ATA 28 Hawker 750/800/800XP/850XP/900XP

FUEL TRAINING MANUAL (B1/B2)

ATA 28
FUEL

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INTRODUCTION
GENERAL
• Fuel is stored in the integral wing tanks and the ventral tank attached to the lower part of the rear fuselage
• The system has both a wing tank-to-tank and ventral-to- wing tank transfer capability, in addition to a cross feed capability from
wing tank to engines.
• Electric fuel booster pumps in the wing tanks deliver fuel under low pressure to the engines. The booster pumps also activate jet
pumps for fuel transfer.
• Re-fuelling and defueling is by (gravity or single-point pressure methods.
• Fuel indications are on the right multifunction display (MFD) and on the engine page of each of the control display units (CDUs).

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FUEL STORAGE
• WING TANKS
• Each main tank is formed by sealing the wing structure between the front and rear spars from rib 0 to rib 14, Thiokol®
(PRC) sealants are used between faying surfaces to provide fillets and to overcoat bolts. All joints are finally over coated
with PR 1005.
• Ribs and the center spar web divide each tank into six compartments (Figure 28-1). Bibs 4and 8 incorporate flap valves for
rapid refuelling.
• Structural gaps and small holes reduce the amount of unusable fuel and to prevent the formation of air pockets during
refuelling.
• Outboard of each tank, the structure between ribs 14 and 15 is sealed to form the surge tank. A NACA duct in the bottom
skin outboard of rib 13 vents the surge tank to the atmosphere. Certain stringers reduxed to the top skin are used for vent
pipes and some bottom stringers feed fuel into the No. 1 tank compartment via check valves.

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Access to each tank is through panels and NOTES manhole covers (Figure 28-2). The manhole cover in the No. 1 compartment of each
wing has the booster pump and fuel drain valve attached. Water drain valves are in the surge tanks and in the No. 1 compartments.

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The gravity refueling filler caps on the wings NOTES (Figure 28-3) have a rubber flap valve on the bottom of the cap adapter to prevent
fuel spillage if the cap is inadvertently left off. A hinged door on the rear left side is over the ventral tank filler cap, and a baulk
prevents closure of the door if the cap is incorrectly installed.

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• Drain Valves
• Wing and surge tanks contain water drain valves. Wing tanks also contain fuel drain valves
• Water Draining
• Accomplish water draining procedures before and after refueling. After refueling, delay the water drain check for 30
minutes, if possible. Extremely fine droplets can remain suspended in the fuel for at least 10 minutes. If the sample
appears cloudy, it contains water and more time is required for settling.

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VENTRAL TANK
• Ventral Tank
• The ventral tank, bolted to the aft underside of the fuselage, is sealed in a manner similar to the wing tanks (Figure 28-5).
Instead of being divided into compartments, it contains anti surge baffles. Ventral tank fuel is transferred to the wing
tanks by the wing booster pumps.
• The ventral tank filler cap is accessible through a hinged door on the left side of the tank rear fairing (Figure 28-6). The
hinged door has a security lock to prevent opening.
• With the cap locked in the filler orifice, the radial position of the engraved arrow on the cap is immaterial.
• A chain secures the cap to the tank.
• To stop closure of the fairing door without correct fitment of the filler cap, a fuel door baulk prevents closure of the fairing
door.

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VENT SYSTEM
• The fuel vent system is illustrated in Figure 28-7. Refer to the AMM for removal and replacement procedures.
• On 750 aircraft, the No. 3 top stringer is blanked off as it comes out of the wing.

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VENTRAL TANK VENTS

• Two vent pipes, one on each side of the tank, are connected at the forward end to vent float valves (Figure 28-8) on both sides
of the tank forward wall.
• At the rear of the tank, the right pipe is open-ended. The left pipe incorporates a lightly spring-loaded non return valve
• An interconnection by a U-shaped pipe incorporating a rubber non return valve to drain trapped fuel back into the tank connects
the forward end. of both pipes.
• An external vent hose through the rear diaphragm of the tank ensures complete venting of both sides of the tank.
• Each fuel tank is vented to the atmosphere through the vent surge tank in the wing tip. Each vent tank incorporates a NACA
intake that pressurizes the vent system.
• Fuel that spills into the vent surge tank syphons back into the wing tanks as the tank level falls.
• Each wing tank is vented to the vent surge tank at its outboard end via a float valve and at its inboard end via stringer in the wing
top skin (Figure 28-9).
• The float valve prevents fuel loss through the vent during in-flight manoeuvring.

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WING TANK
• An integral collector (surge) tank is in each wingtip. Each wing vents to its respective surge tank via a float valve and the No. 1
and No. 2 stringers of the top skin.
• The ventral tank vents into the left wing surge tank. Each surge tank is sealed with Thiokol® and includes a float switch and a
duct to the non- icing NACA vent (Figure 28-10) and water drain on the underside of the wing
• Any fuel collecting in the surge tank is forced back into the wing tank as soon as the wing tank fuel level has dropped sufficiently.

