B767 ATA 32 Student Book

LANDING GEAR CH 32

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ATA 32 LANDING GEAR TABLE OF CONTENTS AIR / GROUND SENSING SYSTEM ................................................... 52 TABLE OF CONTENTS CHAP. 32........................................................ 2 STUDENT NOTES ................................................................................ 3 INTRODUCTION ................................................................................... 4 CONTROLS AND INDICATIONS .......................................................... 6 MLG DESCRIPTION ............................................................................. 8 MLG DOOR ......................................................................................... 10 MLG WING DOORS ............................................................................ 12 MLG LOCK ACTUATORS ................................................................... 14 MLG OPERATION............................................................................... 16 MLG EXTENSION AND RETRACTION .............................................. 18 MLG DOOR GROUND RELEASE LEVER.......................................... 20 NLG GENERAL ................................................................................... 22 NLG DOORS ....................................................................................... 24 NLG HYDRAULIC SCHEMATIC SIMPLIFIED .................................... 26 NLG EXTENSION AND RETRACTION............................................... 28 ALTERNATE EXTEND SYSTEM ........................................................ 30 ALTERNATE EXTEND ACTUATOR ................................................... 32 TAIL SKID GENERAL.......................................................................... 34 TAIL SKID COMPONENTS ................................................................. 36 TAIL SKID OPERATION...................................................................... 38 TAIL SKID INDICATION ...................................................................... 40 PROX. SENSE SYSTEM..................................................................... 42 PROX. SENSE SYSTEM BLOCK DIAGRAM...................................... 44 PROXIMITY SYSTEM ELECTRONIC UNIT (PSEU) .......................... 46 PROX. SENSORS .............................................................................. 48 PSEU - BUILT IN TEST EQUIPMENT ............................................... 50

AIR / GROUND SENSING COMPONENTS ........................................ 54 LANDING GEAR POSITION INDICATION - GREEN LIGHTS............ 56 STEERING CONTROL ........................................................................ 58 CENTERING SPRING AND RUDDER INTERCONNECT ................. 60 BRAKE SYSTEM BLOCK DIAGRAM .................................................. 62 BRAKE CONTROLS AND INDICATIONS ........................................... 64 BRAKE HYDRAULIC SYSTEMS......................................................... 66 BRAKE SOURCE LIGHT & RESERVE BRAKES SWITCH ................ 68 PARKING BRAKE................................................................................ 70 PARKING BRAKE ACCUMULATOR................................................... 72 BRAKE TEMPERATURE SYSTEM..................................................... 74 BRAKE TEMPERATURE MONITOR................................................... 76 ANTI-SKID GENERAL ......................................................................... 78 WHEELSPEED TRANSDUCER .......................................................... 80 ANTI - SKID VALVE MODULES.......................................................... 82 SHUTTLE VALVE MODULE................................................................ 84 AUTOBRAKE GENERAL..................................................................... 86 AUTOBRAKE INPUTS......................................................................... 88 ANTI-SKID / AUTOBRAKE BUILT IN TEST EQUIPMENT (BITE) ...... 90

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INTRODUCTION Main Gear The main gear has standard air-oil struts for shock absorption and to support the airplane. Center system hydraulic pressure is used to operate the landing gear and each main gear door. The main gear are hydraulically tilted 17° forward when the weight of the aircraft is removed. Tilt allows the main gear to enter the wheel well and also provides air/ground sensing. The main gear are locked up by the main gear door linkage and locked down by over center locking of two braces. Each gear has four wheels and brakes on a dual axle truck. An electric actuator mechanically unlocks the main gear doors to allow the gear to free fall during alternate extension. Nose Gear The nose gear strut is also a standard air-oil strut used to absorb landing shock and to support the aircraft. The nose gear strut is operated hydraulically and the doors are mechanically operated by strut movement. One over center lock link locks the nose gear in both the retracted and the extended position. Hydraulic nose gear steering is provided for ground maneuvering. The electric alternate extend actuator mechanically unlocks the lock link to allow the nose gear to free fall during alternate extension.

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CONTROLS AND INDICATIONS WARNING: Extension and Retraction A three-position (UP, OFF, DN) landing gear lever, located on the P3-1 panel controls hydraulic extension and retraction. A lock solenoid in the landing gear lever prevents moving the lever to the UP position until air mode is sensed. A lock over ride button is also provided. A guarded alternate extend switch controls one electric motor which unlocks the main gear doors and the nose gear lock link to allow free fall extension. Position indicators above the landing gear lever include three green gear down and locked lights, a amber gear door open light, and an amber gear disagreement light. Brakes, Antiskid, and Autobrakes Eight hydraulic brake assemblies are operated by either the captains or first officer brake pedals. The autobrake system is controlled by a rotary selector switch on the P3-1 panel. The amber AUTOBRAKES light above the switch indicates an autobrake disarm condition. Normal brake pressure is indicated by a gauge on the P3-1 panel. Parking brakes are set by depressing both brake pedals and pulling a handle of the P-10 quadrant stand. Parking brake operation is indicated by an amber PARK BRAKE light forward of the handle. The reserve brakes and steering switch on the P1-3 panel is used to isolate one center hydraulic system alternating current motor pump and reserve a supply of hydraulic fluid for brakes and nose gear steering. The amber BRAKE SOURCE light on the P1-3 panel indicates a loss of both normal and alternate hydraulic brake sources. An amber ANTISKID light on the P-5 panel indicates antiskid faults. A BRAKE TEMP light provides indication for overheated brake conditions. All amber lights have an associated EICAS message. Nose Wheel Steering A steering tiller, located on the P13 captain's auxiliary panel, provides control (and indication) for 65° left or right nose gear steering. A total of 7-1/2° of gear steering is available using the rudder pedal steering. Dispatch Deviation Landing Gear Door Light "INOP" • Open main gear doors and install door locks.

RAPID ACTION OF DOORS MAY CAUSE INJURY OR DAMAGE IF LOCKS ARE NOT PROPERLY INSTALLED.

• Confirm that advisory level message GEAR DOORS illuminates after 35 second time delay. • Remove door lock and close main gear doors.

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MLG DESCRIPTION Shock Strut The main landing gear shock strut is trunnion mounted between the wing rear spar and the landing gear support beam and is hydraulically operated by a retract actuator. The shock strut is serviced by an air charging valve and an oil charging valve. Torsion links connect the inner and outer shock strut cylinders to prevent inner strut rotation. Trucks Two axles on each truck mount dual wheels and brakes. Brake equalizing rods connect the bearing mounted brakes to the inner strut. An axle jacking point and a tow fitting are located fore and aft on each truck. An up lock fitting on the outboard side of the inner shock strut rests on the door linkage when the gear is up and locked. The door is held closed by an uplock hook. A truck positioner, mounted between the aft side of the inner cylinder and the aft end of the bogie beam, tilts the truck forward. Drag Brace and Side Brace The drag and side brace absorb side and rear loads and lock the gear in the down position. Hydraulic actuators and lock springs provide over-center locking of the drag brace jury strut and side brace lock link. Maintenance TIP Particular attention should be made to the correct BRAKE ROD attachment installation. Be sure the proper configuration is present for the effective aircraft. One configuration shown below, other configurations are similar. The keeper washer should be omitted if a bushing shoulder protrudes from the outer side of the brake housing at the attach pin.

