ey TROUBLE SHOOTING GUIDE FOR THE BAe 146 BRAKING SYSTEM Customer Support Department, Dunlop Limited, Aviation Division, Coventry, CV6 4AA, England. This guide issued March 1990 supersedes all previous issuesDUNLOP ADDRESSES AND CONTACT NUMBERS. Dunlop Limited, Aviation Division Holbrook Lane, Coventry CV6 4AA ENGLAND Tel: (0203) 666655 Telex: 31677 Fax: (0203) 662294 Dunlop Aviation Inc. 9731 Topango Canyon Place Chatsworth California 91331 UNITED STATES OF AMERICA Tel: (818) 700-9731 Telex: 651380 Fax: (818) 7000004 Dunlop Aviation Inc. Dunlop Aviation Inc. 8810 Nw 24th Terrace 351 Steelcase Road West Miami, Florida 33172 Unit No.4, Markham, Ontario L3R 4HR UNITED STATES OF AMERICA CANADA Tel: (305) 5920055 Tel: (416) 940-8181 Telex: 681-1579 DLPMIA Telex: 06-3690048 Fax: (305) 5941070 Fax: (416) 940-8183 Dunlop Aviation (S.E.Asia) Pte Ltd 4 Loyang Link, Loyang Industrial Estate Singapore 1750 REPUBLIC OF SINGAPORE Tel: (65) 5424711/2 Telex: RS39372 DASEA Fax: (65) 5427069 Dunlop Aerospace Australia P O Box 41, Bayswater Victoria 3153 AUSTRALIA Tel: (613) 7216111 Telex: AA31643 Fax: (613) 7204996TROUBLE SHOOTING GUIDE FOR THE BAe 146 BRAKING SYSTEM This guide contains information gathered from actual ‘in service’ ex- perience and is provided as an aid to the professional maintenance tech- nician on some of the more common problems encountered with a new system and where the solution is not always immediately obvious. Information in this guide is not intended in any way to supersede the standard maintenance practices, procedures and requirements of the relevant Aircraft Maintenance Manual (AMM) and Component Mainten- ance Manual (CMM). CONTENTS ? Page Section 1 — General Notes 2 Section 2 — Uneven Braking 3 Section 3 — Hot Brakes 6 Section 4 — Cold Brakes 8 Section 5 — Braking System Noise 10 Section 6 — Tire Scuff 11 Section 7 — Intermittent Fault/Inop Light 12 Section 8 — Integrity Test and Pressurised B.1.T. Checks 15 Section 9 — Brake Fan Motor Removal 19 ILLUSTRATIONS Page Fig. 1 — System Diagram 20 Fig. 2 — Hydraulic Bay Layout 21 Fig. 3 — Anti-skid Control Box Front Panel 22 TABLES Table 1 — Probable cause of ASCB fault indications. 13SECTION 1 - GENERAL NOTES The wheel brake control system utilizes both Green and Yellow hydraul- ic systems to provide straight line or differential braking with or without anti-skid protection. Brakes are also automatically applied through the brake auxiliary pistons whenever the landing gear is raised. A parking brake facility is provided in Yellow system only. The anti-skid system is available on Green and Yellow systems but NOT Emergency Yellow system. Selection is made with the BRAKE CONTROL SELECTOR (flight deck central pedestal). Pressure applied at the brake pedals is transmitted through connecting rods and cables to the brake control valves (B.C.V’s) (refer to Fig.1). Movement of the B.C.V.’s meters fluid under pressure through the four Dual Adaptive Anti-skid Valves (D.A,A.V's). There are four D.A.A.V‘s (2 Green system and 2 Yellow system) and each D.A.A.V. contains two independant skid control valve assemblies, i.e. eight valve assemblies per aircraft. Each skid control valve assembly controls one of the four brake units, depending on system selected. The D.A.A.V’s are installed in the hydraulic bay as shown in Fig.2. The anti-skid contro! box (A.S.C.B.) receives wheel speed signals from transducers fitted within the axles of each main wheel. It commands each skid control valve assembly to independently dump sufficient brake pressure to prevent wheel skid and maintain optimum braking efficiency. When the anti-skid system is switched on, the electrical integrity of the units in the system selected are continuously monitored by the A.S.C.B. An identified defect is indicated on the ANTI-SKID annunciater (Flight deck monitor warning panel). The ANTI-SKID FAULT and/or the ANTI-SKID INOP annunciator (flight deck overhead panel) also illumin- ate. The LED fault