the same time. When installing new O-rings,
soak them in MIL-H-5606 brake fluid before replacing time. Re-install the pistons with care, so that the O-ring
is not damaged.
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Brake Discs

The brake disc is a Cleveland p/n 164-23001 and is attached to the bolts that attach the two rim halves
together. The wheel must be removed from the aircraft per previous instructions, the tire deflated, and the
wheel dis-assembled in order to remove the brake disc. With the new brake disc in place, re-assemble wheel
and tire per previous instructions.

Under average field conditions a brake disc should give years of trouble free service. However, unimproved
fields, standing water, heavy industrial pollution, or infrequent use of the aircraft may necessitate more
frequent inspection of discs to prolong the life of the brake lining.

Generally, the disc faces should be checked for wear, grooves, deep scratches, excessive general pitting or
coning of the break disc. Coning beyond 0.015 inch in either direction would be cause for replacement.
Single or isolated grooves up to 0.030 inch deep should not be cause for replacement, although general
grooving of the disc faces will reduce lining life.

Brake Linings

There are eight pairs of the brake linings on each brake. Four of the pairs are on the front of the brake and
four to the rear. The pairs are located on either side of the brake disc directly beneath each of the eight
pistons.

The end pair of brake linings can be seen on the top and bottom ends of both sides of the brake disc while
installed on the airplane. New brake linings are .250-inch thick. The brake linings should be replaced when
the remaining thickness is less than .100-inch to prevent rivet damage to the brake disc.

Brake Master-Cylinders

The master cylinders are Cleveland p/n 10-86A. The lower end is bolted to aluminum straps connected to the
rudder pedal. Both the strap and the pedal have bronze bushings that can be replaced when worn. The
bushings are oil-impregnated and do not require lubrication. Details of the brake master cylinders are shown
in Figure 33.

The lower end of the master cylinder is attached to a Parker clevis with a Parker check nut. If the rudder pedal
position (angle) should need changing for pilot comfort, the check nut can be loosened, and the Clevis
immediately below can be rotated with finger pressure in either direction to increase or decrease the angle
that the brake pedal makes with the cockpit floor. When desired angle is obtained, snug check nut.
To remove the master cylinder, loosen check nut and rotate plunger out of the clevis. Then removing the bolt
attaching the master cylinder to the steel plates and disconnect the two brake lines at the cylinder.

A repair kit is available for the master cylinder which is Cleveland p/n 199-521. The cylinder may be
disassembled and repair parts installed per instructions furnished with kit. If the check nut at the bottom is left
in the original position, the pedal angle will be the same as before when the master cylinder is re-installed. Be
sure the cylinder is free to swing through the full range of rudder pedal travel. If it does not, the two plates
which attach the cylinder are too close together and require an additional spacer washer.

If a spot of brake fluid appears on the cockpit floor on the L/H side it does not necessarily mean that the
master cylinder is leaking. The usual cause is over-filling the brake reservoir, so that when brakes are used,
and fluid returns to the reservoir, it sometimes leaks through the vent hole in the reservoir cap.

Brake Bleeding

If air enters the brake system because of worn O-rings or the replacement of brake system components, the
brake pedal will become soft and the brakes lose some of their effectiveness. It will then be necessary to
bleed the brakes to remove the air. Details of the brake-bleeding ports are shown in Figure 34.
Page 2-38 Maintenance Air Tractor
June 21, 2018 AT-802/802A

The conventional practice of placing a pressure pot line at the bleed screw location on the wheel cylinder and
forcing fluid up through the system generally does not work. The factory practice is to place one person in the
cockpit and another at the wheel cylinder with a bleed screw wrench and a clean bottle to catch the fluid.
Before the bleeding process beings, it is necessary to obtain a short piece (about 6” long) of windshield wiper
hose which will fit snugly over the bleed screw head so that all the fluid can be caught in the bottle and not
wasted.

The procedure is as follows:

1. The cockpit man pulls on the parking brake and leaves it on. Then he pumps the pedal on
the side being bled several times until the pedal begins to get fir. The parking brake is left on
since it is actually on a one-way check valve.

2. Then the cockpit man pushes on the pedal and shouts “Open” to the man at the wheel
cylinder who proceeds to open the bleed screw with a ¼” open-end wrench. Brake fluid and
air then rush through the bleed screw, through the hose, and into the bottle.

3. The cockpit man, who has held the pedal all the way down, then shouts “Close” as soon as
the pedal reaches the down position, and the other person closes the bleed screw
immediately.

4. The cockpit man uses the procedure outlined in (1) to obtain a firm pedal and again repeats
step (2) and (3).

5. The above procedure is repeated as many as a dozen or so times until a firm brake is
obtained with the parking brake off. Be sure to add brake fluid to the reservoir before the
reservoir is emptied or else you will have to start all over again. Don’t use the fluid in the
bottle as it will have bubbles of air. When the bubbles are gone and the fluid has been
determined to be clean, it is OK to use, however.

6. Repeat the process for the other wheel.

Parking Brake

The parking brake valve sued on later Air Tractor’s is a Scott p/n 4500A-2. Two of these valves are mounted
together with a common lever to pull the valve to the ON position. O-Rings within the valves may be replaced
when needed. An exploded view of the parking-brake valve is shown in Figure 35.

Leaking of brake fluid from the top of the valve body indicates failure to the O-rings that seals the valve stem.
O-ring replacement may be performed by removing the defective valve body only. O-ring replacement may
be done using the following steps:

1. Clamp the fluid-supply line for the brake reservoir to the master cylinder.

2. Remove the long AN3 bolts and nuts that clamp the valve bodies together.

3. Pull both valve bodies free of their support bracket.

4. Remove the AN3 bolt and spacers from the actuating levers. The bolt is threaded into the red
knob.

5. Separate the valve bodies.

6. Remove the brake lines from the ports in the near side and lower the end of the valve body.

7. Clip the end of the 3/32-inch-Dia. x 5/8-inch-long steel rivet that secures the actuating arm to
the valve stem.
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8. Remove the rivets and washers, freeing the arm from the valve stem.

9. While holding the valve body gently in a smooth-jaw vise, remove the elbow-fitting and large
fitting (valve seat) at the lower end of the valve body.

10 Remove the 3/4-inch-OD x 9/16-inch-ID O-ring from the valve seat.

11. Remove the spacer from the top of the valve stem and push the valve stem out of the valve
body through the hole normally filled by the valve seat.

12. Using an O-ring pick, remove the 3/8-inch-OD x 1/4-inch-ID O-ring from the lower end of the
bore that guides the valve stem.

Blow the bore clean with compressed air, then coat the bore with MIL-H-5606 brake fluid. Do not use any
other solvents to clean the bore.

Coat the replacement O-ring with MIL-H-5606 brake fluid and slide into position in the annular groove in the
valve-stem housing. All parts to be reassembled should be coated with fluid before assembly. The remainder
of the replacement can be done by working backwards from Step 11 of the removal procedure. The rivet that
was destroyed in Step 7 above can be replaced with Scott part number 18286 or other suitable 3/32” x 5/8”
R.H. steel rivet.

After the parking-brake valve is returned to the airplane and hoses are reconnected, the brakes must be bled
as described in BRAKE BLEEDING in Section 2 of this manual.

COCKPIT CONTROLS

Details of the cockpit controls are shown in Figure 5, Figure 6, and Figure 7.

The control stick assembly is p/n 70698-1 for the 802A (p/n 70049-9 for the 802-2 seat version) and is
attached to the 70730-1 torque tube assembly with a NAS1304-44 bolt. The lower end of the control stick is a
machined aluminum part (p/n 70043-1) which houses two Fafnir KP4 bearings held in place by two p/n 1300-
93 snap rings. The control stick weld assembly is p/n 70037-1 and is chrome-plated and oiled internally. The
control stick grip is an Automatic Flagman p/n NA1-135.

A p/n 70726-1 push-rod connects the control stick to the forward idler assembly with an AN4-13A bolt in each
end. The push-rod has Fafnir REP4M6 bearings in each end, which allows length adjustment.

The 70730-1 torque tube is supported on each end with a p/n 70721-1 housing assembly, which attaches to
the fuselage fame with AN5-14A bolts. Each housing assembly has a grease fitting installed and the grease
should be applied at least during annual inspections. The needle bearings in the housings are Torrington
B1212, which may be replaced if required. The flange thrust surface, after a period of time, will wear causing
fore- and aft slack in the torque tube as the elevators are moved up and down with the control stick. The slack
may be removed by adding a .010 thick shim (p/n 3088A324) which is 3/4 I.D. x 1 1/8 O.D. With the torque
tube all the way against the rear flange, clearance on the front flange should be between .001 and .005. If the
shim is a little too thick, the face of the forward flange can be faced off slightly if desired.

The forward end of the torque tube has a p/n 70149-2 boot and a 70144-1 boot ring installed, with 9008-1
screws attaching the boot ring to the floor. On the aft cockpit wall, a p/n 70543-1 boot and 70542-1 ring seal
the forward elevator push-rod entrance. The hopper handle has a p/n 80168-1 boot with a p/n 80168-1 boot
with a p/n 70140-1 boot ring, and the spray lever push-rod has a p/n 80131-1 boot with p/n 70154-1 boot ring.
The trim push-rod has a p/n 70817-1 boot and a p/n 70818-1 boot ring.

A p/n 70478-1 control lock assembly is attached to two AN42B-4A eyebolts that are part of the instrument
panel attachment. An Ajax No. 38 spring keeps the control lock pulled up out of the way.
Page 2-40 Maintenance Air Tractor
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ELECTRICAL SYSTEM

General

Each of the separate electrical circuits discussed in this section is accompanied by its particular wiring
schematic drawing shown as a figure in Section 7. The associated Air Tractor part number of a component is
the drawing number plus -1 or -2 for left-hand and right-hand parts, respectively. In the event that the part is
symmetrical, without a hand designation, the suffix number is -1.

All troubleshooting of electrical systems is directed toward the identification of faulty components. The most
valuable tool for use in troubleshooting is the Volt/Ohmmeter.

The Voltmeter is used with electrical power ON for the circuit under examination. It is used to determine that
the proper voltage is available at the appliance or at any location in the circuit between the airplane bus and
the appliance. A socketed 28-Volt bulb may be substituted for the Voltmeter, with one wire lead connected to
a wire or terminal while the other wire lead is connected to ground.

The Ohmmeter must be used with electrical power OFF of the circuit under examination. It is primarily useful
for establishing the continuity of wiring or ground contacts. Here, the resistance of the wiring and gound
circuits should read near ZERO Ohms. The Ohmmeter is of little value in evaluating appliances such as
motors, lamps, etc., since the desirable resistance of the appliance is unknown. The exception is when the
resistance is very high (infinite), indicating an open circuit and a failed component.

The simplest means of ascertaining a faulty component is substitution with a known functioning component.
This is practical if the substituted part is a switch or light bulb, or easily available part.

Starter/Generator

The wiring schematic for the Starter/Generator is shown in Figure 11. When the starter switch is engaged, a
small current is sent to the coil for the starter relay. This relay completes the circuit to provide starting current
to the starter. The Starter/Generator, while acting as a generator, will produce 250 amps continuously.

Voltage Regulator

The wiring schematic for the Voltage Regulator is shown in Figure 11. This solid-state Voltage Regulator
controls the generator output at 27.5 volts. The Voltage Regulator is activated by closure of the generator
switch. When the generator output has risen to near 27.5 volts, a signal from the Voltage Regulator activates
the line contact relay, placing the generator on-line. The line contact relay performs the same function as the
older reverse-current relay in taking the generator off-line when the generator output voltage falls below
residual battery voltage.

The Voltage Regulator uses logic based on the status of the system to control the regulator output. This logic
uses samples of voltages in the system to determine the current system condition. These include voltages on
both sides of the line contactor relay to determine if the relay is open or closed. Also, voltages at the starter
switch are monitored to determine the position of the starter switch.

The voltage output of the Voltage Regulator is pre-set to 27.5 volts. The voltage output may be set to between
26 to 28.5 volts by adjusting the voltage-adjustment screw at the end of the case. The plug screw must be
removed to allow access to the voltage-adjustment screw inside.

Engine Instruments

The NP Indicator, NG Indicator and the ITT Indicator are independent of the airplane’s electrical system. They
are powered by their respective tach-generators or thermocouple.

The Fuel Filter Pressure Light, Low Oil Pressure Light, Oil Temperature Indicator, Air Filter Pressure Light,
Chip Light, and Hour Meter are all powered by the airplane’s electrical system.

The wiring schematics for the engine instruments are shown in Figure 36.
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Voltmeter

The wiring schematic for the Voltmeter is shown in Figure 36. The Voltmeter shows the voltage on the
airplane’s electrical bus. Voltmeter readings may be used to determine the condition of the battery and
Starter/Generator.

When the Master Switch is ON, with the Starter/Generator not charging, with no load on the system, the fully-
charged battery voltage should be between 24 and 25 volts. When the Starter/Generator is charging, the
voltage on the airplane bus should be approximately 27.5 volts.

Low-Voltage Warning Light

The wiring schematic for the Low-Voltage Warning Light is shown in Figure 36. This warning light operates
parallel with the Voltmeter to provide an indication of Starter/Generator failure. The warning light senses the
voltage on the airplane bus. The light comes ON at any time that the master switch is ON and the voltage on
the airplane bus drops below 25 volts. Because the normal battery voltage is 24 volts, it follows that the light
will be ON at any time that the generator is not producing more than 25 volts on the bus.

The Low Voltage Warning Light is a self-contained unit that uses solid-state circuitry and a light bulb. The light
bulb is not replaceable. Failure of the warning light requires replacement of the entire unit.

Engine Overspeed Solenoid

The wiring schematic for the Engine Overspeed Solenoid is shown in Figure 36. The function of this solenoid
is to switch the hydraulic propeller-control circuit from variable RPM to fixed RPM in the event of governor
failure. When activated, this circuit maintains propeller RPM to 30-to-60 RPM below the engine’s maximum of
1700 RPM.

Boost Pump

The wiring schematic for the boost pump is shown in Figure 37.

Fuel Gauging

The wiring schematic for the fuel gauging system is shown in Figure 28. The fuel quantity is shown on the
panel-mounted fuel gauges. Each of the wing fuel cells is gauged separately. The fuel quantity in each of the
fuel tanks is displayed on the respective panel fuel gauge.

Each of the fuel tanks has two fuel-quantity sending elements. These two sending elements are connected in
series electrically. The inboard sending element is active in sensing fuel level when the fuel level is in the
lower third of the tank.

The outboard sending element is active when the fuel level is in the upper third of the tank. Both the elements
are active when the fuel level is in the mid-range.

The inboard sender is insulated from ground by the ten insulating bushings that are used both sides of the
five holes in its flange. The outboard sender is grounded through its mounting bolts.

The panel-mounted fuel gauges are micro-ammeters with a full-scale range of 100 micro amps. A circuit
board is attached to the binding posts of the instruments. Circuitry on this board provides 4.3 -volt power
supply for the fuel-gauging system. A trim-potentiometer is located in the back side of the upper instrument
panel just to the left of center. This trimmer is used to calibrate the full-scale readings on the micro-ammeter.
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Wing Flaps

The wiring schematic for the wing flaps is shown in Figure 28. Power to drive the flaps up and down is
provided by two relays, with one relay for each direction of travel. Each of the UP or DOWN relays is actuated
by placing the cockpit flap switch in the appropriate location. The wiring from the flap switch to the relays is
routed through the micro-switches that serve as limit switches for the full UP and full DOWN positions.

Stall-Warning Horn

The wiring schematic for the wing flaps is shown in Figure 28. The horn is connected in series with the lift-
detector switch that is located near the leading edge of a mid-span of the right-hand wing.

The lift-detector switch is controlled by a tap that projects forward into the airstream. When at rest, the weight
of the tab holds it down, opening the switch. When the airflow around the lift detector shifts to a forward
direction, that tab is lifted, closing the switch and causing the horn to sound.

Windshield Washer

The wiring schematic for the windshield washer is shown in Figure 38. When the switch is closed, the pump’s
motor starts and the solenoid valve is opened. The flow of windshield-washing fluid will continue until the
switch it released. The purpose of the solenoid is to provide a sharp cut-off of fluid when the switch is
released. This prevents the dribbling of fluid into the windshield.

Windshield Wiper

The wiring schematic for the windshield wiper is shown in Figure 39. The wiper switch has three positions,
HIGH, LOW, and PARK. When the switch is in the PARK position, the wiper blades are parked and the power
to the wiper motor is off.

Cockpit Lighting

The wiring schematic for the cockpit lighting is shown in Figure 40. The intensity level of the cockpit lights,
except for the dome and map lights, is controlled by the solid-state dimming circuit.

When the panel light switch is turned ON, power is available to the dimming circuit. The panel-light intensity is
controlled by the panel-light rheostat on the instrument panel.

Flap Light

The wiring schematic for the flap light is shown in Figure 41. The flap light is located in a housing on the upper
side of the left-hand wing just forward of the wing flap, near the center of the span of the flap. The light
illuminates marks on the leading edge of the flap, providing an indication of the amount of deflection of the
flap. The flap light is controlled by the instrument-light switch, but it is not dimmed by the panel-light dimming
circuitry.

Position and Strobe Lighting

The wiring schematic for the position lights and the strobe lights is shown in Figure 40. These lights are
controlled by the navigation-light switch on the lower instrument panel. When the switch is placed in the
DOWN position, power is sent to the red light on the left-hand wing tip, the green light on the right-hand wing
tip, and the white light on the rudder. When the switch is placed in the UP position, power is sent to the three
position lights plus the strobe lights located on each wing tip.
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Taxi Lights

The wiring schematic for the taxi lights is shown in Figure 41. The taxi lights, also called Nose Lights, are the
two 250-watt (p/n 4553) bulbs located in the extreme nose of the airplane, just below the propeller hub.
The taxi-light switch is located on the lower instrument panel. This switch receives its electrical power from
either the airplane bus or from the work-light relay. It may be switched to provide power to the coil of the taxi-
light relay. This relay, in turn, supplies current to both of the taxi lights.

Night Working Lights

The wiring schematic for the night working lights is shown in Figure 42. The Night Working Lights combine the
functions of the 600-watt landing lights (p/n Q4559) and the 250-watt turn lights (p/n 4553) for optimum
visibility while operating at night.

The extension of the landing lights is individually controlled by the extend-and-retract switches located on the
lower switch panel. These switches allow the landing lights to be stopped at any point in their extensions or
retraction to provide the best replacement of lighting to suit the pilot. The landing lights can be turned ON or
OFF by use of the MAIN switch to the right of the extend-and-retract switches on the lower panel.

The turn-light switch is a push-on, push-off button switch located at the upper left of the control stick. When
the landing-light main switch is ON and the turn-light switch is turned on, the turn-light selector switch atop the
control stick is enabled. This switch has LEFT, RIGHT, and center OFF positions. When the turn-light selector
switch is moved out of its center position, left or right, the wing-tip-mounted turn light is turned ON for the
selected side while the landing lights are simultaneously turned OFF. Return of the turn-light switch to its
center position restores the landing light to ON and the selected turn light to OFF.

All of the lamp filament circuits are switched by relays. Since the main landing lights are not individually
selected ON, a single relay switches both lamps simultaneously. This relay is activated ON when the MAIN
switch is ON and both of the double-pole, double-throw turn relays are in their normally-closed positions.
When the working light switch is ON and the turn-light selector switch is moved from its center position, the
coil of the selected turn relay is energized. This causes the plunger of the relay to move, turning the light ON
and simultaneously breaking the circuit to the relay coil that powers the main landing lights.

When the working-light switch is OFF, movement of the turn-light selector switch has no effect.

Lighting System Troubleshooting

Electronic Instrument Light Dimmer

The instrument lights are dimmed by two separate dimmer controls. One of these is for the upper panel
instrument lights and the other is for the lower panel lights. The instrument light switch feeds power to the
dimmer circuits and the flap light through the five Amp instrument-light circuit breaker. The pilot has control of
the instrument light intensity through the knob on the variable resistor, P/N RV4NAYSD-102A, mounted in the
upper panel. There is a separate control for each of the upper panel and the lower panel lights. The controls
for the upper and lower panels are identical except for wire numbers. The variable resistor controls the bias
on the base pin of the P/N 2N3055 power transistor. Power is fed to the collector of the transistor while the
emitter of the transistor outputs current to the lighting bus. The schematic of the dimmer circuit is shown on
drawing 60059 page 2, and the assembly details are shown on the drawing 60647.

Troubleshooting

The following instructions are for the upper panel dimmer circuit. Troubleshooting the lower panel is identical
except that on later aircraft the wires are numbered differently from the upper panel control to the lower panel
control. Use the schematic, drawing 60059 page 2, and the assembly drawing, 60647, to aid in
troubleshooting.
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If one of the electronic dimmers should fail to operate, first check the five-Amp-instrument-light circuit breaker.
If the flap light burns when the master switch and the instrument light switches are activated, the circuit
breaker and switch are good. Open the lower panel and visually inspect the wiring harness for broken wires
and corroded connections.