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MLG DOOR General The main landing gear door provides wheel well aerodynamic seal and supports the weight of the main gear when the landing gear system is de-pressurized during flight. The main gear door is kevlar/graphite composite construction with an aluminum center hinge beam which supports the uplock roller and door actuator reaction forces. The door is supported by an aft hinge from the aft bulkhead and by a forward hinge from the keel beam. A door actuator hydraulically operates the main gear door through mechanical linkage. Door actuator extends to close the door and retracts to open the door. Operation The door is sequenced to allow the main gear to cycle. As the gear retracts, it contacts the gear upstop structure which limits its upward travel. The door closes to fold the gear support underneath the main gear and to lock its uplock roller in an uplock hook. When the landing gear system is depressurized, the weight of the gear rests upon the gear support. Skid bars in the wheel well protect wheel well components from inadvertent untilt of the main gear and subsequent hanging-up of the main gear in the wheel well.

Alternate Extension When the door is opened for alternate extension, the uplock hook is released and the weight of the gear pushes the door open where it remains. The door safety valve is also cycled to depressurize the door actuator and prevent door closure. Ground Release For ground release of the main gear door, the uplock hook is cycled to let the door fall open and the door safety valve is cycled to depressurize the door actuator. A ground safety pin is inserted in the door actuator structure to prevent door closure on the ground.

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MLG WING DOORS General The main landing gear wing doors are positioned by gear movement to provide aerodynamic seal with the gear retracted. Shock Strut Door The shock strut door is mounted directly to the shock strut outer cylinder by five attach fittings. Three offset fittings are adjustable rods for door rigging. Trunnion Door The trunnion door is hinged to the wing and linked to the strut trunnion. A single adjustable rod is used for door rigging. Drag Brace Door The drag brace door is hinged to the wing and linked to the drag brace. An adjustable link between the door and the drag brace is used for door rigging. Pop Up Door When the retract actuator goes through the arc of its stroke, either extending or retracting, the top of its arc passes above the wing skin surface. A washer on the rod end of the actuator contacts a rub strip on the spring-loaded pop-up door moving it up roughly one-half inch. The retract actuator rod end never contacts the pop-up door surface, but rides in a channel in the pop-up door. A torque tube on the forward end of the pop-up door is spring-loaded to provide 180 foot/ pound preload on the door.

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MLG LOCK ACTUATORS General The main gear lock actuators hydraulically lock and unlock the side brace and drag brace in the gear down position. Side Brace Lock Actuator Each main gear side brace lock link has a hydraulic actuator to lock and unlock the over-center locking of the lock link. The actuator rod end is attached to the lock link and the actuator end is attached to the shock strut. For gear retraction, the actuator is pressurized to retract to overcome two lock springs, that are in tension holding the lock links in the over-centered condition. For gear extension, the actuator is pressurized to extend to aid the lock springs in forcing over-center locking of the lock link. The lock springs are contained in a sliding cartridge to keep a compressive load on the springs. A down lock pin is inserted in the apex of the lock link for ground safety. Drag Brace Strut Actuator Each main gear drag brace jury strut has a hydraulic actuator to lock and unlock the over-center locking of the jury strut. The actuator rod end is attached to the jury strut and the actuator end is attached to the shock strut. For gear retraction, the actuator is pressurized to retract to overcome the two jury strut springs and break the ove-center locking. For gear extension, the actuator is pressurized to extend to aid the lock springs in forcing over-center locking of the jury strut. A down lock pin is inserted in the apex of the jury strut for ground safety.

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MLG OPERATION General Landing gear hydraulic operation involves a series of valve actions. A simplified description of their operation is outlined below. Landing Gear Retraction The landing gear lever moves the main gear selector valve to the UP position. The MLG transfer cylinder receives pressure from the selector valve and pressurizes the retract actuator to momentarily retract. Hydraulic pressure flows through the gear operated sequence valve to the door latch actuator. The door latch actuator opens the door uplock hook and then ports OPEN pressure to the main gear door actuator. Door opening causes the door operated sequence valve to open and allow UP pressure to the main gear retract actuator. Gear retraction moves the gear operated sequence valve to the TRANSIT, then UP position. The UP position of the valve ports pressure to close the door. Initial gear UP pressure causes the lock actuators to unlock the side and drag brace actuators and the truck positioner to tilt the truck. Landing Gear Extension Landing gear extension is the reverse of retraction except that initial DOWN pressure causes the transfer cylinder to momentarily retract the landing gear while the uplock hook opens. The lock actuators are pressurized to lock the side and drag braces. The truck positioner is pressurized to tilt the truck. Door Safety Valve and Lock Out Actuator The door safety valve is opened and closed by either the alternate extend system or the ground door release lever. When the valve is closed, pressure cannot close the door. The lock out actuator hydraulically releases a mechanical lock on the ground door release lever. The lock prevents the lever from being placed in the close position without center system hydraulic pressure.

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MLG DOOR GROUND RELEASE LEVER General Each main gear door has its own ground release lever to unlock the door hook and to actuate the door safety valve, located aft of each wheel well in the wing body fairing. Operation Press the latch lever to disengage the door ground release lever from the up detent (6°). Pull on the lever (maximum 50 pound force) to rotate it to the open position (52°) where the latch will lock the lever in the open detent. The latch lever can be pinned in the up or open position to prevent inadvertent door operation. In the open position the ground release lever will align with the safe (green) band on the access door and the latch lever pin can be inserted. If the lever is not latched in the open position and released, the door uplock hook and safety valve reset springs will partially retract the lever until the arming lockout actuator pawl engages (34°). At this position the lever will align with the unsafe (red) band on the door and the latch lever pin cannot be inserted. (If center system pressure is applied the ground release lever will fully retract, open the safety valve and center system pressure will close the door). To stow the lever, remove the pin, depress the latch lever and return the ground release lever to the up position. Note:

The lever may only be stowed when center hydraulic system is pressurized, i.e., the lever can only be stowed when it will result in door closing.

Maintenance Practices Each ground release quadrant is pinned in the 0° rig position to tension the ground door release cables via the turnbuckles. Turnbuckles are accessible through the lever access door.

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NLG GENERAL General Description The nose gear shock strut outer cylinder is trunnion mounted to the wheel well walls and connected to the inner cylinder by a torsion link. The strut is serviced by an air charging valve (located on top of the outer cylinder) and an oil charging valve (located on the lower right-hand side of the outer cylinder). The torsion link is mounted on the outer cylinder steering collar to allow hydraulic nose wheel steering through a pair of forward mounted steering actuators. The nose gear shock strut is supported by a trunnion-mounted drag strut. A hydraulic retract actuator, mounted on an actuator support beam and the upper drag strut cycles the nose gear for extension and retraction. The gear is held, both down and up, by overcenter locking of a lock link, hydraulically actuated and held by a pair of lock springs. Forward and aft doors are mechanically operated by the nose gear. A single axle, integral to the inner shock strut, supports the two nose gear wheels. A jacking pad is located beneath the axle with a tow fitting attached to the front of the axle. A towing lever is provided for towing without de-pressurizing the hydraulic system. The torsion links may be disconnected for towing angles greater than the nose wheel steering system actuator limits.

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NLG DOORS General The nose gear doors are mechanically sequenced to provide aerodynamic seal of the nose wheel well. Aft Doors The aft doors are mechanically linked to the shock strut to open and close with the nose gear. Forward Doors The forward doors are mechanically sequenced by bell cranks and rods to open (for gear extension or retraction) then close and remain sealed after the gear has cleared the doors. Maintenance Practices The doors are constructed of a fiberglass honeycomb covered with a graphite-fiberglass composite and sealed around the edges with aeroseals. Adjustable rods are used to ensure proper door closure. For ground opening of the forward doors, a ground release lever unlocks an internal ball lock in the telescoping rod and the weight of the door, 29.5 lbs, causes the door to swing open, extending the rod. Pushing up on the door, to close it, will cause the telescoping rod to retract and re-lock the internal ball lock. If left open on the ground, the normal sequencing of the gear will re-lock the telescoping rod and the forward doors will close normally.