indicator display on the A.S.C.B. front panel will flag the suspect unit in the anti-skid system.SECTION 2 - UNEVEN BRAKING 1. The flight manual currently requires the aircraft to be landed in the Green system and to taxi in the Yellow system. This procedure can occasionally confuse accurate system diagnosis as not all brake problems can be attributed to the system selected when they become apparent. DEFECTS Typical pilot initiated reports may state:- A) Aircraft pulls/grabs in Yellow B) Brakes grab during taxi. FEATURES WORTH REMEMBERING A) Because of the characteristic of carbon brakes to increase in braking efficiency with the initial temperature increase from cold, a consistently greater amount of pressure applied to one pair of brakes during the landing phase (Green system) allows that pair to heat up faster than its opposite pair. Once this situation is reached, even though equal pressure may then be applied to both pedals during taxi {yellow system), this can result in uneven braking until companion brakes are at the same temperature. The ideal condition is, of course, even brake temperatures at all positions across the aircraft. ADIACENT ‘SOJACENT {Boek} companion A WHEEL TouTBGARO, CONFIGURATIONB) Note: Where an aircraft does not have a Brake Temperature Indicator (B.T.1.), pilots will not be aware of any uneven brake temperatures unless maintenance personnel do a physi- cal check of the temperature of the brake after a landing. Therefore it is strongly recommended, in the absence of a B.T.|., that line maintenance personnel inspect all four brakes regularly and report any obvious brake temperature uneven- ness; such as, one cold or one very hot brake in comparison with other brakes. Furthermore, it is important that brake fans are operative and are used strictly in accordance with flight manual procedures. When carbon brakes are cold, e.g. at the start of the day or following a prolonged stopover, braking action can feel rel- atively normal at taxi speeds even with a system which is not operating at maximum efficiency. This helps to explain why some fixes for brake grab appear to work initially, only for the problem to reappear following the first fully braked landing, or prolonged braking during taxi. POSSIBLE CAUSES A) B) Cc) Brake control valve rigging. Pedal return springs broken or weakened. Equipment faults, Any of the above may cause most of the braking to be done by one adjacent pair of brakes. This may not become readily apparent to the crew on the landing because of the tracking characteristics of the aircraft.S. ADVISABLE CHECKS A) B) c) Brake control valve rigging: Check for even brake pressure response on flight deck brake gages when equal movement/pressure is applied to the pilots left and right pedals. (Refer to A.M.M.). Also check for uniformity of pedal rigging between Green and Yellow systems. Check for even pedal operating loads. Equipment faults: Check for smooth and quiet operation of brake control valves on both Green and Yellow systems. There should be no sudden rises in brake pressure indication on the cockpit gages. Also check for even pressures at brake units, as any significant difference in pressure between adjacent brakes may indicate a defective anti-skid valve, e.g. a pressure difference in excess of 150 psi at an indicated pressure of 1000 psi on cockpit gages.SECTION 3 - HOT BRAKES Where hot brakes have resulted in a blown fusible plug and subsequent tyre deflation, checks and removals shall be performed strictly in accord- ance with A.M.M. and C.M.M. requirements. 1, DEFECT 1 One brake considerably hotter than other positions with no pilot initiated report associated with an ANTI-SKID INOP annunciator coming on. 2. ADVISABLE CHECKS A) Check fan motors are running correctly. Note: Air is drawn over brake and expelled from the debris guard, B) “Check piston retraction and brake running clearance. C) Check D.A.A.V. pressure balance with the anti-skid switched ‘off’ and ‘on’. 