To check for a short in the instrument light fixtures, make sure the master switch is OFF and disconnect the
60302-114 transistor output wire from the lighting bus. Fabricate a test lead with a five-Amp circuit breaker,
two alligator clips, and about 18 inches of 20-gauge wire. Make sure that the instrument lights work by
connecting the test lead, with the circuit breaker in line, between the power bus and the lighting bus. Turn ON
the master switch. If the lights illuminate, the fixtures and wiring are fine. If the circuit breaker in the test lead
pops, there is a short in the instrument light fixtures or wiring. If there is a short, isolate it and make the
necessary repairs. Make sure all of the lights and wiring of the system are working before proceeding, since
shorts are the most common cause of transistor failure.

Once it is known that the instrument lights and wiring are good, and the dimmer still will not control them, use
a Volt meter to make sure that the instrument-light switch is feeding bus voltage to the variable resistor and
the C terminal of the transistor. To access the terminals of the transistor, remove the two screws that hold the
heat sink to the lower panel. The variable-resistor terminal with the 60302-167 wire is the power wire from the
instrument light switch. If voltage is not present at either one or both of these terminals, isolate the trouble and
make the necessary repairs to the wiring. Use the Volt meter to check the voltage at the B terminal of the
transistor. This voltage should vary from 0 to bus level when the control knob is turned.

If the voltage is not proper at the B terminal, remove the transistor and recheck the voltage at the B terminal
of the transistor socket. To remove the transistor from the socket, remove the two screws holding it to the
heat sink. Pull the transistor out of the socket. If the voltage is still not proper at the B terminal, the variable
resistor (P/N RV4NAYSD-102A) is bad or has a bad ground. If the voltages to the B and C terminal of the
transistor are good and the dimmer does not work, the transistor is bad. To install a new transistor (P/N
2N3055), coat the bottom of the transistor with a thin coat of heat-sink compound. Insert the mica insulator
over the two transistor leads and stick it to the heat-sink compound. Coat the bottom of the mica insulator with
a thin coat of heat-sink compound. White heat-sink compound can be obtained at most Radio Shack or
electronic supply stores. Most Radio Shack stores also stock the 2N3055 transistor. Plug the transistor
through the heat sink and into the socket. Install the screws that were removed. Make sure that the shoulders
of the transistor-socket-screw holes seat properly in the heat-sink holes. The case of the transistor is one of
the electrical connections of the transistor, and must not be grounded to the heat sink or the aircraft. If the
case is shorted to ground, with the power on, the transistor will be ruined. Once the wires have been
reconnected and the unit is working properly, mount the heat sink to the lower panel and secure any loose
wires as necessary. Double check the operation of the unit before fastening the lower panel and returning the
aircraft to service.

Hopper Quantity Gauges

The wiring schematic for the hopper quantity gauges is shown in Figure 43. The hopper-quantity circuitry
provides hopper quality information on the pilot’s instrument panel. The optional external hopper-quantity
gauges may be located on either or both sides of the fuselage, aft of the wing, easily visible from the single-
point hopper fill locations. All of the gauges are normally calibrated in gallons. The gauge may be calibrated in
liters at customer option. The external gauges are designed to assist the ground crew in filling the hopper.

The cockpit gauge is a solid-state display whose characters are generated within the display case. The
external gauges are digital repeats of the cockpit gauge. If re-calibration of the cockpit gauge is required, refer
to Report 0707, which is furnished in the Appendix of this manual.

In Figure 43, the Hopper Fill Gauge, near the lower left-hand corner of the drawing, is actually a potentiometer
that is connected to the hopper float. This potentiometer transmits the analog hopper quantity information to
the hopper-contents digital display case. Circuitry within the display case converts this analog signal to a
digital signal that is displayed on the panel digital display.
Air Tractor Maintenance Page 2-45
AT-802/802A June 21, 2018

Oil Cooler Blower

The wiring schematic for the oil cooler blower is shown in Figure 44 with continuation on Figure 11. The Oil
Cooler Blower is controlled by the propeller-governor switch and the beta switch. Whenever the propeller is
feathered or in beta and the aircraft master switch on, the blower motor should run.

Air Conditioner - Engine Powered

The wiring schematic for the engine-powered air conditioner is shown in Figure 4.

The Air Tractor engine-powered air conditioner uses a Sanden 508 compressor with a serpentine type pulley
and electromagnetic clutch. A splined shaft in the compressor-mount casting engages a drive gear in the
accessory case of the engine. This quill shaft (p/n 51628) has a small diameter shear section that protects the
engine in case of a compressor or bearing failure. This pulley drives the compressor’s flywheel by the use of a
pair of matched V-belts. The splined shaft, small pulley, belts, and compressor flywheel are engaged and
moving any time that the compressor section of the engine is turning.

The clutch is engaged any time that the air-conditioner switch is on and the system pressure is within
operating limits. High pressure causes the over-pressure contacts in the trinary switch to open. This opening
breaks the circuit to the clutch and it is de-energized. The trinary switch also has a low-pressure circuit that
breaks the circuit to the clutch in the event that sufficient refrigerant is lost from the system to cause damage
to the compressor.

The condenser is a copper-core, single pass, 12-inch-by 24-inch coil. Refrigerant enters the top of the coil
and exits at its lower side. Air for cooling the condenser is drawn in through louvers in the left side of the aft
fuselage. This cooling air moves athwart ship to the dual pusher-type fans that drive it through the condenser
coil and out through the louvers in the right-hand side of the aft fuselage.

The receiver-dryer is suitable for use with either refrigerant R-12 or R-134a. However, the receiver-dryer must
be replaced if a change is made from one refrigerant to the other.

The expansion valve is a block type with internal temperature and pressure compensation.

The evaporator uses a multi-pass coil and a squirrel-cage blower. A ram-air selector on the aft-cabin wall
allows the input of outside air for mixing with cabin air while the air conditioner is in use.

All hoses in the system are Teflon-sheathed to minimize transpiration leakage of the refrigerant. The hoses
are mated to their end-fittings with bubble-crimp swages. All of the end-fitting connections are made with O-
ring and Tube connectors.

The service valves are close together inside the first removable skin behind the cockpit on the right-hand side
of the airplane.
Page 2-46 Maintenance Air Tractor
June 21, 2018 AT-802/802A

ELECTRONIC STARTING AND CHARGING SYSTEM THEORY OF OPERATION

(Nomenclature: S/G-Starter Generator, GCU-Generator Control Unit, LCR-Line Contact Relay, LV-Low Voltage, VM-Volt
meter)

Starting: Actuating the Start Switch energizes the Start Relay, which applies battery voltage to term C of the
S/G. This operates as a series wound DC motor. Note that at the same time battery voltage is applied to pin N
of the GCU which signals it to remove field excitation from the S/G. The purpose of this feature is to prevent
the poor start performance that would otherwise result if the Generator Switch were left in the ON position.

Note

It is recommended that the Generator Switch be in the OFF position

during START because the high inrush current to the batteries
immediately upon Start termination will result in higher than normal gas
temperature (ITT). It is better to allow the engine to stabilize at Ground
Idle before turning the Generator Switch ON.

Generator Mode

Following engine starting and prior to turning the Generator Switch ON (The engine at ground idle) the
voltage output of the S/G (Terminal B) should be .5 to 1.5 volts. This is a residual voltage that results from
residual magnetism in the S/G even though the field excitation from the GCU is zero. Turning the Generator
Switch ON causes this residual voltage to be applied to pin J, which the GCU in turn outputs on pin M. As a
result the S/G output will build up rapidly and stabilize at the 27.5 Volt setting of the GCU (externally adjusted
from 26.5 to 28.5 volts). Sensing for Voltage Regulation is between pins B and G.

Line Contact Relay (LCR) Control

The GCU monitors the S/G output and the Bus Voltage on pins B and A respectively. As the S/G voltage
builds up to within approximately .2 volts of the Bus voltage the GCU will output system voltage on the pin H
resulting in activation of the LCR. Power of this circuit is derived from pin J, so turning the Generator Switch
OFF disables the LCR as well as the S/G.

Reverse Current Protection

If the S/G voltage drops below the Bus voltage (battery) due to normal conditions such as engine shut down
or abnormal conditions such as loss of field excitation the S/G will draw reverse current (discharge the
battery). The GCU senses this condition via pin D that is connected to terminal D of the S/G. Terminal D
output is a positive voltage proportional to reverse current.

Overvoltage (OV) Protection

In the event that system faults occur, either internal or external to the GCU, that results in over excitation of
the S/G the OV circuit will prevent the Bus voltage from going above approximately 32 volts. This protection is
accomplished by a “Crowbar” circuit in the GCU, which internally shorts pin J to D. This results in immediate
removal of voltage from the S/G field and the LCR coil. At the same time high current flow through the 15A
C/B causing it to trip. The OV Circuit has a time delay to prevent nuisance trips due to system transients.

Charging System Troubleshooting Guide

General Considerations- As a general rule if the Starter Generator functions normally in the Start mode
there will be nothing wrong with it that would prevent it from functioning in the Generate mode.
Air Tractor Maintenance Page 2-47
AT-802/802A June 21, 2018

Before attempting to correct any problem with this system first read and understand the DESCRIPTION and
THEORY OF OPERATION sections and acquaint yourself with the location and function of the various
components. Look for obvious problems such as overheating, burned wires, loose components, and loose
electrical connections. Disconnect the Cannon plug and inspect it and all other electrical connections for
corrosion. Correct any of these problems before proceeding.

Equipment- Equipment recommended for troubleshooting the charging system is shown below:

1) A multimeter capable of .01V resolution in the 0-2.5V range, .15V resolution in the 0-30V range
and capable of reading from a fraction of an OHM to several KILOHMS will be required. An auto-
ranging digital instrument is ideal but any good quality until will work. For point-to-point ringout,
the ohmmeter function will be used.

2) A Breakout Box- This is not absolutely essential but it is very effective in localizing many
problems. It can be fabricated per Figure 45 or it is available from your dealer at a reasonable
price.

Troubleshooting Procedures- Recommended sequences for troubleshooting the charging system are
shown below

Static Tests- Before going into specific Symptoms, which will result in, operational squawks it is productive to
point out a static test routine that is quick and easy and will result in localizing some problems without starting
the engine. This procedure entails removing the connector from the GCU and checking with the ohmmeter fro
designated sockets in test leads will usually have a small resistance, about .1 to .4 ohms, so before starting,
short the probes together and get this reading. Subtract this reading from all point to point readings.

Initial Setup - Master Switch OFF, Generator Switch ON.

From To Normal Notes

Value

GCU L S/G B 0 ohms if high, check Start Switch, Generator Switch, 15A C/B, and
all associated wires and connections.

GCU L S/G E 0 ohms if high, check wire and connections from L to ground.

GCU G S/G E 0 ohms if high, check wire and connections.

GCU M S/G A 0 ohms if high, check wire and connects.

S/G A S/G E 2 ohms if high (over 5 ohms), suspect S/G field is open.

If low (less than 1.5), suspect that S/G field is shorted for
GCU
M to S/G A wire shorted to ground.

GCU D S/G D 0 ohms if high, check wire and connections.

GCU H LCR X2 0 ohms if high, check wire and connections.

LCR X2 S/G E 56 ohms If high (over 75 ohms), suspect LCR Coil is open.

If low, suspect LCR Coil is shorted or GCU H to LCR X2

Wire is shorted to ground.

GCU A LCR AZ 0 ohms if high, check wire and connections.

GCU B LCR A1 O ohms if high, check wire and connections.

Page 2-48 Maintenance Air Tractor
June 21, 2018 AT-802/802A

In the following, the expression “GEN will not come on line” is evidence by a low Lower Instrument Panel
Voltmeter reading (25V or lower) and the LV Light staying on.

Symptom- After engine start, GEN will not come on line unless the Start Switch is engaged momentarily after
the Generator Switch is turned on.

Probable Cause- Field Flash function of GCU inoperative.

Fix- Repair or replace GCU.

Notes- The system can be operated as described without creating further detrimental effects until a
convenient time to have the GCU replaced or repaired.

Symptom- During engine shutdown the starter continues to run if the Generator Switch is left ON.

Probable Cause- Reverse Current Protection function of GCU is defective.

Fix- Repair or replace GCU.

Notes- Turning the Generator Switch off prior to engine shutdown will correct this condition as a stopgap
measure but the operator should be aware that if this precaution is overlooked damage to the starter
generator can result.

Symptom- After an engine start the Generator will not come on line (low VM reading and/or LV Lite ON) but
normal generator output voltage exists (nominally 28V) at A1 of the LCR.

Probable Causes- This symptom would indicate that the Generator has built up and is being regulated but the
LCR is not connecting the Generator to the Bus. This can be caused by:

a) Bad LCR, check for 56 ohms through LCR Coil.

b) Check the 120 Amp Bus Circuit Breaker.

c) No output (nominally 28V) on pin H of the GCU (defective GCU).

d) Output on pin H but no voltage on X2 of LCR (defective wiring).

e) Normal voltage (nominally 28V) from X2 to X1 of LCR (defective LCR).

f) Normal voltage (nominally 28V) from both X2 and X1 of LCR (open ground wire).

Fix-

b) Replace or repair GCU

c) and e) Ring out and repair wiring as required

d) Replace LCR
Air Tractor Maintenance Page 2-49
AT-802/802A June 21, 2018

Symptom - After an engine start the Generator won’t come on line and the voltage at A1 to the LCR is only
about 1 Volt and there is no voltage on pin J of the GCU.

Probable Cause - There is a discontinuity in the circuit feeding power to the GCU, which includes the wiring,
the 15A C/B, Generator Switch, and the Start Switch.

Fix - Make sure that the 15A C/B is not tripped and that the Generator Switch is ON and then proceed to ring
out and isolate the discontinuity from A1 of the LCR to pin J.

Symptom - The Generator won’t come on line and the voltage on A1 of the LCR is low (9-16V).

Probable Cause - The Voltage Regulator section of the GCU is defective.

Fix - Repair or replace the GCU.

Symptom - The Lower Instrument Panel Voltmeter indicates rapidly increasing bus voltage and then at about
32V suddenly drops to about 24V and then slowly decreases as the batteries discharge.

Probable Cause - This is indicative of an Overvoltage trip and may be accompanied by the 15A C/B tripping.
In those cases where the C/B does not trip the system can be restored to normal operation by momentarily
turning the Generator Switch off and back on.

Fix - If resetting the C/B or cycling the Generator Switch restores the system and the Generator stays on line
the GCU is suspect of an intermittent condition. If the symptoms repeat the GCU is faulty and should be
repaired or replaced.

ENGINE MAINTENANCE

Maintenance on your Pratt & Whitney PT6A engine is to be done in accordance with Pratt and Whitney
Manuals that are listed under “Instructions for Continued Airworthiness” in the Description section. Time and
experience have proven that an engine properly maintained will give excellent service with a minimum of
down time and expense. Establish a routine maintenance schedule and adhere to it as closely as possible,
taking into consideration the problems of busy schedules in mid-season.

The proper engine manuals for the airplane are listed below:

“Maintenance Manual - Turboprop Gas Turbine Engine- Models PT6A-45A/-145B/-45R”

Manual Part No. 3027042, Vols. 1 & 2

“Maintenance Manual - Turboprop Gas Turbine Engine- Models PT6A-65AG/-67AR/-65B/

-65R” Manual Part No. 3032842, Vols. 1 & 2

“Maintenance Manual - Turboprop Gas Turbine Engine- Models PT6A-67/-67A/-67R/-67AF/

-67AG/-67T” Manual Part No. 3036132, Vols. 1 & 2

“Maintenance Manual - Turboprop Gas Turbine Engine- Models PT6A-67F” Manual Part No.
3071152, Vols. 1 & 2

All of these manuals may be obtained from:

Pratt & Whitney Canada

1000 Marie-Victorin
Longueuil, Quebec
J4G 1A1 Canada
Page 2-50 Maintenance Air Tractor
June 21, 2018 AT-802/802A

Equally important to proper maintenance is the keeping of records. Maintenance records on a turbine engine
are extremely important and every effort should be made to see that all the work performed is properly
recorded. A record of the number of starts and flights MUST be kept for figuring cycle counts on the rotor
components in your engine at each annual. The cycles are figured using the number of starts and flights, with
a formula found in the applicable engine Service Bulletin. When these parts reach their life limit in either hours
consumed or cycles, they must be removed and discarded. Few of you will ever see a part reach that limit but
the records must be kept for your logbooks to be in proper order. Please refer to Section 5,
AIRWORTHINESS LIMITATIONS.

While on the subject of record keeping, it is a good idea to keep a small pad in the cockpit to record engine
parameters on a regular basis. For example, on the return from your first load each day, at the same pressure
altitude with the same torque and propeller RPM setting, record the following: hour meter time, OAT, IT, Ng,
oil pressure and fuel pressure. When trouble appears, this information will save lots of time troubleshooting
and will also give you a good picture of the trends in you engine. Remember, no two engines will run the
same. The change in your engine parameters over a period of time is what really matters. Keep it written
down because your mind will deceive you over the span of a season and it is the best way for maintenance
personnel to make an accurate diagnosis when problems arise.

Cleaning Engine Exterior

The cleaning of your engine may be accomplished only when the engine is cold. NEVER WASH A HOT
ENGINE. You may wash the engine exterior with water or with a petroleum base solvent. While cleaning your
engine, it is a good time to inspect all the engine externals; tubing, wiring, control linkages, hose assemblies,
etc. You should look for evidence of wear, chafing, cracks, corrosion, fuel and oil leaks, and the security of
hoses, brackets, clamps and connections. Also inspect your air inlet system for signs of leaks that would allow
unfiltered air into the engine.

After cleaning your engine, blow it off with compressed air and run the engine until it is dry. Keeping the
outside of your engine clean will help in spotting problems, make controls easier to operate, and limit the wear
on the beta block and beta ring. Remember also to keep your oil cooler cleaned on a regular basis to maintain
the efficiency of the cooler for operation in hot weather.

Fuel Requirements

The Pratt & Whitney PT6A engine will run on Jet A, kerosene, diesel, or Avgas. Avgas may be used only in
the case of an emergency and for duration of no longer than 150 hours between overhauls. Diesel is not
recommended. Diesel does not burn as clean as Jet A or kerosene, causing problems with fuel nozzles,
combustion liners, and hot section parts.

Air Tractor recommends the use of Jet A fuel that has been treated with a Fuel System Icing Inhibitor (FSII)
such as Prist. Some Jet A comes from the supplier with FSII in it and some does not, so check with your
supplier to be sure. It is also recommended that fuel be treated with a Biocide (such as BioBar) to prevent the
growth of bacteria and fungus in your fuel storage tank(s).

On your ground equipment, install a fuel filter/water separator that will shut off the fuel flow when water is
present. Fuel MUST be kept clean, water free, and free of bacterial and fungal growth. Care should be taken
when fueling the aircraft in dusty conditions to keep dirt form entering the fuel tanks.

See the approved Airplane Flight Manual for details.

Air Tractor Maintenance Page 2-51
AT-802/802A June 21, 2018

Fuel Filter Cleaning

The firewall fuel filter is shown in Figure 46. Should something get into the system, your aircraft is equipped
with a fuel filter located on the firewall between the batteries. The filter element for this is a FRAM CS1133PL.
The firewall filter element is inexpensive, and should be replaced at least every 100 hours. If you are using
fuel from a source not equipped with a water separator, change the element every 50 hours as follows:

1. Loosen the center nut of the top of the filter assembly.

2. Remove the metal bowl.

3. Check the bowl for water and rust particles.

When the fuel filter bowl has been removed for cartridge inspection it must be remembered that the fuel lines
from the engine fuel control to the header tank have been drained, and these lines will be air-locked if a start
is attempted without first priming the lines with fuel. Use the electric boost pump for this.

The engine also has a disposable fuel filter on the high pressure pump located at the 3 o’clock position on the
accessory case. This element is an AN6235-3A. The filter should be changed anytime the firewall filter is
found contaminated or every 300 hours. See the proper engine manual in INSTRUCTIONS FOR
CONTINUED AIRWORHTINESS in Section 1 for details on removing and replacing this filter.

CAUTION
If any contamination is found in either fuel filter,
investigate the cause and rectify the problem.

Fuel Header Tank Sump Draining

Drain the fuel header tank sump DAILY to remove any moisture in the fuel system from condensation or
contamination. Draining the sump daily also will prevent the drain valve from freezing up from contact with
fertilizer and chemicals. The location and access to this drain is shown in Figure 47.

Negative Fuel Pressure Warning

Your Air Tractor is equipped with an electric fuel boost pump and an engine driven low pressure fuel pump.
The electric boost pump is installed as a back-up for the engine driven low pressure pump. It also fills the fuel
lines prior to starting. It can provide fuel to the high pressure pump that requires a minimum of 5 psi at all
times for increased service life. The high-pressure pump alone can keep the engine running normally.