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NLG HYDRAULIC SCHEMATIC SIMPLIFIED General The nose gear selector valve, controlled by mechanical inputs from the landing gear control lever, will port center system hydraulic fluid for gear extension and retraction. Extension The lock actuator will be pressurized to extend, breaking the over-center locking of the lock link. The transfer cylinder provides a time delay to allow the lock actuator to function, prior to pressurizing the retract actuator. Pressure is free flowing through the priority valve and is also supplied to nose wheel steering. As the retract actuator extends the nose gear, the lock actuator continues to be pressurized to extend and will now lock the lock link over-center in the gear down position. Retraction For gear retraction, the lock actuator will be pressurized to retract, breaking the over-center locking of the lock link. The priority value provides a time delay to allow the lock actuator to function, prior to pressurizing the retract actuator. Pressure is also supplied to nose wheel steering and to reset the transfer cylinder. As the retract actuator retracts the nose gear, the lock actuator continues to be pressurized to retract and will now lock the lock link over-center in the gear up position.

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NLG EXTENSION AND RETRACTION

Dispatch Deviation

Gear Extension

Landing Gear Retracting System

• The nose gear selector valve in the right main gear wheel well is positioned to the "down" position by the gear lever in the flight compartment porting center hydraulic system pressure. • The lock actuator extends to override the lock springs and unlock the lock links. • The transfer cylinder delays the retract actuator movement until the gear is unlocked. • The retract actuator retracts to extend the nose gear. • When the nose gear is down and locked the lock links are held over-center by the extended lock actuator and the lock springs. • The doors are mechanically sequenced to follow the gear and re-close as the gear is fully extended. Gear Retraction • The nose gear selector valve is positioned to the "up" position by the gear lever porting center hydraulic system pressure. • The lock actuator retracts to override the lock springs and unlock the lock links. • The priority valve momentarily delays the fluid flow to the retract actuator until the gear is unlocked. This also cycles the transfer cylinder. • The retract actuator extends to retract the gear. • When the gear is up and locked, the lock links are held over-center by the retracted lock actuator and the lock springs. • The doors are mechanically sequenced to follow the gear and close behind it. • The nose gear selector valve is positioned to the "off" position by the gear lever and all nose gear hydraulic lines are ported to return. • The nose gear is held up and locked by the over-centered lock links and lock springs.

• Aircraft may be dispatched with gear down provided: • Open and clamp Gear Lever circuit breaker • Select alternate Vmo/Mmo position on the Vmo/Mmo select switch located on E1 rack, • All associated gear hydraulic leaks are corrected. • Install all three gear down-lock pins.

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ALTERNATE EXTEND SYSTEM

Ground Door Release System

General The nose gear alternate extend and main gear alternate extend systems are inter-dependent; the same electric actuator drives both systems. A guarded switch on the P3-1 panel, below the landing gear lever, energizes the electric actuator for alternate extension.

The ground door release system is an auxiliary system of the main gear alternate extend system. Cables from the ground release levers operate the same control rod and bellcrank system in each wheel well as the main gear alternate extend system. Pulling the Ground Door Release Lever will operate the door safety valve and rotate the door uplock hook, opening the main gear door for ground maintenance.

Nose Gear Alternate Extend System

Landing Gear Alternate Extend Circuit

The nose gear alternate extend system is a solid-link system comprised of control rods and bellcranks which will drive to break overcenter locking of the nose gear lock link and allow the nose gear to free-fall. The system is loadlimited so that in the event the nose gear alternate extend system is jammed, the load-limiter will yield to the driving force of the electric actuator and allow the main gear to extend.

For alternate gear extension, the guarded alternate extension switch on the P3-1 panel energizes the electric actuator to the extend or retract position.

Main Gear Alternate Extend System The main gear alternate extend system is cable driven from the electric actuator to an uplock release quadrant in each wheel well where it is a solid-link control rod and bellcrank system to a door safety valve and to each main gear door uplock hook. Actuating the system will operate the door safety valves and rotate the uplock hooks, unlocking each main gear door and allowing both main gears to free-fall. The cable runs are load-limited so that in the event one of the main gear alternate extend systems is jammed, the load-limiter will yield to the driving force of the electric actuator and allow the nose gear and remaining main gear to extend.

In the extend mode, power from the 28vdc Hot Battery Buss passes to the actuator when the alternate gear extension switch is positioned to extend and when the landing gear lever is not in the UP position. When the actuator has reached the full extend position, the extend limit switch will open breaking power to the actuator. In the retract mode, power from the 28vdc L Main Buss passes to the actuator when the alternate gear extension switch is latched. When the actuator has reached the full retract position, the retract limit switch will open breaking power to the actuator.

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ALTERNATE EXTEND ACTUATOR Operation The electric actuator is energized from the landing gear alternate extend switch on the P3-1 panel. The actuator is reversible, operating in the extend and reset modes to drive through a torque shaft, the left and right main gear door release quadrants for main gear alternate extension and a load-limiter and control rod for nose gear alternate extension. The torque shaft include a stop crank which contacts reset and extend limit switches controlling the electric actuator and which contacts mechanical stops limiting torque shaft travel to 66° of arc. Location and Access The actuator and torque shaft assembly are mounted to support frames below the flight compartment floor at approximately STA 232. Access is via the crawlway to the left forward equipment center above the nose wheel well and below the flight compartment floor, and must be gained via the main equipment center access door. Maintenance Practices GO and NO-GO pins are used to check the proper operation of the limit switches. After each switch has cut power to the electric actuator and the stop crank has coasted to a stop, it should be possible to insert a GO pin (nominal diameter .0190 inch) but not possible to insert a NO-GO pin (nominal diameter.1050 inch) between the stop crank and the mechanical stop of the support frame. Note:

An electrically operated brake will stop the actuator within 1° of output shaft rotation.

The limit switches are adjusted via a slotted bolt hole on the mounting plate until this condition is achieved.

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TAIL SKID GENERAL Purpose A tail skid, electrically controlled and hydraulically operated protects the aft fuselage area if a tail strike were to occur during takeoff or landing. Operation The tail skid, pivoting on airplane structure, is attached to the rod end of the shock strut/actuator assembly and forms part of the fairing when retracted. The lever has a replaceable pad. The shock strut/actuator assembly is mounted to airplane structure with a fuse pin and restrained by breakaway cables, in event a hard tail strike causes shear out of the pin. The strut has a pneumatic charge of 300 - 350 psi and is serviced by an air charging valve on the rod end of the shock strut/actuator. A low pressure indicator (red pop-out button) on the rod end is visible when air pressure is 174-232 psi and servicing is required. The tail skid is retracted and extended by center hydraulic system pressure. The components are located in the stabilizer compartment. Operating time is 14 seconds to retract and 17 seconds to extend. Two proximity sensors, actuated by a target on the lever, provide tail skid position for fault annunciation.

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TAIL SKID COMPONENTS The tail skid components are located in the stabilizer compartment. The tail skid hydraulic system consists of the following components: • Shock strut/actuator and blocking valve: the actuator extends/retracts the tail skid and also functions as a pneumatic shock strut. The blocking valve on top of the actuator provides a hydraulic down lock when the tail skid is extended. • Fuse: a quantity measuring fuse (120 cu in) protects the center hydraulic system from a leak in the tail skid system. The fuse resets automatically and can also be reset manually. • Transfer cylinder: a transfer cylinder provides a measured volume of fluid (200 cu in) to extend the tail skid assembly. • Control module: the control module routes fluid to the actuator and transfer cylinder. The valve is electrically operated but can be manually operated for dispatch with the tail skid extended. The module also contains a flow regulating valve and a pressure-operated valve.