1) Fit gages to the pair of brakes on the affected leg. 2) Select and maintain 1000 psi on cockpit brake gages. 3) Gages at brakes should balance within 150 psi at a pressure not less than 850 psi. If check C)3) fails with anti-skid ‘off’ then replace D.A.A.V. If check C)3) fails with anti-skid ‘on’, then replace A.S.C.B. and check D.A.A.V. pressure balance again. If the same condition still exists, then replace the D.A.A.V.D) Perform pressurized B.I.T. check (refer to section 8 of this guide) to ensure skid valves are correctly relieving brake pressure on Green and Yellow systems. —) Check the adjacent brake temperature. If this is cold, refer to Section 4 of this guide. DEFECT 2 Two brakes on the same axle (adjacent brakes) running hot. ADVISABLE CHECKS A) B) c) D) Check piston retraction and brake running clearance. Perform integrity test and pressurized B.I.T. check (refer to Section 8) to ensure skid and brake control valves are correctly relieving brake pressure on Green and Yellow systems. Check brake control valve rigging and pedal return springs, ensure equal pedal movement and pressure gives equal rise in brake pressure on Green and Yellow systems. Hot adjacent brakes can also result from a pilot using pro- longed differential braking during taxi to and from the gate. In the majority of cases this involves one or other pair of brakes being used to assist in turning the aircraft (left brakes at the majority of airports). Pilots may use brakes on one side of the aircraft together with nose wheel steer to taxi the aircraft.SECTION 4- COLD BRAKES 1s DEFECT 1 One brake much cooler than the other brake units with no reports of the ANTI-SKID FAULT or ANTI-SKID INOP annunciator coming on. DEFECT 2 Pilot initiated report of suspected erratic brake release during normal conditions. POSSIBLE CAUSES These possible causes apply to both defect 1 and 2. A) B) Mechanical failure of a fan installation or transducer com- ponent, i.e. broken shaft, worn splines on shaft or in the debris guard, defective bearing on the shaft or in the transducer. Wheel speed signal from transducer too weak. ADVISABLE CHECKS A) B) Cc) Visually examine components of the fan installation and transducer for damage and the transducer for freedom of rotation, Do an Integrity Test and a Pressurized B.I.T. Check (refer to Section 8) on both systems to check that the skid valves are applying pressure to the brake. If brake fails to function on either system then check that the hydraulic fuse has not operated and that the system is properly bled of air. Check electrical connections for continuity and good insulation (refer to A.M.M. and C.M.M.).DEFECT 3 Two adjacent brakes considerably cooler than other two brakes. (This defect is the reverse of Section 3 defect 2). POSSIBLE CAUSES A) B) Cc) Brake pedal return spring loads unbalanced due to breakage or loss of tension. Brake control valve rigging incorrect, i.e. equal pedal pressure/ movement does not result in equal pressure to brakes. Note: This condition is seldom noticed during landing due to the directional stability of the aircraft and the position of the brake gages on the flight deck. Brake control valve failure to operate on the affected side. ADVISABLE CHECKS A) Check brake pedal return springs. B) Check brake control valve rigging (refer to A.M.M.). C) Do a functional test of the direct braking system (refer to the A.M.M.). DEFECT 4 Operational: Excessive use of differential braking causing symptoms of a defect but the braking system is serviceable.SECTION 5 - BRAKING SYSTEM NOISE This is both disconcerting to passengers and may generate increased rates of heat pack wear through brake chatter. One of the most common causes of noise is air within the system usually introduced during equip- ment replacement or from incorrect bleeding techniques. It is important that equipment replacement is followed by system bleeding strictly in accordance with A.M.M. requirements. To make