The AT-802/802A has a negative pressure switch and warn light with the switch on the outlet side of the fuel
filter. If this warning light should come on, turn on the electric boost pump and have the problem corrected
promptly. A check of the fuel filters is in order here, as one may be starting to clog because of the fuel
contamination. Refer to Figure 48 and your Engine Maintenance Manual for details on cleaning the filters. The
wiring schematic for this negative-pressure warning light is shown in Figure 36. In this figure, the light is
marked FUEL FILTER PRESS SW.

Fuel Nozzle Cleaning

Fuel nozzles are the most important routine maintenance item on your engine. No one single item has as
much direct effect on the condition of the inside of your engine. Dirty fuel nozzles can ruin combustion liners,
guide vanes, turbine blades, and the gas generator case. Fuel nozzles are not cleaned WHEN they are dirty,
but to keep them from BECOMING DIRTY. Your fuel nozzles may be cleaned by your maintenance personnel
or they may be sent to a number of locations for cleaning and returned to you for installation. Air Tractor
recommends nozzle cleaning at 300 hour intervals as long as you are using Jet A fuel, and you are getting
good reports from the personnel cleaning the nozzles you remove.
Page 2-52 Maintenance Air Tractor
June 21, 2018 AT-802/802A

The earlier model of PT6A engines came with 7 primary and 7 secondary nozzles. The engine starts on the
primary nozzles and at about 35% Ng the secondary nozzles come in. The engineers at Pratt & Whitney have
discovered that the engine will start cooler by reducing the number of secondary nozzles, hence Service
Bulletin 1372. All the new engines from Pratt & Whitney come in the 10 primary / 4 secondary configuration.
Most of the older engines have been converted, but if you have one that has not, converting it over will cool
down your starting IT temperatures considerably.

To remove or install fuel nozzles, refer to the proper Pratt & Whitney manual in Section 1, INSTRUCTIONS
FOR CONTINUED AIRWORHTINESS. Write down the location of the primary and secondary nozzles. The
primary nozzle may be identified by a weld spot on the flat area next to one of the bolts. See Figure 48. DO
NOT MARK ON THE GAS GENERATOR CASE WITH A PENCIL.

IMPORTANT
The quality of fuel and the condition of the fuel and fuel nozzles will
have a direct relation to the condition and the longevity of your engine.

Oil Requirements

Oil used in the Pratt & Whitney PT6A engine is synthetic based oil designed for turbine and jet engines.
Unlike petroleum base lubricants, turbine oil cannot be mixed, one brand with another. If you have to change
brands, you should drain the oil tank, oil cooler, gear reduction case, and accessory case. See Figure 49 for
the drain locations.

The oil tank (Figure 49 Item No. 7) is located on the bottom of the air inlet case and may be removed by
removing the clevis pin (Figure 49 Item No. 5), inserting a 1/2-20 NF bolt into the threaded plug and pulling.
The drain plug just has an O-ring (Figure 49 Item No. 6) on it and will come out with a little pull. The oil cooler
may be drained by removing both hoses and allowing the oil to run out. Removing the chip detector (Figure
49 Item No. 2) will drain the gear reduction case, as will removal of the drain plug (Figure 49 Item No. 9)
located in the lowest point to the accessory case. You cannot get it all out, but if you do that much, you will be
in good shape.

Checking the oil should always be done within 10 minutes of shut down. Unlike other Pratts, this one does not
require filling before checking. The reason for checking the level right after shutdown is that it does not allow
the oil time to escape to other areas of the engine. Sometimes bad seals allow the oil to leak back into
cavities inside the engine giving you a false indication on the dipstick. Once the engine starts turning, the
scavenger pump picks up the oil and returns it to the oil tank.

CAUTION
Insure the oil dipstick is properly secured after checking oil level. A loose dipstick can
allow most of the oil to be lost overboard within a short amount of time.

Oil used at the factory is Mobil Jet Oil II or Eastman/Exxon/BP 2380. The oil brand and type will be marked
on the oil access door at the time of delivery from the factory. If a different brand is used, the engine and
lines should be drained and a flushing procedure with the new oil should be carried out in accordance with the
Pratt & Whitney PT6A Maintenance Manual. Also see Flight Manual.
Air Tractor Maintenance Page 2-53
AT-802/802A June 21, 2018

NOTE
For all PT6A-65 and PT6A-67 series engines installed on the AT-802 aircraft, when
performing motoring compressor runs of the engine such as for a compressor wash
and/or a turbine wash, the main oil pressure pump can supply more oil to the engine than
the oil scavenge pumps can return to the main oil tank.

This can lead to engine oil filling the AGB (Accessory Gear Box) to a level high enough
for the oil to drain overboard via the high-pressure fuel-pump drain.

This should not be a cause for concern; once the engine is started and run at idle for
several moments, the oil in the AGB will be scavenged back into the oil tank. After the
engine is shut down, the oil level should be checked within 10 minutes and the oil level
restored to its normal range.

This situation will not have any effect on normal engine operation.

Oil Filter

The oil filter, located to the right side of the air inlet case, is held in place by a cover with 4 nuts. Removing the
oil filter requires a special puller and should not be removed by any other means. Cleaning the filter may be
accomplished by gently agitating the element in clean solvent. After cleaning, allow the element to stand in a
clean environment until dry. Refer to the proper Pratt and Whitney Manual in Section 1, INSTRUCTIONS
FOR CONTINUED AIRWORTHINESS.

CAUTION
Under no circumstances may the element be ultrasonically cleaned, pressure
flushed, or dried with compressed air. Such cleaning and drying causes damage to
the filter media.

Chip Detector

Besides cleaning the filter, pull the chip detector on the bottom of the gear reduction case and keep it cleaned
off every 200 hours. The discovery of ANY magnetic particles should be investigated by qualified personnel.
Refer to Figure 49, Item 2.

Air Filters

The PT6A engine requires a large amount of air at full power settings. To handle this load while adequately
cleaning the air, your Air Tractor is equipped with large, efficient air filters. The length of service for these
filters depends entirely on the operating conditions. When you replace these filters, use the original
equipment filters for replacement. Cheaper, aftermarket filters are not the same quality, so they neither
perform as well nor last as long. Remember, your engine requires a lot of air to perform properly. Filters
should be inspected/cleaned/replaced in accordance with the Inspection Schedule in Section 3. Illumination
of the Air Filter CAUTION light indicates that normal air flow through the filter is restricted. Should the Air
Filter CAUTION light illuminate, land as soon as practical and service the air filter system including cleaning
or replacing the filter(s) as necessary. (See instruction below). Do not rely on this light to determine air
filter cleaning/replacement intervals.

For aircraft with the large, cylindrical commercial truck filters (Donaldson p/n P181047 (alternate is P510336),
removal of these filters is accomplished by removing the airscoop assembly and the aft lower engine cowl.
There is a 3/8” bolt with a check nut on the aft center of each filter, and it is necessary to loosen this bolt
before the filters can be removed. The bolt is to press the filters against the forward wall of the filter box for a
tight seal. With the filters loose, the small support angles are removed and the filters will slide out the bottom
opening. These filters may be cleaned using the instructions in Air Tractor Service Letter 257. The filters are
installed in reverse order of removal.
Page 2-54 Maintenance Air Tractor
June 21, 2018 AT-802/802A

For aircraft with the p/n 52427-16 Ram Air filter, removal of the filter is accomplished by removing the lower
and side cowl skins from the aircraft. Then completely remove the lower plenum cover to gain access to the
filter. From the righthand side of the airplane, remove the filter retaining band on the aft plenum bulkhead by
removing the eight bolts that hold it in place. The heads of these bolts are on the aft side of the aft plenum
bulkhead. Lastly remove the filter by loosening the four worm drive clamps that hold the filter in place. This
filter may be cleaned using the instructions in Air Tractor Service Letter 257. The filters are installed in
reverse order of removal.

For aircraft with the Brackett BA-413E foam Ram Air filter, removal of the filter element is accomplished by
removing the lower and side engine cowls and the lower engine plenum cover. Remove the center filter
support rods by removing the screw on the forward end and sliding them out of their retaining brackets at the
aft end. Remove the old filter element and replace with a new one, ensuring that the filter element completely
fills the stainless steel frame, especially in the corners. Replace the filter support rods, plenum cover, and
cowl skins in reverse order of removal. This filter should not be cleaned, as this may remove the wettant and
decrease the filtering ability of the foam. Any excess dirt or debris that has accumulated on the forward face
of the filter may be brushed off with a bristle brush, like a paintbrush, and vacuumed out of the plenum. The
Brackett air filter has a maximum recommended service life of 12 calendar months, regardless of the actual
flight time. The reason is to ensure that acceptable levels of wettant remain in the filter to adequately capture
dust and debris.

Engine-Control Cables

The controls and control cables should be kept clean and dry. Do not put grease on the controls as it attracts
dirt causing excessive wear and binding.

Engine Rigging Procedures

Power Lever

Rig Engine Power Controls and Reversing System as follows:

(a) Disconnect reversing cable from propeller control cam on aft r/h side of engine. Move fork and
cable assy up & inboard out of the way of the propeller control cam.

(b) Remove propeller reversing lever from fwd. end of push-pull cable assy. Do not lose the
bushing (P&W p/n 3011554) in the top of the arm. Install Hartzell p/n A- 3044 carbon block in
reversing arm.

(c) Install carbon block at end of reversing lever into the beta ring. Block should have .001
clearance. If not, use fine sandpaper on flat sanding surface, sanding a little off block until
.001 clearance is obtained.

(d) Install the new P&W p/n 3011554 bushing on top of the propeller reversing arm and install bolt,
nut, and cotter pin. Check the inside surface of the Beta valve clevis to see if it is flush with the
fwd end of the Beta Valve nut. If not, adjust propeller governor interconnect rod until it is flush.
Governor Air Bleed Link Arm must be against stud. Torque jam nuts safety with MS20995C-
.020 wire. Install nut, P&W p/n 30105566 washers each side of rod end bearing, & cotter.

(e) With Power Lever at Ground idle adjust power cable to position control cam shaft on point of
propeller control cam.

(f) Adjust FCU rod from propeller control cam for preliminary idle setting on FCU.

(g) Tighten all check nuts and rod ends. Safety wire where required and cotter all castle nuts.

(h) Make any other adjustments on flight line after first run of engine.
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Propeller Lever

Refer to P&W Maintenance Manual for appropriate engine for general instructions and drawings. Rig Prop
Controls as follows:

(a) Position governor arm on governor against stop, as shown on drawing. 70621 (502A) 70512
(802).

(b) Position prop lever in cockpit at feather stop and adjust 85043-12 swivel ends and REB3N
bearing so that governor arm is also against feather stop.

(c) With governor arm against high RPM stop prop lever in cockpit should be full forward with 1/16"
min. cushion at forward stop.

(d) Check operation of prop cable fwd. and aft for free movement. Lock all check nuts.

(e) Perform flight line engine run-up. Check feather position and high RPM setting of 1700 RPM.
Adjust high RPM stop if required. Re-set 1/16" min. cushion on forward end of prop lever.

Start Control

Refer to Pratt & Whitney Maintenance Manual for appropriate engine for general instructions and drawings.
Rig Engine Start Control as follows:

(a) Position Start Lever in Cockpit in “RUN” position

(b) Adjust REB3N bearing at end of cable so that condition lever on engine is straight up midway
between stops.

(c) Pull Start Lever in Cockpit all the way back against the quadrant stop. Condition lever on engine
should be at the fuel cut-off position.

(d) Perform flight line engine run-up. Adjust REB3N bearing and/or cable assembly so that in
“RUN” position engine idle speed is set per paragraph “g”.

(e) Set the FCU control rod stop for FLIGHT IDLE speed (68-70% Ng).

(f) Tighten all jam nuts, check nuts for cotters, install MS20995C20 Safety wire where required.

(g) Ground idle speeds as follows: 56-58% Ng

Compressor Washes

Compressor washes are performed to remove dirt and deposits, which hamper the efficiency of the
compressor. The quality of the Air Tractor induction system is so good that most engines require a
compressor wash only once a year. An inspection of your engine inlet is a good indicator of when to perform a
compressor wash. If the first stage compressor blades and/or cone on the inside of your engine inlet are dirty,
then the compressor is too. Anything going into the compressor has to go by here. If the engine inlet cone is
clean, you can be sure the inside of your engine is in pretty good shape. Don’t do a compressor wash just to
be doing one.

See Figure 51 for the location of engine combustion drains to be opened for compressor washes. Regardless
of how many compressor washes you do, there is only one way to accomplish the tank with maximum results.
Remove the engine cowling and the air inlet cover over the engine inlet. Connect and start the battery
charger. Remove the P3 filter (located on the right side at the rear of the engine) and leave the filter bowl off.
If your engine does not have a P3 filter, remove the compressor discharge line from the right hand side of the
FCU. Remove the two gas generator case fuel drain valves to allow the dirty water to escape rapidly. The
newer PT6 engines have a P3 filter bowl that has a drain fitting to allow for compressor washing without
having to disconnect anything.
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If you do not remove the valves, what happens inside you engine strongly resembles the bathtub after the
kids finish their bath. The rings left in the engine will do more harm than the washing does good.

The P&WC maintenance manual lists all the approved compressor washing materials. The manual also gives
the proper mixing ratios for the wash solution.

CAUTION
Do NOT mix compressor washing materials in stronger strengths than shown
in the P&WC manual. The ratios are the MAXIMUM allowed. An operator may
do more damage than good if trying to wash a compressor with a higher
concentration of cleaning agent than that recommended by P&WC.

Prior to performing a compressor wash, the engine MUST be allowed to cool for a minimum of three hours to
avoid stressing HSI components.

Most Air Tractors have a built in wash ring, which allows the washing solution to be injected into the
compressor at the most efficient rate. Access to the wash ring is by removing the AN cap from the fitting
located in the engine cowl corner skin under the left hand exhaust stack. The same wash ring is to be used to
inject fresh clean water of drinking quality for rinsing purposes after the wash solution has been injected. A
small, low pressure (approximately 20 psi) water pump, such as a boat bilge pump, will do the job. If you have
relatively low concentrations of minerals in your tap water, a garden hose can be plumbed to the wash ring
fitting directly to the tap for rinsing. You should use water that is as free form mineral concentration as
possible. If you live in an area that has high concentrations of minerals in the tap water, it is advisable to use
demineralized water. The engine should be rinsed (monitoring the started limitations) until the liquid draining
from the engine drains in clear water. It is most important to insure all the washing agent (soap) has been
rinsed out of the engine. After compressor wash is finished, start and run the engine at high idle for 3 to 5
minutes to dry out the compressor.

A turbine wash using P&WC tool p/n PWC32271 (cost approx. $275.00) is very effective in removing
materials, which may have been allowed to accumulate on CT blades. Some of these materials may cause
sulphidation, a form of high temperature corrosion that actively attacks the parent metal of compressor turbine
blades. Use of this tool has proven to be very effective in reducing the numbers of CT blades rejected at HSI
due to sulphidation.

P&WC will not honor warranty on CT Blades removed due to sulphidation.

After the water stops dripping out of the engine, replace the fuel drain valves and safety them, replace the air
inlet cover, P3 filter and engine cowling. When everything has been replaced, start the engine and run for at
least 15 minutes to dry the engine out. Never put the airplane up without running the engine until it is dry.

Engine Starting Procedures

Starting the PT6A turbine engine is not complicated, but it is the best opportunity you will have to damage
your engine if the proper procedures are not followed. A battery cart will be a good investment. You can take
two 12V truck batteries wired in series for 24 volts, put them in a cart for ease of movement, and connect
them to cables with a plug compatible to your Air Tractor. It is also convenient to wire a trickle charger to a
female socket like your airplane has and you can keep the batteries plugged in when not in use so they will
always be ready when needed.
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Before you begin the starting procedure, make sure all the levers and switches are in their proper positions.
The throttle against the idle stop, the start lever in the cut off position, the propeller in feather, and the ignition
switch in the middle position. Hot batteries or the battery cart will spin your engine between 18% and 20% Ng.
NEVER TRY TO START AN ENGINE TURNING LESS THAN 15%. Once you have obtained an Ng speed
above 15%, turn on your ignitors, wait for the Ng speed to peak, them bring the start lever to the RUN
position. Start counting 1001, 1002, 1003, etc. your engine should ignite before you reach 1005. If it does not,
pull the start lever back to cut off, let off the start switch, and investigate. In any case, allow the fuel in your
engine to drain. You do not want to start an engine with a lot of excess fuel inside. Most engines will light
around 1003. There will be a pause in most engines around 35% Ng, then a continuation on the 58% to 60%
Ng. The ITT will usually peak and be coming down as the engine reaches its idle speed. Engine with the 10-4
fuel nozzle configuration will start well under the red line, (usually more than 100° C) while the 7-7
configuration will start somewhat hotter. In no case should an engine normally exceed the red line on a start,
although the manual allows temperatures above the red line for 2 seconds.

Once the engine is above 56% Ng, release the starter switch. You may leave the ignitor switch in the up
position since the ignitors are OFF as soon as the start switch is released. Turn on the generator. Right after
a start, especially without a battery cart, your generator will be carrying a heavy load while recharging the
batteries, and can drag the engine down. If your Ng speed begins to fall below 58% when you turn on the
generator, you should advance the power level as required to maintain a Ng speed above 58%.

Starting an engine that is turning slow with weak batteries is asking for a disaster. During the start process, if
anything seems questionable, pull the start lever back to the cut-off position with the starter still engaged and
allow the starter to run till the ITT has fallen to safe limits. As stated at the beginning of this section, starting
the engine is not hard, but you have to do it right or you will find yourself in a trap. Most over temperature
conditions occur as a result of improper starting. Repairs to your engine, caused by an over-temperature
condition, can be very expensive!

Ground Run Procedures

The following are Air Tractor’s recommendations on performing ground engine runs. These
recommendations apply to all Air Tractor aircraft:

1. It is recommended that the hopper be filled with water prior to performing ground runs.
2. The airplane should be positioned on the tie-down such that FOD/prop wash damage to other aircraft,
structures, personnel, or equipment will not occur, nor be directed at or across an active runway.
Also pay close attention to the ground surface below the propeller arc. Sand, gravel, dirt, tools,
debris, etc. can be picked up by the prop and can cause damage to the propeller blades.
3. The ideal tie-down anchor is a steel loop or eye set in concrete. A 24” diameter x 24” tall column of
concrete buried 36” in the ground is usually adequate. Soft or sandy soil may require additional
concrete.
4. The airplane should be tied down at the tail using a polyester or nylon tow strap or lift strap looped
around the tailwheel housing attach block and routed through the tailwheel fork. See Figure 1 below
for a suggested strap routing. Exercise extreme caution that the tie-down strap does not contact the
steering pin mechanism at any time during the ground run. Tie-down strap should be minimum 5000
lbs. breaking strength. The airplane should be positioned as close as possible to the tie-down anchor
to provide sufficient vertical tension in the tie-down strap.
5. Chocks should be removed to prevent the aircraft from rotating on the main wheels and nosing into
the ground in the event of tie-down and/or brake failure. Personnel conducting the ground run should
anticipate forward movement of the aircraft in this event.
6. Only qualified personnel should conduct the ground runs.
7. The airplane brakes should be set or held during the ground run.
8. The control stick should be held full aft (nose up) during the ground run.
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Figure 1 - Suggested Tail Tie-Down Method

FIN AND RUDDER

Vertical Fin

Details of the vertical fin are shown in Figure 52. The cantilever vertical fin is attached to the fuselage frame
at the front spar location with two NAS1306-13 bolts and AN365-624 nuts. It has been found that these two
bolts tend to loosen in service. No doubt buffeting from the propeller slipstream during run-up and stresses
from turns tend to produce constant loads from side to side that tend to loosen the nuts.

Check the torque on the two NAS1306-13 bolts at 100 hour intervals. If the bolt is held stationary and the
torque wrench applied to the nut, the torque value should be 420 inch-pounds. For the reverse of this
procedure, torque should be 460 inch-pounds.

The rear spar attaches to the fuselage frame with AN3 bolts of various lengths, depending on the amount of
shims required between the fuselage frame and the rear spar. The shims are of various thickness (.063, .080,
.125) and the upper shims are combinations of p/n 30159-1, -2, or -3 while the lower shims are combinations
of p/n 30160-1, -2, or -3.

The vertical fin rear spar is drilled on installation where the attachment is made to top longeron. If a new fin is
installed, make a drill template from the original fin rear spar in order to drill the four 3/16” holes for the
attachment to the upper longeron. The template should be 2.44” wide and long enough to pick up the two
lower attach bolts. The template should be made of either aluminum or steel, at least .063” thick.

Install the fin on the aircraft and install the bolts at the front and rear spar locations. Be sure the correct
amount of shims is used between the fuselage frame and the rear spar. The NAS1306-13 front spar bolts
have a torque of 420 inch-pounds at the nut. The rear spar bolts have a torque of 60 inch-pounds at the nut.