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TAIL SKID OPERATION General The tail skid is powered by the center hydraulic system. The tail flight control shut off valves do not shut off pressure to the tail skid. Retraction To retract the tail skid (as shown) the control valve is positioned to allow center system hydraulic flow to fill the transfer cylinder, pressure the blocking valve open and retract the shock strut/actuator assembly. The rate of retraction is controlled by a flow regulating valve (.9 GPM). The retract pressure is maintained by the center system with the tail skid retracted as the control valve is in the same position with the landing gear lever up or off. Extension To extend the tail skid the landing gear sense relay is powered by the gear lever position switch (gear lever down) to position the control valve. Center system pressure then moves the pressure operated valve and discharges the transfer cylinder to the extend port of the shock strut/actuator to extend the tail skid. Extended After the transfer cylinder is discharged extend pressure is no longer present and the closed blocking valve hydraulically locks the tail skid in the extend position. Thermal relief is provided by a pressure bleed orifice. Tail Skid During a tail skid strike the shock strut will be momentarily compressed by fluid transfer through the shock absorption bleed, which compresses the nitrogen gas, and through the pressure bleed orifice.

The pressure bleed orifice is sized (.144 GPM, opens at 250 psi;) to allow only a few cubic inches of fluid to pass during tail skid compression with the remainder forced through the shock absorption bleed. After the strike the tail skid is returned to the extended position by the high pneumatic pressure.

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TAIL SKID INDICATION General There is no indication of tail skid position during normal system operation. Tail skid failure indications are controlled by the proximity switch electronic unit (PSEU) using inputs from proximity sensors on the tail skid, nose and main gear up and down lock proximity sensors (system 1) and a switch on the landing gear lever. A tail skid amber light and EICAS advisory message TAIL SKID are displayed when the PSEU detects the tail skid sensor is in disagreement with the landing gear sensors. The PSEU groups the tail skid retract sensor input with the gear up lock sensors and the tail skid extend sensor input with the gear down lock sensors to detect disagreement. An input from a landing gear lever position switch is used by the PSEU to inhibit the light and message for 36 seconds after the lever and gear position inputs disagree. After 36 seconds the inhibit is removed and light and message are displayed if tail skid/gear position disagrees regardless of lever/gear position agreement/disagreement. Dispatch Deviation Tail Skid "INOP" • Should only dispatch with Tail Skid fully down. • If not fully down move manual override lever on tail skid control module to position 2 and check that tail skid extends fully.

TAIL SKID INDICATION B767-3S2F Page - 39

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PROXIMITY SENSE SYSTEM Proximity Switch System The purpose is to provide position sensing for landing gear, doors, slats and thrust reverse’s. The system consists of multiple sensors mounted throughout the aircraft that sense the proximity of targets and provide position signals to the PSEU. PSEU, located in main equipment center, receives discrete signals from sensors and/or micro-switches to control relays, lights, and/or other electronics. The PSEU also incorporates built-in-test equipment (BITE) to provide in-flight position switch testing and on-ground testing, troubleshooting and fault isolation.

Landing Gear Position Indication Air/Ground Sense

6

Thrust

12

Leading Edge Slats

24

Fwd & Aft Cargo Door Control

8

Fwd Left Cabin Entry Door Control

4

All Other Door Warnings‐

27

Totals

103

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PROXIMITY SENSE SYSTEM BLOCK DIAGRAM Proximity Switch System Proximity sensors located throughout the airplane monitor the position of landing gear, door, leading edge slat, and thrust reverser components. Sensor channels on proximity cards in the proximity switch electronic unit (PSEU) convert the position signals from the proximity sensors into logic signals. Logic cards take these logic signals from different combinations of proximity sensors and process the signals together to decide when to operate lights, relays or switches (via the driver cards). An example of this would be the illumination of the landing gear down & locked green lights. The logic cards also receive discrete inputs used in the processing of logic functions (i.e. gear handle position). The drivers on the driver cards, driven by the output logic signals from the logic cards, provide discrete signals to lights, relays and switches of different airplane user systems. The functions of the proximity switch system are monitored automatically by a BITE module inside the PSEU. The BITE Module provides automatic fault isolation and storage of faults into the BITE memory to the LRU level. The BITE Module also has LRU and systems tests that can be performed on the ground. Power is provided to the proximity cards by individual 28V DC supplies from different subsystems. The BITE module has its own 28V DC power supply.

PROXIMITY SENSE BLOCK DIAGRAM B767-3S2F Page - 43

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PROXIMITY SYSTEM ELECTRONIC UNIT (PSEU) Proximity System Electronic Unit (PSEU) The PSEU is located in the main equipment center on E1-2. Access is through the access door aft of the nose wheel well. The PSEU is mounted in the rack by two fasteners and may be removed as a unit, or individual cards may be replaced without removing the unit. Static sensitive procedures required for handling of the PSEU. The proximity, logic and driver cards are accessed through left and right doors on the PSEU face. The BITE cards are accessed through a removable BITE module assembly.

PROXIMITY SWITCH ELECTRONIC UNIT (PSEU) B767-3S2F Page - 45

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PROXIMITY SENSORS Proximity System Sensors Sensors provide position inputs to the proximity switch electronics unit (PSEU) for the following airplane systems control and indication. •

Door control and indication

•

Landing gear indication and air ground sensing

•

Leading edge slat indication and failure protection

The sensor is a two-wire, magnetic field producing device that is contained in a stainless steel case with wires connected to the PSEU proximity switch card. Either cylindrical or rectangular sensors are used depending on installation requirements. Operation is identical with slight differences in rigging procedures. The sensor operates in conjunction with a steel target. The change in inductance as the proximity of sensor and target changes from near to far or far to near is detected by the associated proximity card which switches its output to its associated logic card from 0.3 volt to 13.1 volts (near to far) or 13.1 volts to 0.3 volt (far to near).

PROXIMITY SENSORS B767-3S2F Page - 47

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PSEU - BUILT IN TEST EQUIPMENT

Sensor, Card and Target Lights

BITE Components

One of the lights illuminates during memory recall, system test and target test to indicate that a sensor or a card is failed, or a target is not in the correct position.

The BITE control and display panel is located on the center front face of the PSEU. The left front face of the PSEU lists the operating instructions and display codes while the right front face lists the 3-digit codes for all the sensors, power supplies and discrete inputs. The BITE control and display panel is part of the BITE module. The BITE module can be removed by loosening the two screws on the center panel and pulling the module out of the PSEU. The module contains two BITE cards. The BITE module and cards can be removed and installed without pulling the PSEU out of the rack. Press/Test The PRESS/TEST switch is depressed to perform a lamp test. During the test, all five amber lights should illuminate and code 888 appear on the red LED display. If the lamp test fails, the PSEU needs to be replaced. Target Near and Far Lights One of the indicator lights illuminates at the end of a target test to indicate the position of the target for the selected sensor being tested. Sensor Channel Select Switches The three thumb-wheel switches are used to input the selected 3-digit code for sensor input as well as system code to be tested. Digital Channel Display The digital channel display indicates the 3-digit fault code for a sensor, card, power supply, target or discrete input during memory recall and system test. The LED display indicates the code of the sensor tested during a target test. The display also provides the status of the BITE testing by indicating the appropriate display code from the list on the left front cover.