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VENTRAL TANK (Except 750 Aircraft)

On the ground, vent pipes connect both rear corners of the tank to the vent system within the tank through a vent outlet at the front
left side of the tank (Figure 28-11). From this point, the tank vent is connected to the vent surge tank in the left wing through a pipe
and the No. 3 upper wing stringer. During a climb, the vent pipes at the rear of the tank are sub- merged and the vent float valves are
open to allow continuous venting of the tank.
On 750 aircraft, the ventral tank is replaced with an external baggage unit (EBU). The associated vent pipe is blanked off in the
wing/fuselage fairing
LIMITATION
• Approved Fuels
• The AMM lists the approved fuels and fuel additives which can be used in the aircraft. Fuel additives are listed earlier in
this chapter under maintenance considerations. The engine must be started and operated with fuel conforming to the
specifications listed in Table 28-1.
• The airplane does not require the use of Prist treated fuel; however, it is approved for use.
• Approved Additives
• Biobor JF
• The biocidal additive Biobor JF can be used at a concentration not exceeding 270 ppm for shock treatment only. After
shock treatment, the engine(s) must not be run until the tank(s) has (have) been drained. Fuel with concentrations of
Biobor JF of more than 135 ppm by weight (10 ppm boron) must not be burnt by the engine(s).

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• Approved Fuels
• The AMM lists the approved fuels and fuel additives which can be used in the aircraft. Fuel additives are listed earlier in
this chapter under maintenance considerations. The engine must be started and operated with fuel conforming to the
specifications listed in Table 28-1.
• The airplane does not require the use of Prist treated fuel; however, it is approved for use.
• Approved Additives
• Biobor JF
• The biocidal additive Biobor JF can be used at a concentration not exceeding 270 ppm for shock treatment only. After shock
treatment, the engine(s) must not be run until the tank(s) has(have) been drained. Fuel with concentrations of Biobor JF of more
than 135 ppm by weight (10 ppm boron) must not be burnt by the engine(s).
• Tank Capacities
• The wing tanks each have a usable capacity of 634 U.S. gallons.
• The ventral tank has a usable capacity of 233 U.S. gallons (less 5 gallons with external toilet drain). The total usable fuel is
1,501 U.S. gallons or 10,000 pounds.
• For flight, the ventral tank must be completely filled or empty, but partial fuel loads that are equal are acceptable for the
wing tanks and can be obtained by manually selecting their refuel valves off at the required level during refueling. If the
ventral tank is fueled, each wing must contain at least 3,450 pounds of fuel.

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• Fuel loading
• Fuel imbalance between the left and right wing tanks cannot exceed 500 pounds for takeoff.
• Fuel must not be carried in the ventral tank unless each wing tank contains at least 3,450 pounds of fuel for takeoff.

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Maintenance consideration
• Avimo Pipe Couplings
• Avimo pipe couplings (Figure 28-12) form the pipe-to-pipe and pipe-to-fitting joints in the fuel system. The couplings on
fuel pipes in the rear equipment bay have leakage drains. Any leakage is dumped overboard through the rear fuselage
drain forward of the ventral tank.
• When Avimo pipe couplings are disassembled, all o-ring seals in the coupling must be replaced even if only one half of the
coupling has been disturbed.
• If leakage cannot be stopped by replacing the o-rings, a split washer (Figure 28-13) can be added to increase the
effectiveness of the compression ring. Refer to the AMM for details.

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Leak Detection/ Classification

• To classify the degree of leakage, wipe clean any fuel leakage and residue. Apply a thin coat of developer in the area of the leak.
Allow the airplane to stand for 30 minutes. After the time has elapsed, make sure that the suspect area is checked against the
following criteria:
• Acceptable leakage—any leakage smaller than a stain that shows no signs of forming into drips or runs.
• Leakage requiring a temporary fix:
• Wing and ventral tanks—Stain, seep and heavy seep leakage that shows no signs of forming into drips or runs. Do a
permanent repair at the earliest opportunity.
• Leakage that requires immediate permanent repair:
• -- Any leak caused by a crack or other structural damage or defect
• -- Any leaks in an enclosed area (leading edge, front wing-to- fuselage fairing, over wing-to-fuselage fairing, flap cove area,
wheel well area, rear equipment bay, ventral tank side fairing, ventral aft fuselage fairing, pylon area and engine cowl).
• -- Any leak more than quoted above.