Rudder
Details of the rudder are shown in Figure 53. The rudder is attached to the vertical fin with three AN4-10A
bolts, with an AN960-416 washer under the bolt head, and two washers under the AN365-428A nut. The
rudder hinges have NMB p/n MS14104-4 bearings installed, which are staked on each side of the 1/4” thick
hinge fitting. Since there is a certain amount of drag with these spherical bearings, it is very important to fully
torque (100 inch-pounds at the nut) the three AN4-10A bolts that attach the rudder to the fin. If the bolts are
loose, the bolts will turn on the fin hinge brackets and cause the holes to become elongated.
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The bearings have little wear, but if it is necessary to replace them, construct a puller that will apply force to
the outer ring of the bearing with the opposing force against the aluminum housing. An AN4 bolt through both
parts of the puller should be tightened until the bearing rim is pulled past the stake marks and the bearing
comes out of the housing. When the new bearing is installed, re-stake with a center punch.

The rudder horn is p/n 70092-1 and has two p/n 70093-1 bushings installed for wear at the cable attachment.
The horn is attached to the rudder assembly with two AN4C7A bolts. Rudder control stops are at the rudder
horn and the rudder travel is 24° Left, +/-1°, or 24° Right, +/- 1°.

Rudder Controls

Details of the rudder controls are shown in Figure 9. The rudder cables are p/n 70524-5 (70524-1 for dual
controls) and attach to stainless link plates (p/n 70094-1) at the rudder horn with AN4C10 bolts, AN310C4
nuts, AN960C416 washers, and MS24665-151 cotters. There are four MS24566-3B pulleys in the rudder
cable system to the cockpit.

In the cockpit, the rudder cables attach to a steel p/n 70096-1 plate which is bolted to a p/n 70313-1 aluminum
adjust channel. Also attached to the 70096-1 plate is a p/n 70525-6 (70525-1 for dual controls) cable
assembly, which interconnects the rudder with the aileron control system. The interconnect springs under the
cockpit floor are p/n 70814-1 and attach to the 70576-1 cable assemblies connected to the upper torque tube.

The rudder pedal hanger assembly (p/n 70109-1) slides in the adjust channel and is held in place with a D5-
10T-303 Faspin. The hanger assembly has a spring attached to pull it forward to remove slack from the
rudder cable. The spring is attached to an eyebolt in the hanger assembly and is p/n 70102-1.

The rudder pedal castings are p/n 70115-1 (L/H) and 70115-2 (R/H) and may be removed by taking out the
AN3 bolt through the p/n 1SC Caplug on the inboard end of the hanger assembly and removing the AN4-10
bolt attaching the master cylinder strap. The castings should be removed at 2,000 hour intervals and
inspected for cracks around the bronze bushing (p/n 70116-1), bushing wear, and general condition. Grease
the hanger assembly and slide the casting back in place. Be sure to use the AN310-4 castle nut with an
MS24665-151 cotter on the AN4-10 bolt connecting the master cylinder strap. Also, be sure two AN960-416
washers are installed between the strap and casting, and work the brake several times to be sure clearance
exists between the strap and the casting. While the casting is removed, check the condition of the (p/n 70492-
1) bronze bushing in the master cylinder strap (p/n 70490-1). Oil the bronze bushings with general purpose oil
before re-installing the bolts.

Rudder Trim Tab

The rudder trim tab is also used as a boot tab to reduce pedal forces in normal flight. The tab is made of a
single skin wrapped around a welded-spar-and-rib frame. The tab is controlled by a single control arm on its
right-hand side. This arm has threaded 10-32 studs both sides to attach the two control rods. The tab
installation is shown in Figure 55.

The tab is held in place by two studs that fits loosely into pre-oiled porous-bronze bearings in each end of the
tab spar. The upper stud is fixed to the rudder and the lower stud is attached to the end of a metal strap that
is itself bolted to the bottom-aft of the rudder.

The tab may be removed by first removing the AN365-1032 nuts that retain the control rods. The control rods
can now be disconnected. The tab can be separated from the rudder by removing the two AN3 bolts that
fasten the strap and stud to the bottom of the rudder. The lower stud can be pulled free and the tab can be
removed.
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Rudder Trim Controls

The rudder trim controls in the cockpit are shown in Figure 6. Rudder trim is controlled by a horizontal
handwheel on the left-hand wall of the cockpit. This handwheel is pushrod connected to a Quadra-Stat sector
level in the aft fuselage. The Quadra-Stat is a positioning sector that provides a friction lock at the position
selected by the control lever. The Quadra-Stat is shown in Figure 8. If the rudder trim slips in flight, the friction
screws may be tightened to prevent this.

The Quadra-Stat output arm is connected via pushrods to the idler block that is positioned on the right-hand
face of the fin’s rear spar, just below the horizontal stabilizer. Dual rods attached to the arms of this idler
progress aft to their attachments to the rudder tab.

FIRE RETARDANT DISPERSAL SYSTEM (FRDS)

Refer to the appropriate FRDS Maintenance Manual for service information on the FRDS.

FUEL SYSTEM

Fuel Tanks

The fuel tanks are of the wet-wing type with intermediate ribs serving as baffles. There is one tank in each
wing. The inboard end of the fuel tank is closed by the solid rib at the wing root.

DANGER
The use of open flame, non-explosion-proof lighting, or power tools
inside the fuel tanks or near fuel-tank openings can cause fire,
explosion, or both. When using a flashlight or explosion-proof lighting,
DO NOT SWITCH THE LIGHT ON OR OFF WHILE INSIDE THE TANK.

Fuel Tank Sealing

The fuel tanks are sealed with Products Research PR-1422 A2, which is brushed on, and PR-1422 B2, which
is a thicker putty-like materials for sealing corners or large cracks. Sealing between mating parts is done
during assembly, and final coating is done through the nine inspection openings in the top of the tank.

If a leak develops in service, remove the inspection plates of the lower side of the wing and with a flashlight
and mirror determine which area of the tanks appear to be leaking. This is difficult and sometimes it is
necessary to re-seal a large area of the tank to make sure the leak is covered. Remove the fuel line from the
tank to be drained and cap it off so that both tanks will not need to be drained. Then drain the fuel into clean
containers by removing the drain valve from the tank flange. Then remove the inspection plate on top of the
fuel tank nearest the leak area. There are plate-nuts (NAS680-A4) riveted to the fuel tank top to facilitate
plate removal. Sometimes it is necessary to drill out the screws in the plate.

Inspect inside of the fuel tank with a flashlight and mirror or a drop-light. Observe the warning about lights in
the tanks. A spark from the switch has caused an explosion and injury in a past instance. Look for a void or
bubble of the air that could have popped, leaving a pin-hole leak. If no suspicious areas are found, prepare to
re-seal the general area of the leak.

Clean the areas to be re-sealed with an inhibited alkaline cleaner such as M.E.K. with a clean white rag. A
progressive cleaning procedure should be used. Wash one small area at a time, then dry with a clean cloth
before solvent evaporates to prevent redeposition of oil or fuel traces. To maintain a clean solvent supply,
always pour the solvent on the washing cloth.
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The sealer kit consists of the proper proportion of base compound and accelerator. The accelerator contains
some volatile materials, which usually come to the surface so it is extremely important to stir the accelerator
thoroughly in its container until an even consistency is obtained. Once the accelerator is added to the base
material the pot life is limited to two hours at 75°F, 50% relative humidity. For every 10° F rise in temperature,
application life is reduced by half, and for every 10° F drop it is doubled. High humidity at the time of mixing
shortens application life. For this reason, it is suggested that only 1/2 of the accelerator is mixed with 1/2 of
the base material, so that if the first attempt to seal the tank is unsuccessful, there will be one more mix of
sealer left for another attempt before a new can has to be opened. If this approach is taken, be sure the
accelerator is sealed in an air-tight container as well as the base material, and that care is taken to assure
that exactly 1/2 of each component is mixed together.

Slowly stir the accelerator into the base compound and thoroughly mix approximately 7 to 10 minutes. Be
sure to scrape the sides and bottom of the container in order to include the entire compound in the mixture
and to assure uniform blending. Scrap mixing paddle periodically to remove unmixed compound. Slow mixing
by hand is recommended.

Obtain a small paint brush approximately 1/2” to 3/4” wide and trim the bristles to approximately 1/2” long to
increase brush stiffness. Brush the thoroughly mixed sealing compound over the cleaner suspected leak
areas in generous amounts but feather out any runs that might occur. Watch for bubbles and re-seal any pin-
holes. Inspect your work carefully, as failure means doing the job all over again. Scrape off the old sealer from
the fuel tank cover plate and mating surface, being careful not to get any shavings inside the tank. Seal both
the cover plate and the mating surface and install cover plate. Where the sealer is squeezed out around the
perimeter of the plate, use your finger to make a smooth fillet.

Allow the sealer to dry at least 6 hours (overnight is preferable) before fueling the tank. Check carefully for
leaks before connecting the fuel line to the other tank. If the tank still leaks, repeat the entire process until the
leak is sealed.

Fuel Tank Senders

Each of the fuel tanks has two fuel-quantity sending elements. These two sending elements are connected in
series electrically. The outboard sending element is active in sensing fuel level when the fuel level is in the
upper third of the tank. The inboard sending element is active when the fuel level is in the lower third of the
tank. Both of the elements are active when the fuel level is in the mid-range. The schematic for the fuel gauge
system is shown in Figure 28.

The inboard sender is insulated from ground by the ten insulating washers that are used on both sides of the
five holes in its flange. It has two wires attached. One of the wires exits the fuel-tank wall through a banana
jack en route to the outboard sender. The other wire exits the fuel-tank inboard end wall through a banana
jack en route to the fuel gauge.

The outboard sender is grounded through its mounting bolts. The wire attached to its center post connects it,
through the banana jack, to the inboard sender.

The inboard tank sender is p/n 20680-1 and the outboard sender is p/nC7740-43. The sender is attached with
five AN3-32A bolts, 20194-3 bushings, and AN365-1032 nuts. Both senders have p/n 20173-1 Teflon
washers under the bolt head for sealing purposes. If a sender is not working properly, the procedure is to
remove the inspection cover from the fuel tank top just forward of the five sender attach bolts and before
removing the sender, first push the banana plug firmly into the jack to be sure proper connection has
previously been made. If this has no effect, pull out the banana plug and connect to an Ohmmeter with the
other lead grounded to the flange of the sender. With the float arm all the way down, the Ohmmeter should
read zero and the arm all the way up, the Ohmmeter should read 29-30 Ohms. Cycle the arm and the needle
should not have an erratic movement. If all is OK, the sender does not have to be replaced. If there is still
indication of a faulty sender, remove the five bolts attaching it to the tank top, being careful not to damage the
Teflon washers under the head of each screw. The fuel tank should be drained before the sender is replaced.
The five bushings will probably be held in place by the tank sealing compound if care is taken when removing
the sender. Pull the banana plugs from the jacks and remove the sender.
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When the sender is being replaced, the cork at the end of the float arm should just touch the bottom of the
tank when the arm is at the lower end of its stroke. It should almost touch the top of the tank at the upper end
of the stroke. If it will not quite touch the tank bottom or touches too soon, bend the arm gently by hand to
achieve the desired position.

Before re-installing the inspection plate on the fuel tank top, move the float arm through the full stroke with the
battery switch “On” to see that the sender is working properly. Seal the inspection plate per instruction in “Fuel
Tank” and re-install.

Fuel Tank Receiver

The schematic for the fuel-tank receiver is shown in Figure 28.

The fuel tank receiver is p/n 51274-1. There is an adjustment screw for the “E” side of the needle range on
the center lower side of the instrument face. The trimmer screw for the “F” side of the needle range is
remotely mounted behind the upper panel, just left of center. Since the slotted end of the trimmer screw is
towards the aircraft bottom, it is possible to reach under the panel with a small screwdriver to reach the “F”
trimmer screw. (Be sure the power is off).

To check the receiver settings, drain all the fuel from the aircraft and jack the tailwheel up onto a platform until
the bottom of the wing tanks are level. Be sure parking brake is ON as the tail is quite high in this position.
Sighting fore and aft along the tank bottom with the line of sight meeting the horizon is an easy way to
determine when the bottom of the wing tanks are level. Level the wing tips by placing a barrel and boards
under the low wing tiedown ring until both wing tips are on the horizon.

Remove the L/H fuel line from the tank and cap the L/H tank outlet and plug the line to isolate the two tanks.
Set the needle on “E” with the adjust screw on the face of the receiver. Gradually add fuel to the R/H wing
tank with the battery switch ON. The battery should be fully charged for this check. The receiver needle
should start to move very slightly off the “E” mark after 2 gallons of fuel have entered the tank. To check the
“F” mark, lower the tail wheel to the ground. Reconnect the plugged fuel lines and fittings. Fill both tanks
completely full. Adjust the trimmer screws behind the panel until both tanks show “F”.

Fuel System Drains

Refer to Figure 47 for the location of the fuel tank and header tank drains. These drains are designated for
daily activation during the pilot’s walk-around inspection as shown in the AIRPLANE FLIGHT MANUAL.

Fuel system drains and other drains on the engine are shown in Figure 51.

The wing tanks have Curtis CCA-1650 drain valves and the header tank and the header tank has a Curtis
39000 drain valve. If the valves leak, remove them and check the seals for nicks and look for trash between
the seal and the valve seat. Apply some 3H Permatex or equivalent to the threads of all drains before they are
re-installed. If the seal is bad, replace the valve.

The header tank drain has a tendency to freeze up during fertilization operations if it is not activated daily. If
this should happen, replace it immediately as this is the most important drain in the system. Be careful not to
cross-thread drains when replacing.

Fuel System Screens and Filters

Each wing tank has a finger strainer soldered to the 90° elbow at the tank outlet. This screen should be
removed and cleaned at least once a year during the annual inspection.
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Remove the finger-strainer screen from each wing tank as follows:

1. Defuel both wing tanks by use of the valve outlet in the header tank.

2. Remove the hose-end fitting from the elbow fitting that enter the fuel cell through the inboard
rib of the wing.

3. Remove the elbow fitting from the tank. The strainer screen is part of the elbow fitting.

After inspection and cleaning, the strainer and its fittings may be replaced by reversing the steps shown
above. The threads of the elbow fitting should be cleaned and re-coated with RectorSeal 5 or equivalent fuel-
resistant pipe-thread sealer.

The firewall fuel filter is shown in Figure 46. This fuel filter may be a Fram FS1133-PLM fuel filter or an Air
Tractor p/n 53114-2 fuel filter. Both fuel filters use the Air Tractor p/n 52351-1 fuel filter element. Inspection
and maintenance procedures for both fuel filters are almost identical. The filter should be cleaned and
inspected for general condition in accordance with Service Letter #229 (Fram FS1133-PLM fuel filter) or
Service Letter #229A (Air Tractor p/n 53114-1 fuel filter). A copy of these Service Letters are found in the
Appendix section of your OWNERS MANUAL.

Airframe Fuel Pump

The airframe pump has a pressure adjustment that has been set at the factory for approximately 20 psi with
the engine operating at 80% power. If a new airframe pump is installed, and if a negative pressure is read
after engine start-up, it is a sign that the airframe pump is not set up for proper rotation, and the body of the
pump can be removed and rotated 180° to obtain a positive reading. The engine manufacturer requires that a
minimum pressure of 5 psi is being delivered to the fuel control at all times, with a maximum pressure of 20
psi. A negative pressure switch and warn light has been installed on the outlet side of the fuel filter. If the fuel
filter warn light comes on, the electric fuel boost pump should be turned on. The pilot should land as soon as
possible and investigate. Possible cause would be a contaminated fuel filter. When the light comes on it is an
indication that fuel flow is restricted between the exit side of the filter and the tanks.

FUSELAGE

Fuselage Removable Skins

Details of the fuselage removable skins are shown in Figure 57.

The side skins of the fuselage are attached to the fixed skins with 1/4 turn studs of various lengths. The stud
has a basic part number of 4002 (Camloc) or 1142005 (Monadnock) and the dash number designates the
length. The most common stud is 4002-3 with the next most common a 4002-4. All studs have the dash
numbers on the head. Stud lengths used are -3 through -15. Stud installation requires a 4002-N grommet and
a R4G snap ring. Installation pliers are needed for stud installation or removal. All Camloc receptacles are p/n
40R17-2.

The side skins can be easily removed.

The side skins have a thin strip of cork to prevent chafing. This cork is 1/16” thick by 1 1/8” wide, comes in 10
ft. rolls, has pressure sensitive adhesive backing and is p/n 1/16x1 1/8 CORK. A punch is made of a piece of
3/4” OD tubing and one end sharpened on a grinder. At each 1/4 turn fastener position, the cork is marked
and a 3/4” hole is punched.

The side skins are sheared to size, but the 1/4 turn fastener holes will require drilling on installation. The old
skin may be used for a pattern, or if it is damaged, ask the factory to provide a hole finder. Use a .471
diameter hole saw to drill the side skins to match the receptacles. These hole saws have a No. 30 pilot.
Page 2-64 Maintenance Air Tractor
June 21, 2018 AT-802/802A

Fuselage Fixed Skins

Details of the upper fuselage fixed skins are shown in Figure 54. Details of the lower fuselage fixed skins are
shown in Figure 58.

The fixed skins are attached with 8-32 machine screws and nuts. Nuts in the lower skins are stainless
MS21044-C08 and in the upper fuselage areas are AN365-832. The 100° countersunk machine screws are
p/n 90012-5 for the 8-32 x 1/2 size, 90012-7 for the 8-32x5/8 size. The Truss head machine screws are p/n
90013-3 for the 8-32x3/8 long, -5 for 1/2 long,-7 for 5/8 long, and -8 for the ¾ long.

The long lower skin is attached to the skin under the cockpit floor with rivets, but if it is desired to remove one
skin but not the other, the rivets can be drilled out and replaced with 90013-3 or -5 screws and stainless nuts.
If the baggage floor is to be removed, it is necessary to remove the long lower skin, in order to reach the nuts.

During annual inspections, all screws attaching the fixed skins should be checked to see if they are tight.

The Camloc receptacles are attached to all lower skins and stringers before these parts are attached to the
aircraft. If a skin or stringer is replaced, be sure to install the side skin and attach it to the part being replaced
so that it will be properly positioned for the side skins to fit after installation to the airframe.

Fuselage Cockpit Skins

The cockpit metal skins are riveted to the floor and to the support angles with MS20470AD4 rivets.
Attachments to the door frames are CR9163-4-2 Cherry rivets. The cockpit skins may be removed by drilling
out the rivets where necessary and is not a difficult operation. The hopper should be removed in order to
remove the cockpit floor however.

The upper aft side of the hopper tank forms the forward wall of the cockpit. This portion of the cockpit
enclosure is integral with the hopper tank, so maintenance concerning the hopper is addressed in Section 2,
HOPPERS.

Fuselage Frame

The fuselage frame is made of 4130N tubing. It may be repaired in conventional ways. AC-4313.1A may be
used as a guide for repairs to tubing. All fittings are also of 4130N material. The repaired area should be
sanded and burned paint should be removed to a point where it can be feather-edged by sanding. A good
etching solution would be a mixture of 1/2 fluid oz. of concentrated phosphoric acid in one gallon of
isopropanol (isopropyl alcohol). If relative humidity is extremely low, add 1/4 cup of distilled water to the
solution. Factory finish is R9006 Air Ag Yellow Epoxy with R3203 converter. See the section on stripping and
repainting steel parts for complete instructions.

Windshield

Details of the windshield are shown in Figure 59.

For the plexiglass portion of the windshield be careful to always use clean rag and plastic windshield cleaner
to prevent scratches. If a crack is found near one of the attaching screws, stop-drill with a no. 30 drill bit. The
side windshields are p/n 11197-1 (L/H) and p/n 11197-2 (R/H).

The safety-glass center windshield can be cleaned with a soft rag and any good glass cleaner. The center
windshield p/n is 10665-1 for the AT-802 and p/n 11248-1 for the AT-802A.

The windshield is sealed around the upper and lower edge under the metal flanges with commercial grade
putty. Then the entire perimeter of the windshield is sealed with PR1422-A2 (See FUEL TANKS in Section 2
for mixing instructions). Drill .166 holes through the windshield to match the aluminum attachments. Then
remove the windshield and enlarge the holes in the windshield to 3/16” to prevent the attach screws from
over-stressing and cracking the windshield at any location.
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AT-802/802A June 21, 2018

To remove any of the windshields, the following procedure may be followed:

1. Remove all of the #10 screws that secure the upper and lower retaining strips on the outside of the
windshield.

2. Remove all of the #10 screws in the retaining strips on the left-hand-and right-hand sides of the
respective portion of the windshield that is to be removed.

3. Remove the retaining strips and associated fasteners and fittings that surround the subject windshield
panel.

4. Gently pry the windshield free from the sealing strip beneath. Pry gently around the perimeter of the
panel with a putty knife or other suitable flexible, wide-blade tool.