Verify Switch The VERIFY switch is depressed to activate ground testing of various systems. The digital channel display flashes code CCC during testing, illuminates the 3-digit codes of identified faults and code 999 at the end of the test. Target Test Switch The TARGET TEST switch is depressed to activate testing of the sensor circuit selected with the sensor channel select switches. During the test, the digital channel display illuminates the code of the selected sensor. At the end of the test, the sensor and card lights may illuminate to indicate a faulted component or, if no fault is found, one of the target NEAR or FAR light illuminates to indicate the position of the target. BIT Switch The BIT switch is depressed to recall the faults stored in the nonvolatile memory. The digital channel display illuminates the 3-digit fault code for sensor, power supply, discrete input, card or target for each fault. At the end of the memory recall, the display illuminates code OOO. Reset Switch The Reset switch is depressed to erase the nonvolatile memory. When the memory is cleared, the digital channel display illuminates code EEE.

PSEU - BUILT IN TEST EQUIPMENT B767-3S2F Page - 49

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AIR/GROUND SENSING SYSTEM General The air/ground relays on the airplane switches a number of airplane systems from ground to air mode when the airplane lifts off and vice-versa. Switching is accomplished via a relay system that is actuated by the main gear truck tilt proximity sensors, the nose gear not compressed proximity sensors and associated electronics. Sensors Two tilt sensors on each main gear truck provide dual system bogie tilt information to the PSEU. Two sensors on the nose gear strut provide nose gear strut compression information to the PSEU. Electronics The sensor inputs are processed in the PSEU logic to provide inputs to drive a number of air/ground relays which control various flight/ground critical items. The signals are also provided to the EICAS computers for message format preparation.

AIR/GROUND SENSING SYSTEM B767-3S2F Page - 51

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AIR/GROUND SENSING COMPONENTS Relays All system 1 and system 2 air/ground relays are located in the P33, P36 or P37 panels. The relays are 4-pole, double throw, 2 or 10 amp hermetically sealed relays with pin-type terminals for electrical plug connection. Relays are installed on bracket with socket mounting screws. Power should be removed prior to removal/installation. Relay Adjustment and Test All system 1 and system 2 air/ground relays are tested for ground mode and flight mode operation. The test procedures require continuity and voltage check for relay terminals in both modes. The test is conducted with a breakout box. Simulated Flight Mode Simulated flight mode may be accomplished by jacking the airplane or by placing actuators on the main gear truck tilt sensors and the nose gear not compressed sensors. Airplane with electrical power applied will switch the air/ ground system and all user systems to the flight mode. To prevent equipment damage or personnel hazard from prolonged flight mode operation, consult the Maintenance Manual 32-09 for the list of circuit breakers to be opened. EICAS Indications The PSEU processes the sensor signals to the relays and to the EICAS computers. The following two messages are related to the air/ground sensing system: • AIR/GND DISAGREE - monitors disagreement between system 1 and system 2 for main gear tilt and is stored for status and maintenance pages. • NOSE A/G DISAGREE - monitors disagreement between system 1 and system 2 for nose strut compressed and is stored for status and maintenance pages.

E3 EQUIPMENT CENTER

SYSTEM 2 K200 SERIES RELAYS

E8 EQUIPMENT CENTER P37 PSEU

P33 P36

AIR/GRD DISAGREE NOSE A/G DISAGREE

K514,515,516 517,518,520 522,528,552 643,645 FWD

E8

EICAS COMPUTER

EICAS DISPLAY UNITS (P2)

AIR/GROUND SENSING COMPONENTS B767-3S2F Page - 53

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SYSTEM 1 K-100 SERIES RELAYS

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LANDING GEAR POSITION INDICATION - GREEN LIGHTS General Dual bulbs and dual power are provided for each landing gear to prevent loss of indication due to a single failure. Main Landing Gear Each main gear green light consists of dual bulbs (left main gear shown) powered by separate MD&T circuits and controlled by a pair of relays powered separately by landing gear position - air/ground system 1 and system 2 circuit breakers. Nose Landing Gear The nose gear green light also contains dual bulbs powered by separate MD&T circuits. The grounds are provided by logic in the PSEU responding to down and locked indication from system 1 or system 2.

LANDING GEAR INDICATION - GREEN LIGHTS B767-3S2F Page - 55

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STEERING CONTROL Upper Cable Loop The nose wheel steering system may be controlled by either tiller input or rudder input. 360 degrees tiller input through a gearbox commands 65 degrees left or right nose wheel steering, and full rudder input commands 7-1/2 degrees left or right nose wheel steering. The centering spring and rudder interconnect mechanism combines rudder and tiller inputs through the upper cable loop and provides for centering the tiller when released. A cable compensator transmits upper cable loop inputs through the pivot links to the lower cable loop and protects the lower cable loop from a hard over signal in the event of a cable break. Lower Cable Loop From the steering drum to the summing mechanism, lower cable loop movement provides input to the metering valve module. The lockout cam mechanism forces the steering drum to send a centering signal to the metering valve module for centering the gear or retraction. The steering metering valve module ports hydraulic fluid through a pair of swivel valves to power steering actuators. Actuator movement through the torsion link steers the nose gear. As the gear turns, the lower cable loop follow-up through the summing mechanism will null out input to the metering valve module when the desired steering angle is reached.

STEERING CONTROL B767-3S2F Page - 57

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CENTERING SPRING AND RUDDER INTERCONNECT MECHANISM General The centering spring and rudder interconnect mechanism joins rudder and tiller input for nose wheel steering and provide for centering the tiller when it is released. Operation The mechanism consists of a rudder input arm, two spring arms and a cable quadrant all pivoted about a common center of rotation. The cable quadrant is tied to the tiller through cable NWS1A-2 and to the cable compensator through NWS1A-3. Movement of the quadrant will rotate both the tiller and the cable compensator, providing a steering input. Rudder input through either captain's or first officer's rudder pedals will rotate the rudder pedal jackshaft and cause the input arm to rotate. Rotation of the input arm will drive through the spring arms to rotate the cable quadrant, backdriving the tiller and providing a steering input to the cable compensator. Tiller input will drive the cable quadrant, providing steering input to the cable compensator. Due to feel and centering forces in the rudder system, the rudder input arm will remain stationary with tiller input which will cause the spring arms to separate, stretching the springs. Spring force (4-pound preload) will provide for centering the tiller when the input force is removed. With the cable quadrant fixed, i.e.: gear retracted so no steering input, rudder input will stretch the centering springs. This additional spring force will not be noticeable in the rudder system.

Location and Access The centering spring and rudder interconnect mechanism is below the right-hand side of the flight compartment floor. Access is through the main equipment center access door and around the right crawl way to the forward equipment center. Maintenance Practices The cable quadrant may be pinned for cable rigging of the upper cable loop. Turnbuckles are accessible in the forward equipment center.