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Temporary External Repair Using Oyltite – stik tm

• Oyltite-Stik™ is a leak stopper produced by Lake Chemical Co. of Chicago. The solvent associated with the product is Titanine® TS
(cellulose) thinners.
• To apply, the surface must be free of hydraulic fluid, grease, or jointing com- pound. [f adhesion cannot be obtained, remove
fuel below the leak level. On extremely smooth surfaces, cut off a small portion of the stick and press firmly into the leak with a
suitable tool.
• Avoid scoring the tank surface. Firmly press on an overly of the stick for extra protection.

Temporary Repair Using Bolt

Sealing Fixture
Remove the paint from around the periphery of the bolt using a non-metallic scraper. With a pencil, mark a 2-inch diameter circle
centered on the leaking bolt. With the pressure bolt thread protruding 1/2 inch into the tool body, fill the exposed bore of the body
with Thiokol® PRC. With the large nut touching the tool body head, put a washer over the body and position in the beam slot (Figure
28-14).
Press the assembly to the wing skin, ensuring that the body aligns with the circle previously marked and that the suction cups (wet) are
compressed and clear of the bolt heads. Rotate the large nut until it abuts the beam. Holding the tool body, screw the large nut three
additional turns.
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Temporary Repair Using Bolt

Sealing Fixture
Screw in the pressure bolt until PRC exudes from between the body seal and the wing skin. Leave for 3 minutes. When complete,
operate the levers on the handles of the suction cups and remove the tool. Clean off the surplus Thiokol®.
Click Patch Temporary Repair
• The Click-Patch is a thin aluminium disc that is applied directly over the exterior side of the leak and bonded in place with epoxy.
Patches are available for flush and protruding head rivets. Because the adhesive used with these patches will cure in the
presence of fuel, it is not necessary to drain the tank before patch installation.
• Click-Patches can only be used for the temporary repair of fuel leaks on the bottom surfaces of the wings. There are no
restrictions on the number of patches that can be used at any one time. These patches are only a temporary re- pair, the leak
must be, permanently repaired within 6 months
• Locate the leak and use a non-metallic scraper to remove paint from around the periphery of the rivet. Refer to the AMM to
make sure that a temporary repair is applicable. If the leak- age is around a rivet, restrike the rivet. This can only be done once. If
the leak persists, replace the rivet. An alternative method for repair of rivet leaks is to install a Click-Patch.
• Record the temporary repair in the airplane technical records, stating that the repair must be made permanent within six
months.

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Manhole Covers and Access Panels

• Manhole covers and access panels are at various points on the aircraft structure (Figure 28- 15) to aid in servicing and repair of
the aircraft
• When reinstalling a cover or panel, take care to ensure absolute cleanliness and that a satisfactory seal (if applicable) is made
• Do not apply excessive grease to threads, particularly where bolts enter capped (domed) nuts.

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FUEL DISTRIBUTION
• The fuel feed system delivers fuel from the airplane tanks to the engine fuel system disconnect point. The system uses a
common line with the pressure refuel/defuel system
• It is similar for both engines except that the supply line to the left engine also provides a supply to the auxiliary power unit (if
installed) (Figures 28-16 and 28-17).

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CONTROLS AND INDICATIONS

• Fuel System Controls Levers
• Fuel system control levers are cable-connected to their respective cables. The contro] levers are on the aft part of the
center console (Figure 28-18) and include:
• --- Two L.P. COCKS levers
• --- AUX FUEL TRANSFER lever
• --- WING FUEL X FEED TRANSFER lever
• Before selection can be made, the knob on each lever must be pulled out against spring tension. Each lever locks in the
selected position when the respective knob is released.
• L.P. COCKS Levers
• Two L.P. COCKS control levers are on the © right aft side of the center console (except 750 aircraft) (Figure 28-11).
• The levers control two low pressure fuel valves, one in each engine supply line, which can isolate the engine feed fuel lines from
the fuel tanks.
• Each valve is open when the associated L.P. COCKS control lever is in the up position.
• A hinged guard, above the control levers must be lifted before the levers can be moved to the closed {down) position.

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WING FUEL X FEED TRANSFER Lever

• The WING FUEL X FEED TRANSFER lever is X-shaped for ease of identification. It has three positions: closed, X FEED, and
TRANSFER.
• When the lever is in the closed position, fuel from the left wing is supplied to the No.1 engine and fuel from the right wing is
supplied to the No. 2 engine. Moving the lever to the X FEED position opens the cross feed valve.
• Fuel from both wings is available to either or both engines. A non return valve in the outlet of each pump prevents fuel from
being transferred from one wing tank to the other during cross feed operation.
• Moving the lever to the TRANSFER (bottom) position opens the transfer valve, and the cross feed valve remains open. Fuel
transfer from one wing to the other is achieved by switching off one electric booster pump. Fuel is drawn into the tank
containing the operating pump by jet pump operation.
• AUX FUEL TRANSFER Lever
• A ventral tank transfer valve is operated by the single AUX FUEL TRANSFER lever (except on 750 aircraft). A hinged guard fits
over the lever in the closed (up) position. This guard must be lifted before the lever can be moved to the open (down) position.