5. Lift the windshield panel free of the airplane.

The sealant may be removed from the edges of the panel and the windshield recess in the windshield frame
by scraping gently with a dull blade. The plate glass may be cleaned with the use of acetone or methyl-ethyl-
ketone (MEK).
CAUTION
The use of solvents on the plastic panels will
distort the surfaces and render them unusable.

The windshield may be reinstalled by reversing the removal steps above. After the windshield is in place, it
should be resealed on its outer surface using Courtaulds Aerospace PR 14-22 B-2 sealant. The sealant is
catalyzed with supplied material.

The best method to apply the sealant is to mask the retaining strips first and then mask the windshield leaving
1/8” of windshield surface exposed between the tape and the retaining strip. Apply the sealant sparingly to the
exposed windshield surface, then remove masking tape.

The sealant starts to cure when catalyzed, so time is precious when applying sealant. The sealant should be
allowed a 24-hour cure before stressing.

Canopy Doors

The canopy doors seal against the door frame with X202Bt neoprene sponge. This material has a PSA
backing. Be careful not to stretch the strip during installation or it will come loose.

The door frame has a slight inward bow of 1/8” to allow for door deflection outward at high speeds. The low
pressure around the canopy causes the doors to bow outward. The door latch should provide a snug door fit,
and if it does not, and the weather-strip is in good condition, bend the latch arm that rides on the plated striker
plate (p/n 10354-1 (L/H) or -2 (R/H)).

The door glass is attached with 1/16 x 1 1/4 felt with PSA backing (p/n F-7) around the perimeter. The
machine screws around the glass are AN526-632-8 and the nuts are AN365-632. Be careful not to over-
tighten the screws or the glass will crack.
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June 21, 2018 AT-802/802A

All AT-802s have emergency door releases on the left-hand door. These doors can be removed by supporting
the open door and removing the spring-pins.

The right-hand canopy door may be removed by following these steps:

1. Close and lock the canopy door.

2. Remove nuts and washers from hinge bolts.

3. Open the door and support it while removing the AN3 hinge bolts.

4. Remove the door from the airplane.

The door may be replaced by reversing the order of the steps above.

Seat

The seat is attached to the seat rails with two C4-13R-303 Fastpins. Do not raise the seat above factory
installed position but a tall person may want to lower the seat some. This is done by removing the fastpin and
aligning the holes in the seat attach fitting with one of the other factory pre-drilled holes in the seat rail and
installing the fastpins. Make sure the lowered position clears the push-rod from the control stick.

The seat covers wear and need changing from time to time. The back cover is p/n 10541-1 and the bottom
cover is p/n 10540-1. If the crotch strap is installed through the bottom seat cover (used with AmSafe Airbag
System) use bottom cover p/n 10540-3. Tools are available from the factory to make seat cover replacement
easier.

HOPPERS AND DISPERSAL EQUIPMENT

Hopper Tanks

The front and rear hoppers are made of Derakane and are heat-cured for greater chemical resistance.
However it is not good practice to leave chemicals in the hopper overnight, especially if it is known that these
chemicals have an adverse effect on fiberglass hoppers.

The hoppers attach to the fuselage frame with AN6C11A, C33A, and C34A bolts and MS21044-C6 nuts. The
connecting fairings 80469-1 (2 ea.) and plate (80616-1) are attached to the hopper flanges with 90015-7 (5/8
long) screws, MS21044C3 nuts, and AN960C10 washers. It is very important that the fairings are carefully
sealed with PRC1422-B2 to prevent chemical leaks from getting on the wing splice connection.

The wing center splice fittings may be inspected by removing only the front hopper. To remove the rear
hopper it is necessary to remove the windshield.

Details of the upper view of the hopper tanks are shown in Figure 16. To remove the hopper tanks, the
following procedures may be followed:

1. Remove the hopper gate box and gate box adapter per procedures shown under Hopper
Gate Box and Adapter.

2. Remove the fuselage side skins on both sides of the hopper tank.

3. If the front hopper is to be removed, remove the upper engine cowl skins.

4. Remove the hopper lid.

5. If the rear hopper is to be removed, remove the windshield and rear hopper-to-fuselage fairings.

6. Remove the wide stainless-steel band that connects the hopper tanks beneath the hopper lid.
Air Tractor Maintenance Page 2-67
AT-802/802A June 21, 2018

7. Using a chain hoist with 2 X 6 board across the bottom of the hopper throat, apply slight upward
pressure to relieve load on hopper supports.

8. Remove all bolts from the hopper supports and braces that secure the hopper tank to the fuselage
structure. Movement of the chain hoist will be necessary to relieve the load on the attaching bolts.

9. Use caution to hold the chain in the center of the opening in the top of the hopper and gently lift the
hopper clear of the aircraft.

Replacement of the hopper is done by reversing the order of the above procedure. Clean all sealing surfaces
and apply new sealant and gaskets.

Hopper Gate Box and Adapter

Details of the hopper gate box are shown in Figure 56. Details of the hopper adapter are shown in Figure 60.
The gate box is p/n 80615-1 and the adapter is p/n 80606-1. Gaskets for both should be replaced when either
is removed. Gaskets for the hopper to adapter connection are p/n 11176-1 (4 ea.), 1176-2 (4 ea.), and 1175-3
(8 ea.). Gaskets for the adapter to gate box connection are Transland p/n 60227 (2 ea.) and 60725 (2 ea.).
Bolts for attaching the adaptor to the hoppers are stainless 1.0 inch long p/n 91246A542. Bolts for the gate
box attach are 5/8 long p/n 91246A539. These bolts are installed with AN960C416 washer and MS21044C4
nuts. Gaskets should be sealed on both sides with PR1422-B2. Bolt torque is 150 inch-pounds.

The gate box and adapter may be removed by use of the following procedure:

1. Remove fuselage side skins adjacent to the hopper tank.

2. Remove the gate control rod attachments to the gate box.

3. Remove attachments to spray pump line.

4. Remove the bolts that attach the gate box to the hopper adapter and lower the gate box
gently to the ground.

5. Remove the bottom-load fill attachments to the adapter.

6. Remove the hose couplings between the hopper vent outlets and the vent stacks inside and
on both sides of the hopper adapter.

7. Remove all bolts that connect the adapter to the hopper-bottom flanges and lower the
adapter gently to the ground.

The gate box and adapter may be replaced by reversing the removal procedure. Clean surfaces of all old
sealant. Wipe down surfaces with solvent to remove all residues. Install the adapter and gatebox with new
gaskets and PR1422 sealer.

Hopper Lid

The hopper lid is made of fiberglass. It is sealed with strips of medium density nitrile 3/8 x 1.0.

The lid will not leak if the nitrile is in good condition and the latch assembly is adjusted to tension the lid solidly
against the hopper flange and the four over-center Destako clamps are adjusted properly. The nitrile should
be changed as required during the spray season.

The procedure for seating the lid solidly against the lid opening is;

1. Fabricate a gage from .010-thick 1”X6” stainless-steel sheet.

2. Loosen all of the lid’s hold-down clamps.

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June 21, 2018 AT-802/802A

3. Lubricate the lower end of the strip with mineral oil and place between the hopper door
gasket and hopper flange located beneath one of the center hold-down clamps on the side
opposite the hinge.

4. Clamp the door shut and pull the strip outward free of the gasket. The resistance to pull
should be 3-to-5 lb.

5. Adjust the particular hold-down clamp until desired pull is achieved.

6. Move to other opposite center hold-down clamp opposite the hinge and repeat steps 3 and 4.

7. Move to one of the outboard hold-down clamps opposite the hinge and repeat steps 4 and 5.

8. Move to the other outboard hold-down clamp opposite the hinge and repeat steps 4 and 5.

9. Move to the hold-down clamp farthest from the hinge at the forward end of the door and
repeat steps 4 and 5.

10. Move the hold-down clamp nearest the hinge at the forward end of the door and repeat steps
4 and 5.

11. Move to the hold-down clamp farthest from the hinge at the aft end of the door and repeat
steps 4 and 5.

12. Move the hold-down clamp nearest the hinge at the aft end of the door and repeat steps 4
and 5.

Should the hopper lid leak, the gasket and mating surface should be examined at the leak for tears or gouges.
If the gasket is faulty, it should be replaced. Gouges in the mating flanges of the hopper tank may be treated
with conventional fiberglass repair.

Gate Box Controls

Details of the gate-box controls are shown in Figure 61. The long push-rod assembly attached to the over-
center controls of the gate box is p/n 80172-16 and has a NMB MS14104-4 bearing in the aft end and a
Bunting P26-8 bronze bushing in the forward end. The aft end connects to the p/n 80640-1 torque tube
assembly which is supported on the fuselage lower longerons with two Fafnir PB 1/2 bearings attach with
AN6-7A bolts.

The boot attached to the lower fuselage skin is p/n 80133-1 with a p/n 70140-1 boot ring and 90013-4 screws,
MS21044C08 nuts. A p/n 80672-8 push-rod connects the lower torque tube to the hopper handle in the
cockpit. This push-rod has an adjustable Fafnir RE4M6 bearing on the lower end, and a Fafnir RE4H6
bearing in the other end. The hopper handle (p/n 80866-1) is supported on each end with Fafnir PB 1/2
bearings. Bolts through the bearings are AN6-17A.

Spray Lever Controls

Details of the spray-lever controls are shown in Figure 62. The p/n 80073-9 spray lever assembly is attached
to the aft cockpit wall and has an AG-235 Micro-control attached to limit the lever travel and hence the spray
pressure. Keep the threaded screw on the Micro-control greased and make sure the tab on the spray lever
contacts only the head of the AN4-5A bolt that is attached to the lower adjustment block.

The push-rod from the spray lever is p/n 80580-1 and has an adjustable Fafnir RE4M6 bearing in the lower
end and a Fafnir RE4M6 bearing in the upper end.
Air Tractor Maintenance Page 2-69
AT-802/802A June 21, 2018

The lower bellcrank is attached to the fuselage frame with an AN4-25A bolt. The bellcrank has two Fafnir
KP6A bearings with a p/n 70081-2 spacer bushing that allows the bolt to be fully torqued. The bellcrank is p/n
80068-1 and has a p/n 80132-1 boot, 70140-1 boot ring attached to the lower fuselage skin with 90013-4
screws, MS21044C08 nuts.

The push-rod from the bellcrank to the valve is p/n 80065-8 which has a NMB MS14104-4 bearing in each end.

The spray lever in the cockpit can be adjusted to personal preference by adjusting the Spray Handle
Adjustment Bearing as shown in Figure 62. The procedures that may be followed for adjustment of the spray-
lever position in the cockpit:

1. Remove the bolt that secures the adjustment bearing to the bellcrank.

2. Loosen the check nut on the stem of the bearing.

3. Secure the bellcrank to hold the spray valve in the SPRAY OFF position.

4. Secure the cockpit spray handle in the desired position for SPRAY OFF.

5. Adjust the bearing to align with the bolt holes in the bellcrank.

6. Replace the bolt, washer (s), and nut and retighten the check nut.

7. Check travel of spray handle in cockpit. If necessary, repeat steps 1 through 6 for best fit.

Spray Pump

The spray pump is an Agrinautics p/n 65715 attached to an Agrinautics p/n 60130 strut assembly with AN5-
12A bolts.

The standard fan is the Micronair AT-4300 five-blade fan, which is used for low-to-moderate spray volume.
For high-volume applications, install the Arrowprop A2-AT4T34 four-blade fan or the Weathaero FA100 fan.
Add 48 nozzles to spray booms and change the spray tips on the spray nozzles to larger ones. Figure 63
shows some typical spray configurations. Figure 63 also shows a chart of available flat fan spray tips. This
chart shows the orifice size and flow rate of the various tips at common spray pressures.

We supply the aircraft with Spraying Systems QU-4010 spray tips pointed 10° down from straight back. These
fan tips, with a 40° fan spray angle, oriented this way provide excellent deposition with minimal drift.
Additional information on recommended spray pressures and droplet size is available from the factory.

The procedure for removing the spray pump follows:

1. Remove fan pitch-control cable or brake-control cable.

2. Loosen the hose coupling that secures the pump inlet line to the pump.

3. Loosen the hose coupling that secures the pump outlet port to the spray valve line.

4. Release the latches on the Agrinautics strut assembly and remove the pump and fan.
or
Remove the strut through-bolt on the alternate configuration and remove the pump and fan.

The pump may be replaced by reversing the order of removal shown above.
Page 2-70 Maintenance Air Tractor
June 21, 2018 AT-802/802A

Spray Plumbing

Details of the spray plumbing are shown in Figure 64.

The plumbing from the hopper gate box to the spray pump consists of a p/n 80385-4 tube assembly and an
80376-1 hose attached to the 80385-4 tube. The hose is clamped with QS200M56S clamps which are entirely
stainless.

The plumbing from the discharge side of the pump to the valve is p/n 80636-1 and has a p/n 80743-2 coupler
at the valve end. The hoses are p/n 80399-1 and are double clamped with QS200M48S clamps. In addition a
QS200M36S clamp is attached to the 80636-1 tube just outboard of the hose at the pump and p/n 80655-1
strap is used to safety the clamp to the top of the pump to prevent the 80636-1 tube from blowing off due to
high pressure and water hammer effects.

The tube attaching to the strainer is p/n 80637-1 assembly (2 ea.). The straps on the support assemblies are
p/n 80383-1 and are attached with AN4C6A bolts. D4-13T-303 Faspins are used to attach the support
assemblies to the fuselage frame.

Bottom-Load Plumbing

Details of the bottom-load plumbing are shown in Figure 65. Bottom load valves are 3-inch and are located
on both sides of the aircraft. These are Agrinautics p/n 79410 and 79450. The aft half of the bottom load
plumbing is a 3-inch “Y” assembly and is p/n 80558-1. The forward tube is p/n 80555-1.

A 3-inch hose adapter p/n 79406 is each attached to each. The valves are attached to a bracket inside the
fuselage with AN4C10A bolts. A p/n 70533-1 bracket supports the forward tube that attaches the support
bracket are QS200M22S.

Spray Nozzles

Forty-eight spray nozzles are standard. These are Spraying Systems Inc. p/n 4666 diaphragm check valve,
p/n 1/8QJJ body, and p/n QU-4010 spray tip. The aircraft is equipped at the factory with QU-4010 tips, which
are for medium volume applications. For high volume spraying, larger spray tips should be installed and if
necessary an additional 48 nozzles should be installed. Remove the p/n 3151x2 plugs and install p/n 3325x2
hex nipples for the extra nozzles. Be sure to apply 3M Permatex or equivalent to the threads of the hex
nipples during installation.
Air Tractor Maintenance Page 2-71
AT-802/802A June 21, 2018

Spray System Inc. Flow Rate Chart

Capacity Quick Equiv. Capacity

Size VeeJet Diam. (Gallons per Minute)
Spray Nom. 5 10 20 30 40 60 80 100 200 300
Tips Inches psi psi psi psi psi psi psi psi psi psi

400017 QVV .011 .012 .015 .017 .021 .024 .027 .038 .047
400025 QVV .013 .018 .022 .025 .031 .035 .040 .06 .07
400033 QVV .015 .023 .029 .033 .040 .047 .052 .07 .09
400050 QVV .018 .035 .043 .050 .06 .07 .08 .11 .14
400067 QVV .021 .05 .06 .067 .08 .09 .11 .15 .18
4001 QVV .026 .07 .09 .10 .12 .14 .16 .22 .27
40015 QVV .031 .11 .13 .15 .18 .21 .24 .34 .41
4002 QVV .036 .10 .14 .17 .20 .25 .28 .32 .45 .55
4003 QVV .043 .15 .21 .26 .30 .37 .42 .47 .67 .82
4004 QVV .052 .20 .28 .35 .40 .49 .57 .63 .89 1.1
4005 QVV .057 .25 .35 .43 .50 .61 .71 .79 1.1 1.4
4006 QVV .062 .30 .42 .52 .60 .73 .85 .95 1.3 1.6
4008 QVV .072 .28 .40 .56 .69 .80 .98 1.1 1.3 1.8 2.2
4010 QU 5/64 .35 .50 .71 .83 .95 1.2 1.4 1.6 2.2 2.7
4015 QU 3/32 .53 .75 1.1 1.3 1.5 1.8 2.1 2.4 3.4 4.1
4020 QU 7/64 .71 1.0 1.4 1.7 2.0 2.5 2.8 3.2 4.5 5.5
4030 QU 9/64 1.1 1.5 2.1 2.6 3.0 3.7 4.2 4.7 6.7 8.2
4040 QU 5/32 1.4 2.0 2.8 3.5 4.0 4.9 5.7 6.3 8.9 11.0
4050 QU 11/64 1.8 2.5 3.5 4.3 5.0 6.1 7.1 7.9 11.2 13.7
4060 QU 3/16 2.1 3.0 4.2 5.2 6.0 7.3 8.5 9.5 13.4 16.4
4070 QU 13/64 2.5 3.5 4.9 6.1 7.0 8.6 9.9 11.1 15.7 19.2

Filling the Hopper Tanks

Normal filling of the hopper tanks is accomplished by use of either of the single point filling connections that
are located below and aft of the inboard end of the wing flaps.

In normal operations, spray solutions are pumped directly into the airplane’s hoppers from a remote storage
tank. A male quick disconnect fitting and flow-control valve are provided at both of the single point filling
connections.

After a quick disconnect hose is attached to the filling connection, the filling valve is opened and the solution
is pumped into the hopper tanks at a rate up to 500 gallons per minute. The quantity of material in the tanks
can be monitored by use of the hopper quantity gauge that is mounted in the side of the fuselage, just above
the single point connections.

The hopper tanks are vented to allow the release of air that is displaced during the filling process at a filling
rate up to 500 gallons per minute. The hopper vents normally will not accommodate the flow of liquid in the
event the tanks are overfilled. An over-fill protection valve has been installed on later models, which allows
passage of hopper liquid out through the vent tubes.
Page 2-72 Maintenance Air Tractor
June 21, 2018 AT-802/802A

CAUTION
Structural damage to the hopper tanks can occur if the tanks are
overfilled using the single-point filling connections. It is imperative that
the hopper quantity gauges are monitored through the filling process
and the flow of materials is shut off prior to the tanks becoming full.
Sufficient margin should be allowed to ensure that the quantity of
material in the tanks does not exceed their FULL level.

When the desired hopper tank quantity is reached, the valve is closed and the quick disconnect hose is
removed, allowing a quick return of the aircraft to service.

Alternatively, the hoppers may be filled using the doors in the tops of the hopper tanks.

HORIZONTAL STABILIZERS AND ELEVATORS

Horizontal Stabilizers

The details of the horizontal stabilizer are shown in Figure 66. The horizontal stabilizers require very little
maintenance since they are all metal. They are attached to the fuselage frame with two AN5-7A bolts, which
have a washer under the head, and two under the nut. On annual inspections the gap cover should be
removed from the stabilizer and the bolt condition and torque checked. At the same time inspect the fuselage
fittings closely for cracks. Torque is 200 inch-pounds at the nut. The gap covers are attached with 90008-1
stainless self-tapping screws which are Phillips truss head #4x1/4” long. A No. 39 hole is drilled for the screw
installation. The S202VW rubber channel is a Cessna part and is attached with 3-M 8001 Adhesive.

The stabilizer is sealed on the ends with PR-1422 A2 to prevent chemical entry. There are two eyebolts that
attach to a welded steel brace inside the stabilizer. The eyebolts are for strut attachment and both eyebolts
are AN47-30A. Under each nut are two N960-718 washers and the nut is an AN365-720A. The factory
procedure is to align the face of the eyebolts with the strut clevis before the nut on the eyebolt is fully torqued
(550 inch-pounds). Above the nut is a 7/8 plug button (TRW p/n SS-48155). The eyebolts require replacement
after 1350 hours TIS and thereafter at 1350 hour intervals in accordance with S/L #129.

There is a p/n 30602-1 (L/H) and 30602-2 (R/H) trim control idler attached to each stabilizer rear spar on the
inboard end. Each trim idler has three Bunting P26-10 bushings press fit inside the welded assembly and a
p/n 30605-1 spacer bushing that allows the AN3H43 attach bolts to be fully torqued (60 inch-pounds at the
nut). The brackets that attach the trim idlers are p/n 30255-1 and 30255-2 but should never need replacing
unless the AN3H43 bolt has become loose and caused wear in the holes.

Two of the idler arms are attached to the push-rods connected to the trim tab horns and these arms have a
Bunting P19-1 bushing press-fit into the idler arms. Both should be replaced when excessive trim tab free-
play develops. The Bunting bushings are oil-impregnated, but if new ones are installed, fill the bushings to
overflowing with general purpose oil and with finger pressure squeeze on the bushing ends to force the oil
into the small cavities inside the bushings. The bushing connections should be oiled regularly.

Stabilizer Struts

Details of the stabilizer struts are shown in Figure 66 and Figure 67.
The stabilizer struts attach to the fuselage fame with an AN6C13A bolt and to the stabilizer eyebolts with
AN6-11A bolts. There are p/n 30256-1 stainless terminals with AN316C8 check nuts at each strut end to allow
for adjustment.