CENTERING SPRING AND RUDDER INTERCONNECT MECHANISM B767-3S2F Page - 59

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BRAKE SYSTEM BLOCK DIAGRAM Mechanical Input Two sets of brake pedals provide for full and differential braking capability. The captain's and first officer's pedal sets are connected by a bus rod and linkage. Cables on the left and right side of the airplane connect the pedals to a brake metering valve module in each wheel well. Each brake metering valve module contains a normal and an alternate brake metering valve. Hydraulic Control The normal brake system is powered by the right hydraulic system. The alternate system is powered by the center hydraulic system and is automatically selected upon loss of the right hydraulic system. A reserve source of hydraulic fluid is also provided by the center hydraulic system. An accumulator in the normal system is automatically selected when the alternate system is lost. The brake metering valves mechanically meter the selected hydraulic system pressure to the normal or alternate anti-skid system. The normal anti-skid module receives normal brake metered pressure or autobrake pressure and supplies the brakes. The alternate anti-skid module receives pressure from the alternate brake metering valves if active and supplies the brakes. Electrical Control The anti-skid/autobrake control unit provides electrical control to four anti-skid valves for control of skidding wheel conditions and to the autobrake valve module to meter brake pressure automatically per a preset adjustable setting. Wheel speed inputs are transmitted to the anti-skid/autobrake control unit by wheel transducers. Selected deceleration requirement is input to the autobrake system from the autobrake selector switch.

BRAKE SYSTEM BLOCK DIAGRAM B767-3S2F Page - 61

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BRAKE CONTROLS AND INDICATIONS

Brake Temperature Monitor

Parking Brakes

A white BRAKE TEMP light on the P3-1 panel provides an indication of a hot wheel brake. Individual wheel temperature is displayed on EICAS.

The parking brake handle on the control stand sets the parking brake. An amber PARK BRAKE light and EICAS advisory message illuminate to indicate parking brakes are set. A brake pressure gage (P3-1) indicates pressure available for braking (Accumulator or normal system pressure). Brake Hydraulic Source A BRAKE SOURCE light and EICAS advisory message illuminate when no active source of hydraulic pressure is available to the brake system. A reserve brakes and steering switch selects a center hydraulic system reserve source of hydraulic fluid and isolates this fluid to the brakes and steering systems. Antiskid An amber light on the P5 panel and EICAS advisory message illuminate for faults in the active antiskid system. Normal and alternate antiskid system fault messages also appear on the status and ECS/MSG pages. An ANTISKID/ AUTOBRK message also appears on the ECS/MSG page for all antiskid system faults. Autobrake A control switch (P1-3) provides for selection of deceleration levels during landing and for rejected takeoff. An AUTOBRAKES light and EICAS advisory message illuminate with the switch in the DISARM position, indicating that a fault has been detected or arming requirements are not met. An ANTISKID/AUTOBRAKE message also appears on the ECS/MSG page for autobrake system faults.

BRAKE CONTROLS AND INDICATIONS B767-3S2F Page - 63

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BRAKE HYDRAULIC SYSTEMS

Alternate Brakes

Hydraulic Pressure Source

Center hydraulic system pressurizes the alternate brake system.

When right system drops to 48% of center system pressure, the ABSV opens and the AIV closes due to differential piston areas. The alternate brake metering valve meters pressure to alternate antiskid valves, then through shuttle valves to wheel brakes. Return to reservoir through the alternate brake metering valves when brakes are released or through the alternate antiskid return lines if the valves relieve brake pressure.

Source Selection Valves

Accumulator Braking

The Alternate Brake Selector Valve (ABSV) is located on the keel beam, left wheel well. The Accumulator Isolation Valve (AIV) is located on the aft wall, right wheel well.

When right and center systems fall below 1440 psi, the accumulator opens AIV and is available for limited braking through the normal brake system.

Right hydraulic system pressurizes the normal brake system and the accumulator.

The two valves are identical, pressure operated slide and sleeve valves. They contain system and control pressure ports, brake pressure output port, return port and pressure switch port. (Pressure switch port and return port plugged on the AIV). The ratio of area of the slide to the area of the control piston is such that if control pressure drops to 48% of system pressure, the valve opens. Normal Brakes Right hydraulic system pressurized and holds ABSV closed. Right system pressurizes the accumulator and the normal brake system. Pedal input activates the Brake Metering Valves (BMV) and meters normal system brake pressure through the shuttle valve, through the normal antiskid valves and through another shuttle valve to brakes. Return to reservoir is through the brake metering valves when the brake pedals are released or through the normal antiskid valve return line if the antiskid system relieves brake pressure.

Brake accumulator pressure can be read at a gage in the right wheel well. A pressure transmitter supplies indication of pressure on the gas side of the accumulator to a brake pressure gage on the P3-1 panel. Gear Retract Braking With the gear handle in the UP position, up line pressure is ported through the ABSV to the alternate BMVs. Up line pressure is also ported to the retract braking actuators on the alternate BMVs. This meters gear up line pressure through the alternate antiskid valves to the brakes. When the gear lever is placed in "UP" position, the alternate antiskid valves are deactivated for 12.5 seconds to allow the brakes to fully stop wheel rotation.

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BRAKE SOURCE LIGHT & RESERVE BRAKES SWITCH Brake Source Light The brake source light indicates that no active source of hydraulic power is available for the braking systems. (The accumulator is a passive source.) Activation Loss of the right hydraulic system is monitored by the ACMP pressure switch (S-32) during automatic ACMP operation or by the electric hydraulic pump right control pressure switch (S-30) when the ACMP is not automatically operated. Loss of the center hydraulic system is monitored on the downstream side of the alternate brake selector valve by switch S415. The brake source light illuminates when both systems indicate low pressure. EICAS Message The light is accompanied by a "BRAKE SOURCE" advisory level "C" message on the upper EICAS display.

BRAKE SOURCE LIGHT & RESERVE BRAKES B767-3S2F Page - 67

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PARKING BRAKE

Control System

General

The cam driven parking brake switch has two contacts; one contact controls the parking brake shutoff valve and the parking brake light, the other contact inputs to the takeoff warning system.

The parking brake system provides a means of engaging the brake pedals to hold the BMV’s in the braking mode. A fully charged accumulator will hold the brakes for a minimum of 8 hours. Latching System The T-handle on P-10 is attached to the latching mechanism by a flexible cable. Pawls on the latch mechanism engage catches on the bell cranks. Both pedals must be depressed before either pawl will engage. A cam on the left pawl drives a parking brake indication and valve control switch. (S-459) The latch engages with pedals depressed 9 degrees and T-handle pulled. The latch is disengaged by depressing pedals to 11°, releasing handle. Four adjustments can be made to the latching mechanism. • Parking brake pawl is adjustable to allow clearance of pawl stop. • The tabs on the micro-witch are adjustable to allow switch actuation as pawl lobe moves within 0.22 - 0.25 inches of pawl stop. • Input crank stop can be adjusted till crank is 12° below horizontal with crank against stop. • Jam nuts on cable can be adjusted so that the pin connecting the flex cable rod to the input crank arm can be freely inserted when parking brake handle is against control stand and input crank is against stop.

Brake pressure for setting parking brakes is indicated on brake pressure gage on the P3-1 panel. Gage shows right hydraulic system pressure if system is pressurized or accumulator pressure if right hydraulic system is not pressurized. Parking brake valve is located in the return line from the normal antiskid valves and prevents bleed down through the antiskid valves. Indications Park brake light - located on the left side of the P-10 panel and illuminates when the parking brake valve is not fully open. EICAS display - a PARKING BRAKE message on the upper display unit (advisory C level) indicates that the parking brake valve is not fully open. Parking brake message on upper scope at warning level indicates that the parking brakes are set with takeoff power set. (T/O configuration warning system)

PARKING BRAKE B767-3S2F Page - 69

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PARKING BRAKE ACCUMULATOR General The 300-cubic inch accumulator is located on the keel beam in the right wheel well. The accumulator has three functions: • Provide brake pressure for the parking brake system • Reduce pressure droop during normal brake system operation • Provide a passive source of braking when both normal and alternate active pressure sources are not available A direct reading pressure gage and charging valve are installed on the keel beam. The pressure transmitter provides a signal to a flight deck brake pressure indicator. The pressure gage and transmitter are connected to the gas side of the accumulator. The charging valve is used to service the accumulator (nitrogen). The accumulator air charge can be checked by depressurizing the center and right hydraulic system and cycling the brake pedals until the brake pressure indicator stops decreasing. Proper servicing is verified by comparing the air charge to the ambient temperature. A servicing decal is located by the accumulator charging valve.