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ANNUNCIATORS
• The FUEL 1 LO PRESS and FUEL 2 LO-PRESS annunciators are on the FUEL section of the roof panel (Figure 28-18). They illuminate
when the fuel pressure in the engine fuel link falls below 6—7 psi). \
• The illumination of either annunciator is repeated by an amber FUEL annunciator on the master warning system (MWS) center
panel.
• A white AUX FUEL TFR annunciator (except on 750 aircraft) on the FUEL section of the roof panel illuminates whenever the AUX
FUEL TRANSFER lever is moved to the open position. This advisory is repeated by a white FUEL XFD TFR annunciator on the MWS
center panel.
• A white WING FUEL XFD/TFR annunciator on the roof panel illuminates when the WING FUEL X FEED TRANSFER lever is moved
to the X FEED (center) position. This advisory is repeated by the white FUEL SFD TFR annunciator on the MWS panel. In the
TRANS FER (bottom) position, the annunciators remain on.
• BOOSTER PUMP Switches
• The electric booster pumps are controlled by three-position switches (ON, OFF, EMERG) (Figure 28-18). The left and right electric
booster pumps are normally supplied from bus bars PS1 and PS2, respectively. The pumps are connected to bus bar PE when
EMERG is selected. Bus bar PE also powers the pumps during an internal engine start.

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COMPONENTS
• BOOSTER PUMPS
• A booster pump normally supplies fuel through a low pressure valve to its respective engine (Figure 28-19).
• A cross feed valve lets one of the two booster pumps feed the two engines if the other booster pump has a malfunction
and a transfer valve permits the transfer of fuel between the wing tanks to maintain fuel balance during a cross feed. An
additional transfer valve allows fuel to be transferred from the ventral tank to the wing tanks.
• In the event of failure of both booster pumps the engine may be operated on suction feed.
• The booster pumps are each powered from separate busbars during normal operation but they may also be powered from
the emergency busbar.

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BOOSTER PUMP Installation

A submerged centrifugal fuel booster pump (Figure 28-20) is in each No. | Compartment of the wing tanks and is capable of giving a
flow of 1,320 gph at 19.2 psi.
• To change a pump the wing must be drained. Points to note on the assembly are:
• Check for sharp edges, particularly at the base plug recess.
• Install new O-rings.
• Install the drain assembly with the 45° cut off facing aft (Pre Mod. 3256A).

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OPERATION
• Normal
• Under normal conditions, each electric booster pump delivers fuel under pressure to the engine on the same side via a
low pressure fuel cock. If both electric booster pumps fail, fuel gravitates into each No. 1 compartment. This enables the
engine-driven fuel pumps to receive fuel for operation by suction feed.
• The low pressure fuel cocks, one in each supply line, isolate the engine fuel feed pipes from the tanks (Figure 28-21).
• Pressure switches, tapped into each engine fuel line at the inlet of the engine-driven pump, are connected to FUEL 1 LO
PRESS and FUEL 2 LO PRESS annunciators. Illumination of these annunciators during normal fuel operation indicates a loss
of pressure and signals a possible electric booster pump failure.
• A temperature bulb permits an indicated fuel temperature to be read from the No. 1 engine fuel supply line. The metered
fuel from the fuel control unit passes through a flow meter to provide a fuel flow indication.

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Fuel Transfer
• Fuel Transfer
• The fuel feed system to both engines is similar. Fuel is drawn into each No. 1 compartment by two jet pumps activated by
the respective booster pump.
• One jet pump draws fuel from the various wing tank compartments. The other jet pump draws fuel, either from the
opposite wing tank or from the ventral tank, depending on the selection of the appropriate transfer valves. It cannot draw
any fuel if both transfer valves are closed.
• In addition to pumping fuel to the respective engines, the fuel boosters pump in the No. 1 compartment of each wing
tank also pumps fuel to two jet pumps.
• One jet pump drains fuel from the wing tank manifold stringers and maintains the booster pump during momentary
negative G conditions. The other jet pump forms part of the fuel transfer system and induces a fuel flow into its respective
wing tank reservoir from either the opposite wing tank or the ventral tank
• The transfer system jet pumps also operate a scavenge system which continuously transfers fuel from between the beams
of the center section to the booster pump reservoir, thereby ensuring that water does not accumulate in an undrainable
location.
• Non return valves are fitted to the various pipes and sides of the booster pump reservoirs to ensure that the general
direction of fuel flow is from the tanks to the reservoir.
• . A non return valve to the feed line of each engine ensures that, during cross feeding, fuel is not transferred to the
opposite wing tank.
• The non return valve in the engine suction feed line has a strainer to protect its inlet.