the bleeding procedure easier, Dunlop supply hydraulic fuse bleed hoses (part numbers AM21932 straight and AM22089 right angled). These are resistant to Phosphate Ester based fluids (HYJET IV). After brake system bleeding, the bleed hoses can be removed with negligible spillage in the hydraulic bay. Equally important from a safety and cleanliness point of view there is less risk of hydraulic fluid on you. Brake system bleeding operations have been further improved by the introduction of a new hydraulic fuse which incorporates a by-pass lever. Operation of the by-pass lever prevents the fuse shutting off thus allow- ing bleeding of the brake system to take place. CAUTION: After brake system bleeding the by-pass lever must be locked in the DOWN FOR FLIGHT position (refer to A.M.M.). Note: Brake control valves are sensitive to large quantities of air within the system as this may cause the valve in the affected system to become noisy by causing the spool within the unit to oscillate at low pressures, B.C.V’s may also ‘HUNT’ because of air. This problem can usually be observed on the flight deck brake pressure gages, i.e., a cyclic rise and fall in brake pressure whilst a steady pedal position is maintained. Therefore, it is advisable before removing a unit that the system is bled thoroughly and a further check performed to see if the problem has been eliminated and prevent unnecessary removals. 10SECTION 6 - TIRE SCUFF a POSSIBLE CAUSES A) The most common cause of this defect is a mechanical failure in the fan installation or transducer. B) This defect may also be associated with a cold brake or result from an anti-skid valve failing to relieve pressure from a brake. ADVISABLE CHECKS These checks should also be done at each tire removal. It could save time later. A) Remove the debris guard. Check the items of the fan install- ation and transducer for damage. Pay particular attention to the splines of the debris guard and the transducer drive shaft. Ensure that the debris guard and fan duct are not distorted, or cracked. Also pay particular attention to the webs and around the bolt holes. 1SECTION 7 - ANTI-SKID FAULT AND/OR ANTI-SKID INOP ANNUNCIATORS COME ON INTERMITTENTLY 1. This intermittent defect has often resulted in the unnecessary removal of an anti-skid control box (A.S.C.B.). The A.S.C.B. continuously monitors the electrical integrity of the anti-skid system when it is switched ON. 2. FEATURES WORTH REMEMBERING A) Only the electrical circuits of the anti-skid valves in the SELECTED SYSTEM are monitored. e.g. Green system selected - only Green system anti-skid valves monitored. B) An open or short circuit in the monitored anti-skid valve will illuminate the ANT!I-SKID INOP annunciator. C) An open or short circuit in any ONE of the four transducers will illuminate the ANTI-SKID FAULT annunciator, regardless of which system is selected. D) An open or short circuit in any TWO transducers on the same axle (adjacent wheels) will illuminate the ANTI-SKID INOP annunciator, regardless of which system is selected. E) When the ANTI-SKID INOP or FAULT annunciator illumin- ates, the fault indicator display on the A.S.C.B. will flag the components affected. However, if the aircraft crew or main- tenance personnel select system change over, switch the anti- skid system off or do a B.I.T, check, then the fault indication on the A.S.C.B. goes off and is lost until the defect occurs again or becomes a hard fault. Note: Table 1 indicates the probable causes when the A.S.C.B. fault indicator LED's are illuminated. 