BRAKE PRESS

28V AC R BUS

(J-25) P11-3 OVHD CB PANEL

BRAKE PRESS 4 PSI X 1000 3

0 2

HYDRAULIC CONNECTOR

1

N10 BRAKE PRESS IND (P3-1) TS90 HYD BRAKE PRESS TRANSMITTER CHARGING INSTRUCTIONSHYDRAULIC ACCUMULATOR.

R WHEEL WELL KEEL BEAM

PRESSURE GAGE 1200 CHARGING VALVE

1100 PRESSUREPSI GAGE

HYD BRAKE PRESSURE TRANSMITTER

WITH SYSTEM DEPRESSURIZED, CHARGE WITH DRY NITROGEN TO APPLICABLE PRESSURE PER CHART BELOW ± 100 PSI

1000 900 800 700 -50 -25 0 +25 +50 +75 AMBIENT TEMP - °CENTIGRADE

ACCUMULATOR

PARKING BRAKE ACCUMULATOR B767-3S2F Page - 71

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BRAKE TEMPERATURE SYSTEM Each brake temperature sensor inputs to the brake temperature monitor unit. The monitor unit inputs a voltage signal to the EICAS computers which display eight boxes with numbers on the status page. Each box and number is color coded (blue or white) with the number (0 to 9) within the box representing a brake temperature of 90-695°C. The color of the numbers and boxes will be as follows: • Normal condition - the number will be 0 through 2 with both box and number blue. • Threshold condition - with the first number in a respective group (left main gear truck or right main gear truck) increasing to 3, the box will become white and the number remains blue. Only the box with the highest number (3 or 4) in the group will have a white box. If more than one box has the high number (3 or 4), only the first box reaching the highest number will have a white box. • Abnormal condition - any brake with a number of 5 or greater will have a white box and number. A brake overheat white light (P3-1) will illuminate when any box has a number 5 or greater. This light is controlled directly by the Brake Temperature Monitor. The temperature monitor unit will indicate an overheated brake as follows: • Carbon brake (300) - 427°C

BRAKE TEMPERATURE SYSTEM B767-3S2F Page - 73

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BRAKE TEMPERATURE MONITOR Components A thermocouple type temperature sensor (chromel-alumel) is installed in the inboard side of each brake. A Brake Temperature Monitor Unit is located in the main equipment center (E2-4). This unit controls a BRAKE TEMP light on P3-1 and inputs to both EICAS computers which provide a color-coded, numerical brake temperature indication. Brake Temperature Monitor Bite The monitor unit has built-in test equipment (BITE) circuits which include a monitor test and sensor test. Monitor Test When the MONITOR TEST position is selected the nine indicators will illuminate on the face of the monitor unit, the EICAS indicators will all show uniform temperature values of 5 or above and the BRAKE TEMP light will illuminate. The sensors are not tested. If any light does not illuminate, change the monitor unit. System Test When the SENSOR TEST position is selected, a test signal is applied across each of the eight brake sensor thermocouples. If either the sensor or its cabling is open or shorted, the signal will not be received by the monitor unit. A sensor fault will be indicated by an extinguished light for that sensor and the monitor unit. If a sensor LED and monitor light do not illuminate, change the sensor. With the BITE switch in either test position the white "BRAKE TEMP" light (P3-1) will illuminate and the eight digital displays on EICAS will display "5" or above.

BRAKE TEMPERATURE MONITOR B767-3S2F Page - 75

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ANTI-SKID GENERAL

Outputs

Purpose

Anti-skid cards provide the valve driver signals to the normal and alternate antiskid valves. Fuses mounted to the valve modules provide leakage protection.

The anti-skid system primarily utilizes wheel speed information to command brake pressure that will give a maximum braking level below wheel skid. Antiskid system will never command brake pressure greater than metered pressure. Control Unit The anti-skid function is controlled by four microprocessor cards within the antiskid/autobrake control unit. Each card controls a fore/aft pair of wheels and is powered through a separate circuit breaker. Inputs Wheel speed inputs are generated in eight wheel speed transducers and input to anti-skid cards. Gear handle position (not down) provides an inhibit signal to the alternate antiskid system for gear retract braking. Gear handle position (down) energizes the hydroplane/touchdown protection system. Parking brake valve position is monitored. Valve must be fully open for operational anti-skid system. Inertial reference system signals provide ground speed signals for hydroplane/ touchdown protection. Brake source signal is monitored to remove anti-skid valve bias signal when normal and alternate brake hydraulic systems are lost.

Shuttle valve modules between the normal and alternate anti-skid valve modules route pressure from the active system to the brakes. Fault annunciation signals control: • Amber ANTISKID light on P5 • EICAS displays on advisory, status and maintenance levels.

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WHEELSPEED TRANSDUCER Purpose The anti-skid transducers supply wheel speed data to the antiskid/autobrake control unit to get wheel speed data. This data also goes to the antiskid/ autobrake control unit for autobrake operation. Location There are eight anti-skid transducers. Each main landing gear wheel has a transducer in the axle. Physical Description When the transducer shaft turns, it provides wheel speed input to the transducer.

IN-AXLE ASSEMBLY INSTALLATION

HUB CAP CLAMP TRANSDUCER DRIVE ASSEMBLY

CUP

HUBCAP

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ANTI - SKID VALVE MODULES Anti-skid Modules Two modules, normal and alternate mounted in each wing forward of the main gear support beam and outboard of the gear trunnion door. Normal module has four control valves, four fuses, a shutoff valve assembly, two filters, a check valve and a restrictor. Each control valve controls the flow of metered brake pressure to a single brake. Alternate module has two control valves, two fuses, two filters and a check valve. Each control valve controls the flow of metered brake pressure to a pair of wheel brakes. The in-line fuses are quantity measuring fuses with a capacity of 60 cubic inches. Prevent loss of hydraulic fluid from a downstream rupture. Maintenance Operations Access to normal anti-skid valve module is through wing trailing edge inboard lower surface skin panel 551 SB forward of main gear support beam and outboard of gear trunnion door. Access to alternate anti-skid valve module is through wing trailing edge inboard lower surface door panel 552 BB forward of spoiler support beam. Control valves, fuses, filters and shutoff valves are line replaceable. Fuses are manually re-settable by rotating the reset knob. This equalizes the pressure on both sides of fuse and allows the fuse to reset. When the reset knob is released, a spring forces the knob back to normal position.

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SHUTTLE VALVE MODULE

MAINTENANCE TIP

Module

Dispatch pin can be found in the MLG pin pouch.

Two identical modules, one located immediately below the anti-skid valve module on each side of airplane are installed. Panel 551 SB provides access to the module. Each module contains four shuttle valves and four filters, one for each brake. The inputs come from the four normal anti-skid valves and the two alternate anti-skid valves. The output is to each brake. The shuttle valve responds to the highest input pressure and ports that pressure through a filter to an individual brake. The shuttle valve operates on a 30-70 psid. A replaceable 117-micron filter, in each brake line, filters the fluid returning to the anti-skid valves from the brakes.