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Fuel Cross feed

• Fuel in the left wing tank is normally sup plied to the No. 1 engine and APU (if in- stalled), and fuel from the right wing is supplied
to the No. 2 engine.
• Fuel from both wing tanks can be made available to either or both engines through the cross feed valve.
• In the event of a single electric booster pump failure, opening the cross feed valve enables the operating pump to supply both
engines.
• The wing transfer valve allows fuel to be drawn from one wing tank to the other. Figure 28-22 shows two conditions of cross
feed operation.

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Maintenance Practices

• Control Valve Cable Routing

• Control valve cable routing is shown in Figure 28-23. Procedures for rigging the low pressure fuel valve controls and the
cross feed and wing transfer valve controls are found in the AMM.
• Fuel Transfer System: Test transfer- Between wing tanks
• With 2,000 pounds of fuel in each wing and both LP valves closed, select left wing tank booster pump operation.
• Select transfer position on the WING FUEL X FEED/TRANSFER lever and check that the time taken to reach a gage reading
of 3,000 pounds in the left wing tank does not exceed 13 minutes.
• Select the booster PUMP switch OFF and close the cross feed/transfer valves.

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• Test Transfer- Ventral to Wing Tanks

• Refuel or off-load fuel until both wing tank content indicators read 800 Ib. (363 kg).
• Refuel the ventral tank. Make sure the indicator shows FULL. Make sure the cross feed and auxiliary transfer valves are
shut. Switch on the left and right booster pumps.
• Open the auxiliary transfer valve and make sure the time (from valve opening) for the ventral tank indicator to change to
EMPTY is not more than 12 minutes.
• With a single electric booster pump operating, fuel transfers to the wing tank containing the operating pump. Transfer
time, in this condition, can increase to more than 20 minutes. If both electric booster pumps become inoperative, ventral
tank fuel cannot be transferred.
• Maintenance Practices
• Trimming Fuel Contents Indicators
• The fuel contents indicators are trimmed in accordance with procedures provided in the AMM.

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REFUELING/DEFUELING
• Description
• Refer to Figures 28-24, 28-25, and 28-26 for pressure refueling system schematics. All tanks are pressure refueled and
defueled through a coupling in the fuselage side.
• Alternatively, the wing and ventral tanks may be gravity-filled through a filler neck in each of these tanks. The ventral tank
must always be refueled or defueled completely, but the wing tanks can be refueled or defueled to partial levels.
• On 750 aircraft with an external baggage unit (EBU), the related FUEL VENT and TRANSFER SYSTEM are removed. This
includes the AUX FUEL TRANSFER lever, ventral tank transfer valve and cable circuit. The related refuel/defuel, and ventral
tank contents indicators are shown as Inoperative.
• CONTROLS & INDICATIONS
• Pressure refueling/defueling is controlled from a panel adjacent to the vestibule right side bulkhead. The control panel
remains illuminated until switched off by either the ENTRY DOOR or vestibule ENTRY LIGHT switch.
• Electrical power for fuel valve positioning is directly from the PE(a) buses through the refueling control panel switches.
• Contents of the fuel tanks is indicated on the co-pilot MFD.
• When the MASTER switch is selected to ON and the master valve is open, the FUEL annunciator on the MWS panel and the
REFUEL ON annunciator on the roof panel illuminate.

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Components
• Components
• Fuel is loaded or off-loaded through a self-sealing coupling, accessible through a hinged door at the right rear side of the
ventral tank or the EBU.
• A pressure-reducing valve attached to the coupling reduces refuelling pressure within the system to 25 psi (Figure 28-27).
Restrictors (attached to the low pressure cocks) and surge relief valves modulate transient high pressures and regulate
refuel rate to wings vs. ventral tanks.

• One thermal relief valve (Figures 28-28 and NOTES 28-29) is in the main supply pipeline in the ventral tank and one is in each
section of the pipeline in each No. 1 wing tank compartment. They provide protection against thermal expansion.

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• Fuel flow into or from the system is controlled by an electrically operated (Figure 28-30). Additionally, each wing tank and the
ventral tank have an electrically operated refuel valve. Each tank refuel valve can be mechanically positioned in the event of
electrical failure.
• Magnetic indicators on the control panel show SHUT, crosshatch, or OPEN for each of the valves in the system. As each tank fills,
the respective high-level float switch causes the related tank valve to close.
• The tank valve indicator on the control panel shows SHUT, and the tank FULL indicator illuminates. The valve indicators show
crosshatch when electrical power is off.
• If a malfunction causes any tank to overflow into its surge tank, an over fill float-operated switch in the surge tank causes the
master refuel valve and any open tank refuel valves to close. The appropriate OVER FLOW indicator on the control panel
illuminates.
• All tanks can be pressure-refueled simultaneously. Partial fuel loads are acceptable for the wing and can be obtained by selecting
the refuel switch off at the required fuel level.