12TABLE 1 PROBABLE CAUSE OF ASCB FAULT INDICATIONS ANTI-SKID CONTROL (ASCB) LED" Respective wheel transducer IR ol 10V d.c. supply to respective wheel card in ASCE Wheel transducers 1&2 OR 10V d.c. supply to ASCB wheel cards 1&2 Wheel transducers 3 & 4 OR 10V d.c. supply to ASCB wheel cards 3&4 Respective D.A.A.V. operating in green system Respective D.A.A.V. operating in yellow system Indicates LED's illuminated DEFECTS Examples of pilot initiated reports are: A) ANTI-SKID FAULT annunciator came on at gear up/down and went off at system change over. B) ANTI-SKID INOP annunciator came on at gear up/down and went off at system change over. 13POSSIBLE CAUSES Service experience has shown that a significant number of inter- mittent ANT! SKID INOP and ANTI-SKID FAULT indications are caused by a short or open circuit. A) B) Cc) Transducer connections loose. The early standard of connector requires safety wiring to prevent the connector coming apart or loosening due to vibration. Safety wiring should lock the cable clamp screws to the connector back shell, the back shell to the main thimble and the thimble to the transducer receptacle screws. Wiring to the transducer connector loose. The early standard connector wiring has been found loose under the connector cable clamp resulting in bare wires due to cable pulling and/or chaffing of wires. Pins pushed back in a transducer receptacle. ADVISABLE CHECKS A) B) Cc) Examine the aircraft wiring to the transducer. Examine the transducer connector safety wiring etc. Do a resistance check on the coils of the anti-skid valve (refer to the C.M.M. for the full test procedure): 1) Using digital multimeter check that the coil resistances are between 330 and 350 ohms. — from pin A(+ve) to pin B(—ve). — from pin D(+ve) to pin E(—ve). Note: The resistance of the coil should be measured at an ambient temperature of between 18 and 24 deg.C (65 and 75 deg.F). 14SECTION 8 - ANTI-SKID SYSTEMS INTEGRITY TEST AND B.1.T. CHECK SEQUENCE (PRESSURIZED) 1. INTEGRITY TEST This test, fully described in the A.M.M. and performed after trans- ducer drive shaft replacement ensures that a transducer, the associated wiring and the anti- skid control response of the brake unit of the companion wheel is satisfactory. 2. PRESSURIZED B.1.T. CHECK A) B) c) A functional test of the anti-skid control box (A.S.C.B.) some- times known as a B.I.T. check simulates the electrical control function of the anti-skid system. During the test with the system pressurized, an indication of both anti-skid valve and brake control valve functions can be ascertained. Before a pressurized B.I.T. check is done, refer to the A.M.M. and complete: — A functional test of the direct braking system. — A functional test of the anti-skid control box. Equipment required: Accurate pressure gages fitted to each main cylinder bleed port of all 4 brake units. 15D) Pre B.I.T. check procedure: Exercise both the Green and Yellow systems as follows, 1) 3) 4) 5) Make sure that the aircraft Green and Yellow hydraulic systems are pressurized, and the aircraft bus bars are energised. Note: On aircraft construction No.E3156 and sub- sequent, and any other aircraft with BAe 146 Mod. No. HCM00716B embodied (SB 32-52-00716 refers), ensure that the WHEEL SPIN switch (maintenance test panel 132-08-00) is set to TEST and the AVIONICS MASTER switch ‘A’ (flight deck overhead panel) is selected ON. Depress and hold depressed captains pedals to achieve 3000 psi on flight deck gages. Depress L SQUAT SWITCH (overhead ground test panel). Pressure should drop to return line pressure at all positions. Release switch and pressure should return. Depress R SQUAT SWITCH. Pressure should drop to return line pressure at all positions. Release switch and pressure should return. Repeat steps 2), 3), and 4) five times following any prolonged period of aircraft inactivity. With 1000 psi indicated on flight deck gages, check that the pressures at brake units of adjacent wheels are balanced to within 150 psi at a pressure of not less than 850 psi. Failure to achieve this may indicate the skid valve in the system selected is out of adjustment. 16E) Pressurized B.1. systems: . Check procedure for Green and Yellow 1) Set BRAKES control selector (flight deck centre ped- estal) to GRN. 2) Depress and hold depressed captains pedals to achieve 1000 psi on cockpit gages throughout the steps which follow. 