The struts are constructed of 2.36 X 1.00 X .0494130N streamlined tubing and may be repaired if necessary.
Check the factory for instructions since an internal tube is installed. They are oiled internally through the
threaded fittings on the ends, and should be re-oiled if repaired. They are sand-blasted and given a baked
Air Tractor Maintenance Page 2-73
AT-802/802A June 21, 2018

powdered coating for abrasion resistance. At various intervals, the struts should be re-sand-blasted and
finished as called out above. Be sure to remove the terminals and plug the open holes before sand-blasting.
To further abrasion resistance the leading edge of the strut is covered with 3” wide clear vinyl tape, p/n 8671-
3. This tape should be replaced when it becomes loose or tattered.

Stabilizer Rigging

Details of the terminals and clevis bolts used for stabilizer rigging are shown in Figure 67.

To rig the stabilizers, the elevators must be removed. The factory practice is to adjust the terminal in the
forward strut so that approximately the same amount of threads is showing on both R/H and L/H struts. The
struts are pinned to the fuselage fittings and the stabilizers are pinned to the fuselage attach fittings (Don’t
forget the washers under each bolt head) but no nuts yet. Have someone hold up the stabilizer tips when they
are being attached. Then attach the struts to the rear eyebolts only. Sight down the elevator hinge line to see
that the hinges on both sides of the aircraft line up within .03”. Adjust each strut length the same amount until
the hinges are in line. Stand directly behind the aircraft on the exact fuselage centerline and raise or lower
your line of sight until the same part of each stabilizer falls in the line of sight with a reference point on the
wings. It is likely that the terminal on one strut will have to be lengthened a certain number of turns and the
opposite strut shortened the same number of turns so that the stabilizers are perpendicular to the vertical axis
of the aircraft.

Adjust the terminal at the front eyebolt on each side so that the bolts can be inserted without causing a twist in
the stabilizers. All bolts are now in place and it is necessary to re-check the hinge alignment from side to side,
and re-check the stabilizer position with the wings. If all is still in order, install the washers and nuts on all ten
attach bolts (five each side). Torque the AN 5 (5/16”) bolts to 200 inch-pounds on the nut and torque the AN6
(3/8”) bolts to 300 inch-pounds on the nut. Tighten the check nuts of each terminal to 290 inch-pounds
torque. Insert a piece of safety wire in the small inspection hole at each terminal location to be sure the
terminal is screwed into the strut fitting far enough.

Re-check nut installation on the stabilizer to frame location and install the gap covers with the 90008-1
screws. If the rubber channel is loose on the gap cover, re-attach with 3-M 8001 adhesive before the gap
cover is installed.

Elevators

The elevators are attached to the stabilizers and to the pedestal in the fuselage with AN4-10A bolts, with an
AN960-416 washer under the bolt head and two washers under the AN365-428A nut, except at the pedestal
where only one washer is under the nut. The elevator horns connect to the aft push-rod with an AN4-10A bolt,
two AN960-416 washers (placed to give maximum fuselage clearance), and an AN365-428A nut.

Like the rudder, the elevators and center pedestal have NMB p/n MS14104-4 spherical bearings installed,
and due to bearing drag, it is very important for all bolts connecting the elevators and the horns to be fully
torqued (100 inch-pounds at the nut). We have seen elevator horns with badly elongated holes because the
elevators had been replaced in the field and the bolts were not fully torqued.

A repair for elongated holes in the horns has been to drill out the holes to 9/32”, ream with a special .3120
reamer (available at the factory if required), and installing a press-fit 4130N steel bushing 3125 to .3130 O.D.
x .250 I.D. x .080 thick. With the bushing in place, heli-arc weld the bushing to the horn in two places with 1/8”
long weld beads. After welding, sand, etch, prime, and refinish the horn.

To replace the bearings, see the section on RUDDER for instructions.

Elevator stops are at the elevator horn. The down stop has a p/n 70067-1 neoprene washer in compression to
absorb shocks. Sometimes this washer splits and falls out so during 100 hour inspections, check to see if this
washer is in place. Also, if the control stick is pulled back sharply against the up stop or if a wind gust blows
the elevator up, the up stop bracket may bend and should be straightened if found to be bent.

Check the elevator and make sure that it is within the limits specified in the Type Certificate Data Sheet.
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Elevator Controls

Details of the elevator controls are shown in Figure 68. The aft elevator push-rod that connects to the
elevator horns is p/n 70522-1 and is adjustable on the forward end, which has a Fafnir RE4M6 bearing
installed. The aft end of the push-rod has a NMB p/n MS1404-4 bearing same as the elevators and rudder
and is pressed into place and staked just as in other applications. If it is to be removed, see the RUDDER
section for removal instructions.

Due to dynamic forces at airspeeds above 140 mph, some aircraft may develop an oscillation about the pitch
axis if flown with hands off the control stick, and rough air is encountered. Full control of the aircraft is
accomplished by hands on the control stick, which will stop the oscillation.

The factory has determined that by adding a small amount of friction in the elevator control system, the
oscillation is damped with hands off the control stick.

A friction device has been designed which bolts to the fuselage frame at the support bracket for the p/n
70117-1 elevator idler. This device is shown in Figure 68A. Friction is achieved by the clamping action about
the elevator idler housing.

If at any time an oscillation is noted when the aircraft is flown hands off, the clamping action of the friction
device should be increased. This is accomplished by tightening the bolt as shown in Figure 68A. It is called a
“damper” and is mounted per drawing 71335.

To measure the amount of friction required conduct the following procedure:

1. Remove the 71340-1 bolt that attaches the damper to the support bracket for the p/n 70117-1 or -7 elevator
idler.

2. Wrap a piece of safety wire around the top of the control stick just above the trigger and hook a small fish
scale to the safety wire on the aft side of the stick grip.

3. Measure the pounds of force required to move the control stick from the full forward position to the
elevators neutral position. Flaps should be retracted.

4. Now reinstall the damper to the support bracket.

5. Tighten the bolt as required to provide a small amount of friction. Attach the fish scale to the control stick
and determine the force required to move the stick from the full forward position to the elevators neutral as in
step #3.

6. The additional force should be at least 1.0 lbs, but not more than 3.0 lbs.

Elevator Trim Tabs

Details of the elevator trim tabs are shown in Figure 69. The elevator trim tabs are p/n 30600-1 L/H, 30600-2
R/H and attach to the elevators with a p/n 30610-1 hinge that bolts in the inboard rib with AN3-5A bolts and
AN960-10 washers.

Two p/n 70559-1 push-rods attach to the trim tab horn with AN3-7A bolts, AN365-1032 nuts and to the idler
arm in the stabilizer with AN3-6 bolts, AN310-3 nuts, AN960-10 washers, MS24665-151 cotters. Be sure the
push-rod is positioned with the bend on the fwd end approximately under the elevator spar tube. There is a
Bunting P19-1 bushing at the forward joint, which should be replaced if the tab free play at the trailing edge
exceeds .14 inches. If there is still excessive free play check the bolts for wear and check the push-rod ends
for wear. Install new push-rods if the holes are worn.

The trim tabs are shimmed laterally with shims. Lateral free play should be between .050 and .020 in. To
lubricate the tab bushings remove the #8 machine screw. Oil the bushings through the screw hole and at the
end of the tab. Use general purpose oil for this. Replace the #8 oil hole plug screw.
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Elevator Trim Tab Controls

Details of the elevator trim tab cockpit controls are shown in Figure 8. The elevator trim tab system uses the
elevator tabs as both trim tabs and as elevator boost tabs. The boost tabs function to relieve a portion of the
control load during maneuvers.

Elevator trim is controlled by a handwheel on the left-hand wall of the cockpit. The handwheel is shaft-
connected to a two-sheave drum that drives two taut and opposing cables. These are connected at their
opposite end to a pulley shaft that positions a worm gear in a gear box that is located in the aft fuselage. The
worm-gear box is shown in Figure 18.

The worm gear drives a sector gear with an exposed sector arm attached on the aft side of the gatebox. The
sector arm is connected by a pushrod to a bellcrank that transmits the motion to an idler just forward of the aft
edge of the horizontal stabilizer. One of these idlers is shown in Figure 70.

The bellcrank has output arms on both the right and left ends. Each of these ends connects to an idler in each
of the horizontal stabilizers. Motion is then transmitted via dual control pushrods to the control horns of the
elevator tabs on both sides of the airplane. The worm-and-sector arrangement allows the selected position of
the tab to be maintained by sliding-face friction between the worm gear and the gear sector. If the trim tabs
creep in flight, rework the friction bellville washers as detailed in SIL 802-0043.

A p/n 70742-1 trim bellcrank is attached to the fuselage frame with AN3-14A bolts, Bunting P26-8 bushings,
p/n 70065-1 spacer bushings, AN365-1032 nuts, and AN960-10 washers under the nuts. The bellcrank
should be removed during annual inspections and the bushings inspected for wear and lubricated.

The push-rods from the trim bellcrank to the idler arm on the stabilizer rear spar are p/n 70532-1 and are
adjustable. The ends are AN485-4 clevis ends with AN316-4 check nuts Attachments are with AN3-6 bolts,
AN310-3 nuts, AN960-10 washers, and MS24665-151 cotters. The push-rods going forward from the
bellcrank is p/n 70756-1 and has a Fafnir REB3N bearing attached to the bellcrank with a AN3-7A bolt,
AN970-3 washer under the bolt head, AN960-10L washer under the AN365-1032 nut.

Fairleads are p/n 70122-1 with 40081-00 snap rings. The forward end going into the cockpit connects to the
top hole in the trim lever with the same hardware as connecting to the trim bellcrank.

HYDRAULIC SYSTEM - FIRE GATE

For maintenance instructions on the firegate see the firegate service manual.

ITT INSTRUMENT CALIBRATON CHECK

Description

This section provides instructions for checking the calibration of the ITT indicator for Air Tractor
aircraft with Pratt & Whitney PT6A turbine engines. These instructions are written for use with a Barfield
TT1200 Turbine Temperature Test Set. Other ITT calibration equipment may be used if that equipment is
appropriate for use with Air Tractor ITT systems. When other equipment is used, the operator shall follow the
manufacturer’s operating instructions. Ensure that the test equipment has a current calibration before
performing a calibration check of the engine instrument.
Approved tolerances for each gauge are different. Two tables are provided in this supplement
showing the tolerances for each engine.
The ITT system may be in one of two configurations: with lead resistance or without lead resistance.
Calibration checking instructions for each style are different. Systems without lead resistance use an
electronic indicator and are easily recognized by multiple pin connectors on the back of the instrument.
These systems typically use a 2” instrument and are more common on newer aircraft. Systems with lead
resistance have only two wires connecting the instrument to the engine. These systems typically use a 3”
instrument and are more common on older aircraft.
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Most aircraft manufactured after mid-2000 have an ITT instrument without lead resistance. These
systems will not provide a temperature indication unless the indicator is powered with 24 to 28 volts, or
normal aircraft power. The tester will be set up to simulate the ITT sensors in the engine. The output of the
tester will be adjusted until the cockpit indicator shows a marked temperature (ex. 600°C). The calibrated
temperature will then be read from the display of the tester. Use the format of the temperatures from the
Sample Test Card provided in this section.

SCHEDULED INSPECTION

1. (2 Years) Calibrate the ITT gauge or follow the procedures within this section to check the
calibration.

Procedure

SYSTEMS WITHOUT LEAD RESISTANCE (Power Required)

1. Disconnect aircraft power to the instrument. The simplest way to do this is to disengage, or
pop out, the 5 amp “Engine Instruments” circuit breaker.
2. Disconnect at least one of the instrument leads from the engine thermocouple terminal block.
Note which lead was connected to which terminal.
3. On the TT1200, set the “FUNCTION” switch to “IND TEST.”
4. Set the “RANGE” switch to “20K=0Ω Sys Res.”
5. Set the “1°C/.1°C” switch to “1°C.”
6. Set the “°C/MV” switch to “°C.”
7. Connect the TT1200 harness to the “TEST” connector on the TT1200 test set.
8. Connect the black clip of the tester to the end of the instrument lead (Red) that was
connected to the Alumel (-) terminal on the engine thermocouple block. Connect the red clip
to the lead (Yellow) that was connected to the Chromel (+) terminal.
9. Connect aircraft power to the instrument and turn the Master switch ON. Set the “ON/OFF”
switch of the TT1200 to “ON”
10. For the calibration check, the operator will need to take readings from the gauge inside of the
cockpit as well as at the test set near the engine.
a. Rotate the “TEMP ADJ” knob on the test set so that a temperature of 200°C is indicated
on the ITT indicator in the cockpit. Record the temperature off of the TT1200 test set.
b. Repeat this for each temperature shown on the Sample Test Card.
c. Adjust the temperature knob on the test set so that the ITT indicator lines up exactly with
the red line. Record the temperature of the line, as well as the temperature indicated on
the test set.
d. Lastly, adjust the temperature knob on the test set so that the ITT indicator points at the
red triangle. Record the temperature of the red triangle, as well as the temperature
indicated on the test set.
11. Once all temperatures are recorded from the TT1200 and the instrument, turn the airplane
Master switch OFF, turn the TT1200 OFF, disconnect the test equipment, and return the
aircraft to the configuration prior to testing.
12. Compare the readings from the TT1200 and instrument. See the appropriate table below for
tolerances. If the instrument is not within acceptable calibration, send the instrument to a
shop for overhaul and calibration.

SYSTEMS WITH LEAD RESISTANCE (Power NOT Required)

1. Aircraft power should be OFF during this procedure.

2. Disconnect the leads from the back of the instrument in the cockpit. Note which lead connects to
which terminal.
3. On the TT1200, set the “FUNCTION” switch to “RES MEAS.”
4. Set the “RANGE” switch to “200.”
5. Attach the harness to the “TEST” connector on the TT1200.
6. Set the “ON/OFF” switch of the TT1200 to “ON.”
7. Short the tester by connecting the red and black clips of the harness together. While the tester is
shorted, press and hold the “PTS” button while adjusting the “SYS RES” control knob until the
“08.00Ω” is displayed on the tester.
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AT-802/802A June 21, 2018

8. Disconnect the harness clips and set the “FUNCTION” switch to “IND TEST.”
9. Set the “1°C/.1°C switch to “1°C.”
10. Set the “C/MV” switch to “C.”
11. Connect the black clip of the harness to the instrument terminal that had the Red (-) lead
attached, and connect the red clip to the instrument terminal that had the Yellow (+) lead
attached.
12. For the calibration check, the operator will need to take readings from the gauge inside of the
cockpit as well as at the test set near the engine.
a. Rotate the “TEMP ADJ” knob on the test set so that a temperature of 200°C is indicated
on the ITT indicator in the cockpit. Record the temperature off of the TT1200 test set.
b. Repeat this for each temperature shown on the Sample Test Card.
c. Adjust the temperature knob on the test set so that the ITT indicator lines up exactly with
the red line. Record the temperature of the line, as well as the temperature indicated on
the test set.
d. Lastly, adjust the temperature knob on the test set so that the ITT indicator points at the
red triangle. Record the temperature of the red triangle, as well as the temperature
indicated on the test set.
13. Once all temperatures are recorded from the TT1200 and the instrument, turn the TT1200 OFF,
disconnect the test equipment, and return the aircraft to the configuration prior to testing.
14. Compare the readings from the TT1200 and the instrument. See the table below for tolerances.
If the instrument is not within acceptable calibration send the instrument to a shop for overhaul
and calibration.

Red Red
Engine Model Tolerances
Line Triangle

500°C to 750°C 750°C to 850°C Beyond 850°C Varies 1000°C

PT6A-60
Series + 30°C + 10°C + 30°C + 30°C + 30°C

500°C to 750°C 750°C to 850°C Beyond 850°C Varies 1000°C

PT6A-67
Series + 30°C + 10°C + 30°C + 30°C + 30°C

500°C to 750°C 750°C to 1000°C Beyond 1000°C 870°C 1000°C

PT6A-67F
+ 30°C + 10°C + 30°C + 30°C + 30°C
Page 2-78 Maintenance Air Tractor
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Sample Test Card

Date 2/16/11
Aircraft Model AT-502B
Operator J. Smith
s/n 502-5555
Engine PT6A-34AG
TIS 1000
Power Rqd? No

Indicated Temp (ITT in Cockpit) Calibrated Temp (Barfield TT1200)

200 211
400 392
500 512
600 609
700 697
800 804
Red Line 725 731
820 (Large Engines Only) n/a
Red Triangle 1090 1080
Within Calibration? Yes

LEVELING

The airplane is leveled to “level flight attitude” by jacking the tailwheel. See LIFTING AND JACKING section
of this manual. The airplane should be in this level position for aircraft weighing and other maintenance/
installation items that require the aircraft to be in level flight attitude. The airplane is in level flight attitude
when the top (right next to the side of the fuselage) of the L/H landing gear leg is at an angle of 5 degrees (tail
down) from level. To measure this angle, use an electronic level placed atop the main gear leg.

Alternately, the airplane may be leveled with an accurate bubble level and a wedge. The wedge may be
fabricated of wood with an included angle of five degrees (1:11.43). The wedge would be placed on the flat
part of the landing gear leg next to the fuselage with the sharp end of the wedge pointing toward the front of
the airplane. A bubble level placed on top of the wedge will indicate level when the aircraft is level.

On aircraft equipped with the aluminum engine air scoop on the bottom of the cowling (non-ram air induction
system), there are two small screws provided on the left hand side of the engine air scoop that provide a level
reference. When a bubble level is aligned with the heads of these screws, the bubble level will indicate level
when the aircraft is level.

LIFTING AND JACKING

CAUTION
Care should always be taken when the aircraft is lifted to
prevent damage to the aircraft or harm to people near it.
The hopper should be EMPTY before jacking.

A jack pad is provided with each aircraft for the main gear. This jack pad is to be used for changing or
removing a wheel or tire. To install the jack pad, lay a soft rag on the inside so that it will not chip the paint
from the main gear leg and slide the jack pad up the lower end of the main gear leg until it is snug. It will be
necessary to remove and replace the lower plastic bands that hold the brake line in place. The band is Tyton
T150M-0 and should be stocked as a standard spares item. After the jack pad is in place, install the bolt and
nut through the pad flanges with the bolt on the top side of the gear leg. This is to keep the pad from
spreading apart and slipping. Use a hydraulic bottle jack on adequate capacity to lift the wheel off the ground.
Be sure the tail wheel is locked, and chocks are in place on the other main wheel. The hopper should be
empty before jacking.
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AT-802/802A June 21, 2018

Alternately, to service the main wheel, tires or brakes, the plane may be jacked utilizing a typical tripod
general aviation wing jack of at least 3000 lb capacity and the jack point included in the delivery kit. To
accomplish this, remove the main landing gear cuff and expose the main gear spring clamp. Insert the jack
point into the head of the socket head bolt attaching the clamp block. You may need to place a dab of grease
or putty in the socket head of the bolt to temporarily hold the jack point in place. Position the jack under the
jack point and lift the wheel off the ground. Before lifting the plane be sure the other main gear is chocked
and that the tail wheel is locked. Use caution making sure the jack is stable understanding that the main gear
spring deflects latterly as the plane is lifted and lowered.

To jack the tail wheel, place a small board (a short 2x4) under the tail spring about mid-way between the
forward spring attach bolt and the main clamp block that attaches the spring to the fuselage. Place the jack on
the board and lift the wheel. Be sure the parking brake is set before jacking.

If the tail spring is to be removed or checked for looseness, or have bolts changed, place the hydraulic jack
under the point of the L/H stabilizer strut attach fitting that welds to the lower fuselage longeron. Again, be
sure the parking brake is set before jacking.

If the main gear springs are to be checked for looseness, replaced, or bolts changed (other than the forward
clamp bolt), the aircraft must be lifted with a hoist, as there are no jack points on the wing due to the large
deflections of the main gear springs. A sling should be constructed with each side of the sling attaching to a
chain or cable wrapped around the aft end of the engine mount at the firewall. Be sure to wrap rags around
the mount structure so as not to scratch the paint, and have the hopper empty before lifting. A three-ton hoist
should be used, and as the wheels clear the ground, place an empty 55 gallon drum with sufficient boards
under each wing at the tie-down location to steady the aircraft and provide safety in case the hoist should fail.
Do not attempt to jack the wings at the tie-down rings.

MAIN AND TAIL GEAR ATTACH BOLTS

Details for the main-gear attachment bolts are shown in Figure 72. Details for the tail-gear attachment bolts
are shown in Figure 73. The bolts attaching the main and tail gear springs to the fuselage structure are
among the most important structural components of the aircraft. Being structural components under constant
stress, these bolts have definite fatigue lives. The predictability of the fatigue life of each bolt is impossible
due to the wide variety of operating conditions that include smoothness of landing strips, number of landings
per hour, pilot landing technique, load carried, the way the turns on the ground are made, the way the brakes
are used, and many other small but significant factors. Dropping in over the trees and hitting the ground
during a spray run may not cause a gear bolt failure, but the effect on the fatigue life of the bolt could be the
same as several thousand landings on a rough strip. A bolt that is not tightened to the proper torque,
especially when there is visible clearance between the gear spring and the fuselage, will last only a fraction of
the time normally expected.