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SAFETY DEVICES
• Safety devices in the refuel/defuel system (Figure 28-31} provide protection against:
• Overpressure
• Overflow
• Thermal expansion
• Pipe fracture
• Surge relief

OVER PRESSURE
• A pressure switch is in the line between the refuel/defuel coupling and the master refuel valve, just forward of the ventral tank.
• When subjected to an overpressure of 45 psi exceeding 0.4 seconds in duration, the switch causes the master refuel valve and all
other refuel valves that were open to close.
• Indications of valves closing are given at the refuel control panel.
OVER FLOW
• Fuel entering either vent surge tank during refueling actuates the overflow float switches. When actuated, the master refuel
valve and all other open refuel valves close.
THERMAL EXPANSION
The required protection comes from thermal relief valves in the refueling pipe in each No. 1 tank compartment and in the pipe
connecting the coupling to the master refuel valve. The valve relieves at 27.5 psi to 32.5 psi.

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SURGE RELIEF
Relief valves in the No. I tank compartment of each wing reduce the pressure of transient surges. Surges are most likely to occur during
the initial stage of refuelling and on tank valve closure. The surge relief valve opens at 50 psi pop-off pressure.

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OPERATION
• Refueling System Operation
• Flow into or from the system is controlled by an electrically operated master refuel valve and electrically operated
refuel/defuel valves, one for each tank.
• When any tank is full, refuelling to that tank is terminated automatically by a high-level float switch that causes the
respective refuel valve to close.
• The associated tank indicator indicates SHUT, and the associated tank FULL indicator on the refuel control panel
illuminates (Figure 28-32).
• NOTE:
• The following is sequence of events that must take place for pressure refueling to be completed. When performing pressure
refueling. Follow instruction s and procedures listed in the AMM
• Before starting refuelling:
• PE bus must be powered
• Airplane is weight on wheels
• MASTER refuel switch ON
• No overflow in either surge tank
• No overpressure existing
• Master refuel valve open
• Test refuel control panel to show compliance with U.S. 4 CFR Part 25.979

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The WING and VENTRAL refuel switches must be in the REFUEL position and their respective valves open. The LP valves must also be
open (Figures 28-33).
• 1. When the MASTER switch is selected to ON:
• Master refuel valve opens.
• MASTER VALVE magnetic indicator (MI) displays OPEN.
Select the appropriate tank switches to REFUEL, and check that the associated VALVE MIs display OPEN.
3. Start refuelling (Table 28-3).

4. When the tank(s) high level float switch operates:

• Associated FULL indicator illuminates.
• Refuel valve closes and respective MIs display SHUT.
• . Select the appropriate tank switches to OFF.
• 6. Turn the MASTER switch to OFF.

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OVER FLOW
• In the event of a malfunction during refuelling that allows fuel to enter and reach a high level in either wing vent surge tank, the
following occurs:
• Overflow float switch closes.
• OVER FLOW indicator illuminates.
• Master refuel valve and all other valves close.
• All valve MIs display SHUT.

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OVER PRESSURE
• If the refuelling pressure exceeds 45 psi, the following occurs:
• Overpressure switch closes.
• OVER PRESS indicator illuminates.
• Master and all other refuel valves close.
• All valve MIs display SHUT.

Defueling System Operating

• For complete defueling, select the MASTER switch to the ON position. To defuel the wings, the LP valves must be open. When
defueling the ventral tank only, the LP valves must be closed. (Figure 28-34).

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Wing Tank Defueling

The wing tanks are defueled through non return valves associated with the suction feed supply to the engines. The valves are in the
No. 1 tank compartments.
• Select the MASTER switch to ON and check that the MASTER VALVE MI displays OPEN.
• Open the LP valves.
• Apply suction. Fuel now off-loads through the non return valves in the No.1 tank compartments.
• Observe the fuel contents gages. When they indicate the required fuel quantity, select the MASTER switch to OFF to terminate
wing tank defueling (Figure 28-36).

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Ventral Tank Defueling

The ventral tank is defuled through its refuel valve and the master refuel valve. The low level float switch of the automatically
terminates defueling, which cause the tank refuel valve to close.
• Close the LP valves (Figure 28-37).
• Select the MASTER switch to ON, and check that the MASTER VALVE MI displays OPEN.
• Select the VENTRAL tank switch to DEFUEL.
• Check that the VALVE MI displays OPEN.
• Apply suction.
• Check that the ventral tank FULL indicator light extinguishes.
• Observe the ventral FULL—cross hatched EMPT MI on the center instrument panel.
• Check that the VALVE MI displays SHUT. NOTES
• Select the ventral tank switch to OFF.
• Select the MASTER switch to OFF, and check that the MASTER VALVE displays SHUT (Figure 28-38).