Flight Dispatch Plug The flight dispatch plug can be used in the event of a malfunctioning normal anti-skid valve or wheel speed transducer to hydraulically disable the normal brake system input to a brake. The alternate brake system still brakes the wheel on gear retraction so the plug cannot be used for a hydraulic brake leak. The cap on the shuttle valve is removed to install the flight dispatch plug which positions the valve to block the normal brake port and open the alternate brake port. The flight dispatch plug is equipped with a ring to allow an indicator tag to be attached while installed. Only one plug is authorized for dispatch with seven brakes operating during normal brake system operation and all brakes operating during gear retraction.

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AUTOBRAKE GENERAL Purpose The autobrake system provides automatic brake application upon landing. The deceleration rate of the airplane is monitored by the Anti-skid/Autobrake Control Unit. Normal system brake pressure is applied to the brakes in order to obtain the crew selected deceleration. The system also provides for autobrake application to stop the airplane during a rejected takeoff. Selector Switch The autobrake selector switch, located on the P1-3 panel, controls the electrical power supply to the autobrake microprocessor card of the anti-skid/autobrake control unit. The switch allows the selection of five increasing deceleration rates and the rejected takeoff function (RTO). When the autobrake arming requirements are met, a solenoid located behind the switch panel energizes and latches the switch in the selected position. When the autobrake function is lost, the solenoid de-energizes and the switch is spring-returned to the disarm position. In the disarm position, the AUTOBRAKES amber light located on the switch panel illuminates and the level C message AUTOBRAKES appears on EICAS. When the rejected takeoff arming requirements are met, the selector switch is latched in the RTO position. Upon takeoff, the switch is spring-returned to the OFF position. If the autobrake function is lost when RTO brakes are applied, the switch remains in the RTO position and the amber light AUTOBRAKES illuminates with the EICAS level C message AUTOBRAKES. Input Signals Air/ground relays, controlled by the main gear truck tilt, input the ground mode to the autobrake card. The ground signals are used for arming and application of autobrake. The left and center ADIRU input through a switching system to the autobrake card and provide ground speed and deceleration signals. The speedbrake handle position switch provides a signal to disarm the autobrake card when the handle is stowed after deployment.

Thrust lever position switches provide signals to the autobrake card when the thrust levers are in the retarded position. The signals are used for arming and activation of the autobrake system. Brake metered pressures applied by pilot command of the brake pedals are monitored by brake pressure switches. The signals are used for disarming the autobrake when pedal pressure is applied.

Antiskid/Autobrake Control Unit Wheel speed signals are provided by the anti-skid cards to the autobrake card for determining wheel spinup upon landing. When arming and application requirements are met, the autobrake card outputs electrical signals to the solenoid valve and the electro-hydraulic servo valve of the control module. The BITE card performs self tests and provides fault identification to the display card. Fault information signals are also provided to the EICAS computers for storage and annunciation. Autobrake Control Module The autobrake control module meters right hydraulic system pressure to the brakes in response to the electrical command signals of the autobrake card. The module includes a solenoid valve, an electro-hydraulic servo valve and monitoring pressure switches.

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AUTOBRAKE INPUTS

Air/Ground Sensing Inputs

Thrust Lever Position Switches

Two independent air/ground system inputs are sensed by the autobrake and monitor/BITES subsystems. Proximity switches sense the tilt position of the left and right main landing gear truck beams and provide air/ground mode signals through the PSEU and associated relays.

Two micro-switches on each thrust lever provide lever position. The switches are installed in the auto-throttle switch pack located beneath the thrust lever quadrant stand. Access is through the door forward of the nose wheel well. The switches are rigged to open when the lever is 4.5° from idle when advancing. The normally open contact on the switch ensures that any failure that releases the switch will result in a thrust lever advanced indication. One switch per thrust lever is supplied with 28 volt dc power: the powered switch on the left thrust lever controls power to the solenoid valve and the powered switch on the right thrust lever controls power to the valve control relay. This interlocking prevents application of brake pressure with either thrust lever advanced regardless of any control unit failure. The other switch on each thrust lever senses ground when the thrust lever is fully retarded. The continuous checking of the switches' condition by sensing power in one switch and ground in the other within the logic circuitry provides for protection in case of massive short to power or to ground - for example: If all four switches were grounded by water or heavy moisture, the logic circuitry would detect a contradicting and faulty condition of the switch and interpret it as thrust lever advanced. Speed Brake Handle Switch A micro-switch is installed on the speedbrake lever mechanism in the quadrant stand. Access is through the left side of the quadrant stand. The switch is opened when the speedbrake handle is near the fully extended position. The autobrake system disarms if the speed brakes are extended then stowed while on the ground.

Pressure Switches Metered pressure switches are installed on the left and right autobrake shuttle valves in the left and right wheel wells, respectively. The switches monitor pilot's left and right metered brake pressure, and are used to disarm the autobrakes when metered pressure application is detected. Switches actuate between 450 and 550 psi and de-actuate at a minimum of 200 psi and 50 psi less than the actuating pressure. Autobrake Control Switch An eight-position control switch mounted on the P1-3 panel provides the power and deceleration selection functions for the landing autobrakes and RTO autobrakes. The control unit also contains an amber warning light indicating loss of autobrake function.

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ANTI-SKID / AUTOBRAKE BUILT IN TEST EQUIPMENT (BITE)

Display Test

General

Moving the toggle switch to PRESS/TEST position will initiate the display test. The caution warning light (P-5) and EICAS advisory messages will be displayed and all 8 segments of the alphanumeric display will illuminate on the control unit. EICAS messages displayed:

The monitor/BITE subsystem card in the control unit contains the BITE to perform self-test and fault isolation of the anti-skid and autobrake systems without removal from airplane and without additional test equipment. BITE functions isolate failures to the line replaceable unit (LRU) and to the individual card level within the control unit. Intermittent faults are stored in memory for later recall. Failures are displayed in alphanumeric format on the front of the control unit. Module Module is mounted in the E1-1 rack in the aft equipment center. The 4 anti-skid cards, 1 autobrake card, monitor/BITE card, and interface/display card may be replaced through the top of the module.

• Anti-skid off (advisory) • Autobrake (advisory) • Anti-skid/autobrake (S,M) Memory Recall Moving the toggle switch to the BIT position will recall and display faults stored during continuous monitoring of the anti-skid/autobrake system. Successive faults are displayed by depressing the BIT toggle down until the message TEST END is displayed. Each message displayed for 45 seconds or until BIT button is depressed again. Faults are recalled on a first in - first out basis. Reset (Memory Clear)

BITE Functions The tests are conducted by use of switches on the front of the module. Abbreviated instruction for test procedures are contained on a placard on the front of the module. The following tests may be performed: • • • • • • • •

Display test BIT memory (recall) test System test Anti-skid brake operational test Autobrake test Configuration identification test Reset (memory clear) RTO (OPT) brake test

This switch causes erasure of failures currently stored in the failure storage memory. When this function is invoked, the BITE first scans the storage memory until it finds an active fault. The BITE then checks the present status of the identified LRU and if the status indicates good LRU, the fault is erased from the failure storage memory. Next, the memory is scanned again, and the process is repeated for all possible faults. When completed, message MEM CLR is displayed for 2 seconds. Disable Function The fault indication may be deactivated for one wheel by using the rotary switch to make the wheel selection. This removes the selected wheel from the fault annunciation circuitry to the amber anti-skid light and the EICAS display. This function is used when a single normal anti-skid valve system has malfunctioned and is disabled by using a flight dispatch plug to block the affected valve output. Faults occurring on other wheels will continue to be displayed. The disabled wheel fault will be identified on the EICAS maintenance page (Anti-skid/ Autobrake S,M).

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