We have established what we feel is a conservative, yet realistic time period for gear bolt changes, based on
field experience at this time. The bolt life shown is based on normal operations. If you discover slack in the
large 1 1/8” bolt attaching the main gear leg, change it immediately.

Main and tail gear attachment bolt fatigue lives are listed in Section 3, TIME-LIMITED PARTS, in this manual.

MAIN LANDING GEAR

Main Wheels

To remove a main wheel, jack the wheel clear of the ground per LIFTING AND JACKING instructions. See
Figure 74 for details of the main wheels. Remove the twelve bolts attaching the two halves of each brake
assembly. Leave the brake line connected and slide the brake assembly out of the way. Remove the outer
snap ring and dust cap, remove the two cotters in the castellated nut, and back off the castellated nut. The
wheel can then be pulling free of the axle.
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June 21, 2018 AT-802/802A

If the tire is to be removed, deflate the tire by removing the air valve stem Schrader valve. Remove the bolts
holding the two wheel halves together. Torque wheel bolts 300 inch-pounds at the nut. Inflate to 60 psi. Clean
bearings and hand-pack with grease. Before the wheel is re-installed, inspect the cast aluminum torque plate
for cracks and check the five axle attach bolts for proper torque (800 inch-pounds at the nut). Wipe axle clean
and slide inner grease seal and bearing on axle. Position wheel and tighten castellated axle nut until a slight
bearing drag is felt when wheel is turned. Back off nut to nearest castellation and install two MS24665-351
cotters. Position inner grease seal and install snap ring. Install outer dust cap. The cotter head should
protrude no more than 1/8” above the flat for dust cap clearance. Check brake linings for wear and re-install
on torque plate. The twelve bolts in each wheel cylinder require 80-85 inch-pounds torque. Safety with
MS20995C32 wire.

Main Wheel Alignment

The need for main wheel alignment is indicated by a number of subjective observations. The first probable
sign of the need for alignment is excessive tire wear or feathering at the edges of the tread beads. Dog-
tracking, or the tendency of the airplane to crab during taxi and roll out after landing, is another sign that
alignment may be required. A visual observation of both of the wheels for symmetry of angle with respect to
the airplane center-line when viewed from the front may show the need for alignment.

Manufacturing differences in forming of the main gear legs calls for the use of tapered shims to provide the
correct camber and toe-in on the main wheels. No caster adjustment is available. A diagram of the chamber
and toe-in measurements is shown in Figure 75.

The following procedure should be followed to align the main wheels:

1. The aircraft is to be fueled, but with empty hopper. Taxi the aircraft a short distance in a straight line to
allow the gear legs to assume the natural position. The aircraft should be on paved surface or flat smooth
ground.

2. A long straight edge is placed across the front of the tires approximately at axle height. This straight edge
is supported by blocks, or cans, or both. A 24-inch or larger carpenter square is placed against the
straight edge and the outside surface of the tire, and held level with the ground at the axle height. The
tire should be square with the straight edge, or have up to 1/16-inch toe-in, measured at the center-line of
the thread of the tire.

3. Camber is then measured by placing a protractor on the vertical axis of the wheel through the axle.
Camber should measure 1° to 2°.

4. Should the wheel fail to check within these limits, the axle bolts are removed and the tapered shims
rotated, deleted, or added to until the wheels check with these limits. With the aircraft hoisted and the
wheels barely touching the ground, toe-in should measure 1/4-inch to 3/8-inch and camber should
measure 2-1/4-inches.

Main Gear Spring

Details of the main-gear spring are shown in Figure 72. The main gear spring is p/n 40091-3. It will fit on
either side of the aircraft. It is machined of E-4340 aircraft quality steel, formed, heat-treated, and shot-
peened for fatigue resistance. It is sandblasted and primed with an epoxy primer (US Paint R9006 Epoxy
Primer) and finished with Alumigrip G-9046 yellow polyurethane paint.

The inboard attachment of the spring to the fuselage frame is with a NAS158A106 bolt, MS20002C18 washer
under the bolt head (be sure the chamfered side of the washer is next to the head), one or more MS20002-18
washers under the nut, AN310-18 nut, and MS24665-360 cotter. The bolt is installed upside down and torque
should be 6,400 inch-pounds (torque wrench on bolt head). A simple adapter for your torque wrench is a short
piece of 1 1/8” hex stock to enter the bolt head, and a 1 1/8” socket for your torque wrench.

It is necessary to hoist the aircraft as described under LIFTING AND HOISTING when changing the inboard
bolt. Be sure to grease the bolt with general purpose grease before installing. Also, be sure the bolt is marked
R on the head to indicate the threads were rolled after heat-treat.
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AT-802/802A June 21, 2018

The gear spring is clamped to the fuselage frame with a p/n40145-1 clamp block with one NAS156A129 bolt
and one NAS154DH59 bolt. MS20002C14 washers go under the aft bolt head and MS20002C16 washers go
under the forward bolt head (Make sure the chamfered side of the washer is under the bolt head). Various
numbers of 3088A325 round shim washers go between the clamp block and fuselage frame at the aft bolt
location. The fwd bolt uses p/n3088A326 shims. The shims are selected to allow the bolts to be fully torqued
without bending the clamp block. The 3088A shims are .010 thick. If too many thick shims are used the gear
connection will be too loose and will rattle during taxi or landing. If the gear leg becomes loose during service
even though the clamp block bolts are at full torque it is necessary to re-shim the clamp block.

The method employed at the factory to determine the amount of shims required is to install the clamp block
and fully torque the bolts before installing the large inboard bolt. The block is checked for straightness with a
small straight edge (a six-inch steel scale is OK) to be sure the block is not bent by not having sufficient
shims. Then the gear leg is grasped at the lower end, given an outboard tug by hand. A moderate tug should
move the inboard end of the leg down from the attach bushing in the fuselage frame a distance 1/8” to 1/4”. If
it is a greater distance than 1/4” the connection is too loose, and a thinner shim is tried and the process
repeated. Once the proper shims are determined, the bolts are loosened and the large inboard bolt is
installed. Then the clamp block bolts are tightened to full torque (4,000 inch-pounds on aft bolt, 6,000 inch-
pounds on fwd bolt).

An adapter for your torque wrench may be made from a short piece of 7/8” hex stock to enter the aft bolt
head, and a 7/8” socket for the torque wrench. Be sure to grease the bolts before installing. The clamp block
bolts should also have the letter R stamped on the head to indicate the threads were rolled after heat-treat.
1.0” Hex stock is used for the forward bolt head.

If an obstruction is hit with the main gear, change the forward clamp bolt immediately and check the clamp
block for straightness. The forward clamp bolt can be changed without hoisting the aircraft. The parking brake
should be set, and use care so as not to disturb the shims that are in place.

Since each main gear leg is slightly different in thickness, and since each clamp block is machined within a
specific tolerance, it is necessary to make a shim selection as described earlier, if either the gear leg or the
clamp block is changed.

As in the case of the tail gear spring, the main gear spring will fatigue and break at some point in the life of the
aircraft. Again, the number of hours before failure will vary considerably as some operators make more
landings per hour than others, or carry heavier loads, or operate form very rough strips. Pilot technique is
again a factor, as some pilots are very rough on airplanes. See the Airworthiness Limitations section for the
fatigue life of the main gear springs.
When the main gear springs are changed, use new bolts and nuts at all locations. The axle attach bolts are
NAS148-70, -72, or sometimes -74. Install the springs to the fuselage in accordance with the instructions in
this section, and install the axles to the spring using the procedure to check camber and toe-in outlined in the
section on MAIN WHEEL ALIGNMENT. Be sure to make log book entries when bolts or gear springs are
changed.

When ordering new main gear springs or clamp blocks also order 4 ea. 3088A325 and 4 ea. 3088A326 shims
in case they are needed. In addition, the large aluminum tapered shims at the axle attachment might need an
addition or change so it would be a good idea to order 2 ea. 4040141-3 shims and 2 ea 40114-2 shims in
case they are needed. Whenever the airplane is ground-looped or involved in an incident that puts a
permanent bend in one gear spring, the other spring must be changed as it may have been overstressed.

TIE-DOWN INSTRUCTIONS

To help protect against damage from strong or gusty winds when parked, your Air Tractor airplane should be
tied down to ground tie-down facilities using lines made of nylon rope, vinyl-covered chain or cable, or nylon
webbing. The lines should have a tensile strength of more than 3,000 lbs.
Page 2-82 Maintenance Air Tractor
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The airplane should be parked with the nose pointed into the anticipated wind, if possible. The parking brake
should be set and the main landing gear tires should be chocked front and rear. (CAUTION: Do not set the
parking brake when the brakes are overheated or during cold weather when accumulated moisture may
freeze the brakes. The main wheels should always be chocked when parked, but this is especially important
if the parking brake is not set.) Install the control stick lock and rudder lock and set all trim tabs to neutral
position. If available, install a pitot tube cover, engine inlet cover, engine exhaust covers (when cool), and
install the propeller tether.

Secure the wings to the ground anchors using the wing tie-down rings located beneath the front spars of each
wing, and secure to the ground anchors. These lines should be oriented as close to vertical as possible
(within 30 degrees of vertical). The tail wheel is secured by wrapping and tying the tie-down line around the
tailwheel spring. This line should be tied to a ground anchor located slightly aft of the tail wheel. Use care to
avoid damaging the tail wheel lock mechanism.

If winds in excess of 20 mph from the rear of the aircraft are expected or possible, suitable blocks should be
used to lock the control surfaces (ailerons, elevators, and rudder) in place and relieve strain on the control
systems. Very large damaging dynamic loads are possible with a gusty reverse flow of air over the control
surfaces. Should this happen without blocks in place, be sure to check all push-rods and rod-ends in the
aileron control system for damage before flight.

PROPELLER MAINTENANCE

Maintenance on your Hartzell propeller is to be done in accordance with the Propeller Owner’s Manual and
Log Book listed under “Instructions for Continued Airworthiness” in the Description section. Establish a
routine maintenance schedule and adhere to it as closely as possible. The proper propeller maintenance
manual for this airplane is: “Propeller Owner’s Manual and Log Book” Manual 139. The manual may be
obtained from:

Hartzell Propeller Inc.

One Propeller Place
Piqua, Ohio 45356-2634 USA

Propeller pitch settings are -10.0° (reverse), 13.9° (low pitch) at the 42” station for the -67 series propeller.
Propeller pitch settings are -11.0° (reverse), 16.5° (low pitch) at the 42” station for the -65 series propeller.
See Propeller Owner’s Manual for required maintenance and life limited parts.

The procedure for checking the overspeed governor is as follows:

POWER LEVER ............................................................................................... IDLE

PROP LEVER (P) .......................................................... Full forward for 1700 RPM
PROP OVERSPEED TEST SWITCH ................................................................. ON
POWER LEVER ......................................................................................ADVANCE
PROP RPM ........................................... ENSURE Np stabilizes at 1550 ± 50 RPM
POWER LEVER .................................................. REDUCE to less than 1500 RPM
PROP OVERSPEED TEST SWITCH ..................................... OFF and GUARDED
POWER LEVER ...........................ADVANCE (Ensure that 1700 RPM is available)
POWER LEVER ............................................................................................... IDLE

This check should be made at 100-hour intervals as called out in Section 3, INSPECTIONS.
Air Tractor Maintenance Page 2-83
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ROUTINE MAINTENANCE INSPECTION

The following is a guide to your routine maintenance inspections. It is not an absolute, but intended to be a
guide to help you in establishing a schedule that will maintain your aircraft in the proper manner.

The engine and propeller should be inspected and maintained in accordance with the appropriate
maintenance manual listed under “Instructions for Continued Airworthiness” in the Description section.

CHANGE OIL IN ACCORDANCE WITH APPLICABLE PRATT AND WHITNEY

SERVICE BULLETIN.

REMOVE AND REPLACE INDUCTION AIR FILTER (BRACKETT FOAM AIR FILTER ONLY)
AT 12 MONTH INTERVALS

VERIFY ACCURACY OF ITT GAUGE AT TWO YEAR INTERVALS.

OVERHAUL STARTER-GENERATOR AT 1000 HOUR INTERVALS.

DYNAMIC BALANCE PROPELLER AT 1000 HOUR INTERVALS.

REPLACE AN47-30A (THRU S/N 802A-0188) OR 30775-1 (S/N 802A-0189 AND SUBS AND
THOSE MODIFIED IAW SL#129A) EYEBOLTS ON HORIZONTAL STABILIZER
(REFERENCE SL 129). TORQUE TO 600 IN-LB FOR AN47-30A, 1210 IN-LB FOR 30775-1
AT 1350 HOUR INTERVALS.

REPLACE OR OVERHAUL COMMERCIAL AIRCRAFT PRODUCTS

P/N C100168 ACUATOR AT 1500 HOUR INTERVALS.

REPLACE RE4M6 BEARING ON THE AFT END OF THE FLAP PUSH-RODS

AT 2000 HOUR INTERVALS.

OVERHAUL PROPELLER PER HARTZELL REQUIREMENTS (See Hartzell

Service Letter HC-SL-61-61Y, Rev 1 or later).

CHANGE MAIN GEAR BOLTS IN ACCORDANCE WITH SCHEDULE IN “MAIN

AND TAIL GEAR ATTACH BOLTS” OF THIS SECTION

CHANGE TAIL GEAR BOLTS IN ACCORDANCE WITH SCHEDULE IN “MAIN

AND TAIL GEAR ATTACH BOLTS” OF THIS SECTION
Page 2-84 Maintenance Air Tractor
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STATIC SYSTEM

The static port on the AT-802 is contained within the wing-mounted pitot head. The static system on this
airplane can be drained by opening the static line inside the leading edge of the wing. Alternatively, the line
can be blown out with compressed air. In this case, the static line is accessible beneath the right-hand
fuselage skin that attaches to the top of the hopper tank.

CAUTION
Apply air pressure only to the line that leads to the pitot-static
head. Do not apply air pressure to the line that leads to the
instrument panel. Sensitive instruments may be damaged.

The static ports on the AT-802A are the low points of the system and are normally self-draining. There are “T”
fittings on the rear face of the static port buttons. The downward-facing arm of the “T” fittings are plugged.
These plugs must be removed to drain residual moisture in the static-system lines.

STORAGE

When leaving your airplane outside, be sure and cover the exhaust ports and keep the propeller tethered. The
propeller needs to be tethered to prevent the windmilling of the power section. The reason for this is that the
oil pump is in the rear of the engine and will not turn with the prop and therefore, will not provide oil to the
front of the engine. Don’t be too embarrassed the first time you start the engine with the propeller tethered, I
can assure you that you are not the first.

Be sure to secure the ailerons as discussed in the section on MOORING AND TIE DOWN above.

STRIPPING AND REPAINTING

Stripping and Repainting Aluminum Parts

1. The paint stripper most effective on urethane paint is Turco #5351.

2. The stripper is either sprayed on with a barrel pump or applied on small parts with a large paint brush. If
sprayed on be sure to consider wind direction so that over-spray will not damage surrounding vehicles or
aircraft.

3. When applying stripper, wear protective clothing and safety goggles.

4. Apply a medium to heavy coat of stripper. Temperature should be 50° F or warmer for best results.
Allow stripper to react with paint and remove with special brush having stiff bristles that will not soften with
stripper.

5. Spray on a second light coat of stripper as necessary and remove remaining paint with brush.

6. Rinse thoroughly with (approx. 150° F) water under pressure. Be sure entire film of stripper is removed.

7. Apply Acid Etch with Scotch Brite pads and scrub metal surfaces thoroughly. Rinse with cold water.

8. Before the part is dry, apply generous amounts of Alodine with a clean white rag. The Alodine should act
within two or three minutes and when rinsed off with cold water should leave a very light gold surface. Do not
leave the Alodine too long or allow it to dry as a dark brown film will result which is undesirable and should be
removed and the part reprocessed.
Air Tractor Maintenance Page 2-85
AT-802/802A June 21, 2018

9. When the part is completely dry, apply a coat of High Solids Epoxy Primer:

9.1 Always follow manufacturer’s recommended mixing ratio of pigmented component to adduct.

9.2. Surfaces must be clean and free of grease, dirt, oil, rust, fingerprints, and other contaminants
to insure optimum adhesion and performance properties. Parts may be cleaned using an
alcohol soaked soft white rag.

9.3. Apply primer using conventional spray equipment or HVLP spray equipment.

9.4. Ideal coating thickness is 0.5 mils dry.

9.5. Spray coatings with smooth, even strokes. Runs and sags are to be avoided.

9.6. Application temperature should be between 65°-100° F.

9.7. Epoxy primer should be allowed to flash before recoating with epoxy primer.

9.8. Air dry time to topcoat at 77°-100° F is 2 hours minimum.

9. 9. Full cure is achieved after approximately 18 hours of air dry.

9.10. If parts are allowed to dry in excess of 48 hours before topcoat application, they must be
sanded and reprimed.

10. Apply Urethane Topcoat on Primed Parts:

10.1. Always follow manufacturer recommended mixing ratio of hardener, base component, and
activator.

10.2. Surfaces must be clean and free of grease, dirt, oil, rust, fingerprints, and other contaminants
to insure optimum adhesion and performance properties. Parts may be cleaned using an
alcohol soaked lint-free cotton cloth.

10.3. Parts should be wiped with a urethane grade tack cloth and then air blown to remove any
foreign materials.

10.4. Mix topcoat in accordance with manufacturer instructions. Do not deviate from manufacturer
recommended mixing ratios.

10.5. The paint booth temperature should be maintained between 65°-100°F. Ideal booth
conditions are 75°-85° F and a relative humidity of 45%.

10.6. Apply topcoat using conventional spray equipment or HVLP spray equipment.

10.7. Ideal coating thickness is 2.8 - 3.5 mils dry.

10.8. Spray coatings with smooth, even strokes. Runs and sags are to be avoided.

10.9. Cure time is 4.5 hours to tape at 120° F, or 6-8 hours to tape at 77° F.

10.10. Clean equipment using Ketone (MEK) solvent. Do not allow material to cure inside spray
equipment.
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Priming Aluminum Parts with Chromated Alkyd Primer

Parts that do not receive a finish coat of paint (such as wing ribs) are primed with Chromated Alkyd Primer
conforming to spec TT-P-1757B, Type I, Class C. Surfaces must be clean and free of grease, dirt, oil, rust,
fingerprints, and other contaminants to insure optimum adhesion and performance properties. Parts may be
cleaned using an alcohol soaked soft rag. Follow the Acid Etch and Alodine process described in the
“Stripping and Re-painting Aluminum Parts” section above. Apply a light coat of Chromated Alkyd Primer
thinned with Toluene R2K1 or Xylene R2K4 if necessary to achieve proper viscosity. Spray coatings with
smooth, even strokes. Runs and sags are to be avoided. The primer application should be a thin film.

Stripping and Repainting Steel Parts

Steel parts are to be cleaned of all oils and then sand-blasted. If sand-blasting is not available, clean the part
thoroughly, wipe dry, sand, and etch with a mixture of 1.0 gal. Isopropyl Alcohol and 1/2 fluid oz. of
concentrated Phosphoric acid. If applying finish coat over bare metal, prime first with High Solids Epoxy
Primer (see instructions above) and paint using Urethane Topcoat process (see instructions above).

Materials Used for Stripping, Painting, and Preservation

Urethane Topcoat Materials

At the time of this writing the factory uses materials produced by PRC Desoto Aerospace Coatings.

High Solids Epoxy Primer on Aluminum Parts

Desoprime (TM) HS CA 7700/CA 7755 (with BE activator) by PRC DeSoto Aerospace Coatings. These
primers are to be mixed and applied according to the Technical Data Sheet and CA 7700 series Application
Guide.

Urethane Topcoat on Aluminum Parts

Top coat is Desothane HS CA 8800 series or CA 8200 by PRC DeSoto Aerospace Coatings. CA 8800 is to
be used for high gloss top coat colors. CA 8200 is to be used for matte or flat colors. The topcoats are to be
mixed and applied according to the appropriate Technical Data Sheet and Application Guide.

Chromated Alkyd Primer Materials

Part No. Description Amount used per A/C

TT-P-1757B Yellow zinc chromate primer 5 gal.
TT-T548C Toluene (R2K1) 5 gal.

Surface Preparation Materials

Part No. Description Amount used per A/C

Turco #5351 Stripper 10 gal.
Acid Etch 3 gal.
Alodine 2 lbs.
Isopropyl Alcohol 2 gal.
Phosphoric Acid 1 fluid oz.

Internal Oiling Steel Parts

Part No. Description Amount used per A/C

Linseed Oil 1 gal.
Air Tractor Maintenance Page 2-87
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TAIL LANDING GEAR

Tail Wheel

The tail wheel is a Cleveland p/n 40-14003. Keeping the bearings properly lubricated is the key to long
bearing life. A grease fitting is installed in the side of the wheel. Details of the tail wheel are shown in Figure
77.