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Alternate Ventral tank Defueling

The ventral tank can be off-loaded by transfer to the wing tanks. To do this, select the booster pumps on and move the AUX FUEL
TRANSFER lever to the open position.
NOTE :
Booster pumps are powered by the respective PS buses (PSI or PS2) when the booster PUMP control switch is in the ON position. In
the EMERG position, they are powered by the PE bus.

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GRAVITY REFUELING/DEFUELING
• The airplane can be gravity refuelled through a filler cap on the outboard section of each wing and in the left rear side of the
ventral tank.
• A rubber flapper valve is beneath each wing filler cap and closes the outlet in the event of an improperly closed cap. Fuel can be
off- loaded by gravity into a container or into a fuel pit.
• The wing tanks must be filled simultaneously. If this is not possible, half fill one wing, completely fill the other wing, and then
finish filling the first wing.
• Before installing the wing filler cap, make sure that the rubber flap valve is correctly seated. Then install the filler cap with the
engraved arrow facing forward.

GRAVITY REFUELING/DEFUELING
• The ventral tank filler neck incorporates a baulk that prevents the door from closing unless the filler cap is locked. After servicing
the ventral tank, ensure that the ventral tank MI displays FULL.
• A fuel drain valve IS in each tank. They are on the booster pump panels of each wing tank and on the lower forward skin of the
ventral tank. When the cap is removed, the valve can be unseated with adapter 25Y867A for gravity defueling. During suction
defueling, use adapter 25Y635A.

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MAINTENANCE CONSIDERATIONS
• Refueling Safety
• For safety, the airplane must always be properly grounded, whether it is being gravity refueled or pressure refuelled. As a
minimum precaution, make sure that:
• An uninsulated grounding cable is connected from the servicing facility to a satisfactory ground.
• An uninsulated grounding cable is connected from an unpainted structural air frame member to a satisfactory ground.
• An uninsulated bonding cable is connected from the fuel servicing facility to a satisfactory point on the airframe.
• When possible, when gravity refueling, connect a bonding cable from the fuel nozzle to the airplane before removing the
filler cap. If a cable is not available, make and maintain solid contact of the nozzle with the edge of the tank opening
before removing the cap

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• MASTER CONTROL CHECKS

• Overflow
• 1. Select the MASTER switch to the ON position, and check that the MASTER VALVE MI displays OPEN.
• 2. Press the OVER FLOW indicators individually, and check the following:
• a. The indicator is illuminated.
• b. The MASTER VALVE MI displays SHUT.
• An uninsulated grounding cable is connected from an unpainted structural air frame member to a satisfactory ground.
• 3. Release the OVER FLOW indicator and check that the light extinguished.
• 4. Select the MASTER switch to OFF.

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MASTER CONTROL CHECKS

• Overpressure
• 1. Press the OVER PRESS indicator and check the following:
• a. The indicator is illuminated.
• b. The MASTER REFUEL VALVE MI displays SHUT.
• 2. Press the OVER PRESS indicator and check that the light is illuminated (the electrical circuit has a hold-on facility).
• 3. Select the MASTER switch to OFF and check that the OVER PRESS indicator light extinguished.
• 4. Reselect the MASTER switch to the ON position and check that the MASTER VALVE MI displays OPEN.

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MASTER CONTROL CHECKS

The operation of all three FULL indicators is the same. The following is an example using the left wing tank:
• Tank full
• 1. Select the L WING switch to REFUEL.
• 2. Check that the VALVE MI displays OPEN.
• 3. Press the FULL indicator and check that it is illuminated.
• 4. Check that the VALVE MI displays SHUT.
• 5. Release the FULL indicator and check that the light extinguishes.
• 6. Check that the VALVE MI displays OPEN.
• 7. Select the L WING switch to OFF.
• 8. Check that the VALVE MI displays SHUT.
• 9. Select the MASTER switch to OFF and check that the MASTER VALVE MI displays SHUT.

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QUANTITY INDICATING SYSTEM

• Description
• The Smiths fuel contents indication system comprises two subsystems, each measuring the electrical capacitance of a set
of seven capacitance-type transmitter units in each wing tank (Figure 28-39).
• The varying value of capacitance is processed electrically and displayed on the electronic flight instrument system (EFIS)
right multifunction display (MFD) and on the engine page of each of the control display units (CDUs).
• If MFD/primary flight display (PFD) reversion occurs the display is transferred to the PFD.