3) Press and hold GRN ANTI-SKID FAULT switch (ground test panel on flight deck overhead panel) — alternatively, press and hold Green press-to-test button at the front of the anti-skid control box and check that the sequence of events is as follows. a) ANTI-SKID INOP and ANTI-SKID FAULT annun- ciators (hydraulics panel of flight deck overhead panel) come on; and simultaneously all brake pressures reduce to return line pressure for approximately 2 seconds. b) Then all brake pressures return to more than 850 psi for approximately 2 seconds before they reduce again to return line pressure and the ANTI-SKID FAULT annunciator goes out. c) Release the GRN ANTI-SKID FAULT switch — alternatively, release the green press-to-test button on the anti-skid control box. d) Approximately six seconds after b) all pressures in- crease to more than 850 psi and the ANTI-SKID INOP annunciator goes out.4) Repeat the above check procedure for the Yellow system checks. Set the Brakes Control selector to YEL and operate YEL ANTI-SKID FAULT switch. Note: Following pressurized B.I.T. check and when fitted, set the WHEEL SPIN switch (maintenance test panel 132-08-00) to NORM and ensure that the switch guard covers the switch lever. 5) ‘If the pressurized B.I.T. Check is unsatisfactory, refer to TABLE 1 and subsequent notes to identify the probable causes. NOTE 1. Failure of any one brake unit to function correctly would in- dicate that particular system skid valve may be defective. Cross check by seeing if the other system valve operating the same brake unit is okay. If it is, replace the suspect skid valve. However, if the other system skid valve is also affected, replace the anti-skid control box and recheck. NOTE 2, Failure of two adjacent brake pressures to respond normally (ie. slow pressure increase or dump) check both systems. If the problem affects only one system, the B.C.V. response to delivery/return or the D.A.A.V. response to delivery/return may be at fault. 18SECTION 9 - BRAKE FAN MOTOR REMOVAL It is important that when replacing a fan motor the complete fan installation housing is withdrawn from the axle. Service tool A0124471 is available for this purpose. Problems have occurred ‘in service’ with wiring damage due to fan motors being removed on their own. When the motor is then returned to the housing, it is impossible to ensure that the cable has been correctly routed. Removal of the complete installation is a simple procedure and ensures that no further fault is caused by a poor maintenance practice. 19BRAKE ‘ACCUMULATOR YeLiow, sysreH Yet__gn Greg sysren eps a Seely pusal EHRCL/) | puto pan Bai ace, vet on veutow = GW BES, TBRAKE SYSTEM 4 Seuecran Lever : Sib TAPTANS |} [ RaST OFFICERS Seu BRAKE PEDALS RAKE PEDALS {] SokENOD wwe Th 1, BRAKE CONTROL VALVES PRESSURE, TRANSMITTERS OuaL_aDaPTIVE AANTISSKID \ALVES 1 Z 3 4 NoTE=- os + SOLENOID VALVES SHOW! AS'GREEN'SYSTEM SELECTED aera CANONS, SEAR oe HYORAULIC FUSE FIG 1 SYSTEM DIAGRAM 20DOAAV (GREEN SYSTEM) AAV (YELLOW SYSTEM) HYORAULIC FUSES (aux SYSTEM) HyORAULIC x2] _HyoRAUUc Fuses ‘ Ss—ruses (ELLOW SYSTEM V7 (YELLOW svsTEM) acy acy [GREEN SYSTEM) WELLOW SYSTEM) HryoRauUc Fuses (GREEN SYSTEM) oe mH os va em GY f JU i 3 2 AUX BRAKE LINE | LANDING GEAR RETRACTION ‘BRAKE UNIT ‘BRAKE UNIT 4a jor FIG 2 HYDRAULIC BAY LAYOUT (FACING AFT) 21TEST SWITCH TEST SWITCH TEST SWITCH GREEN SYSTEM YELLOW SYSTEM AUTOBRAKE (NOT USED) 2g Tow AUTOBI PRESS TO TEST S| WHEELS|VALVES {er S 12341 2 3 &|aBcoer nn a Weg E's C,D,E,F ONE LED FOR EACH NOT USED) TRANSDUCER INSTALLED INE LED MARKED 8. AT WHEEL POSITIONS: FOR ANTI-SKIO FAULT 1,2,3 AND 4. LED COLOR=RED LED COLOR= RED NE LED MARKED A FOR ANTISKID INOP LED COLOR=RED TWO LED's FOR EACH D.A.AV. OPERATING THE BRAKES. INSTALLED AT WHEELS POSITIONS 4,2, 3 AND 4 LED's COLOR=GREEN-GREEN SYSTEM 4 LED's COLOR=YELLOW—YELLOW SYSTEM Peer stiee oe eer ta Go ti sea Taal | FIG 3 ANTI-SKID CONTROL BOX, FRONT PANEL DETAILS ts 22