To remove the tail wheel, jack the wheel clear of the ground per LIFTING AND JACKING instructions and
remove the long AN7C84A bolt that attaches the axle to the fork. Note the method of safety wire on the large
stainless jam nut and cut the wire loose from the fork. The tail wheel is now free and ready for dis-assembly.
Back off the jam nut from the axle and remove the axle. Inspect the axle for wear at the bearing positions, as
insufficient greasing procedures will cause the bearing to turn on the axle and ruin both parts. Inspect the AN7
bolt for wear and straightness, and slide the bolt through the fork to check the hole in the fork for wear. There
should be no wear in the fork holes since there is no movement between fork and bolt. If the tire is to be
removed, deflate and remove the bolts holding the wheel halves together.

Clean all parts and re-assemble. Partial inflate the tube to keep from pinching it.

Tail wheel bearings are Timken 13889 cone (the part with the rollers) and 13836CP cup (the part pressed into
the wheel half). Hand pack the bearings with grease, MIL-G-81322, and install wheel on the axle. Install the
40139-1 jam nut and 40138-1 tongue washer on the axle with the round shoulder inboard and tighten until all
bearing slack is removed but the wheel is free to turn. Inflate the tire to 60 psi. Grease the axle bolt and install
wheel and axle assembly on the fork. Torque the nut to 550 inch-pounds. Safety the jam nut against the
rotation of the wheel with MS20995C32 stainless safety wire.

Tail Wheel Fork

Details of the tail-wheel fork are shown in Figure 78. The tail wheel fork may be removed from the housing by
removing the single AN5C32A stainless bolt from the arm assembly that connects to the centering springs.
With the fork removed, check for wear on the spindle at the bronze bearing location. Also check for condition
of the steel bushing that the lock pin drops into. This bushing is pressed into the steel plate at the bottom end
of the spindle and staked in four places on each side of the plate with a center punch. This holds the bushing
in place since it has a beveled edge on both sides. This bushing is p/n 40042-1. Excess wear on the fork
spindle at the bronze bearing location is indication that grease is not reaching the proper areas. To grease the
bronze bearing properly, jack the tail wheel clear of the ground and apply MIL-G-81322 grease at the fitting on
the housing, and rotate the fork until grease is running out of the full perimeter of both upper and lower
bearings. Excessive wear in the spindle will require a new fork assembly, which is p/n 40117-1 and includes
the steel lock pin bushing. The centering springs are p/n 40044-1 and attach to a p/n 40044-1 and attach to a
p/n 40035-1 bracket that wears on a p/n 40036-1 bushing. The bolt is an AN4C7A.

Tail Wheel Fork Housing

Details of the tail-wheel fork housing are shown in Figure 78.

The housing is attached to the tail spring with two NAS154DH-32 bolts, and MS20995C32 safety wire ties the
bolt heads together. These bolts have a tendency to loosen in service, particularly in the first 100 hours of
operation as pain between mating surfaces is compressed. At 100 hour intervals, the tail wheel should be
jacked clear of the ground, and with the locking pin in place give the tail wheel a vigorous tug from side to side
to check the movement between the housing and the spring. See the Table under MAIN-AND TAIL ATTACH
BOLTS for recommended replacement times and bolt torques. Be sure to grease the bolts before installation
with anti-seizing lubricant per MIL-A-907E or equivalent. An added precaution would be to apply this lubricant
to the threads of the housing to prevent the bolt from seizing.

A Timken Roller bearing is installed at the lower end of the fork housing assembly. This bearing consists of a
Timken 28995 cone and a 28920 cup. The seal is a p/n 40115-1. The large bronze bushing inside the housing
is p/n 40124-1 (upper). The bushing is pressed into place and may be driven out with a pin punch. The
housing assembly is p/n 40118-1 which is less bushing, bearing, seal, and grease fitting.
Page 2-88 Maintenance Air Tractor
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Tail Wheel Lock Pin and Housing

Details of the tail-wheel lock-pin housing are shown in Figure 78.

The lock pin housing is p/n 40025-6 and attaches to the steel plate on the lower end of the fork housing with
four countersunk screws. The four holes in the base of the lock pin housing are oversize to allow adjustment
of the locking pin. If the aircraft tends to steer to the left or to the right on the ground with the lock pin
engaged, it is necessary to re-position the lock pin housing. Jack the tail wheel clear of the ground, lift the lock
pin up and swivel the fork to one side so that the four screw heads are exposed. Make a pencil mark along
the edge of the lock pin housing plate for a reference and estimate the amount of movement for the lock pin
housing.

Loosen the 4 screws and move the housing the desired direction. Swivel the fork back into position and allow
the locking pin to engage the fork, then tighten the two outboard screws. Then rotate the fork back so that the
two inboard screws can be tightened. Check the lock pin again to see that it freely engages the fork. Taxi the
aircraft on a smooth level surface in a no-wind condition, or if there is a light wind, taxi both up-wind and
down-wind with the rudder pedals in the neutral position and the stick back so that you are sure the lock pin is
engaged. Keep adjusting the locking pin housing until the aircraft will taxi in a straight line.

During annual inspections (or more frequently if required) remove the housing and slide out the locking pin to
check it for wear and straightness. The compression spring inside the housing should also be checked for
broken coils. The locking pin is p/n 40131-1 and the spring is p/n 40026-1. If the lock pin bushing is worn it
should be replaced by installing the SL #171 repair kit, available from your Air Tractor dealer.

Tail Gear Spring

The tail-gear spring is shown in Figure 73.

The tail gear spring is p/n 40092-6. It is machined of E-4340 aircraft quality steel, formed, heat-treated, and
shot-peened for fatigue resistance. It is sand-blasted and primed with an epoxy primer (See Urethane
Topcoat Materials) and finished with yellow polyurethane paint.

The forward attachment of the spring to the fuselage frame is with a NAS1308-34 bolt. It is clamped at the
rear attachment with a p/n 40140-1 clamp block, which attaches to the fuselage frame with two NAS148-69
bolts. There is a p/n 40146-1 aluminum pad that is installed between the clamp block and the spring to allow
the spring to work without putting secondary loads into the fuselage frame or attach bolts. There are .010
thick shims (p/n 3088A322) and sometimes a spacer washer located between the clamp block and the
fuselage frame. During annual inspections the tail gear should be jacked at the stabilizer strut fittings as
described under LIFTING AND JACKING and the tail spring checked for looseness at the clamp block.
Looseness can be eliminated by removing one or more of the shims from under the clamp block. With the
clamp block removed, also check the aluminum pad for condition.

Besides saving a possible fatigue failure, the forward bolt tends to freeze up if not changed often. Be sure to
grease the bolt and snug the nut only (no torque) as the spring must move on the bolt. Torque the clamp bolts
to 900 inch-pounds (torque wrench on bolt head), and make sure there are sufficient shims between the
clamp block and the fuselage frame to prevent bending the clamp block as the bolts are torqued.

The tail gear spring will fatigue and break at the same point in the life of the aircraft. The number of hours
before failure will vary considerably as some operators make many more landings per flight hour than others,
or carry heavier loads, or operate from very rough strips. Pilot technique is a factor also, since some pilots are
very rough on airplanes. See the Airworthiness Limitations Section for the fatigue life of the tail gear spring.

Destruction of the old spring with a cutting torch is recommended.

Air Tractor Maintenance Page 2-89
AT-802/802A June 21, 2018

TIME-LIMITED PARTS

Time-limited parts are those parts recommended for replacement at the times indicated below. Failure to
replace these parts at the time shown may result in unexpected failure of these parts during aircraft operation.

Main-and-Tail-Gear Attach Bolts

Hours shown are for normal operations in row-crop or rice operations. If your business combines both types
of flying, use an average of the two figures. If your strips are rougher than normal, then cut the hours shown in
half.

Tail Spring

The tail spring should be changed about every 1500 hours for worst conditions of rice operations from rough
strips, and every 3,000 hours for the best conditions of row-crop work from smooth strips. Each operator
should determine at what point in between these extremes his operation fits and change the tail spring at the
appropriate interval, unless the measuring process described earlier indicates yielding. In that case, the
spring should be changed immediately. See LIFE LIMITED AIRFRAME PARTS in Section 6,
AIRWORTHINESS LIMITATIONS.

Main Gear Spring

In the interest of safety and the high financial consequences of a broken main gear leg, it would be advisable
to take a highly conservative approach and change the main gear springs well before the probable fatigue life.
The main gear springs should be changed after 3,000 hours or 8,000 landings, whichever comes first. See
LIFE LIMITED AIRFRAME PARTS in Section 6, AIRWORTHINESS LIMITATIONS.

AmSafe Airbag System (if installed)

If the AmSafe Airbag System is installed, the following are time-limited parts

The EMA (Electronics Module Assembly) is to be removed for disposal after:

x a maximum storage period of fourteen (14) years calculated from the month of manufacture, or;
x upon expiration of the service life defined as the total sum of storage life and installation life, which
must not exceed fourteen (14) years calculated from the month of manufacture.
Upon expiration of the service life (total life), the EMA cannot be renewed.
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The Inflator Assembly is to be removed and returned to AmSafe Aviation for disposal after:
x a maximum storage period of ten (10) years calculated from the month of manufacture as indicated in
the expiration date stamped on the gas cylinder, or;
x upon expiration of the service life defined as the total sum of storage life and installation life, which
must not exceed ten (10) years calculated from the month of manufacture as indicated in the
expiration date stamped on the gas cylinder.
Upon expiration of the service life (total life), the Inflator Assembly cannot be renewed.

In addition, the EMA is to be removed and returned to AmSafe Aviation for refurbishment after:
x a period of seven (7) years calculated from the month of manufacture regardless of storage or service
time or combination of both.
The EMA can only be renewed by AmSafe Aviation.

TIRE INFLATION

The main tires are inflated to a pressure of 60 psi (unloaded) or 62 psi (loaded). The tail wheel tire is inflated
to a pressure of 60 psi (loaded or unloaded).

TORQUE VALUES FOR SHOP USE

Torque Value (inch-pounds)

Size of Nut or Bolt Tension Type Nuts Shear Type Nuts

1032 60-70 20-25
1/4-28 100-120 30-40
5/16-24 200-240 60-85
3/8-24 300-330 95-110
7/16-20 550-600 270-300
1/2-20 800-900 290-410
9/16-18 1,100-1,300 480-600
5/8-18 1,700-1,900 660-780
3/4-16 2,800-3,000 1,300-1,500
7/8-14 3,500-4,000 1,500-1,800
1-14 6,000-6,400 2,200-3,300
1 1/8-12 6,000-6,400 -----

NOTE:

1. The chart applies to all standard or high strength aircraft alloy steel bolts.

2. The lower value is used when the bolt is held stationary and torque applied to the nut. For
the reverse of this procedure use the upper value.

3. Tension type nuts are AN365, AN636, and AN310.

4. Shear type nuts are AN364, AN320.

TOWING

The airplane can be towed with the use of an appropriate tow bar attached to the main landing gear. The
proper towing points are the metal rings on the inner side of the landing gear strut in the same plane as the
axle. Towing with attachment to the tail-wheel spring is not recommended. The tail-wheel lock should always
be disengaged while the airplane is being towed.

A towing bar can be made from two 12-foot-long 4130 steel tubes and a three-quarter-inch steel bar. The
tubes outside diameter should not be less than two inches and the wall thickness should be at or above .065
inch.
Air Tractor Maintenance Page 2-91
AT-802/802A June 21, 2018

The tubes are pinned together at one end with a loose 1/2-inch bolt and an attachment to join to the towing
lug or ball on a vehicle. The three-quarter-inch steel bar is bent at 90 degrees with six inches of bar extending
in one direction and three inches in the other dir ection from the bend. These bent bars are welded to the free
ends of the tubes. The three-inch leg is pointed downward and the other is fillet-welded to the outside of the
tube. These downward-projecting pintles fit loosely into the towing rings in the airplane’s landing gear. A hole
may be drilled through the three-inch leg at a quarter-inch from its end for a spring pin, if desired.

The airplane can be pulled or pushed using the tow bar. If the airplane is towed into tight quarters, a wing-
walker should be engaged to avoid damage to wing tips and tail members where visibility is limited.

The airplane should not be towed faster than 5 miles per hour on a smooth surface without pot-holes or sharp
bumps. Landing gear damage, particularly tail-wheel damage, can result from dropping the gear into holes at
high speeds.

Excessively bumpy surfaces must be negotiated cautiously to avoid landing gear damage. Also, bumpy
surfaces may cause the tow bar to bounce and disengage from the tow rings on the landing gear. Should this
occur, directional control of the airplane is lost. A gentle stop should be executed immediately to minimize
damage. The safest approach to towing on bumpy surfaces is to station a crew member in the pilot’s seat to
actuate the airplane’s brakes if the hitch or tow bar should fail or disengage. Use of a spring pin through the
drilled holes minimizes the likelihood of disconnect on a rough surface.

Sloped surfaces with a grade more than ten degrees should be approached diagonally to reduce the load on
the tow bar and hitch points.

Sudden starts and stops must be avoided, particularly with a heavily-laden airplane, to prevent failure of the
tow bar or tearout of the towing rings.

WEIGHT AND BALANCE

The proper maintenance of weight and balance records is important to ensure that the airplane is operated
within the weight and center of gravity limits that are established in the Flight Manual. The weight-and-balance
diagram with sample calculation is shown in Figure 80. The airplane must be weighed in the attitude
described under LEVELING.

WINGS

The wing is of all-metal construction with the main spar designed to take the entire bending load. Thick wing
skins are employed near the wing root with a gradual drop in thickness at each skin lap as wing loads
diminish. No span-wise stringers are used in order to simplify construction and repairs and for that reason
wrinkles in the upper skin and cans between the ribs will be noticed during maneuvers with heavy loads. This
is a natural condition and unless the cans or wrinkles change noticeably in a particular location there is no
cause for alarm. Any changes as mentioned would require close inspection of all internal structural parts in
the area where the change has taken place.

The wing leading edge is of .040 thick 2024-T3 and can be replaced in the field as described under the
Repairs section of this manual. The wing rear spar attach plate is of 5/16” thick 4130N steel for extra strength
and resistance to corrosion during fertilizer applications. It is cadmium plated and primed with Chromanoxide
epoxy primer before assembly to the rear spar.

All wing parts are cleaned with a detergent soap, scrubbed with an etching solution, and dipped into an
Alodine 1200 solution, then primed before assembly. Skin laps on the top side of the wing are sealed with PR-
1422 A2 as in the wing root to prevent chemical entry.
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Wing Attachment to Fuselage

Details of the wing’s front-spar attachment to the fuselage are shown in Figure 79. The wing’s rear-spar
attachment to the fuselage is shown in Figure 81.

Two aluminum and two steel wing-attach angles are used to attach the wing main spar to the fuselage vertical
tube just aft of the main spar. There are four AN6-31A bolts that attach each vertical tube to the wing angles.

It should also be noted that there is no bolt through the attach angle and through the small leg of the lower
spar cap. This is to eliminate bolt fretting and make the joint more fatigue resistant.

The wing attach angles are p/n 20605-1 (aluminum) and p/n 20475-1 (steel). They are attached to the main
spar with six AN6-15A and two AN6-16A bolts. If it is necessary to change the wing attach angles due to bolt
wear or fuselage repairs, ask the factory for detailed instructions on how to drill the attach angles at the time
they are ordered, as these angles are drilled to match each individual aircraft.

The rear spar plate is attached to the fuselage frame with a single NAS1309-25 bolt. These bolts wear slightly
and should be checked at 1,000 hour intervals, and replaced if worn or rusty. Do not use AN bolts at this
location. To remove the bolts, first remove the lower wing gap cover, which is attached with screws. Removal
detail of the gap cover is shown in Figure 82.

Place a small hydraulic jack under the wing rear spar plate and apply only a small amount of pressure to
support the wing when the bolt is removed. Lock the parking brake so the aircraft will not move. Remove the
nut and drive the bolt out with a small hammer gently, protecting the threads from damage. Inspect the bolt
visually, then place it on a smooth plate and rotate to see if it is bent. Inspect for thread damage or rust. Do
not use excessive force to remove the bolts, and do not heat. If there is difficulty in removing the bolts, contact
the factory.

We encourage replacement of old bolts with new bolts at all times, but if the old bolts are in good shape and
the time intervals mentioned above are not exceeded, they may be re-installed. Be sure to grease the bolts
with MIL-G-81322 grease before installing. Torque values are 1100 inch-pounds (Torque wrench on nut).

Wing Center Splice Connection

Details of the wing center-splice connection are shown in Figure 83.

The main spar caps of each wing are attached to each other with p/n 20976-1/-2 (Upper), 21082-1/-2 (Lower)
attach blocks. The main spar webs are attached to each other by p/n 20994-2 plate of .59” thick heat treated
4130 steel. The connection to the fuselage on the aircraft centerline is made with a p/n 20618-1 steel plate of
.125 4130N connected to the fuselage structure with two AN6-25A bolts, and to the two 3/4” bolts through the
20976-1 upper spar cap attach block. There are four p/n 20606-1 tube-nut welded assemblies and two p/n
20608-1 sleeves in each wing installation. The sleeves and tube-nuts are drilled 23/64” and reamed .374 after
the tube-nuts have been fully tightened, and two AN6-21A bolts installed in each sleeve. If the wings are
removed from the aircraft, it is usually necessary to replace the four tube-nut assemblies and the two sleeves
since the .374 reamed holes through both parts will probably not line up. In this case, tighten the new tube-
nuts 1920 inch-pounds torque, position the new sleeves mid-way between the tube nuts, drill 23/64” through
the sleeve and tube-nut, and ream .374 for the AN6-21A bolt installation.

The tube-nut and sleeve installation is to take the “kick-load” imposed by dihedral angle and cancel it out by
transferring this load from the upper spar caps to the lower spar caps.

To remove the wings, or to inspect the wing center splice connection properly, the front hopper should be
removed.
Air Tractor Maintenance Page 2-93
AT-802/802A June 21, 2018

Torque values should be checked on the nuts to learn if the bolts have elongated or if fretting has loosened
the fit of the joint. Torque values to be checked are as follows:

300 inch-pounds on the 3/8” nut

550 inch-pounds on the 7/16” nut

800 inch-pounds on the 1/2” nut

1,100 inch-pounds on the 9/16” nut

1,700 inch-pounds on the 5/8” nut

2,800 inch-pounds on the 3/4” nut

1,920 inch-pounds on the 3/4” tube-nut assembly

There are seven 90050-6-25 bolts through the small leg of each spar cap that attach to the 20994-2 plate on the
aft side of the web. On the lower spar caps, there are an additional three 90050-6-22 bolts through the small leg
of each cap and seven 90050-6-22 bolts through the spar web plates. These 3/8” nuts are checked for torque
(300 inch-pounds). The two NAS1304-26, eight NAS1304-22, and ten NAS1304-25 bolts through the 20994-2
plate and spar have a torque of 100 inch-pounds applied to the nut. The six NAS1305-22 and eight NAS1305-26
bolts have a torque of 200 in -lbs applied at the nut. The two NAS1205-26 screws have a torque of 150 in-lbs
applied at the nuts.

Inspect the entire splice connection carefully for signs of bolt working, corrosion, or cracks. The critical area for
cracks is the lower spar cap at station 10.3” from the aircraft center-line where the 3/8” NAS bolt attaches the
21082-1 and -2 blocks to the main leg of the cap. If a crack were to develop at that point, it would probably
progress out of the 3/8 bolt hole across the cap at station 10.8” where the most inboard of the seven 90050-6-25
bolts are located. The next critical area of the lower spar cap would be in the lock bolt pattern attaching the small
leg to the web from approximate stations 25.0” to 30.0” which is where the inboard fuel tank wall is located. It
would also be advisable to check carefully the lower side of the main leg in the area where the fuel tank bottom
ends.

Always use a new nut for replacement after a nut is removed.

For appropriate inspection intervals of the wing center splice connection, see the INSPECTION section of this
manual. If a new wing is to be installed, contact the factory for wing installation instructions at the time the wing
is ordered.

CAUTION
Consult the factory for tools, jigs, and fixtures
to ensure proper installation of a new wing.

Wing Walk

The main wing walk is made of 3-M safety walk 12” wide and is p/n 20232-2. The small round walk part is
p/n20234-1 and the flap walk is p/n 20427-1. The walk outboard of the main walk is p/n 20565-2. The trim plate
on the forward edge of the walk is p/n 20231-1 and p/n 20718-1 is on the aft edge.

The walk material has adhesive backing but in order to improve the bond to the wing skin, 3-M safety Walk
Adhesive is applied to the wing surface. To prevent fuel from getting under the walk and lifting it, 3-M Edge
Sealing Compound is applied along the perimeter of the walk. If the walk is changed, be sure to order the
adhesive and the edge sealing compound for best results.