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FUEL CONTENTS INDICATING SYSTEM

• The tank units are open-ended concentric capacitors and are positioned in the fuel tanks so that, between certain limits, the
value of capacitance is independent of aircraft attitude.
• As fuel and air have different permittivities, changes in fuel level produce proportionate changes in capacitance. The resultant
change in current output from each tank unit is rectified by diodes in the tank unit terminal blocks. The DC current output signal
is connected to the appropriate channel of the processor unit (Figure 28-40).
• The processor unit consists of two identical processing channels on printed circuit boards (PCBs) in a single case. The channels
contain individual, regulated, 28 VDC power supplies.
• The PCBs also contain an oscillator which produces a drive signal for the tank units. The resultant, individual tank unit DC signals
are brought together at two connectors on the front spar and are then applied to the processor. The diodes of each tank unit
conduct during each half cycle, thus preventing a build up of charge in the tank unit.

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FUEL CONTENTS INDICATING SYSTEM

• The tank unit DC signal is processed by the current/voltage converter in the processor which produces a DC voltage from 0 to 5
VDC for a change in capacitance corresponding to the initial and full scale indicator values. This voltage is then converted to a
current which varies between 2mA and 7mA, which corresponds to the empty and full fuel tank conditions.
• Two identical screened cable harnesses connect the processor to the two 19-way connectors on the front spar.
• The processor output is fed to the appropriate onside data concentrator unit (DCU) for each wing tank which supplies the signals
to the MFD, PFD, or CDU as selected.

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VENTRAL TANK INDICATING

• A grey VENTRAL legend is to the left of the ventral tank status display below the wing contents indication. The ventral tank status
display consists of a white box containing the status legend, FULL, EMPTY or //// (tank transfer). Each status legend or ////
displays when the valid logic state is true (Table 28-4).
• The CDU display is shown below the wing fuel contents line and is either FULL or EMPTY.

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Ventral Tank Float Switches

• The ventral tank high and low float switches supply the appropriate signal to both DCUs which then supply the signal to the
MFD, PFD or CDU as selected (Figure 28-42).
• Automatic source selection between DCUs is provided. The L DCU is the priority source and the R DCU is the secondary source.
• Processors below the cabin floor or forward of the pilot seat convert the electrical capacitance into fuel content readings (Figure
28-41).
• The tank units are open-ended concentric capacitors positioned in the fuel tank to measure capacitance values regardless of
airplane attitude.
• Fuel and air have different capacitance characteristics. Therefore, changes in fuel level produce proportionate changes in
capacitance. The resultant change in current output from each tank unit is rectified by diodes in the tank unit terminal blocks.
The DC current output signal is fed to the appropriate channel of the processor.
• The processor consists of two identical processing channels on PCBs housed in a single case. The channels contain individually
regulated 28 VDC power supplies and an oscillator to produce a drive signal for the tank units. The resultant individual tank unit
DC signals merge at two connectors on the front spar and are then applied to the processor.
• The diodes of each tank unit conduct during each half cycle, thus preventing a buildup of electrical charge in the tank unit.
• The tank unit DC signal is processed by the current/voltage converter in the processor, producing a0 VDC to 5 VDC for a
capacitance change corresponding to the initial and full-scale indicator values. This voltage is then converted to a current varying
from to 2 mA to 7 mA, corresponding to fuel tank levels.

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FUEL TRAINING MANUAL (B1/B2)

INDICATIONS
• Multifunction Displays
• A gray FUEL QTY LBS legend displays between the left and right digital readouts in the top left corner of the right
multifunction display (MFD) (Figure 28-44).
• Fuel quantity for the left wing fuel readout is up to 4 digits, with the left wing fuel readout left justified, the right wing fuel
readout right justified, and with the leading zeros suppressed.
• The wing fuel readout is green with a display resolution of 10 Ibs.
• Four yellow dashes are displayed if the wing fuel contents, from all sources, has a sign signal matrix (SSM) of FAIL,
MISSING, or NO COMPUTED DATA (NCD).
• Automatic source selection between the DCUs is provided. The L DCU is the priority source for the left wing fuel contents.
The R DCU is the priority source for the right wing fuel contents. The cross-side DCU is the secondary source.
• Control Display Unit
• A green FUEL QTY LBS legend displays between the left and right green digital readouts at the bottom of the CDU screen
(Figure 28-45). The range available is from 0-4990 pounds. If the data is flagged or missing, four yellow dashes appear.

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FUEL TRAINING MANUAL (B1/B2)

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 ATA 28 Hawker 750/800/800XP/850XP/900XP
FUEL TRAINING MANUAL (B1/B2)

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 ATA 28 Hawker 750/800/800XP/850XP/900XP
FUEL TRAINING MANUAL (B1/B2)

DIAGNOSTICS
• Functional Checks
• The AMM details the fuel system operational checks and calibration requirements. When making any checks or calibrating
the system, observe all maintenance and operational limitations as specified in the AMM.
• Fault Analysis
• The AMM provides troubleshooting charts listing the most likely cause for a fault first and working toward causes of lesser
probability. They do not contain all the possibilities of trouble and isolation.
• Fuel system troubleshooting charts are contained in the 4MM. Figure 28-46 shows a typical troubleshooting chart.

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