citation mustang operating manual chapter · pdf filerelease and pneumatic system provide for...

GENERALThe Citation Mustang has retractable tricyclelanding gear that is electrically controlled andhydraulically actuated. Each gear is retractedby its own hydraulic actuator. When retracted,the nose gear and the struts of the main gearare enclosed by mechanically actuated doorsconnected to the gear struts. The trailing-linkmain gear wheels remain uncovered in thewheel wells. Gear position and warning areprovided by colored indicator lights and anaural warning.

In the event of hydraulic gear extension sys-tem failure, an independent mechanical uplockrelease and pneumatic system provide foremergency gear extension.

Nosewheel steering is mechanically actuatedthrough linkage from the rudder pedals. A fric-tion shimmy damper is contained within thenose gear strut. A bungee allows tighter turnswith differential power and braking. The aircraftis towed by connections on the nosewheel strut.

INTRODUCTIONThis chapter describes the landing gear, nosewheel steering, and brake system of theCitation Mustang.

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CITATION MUSTANG OPERATING MANUAL

CHAPTER 14LANDING GEAR AND BRAKES

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Power braking (hydraulically actuated) is pro-vided with or without antiskid protection. A“touchdown protection” feature is provided toprevent landing with brakes locked. A spin-down feature stops tires from spinning beforeretracting into the wheel wells. In the event ofa hydraulic brake system failure, an independ-ent pneumatic system provides for emergencybraking. A parking brake system is availableto temporarily lock the brakes on the ground.

Crew alerting system (CAS) messages report thestatus of the braking and hydraulic systems andrelated systems. The rotary test switch tests allindications of the landing gear and brakes.

LANDING GEAR

DESCRIPTIONThe main landing gear struts are trailing-linkstruts, supporting the wheels with a trunnionand air-oil (oleo) strut, connected by a trail-ing link (Figure 14-1). The nose landing gearstrut is a conventional air-oil (oleo) strut ex-tending from the trunnion (Figure 14-2).

Normally, the landing gear is hydraulicallyactuated, but if the normal gear actuation sys-tem fails, the gear can be mechanically andpneumatically released and extended. At air-speeds up to 250 KIAS, the gear can be ex-tended (VLO). The aircraft can be flown withthe gear extended at airspeeds up to 250 KIAS(VLE). However, the gear cannot be retractedwhen the airspeed is above 185 KIAS.

It takes 6 seconds to extend the landing gear.At airspeeds between 100 and 160 KIAS, ittakes 11–14 seconds to retract the landinggear. At airspeeds between 160 and185 KIAS,retraction takes 18–20 seconds.

Each inboard-retracting main gear uses two hy-draulic actuators (one for uplock release and onefor gear actuation). Three more hydraulic actu-ators perform these duties for the forward-re-tracting nose gear. An electrically positionedgear-control valve directs hydraulic pressure


Figure 14-1. Left Main Landing Gear and Door

Figure 14-2. Nose Landing Gear and Doors

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for gear extension or retraction. If hydraulicextension fails, the emergency gear T-handle al-lows the landing gear to mechanically releaseand free fall. A bottle of compressed nitrogen,activated by the knob behind the T-handle, pro-vides pressure to ensure gear extension anddownlock (Figure 14-3).

Main Gear SystemMain Gear Extension SystemFigure 14-4 displays the landing gear actu-ation during gear extension.

Uplocks

The main landing gear struts are mechanicallylocked in the retracted position by a spring-loaded, hydraulically released uplock hook.

In normal operation, to release a strut from itsuplock, the gear-control solenoid valve routesfluid to the uplock hook actuator, retracting thepiston into the actuator. When the piston re-tracts completely, it pulls the uplock hook

free of the uplock roller, and the gear strut isunlocked to start extension.

Extension

When the uplock actuator is fully retracted,fluid passes through the uplock actuator to thegear-extend side of the gear actuator. Hydraulicpressure is then applied to the actuators, whichextend until the gear is down- and-locked. Tospeed gear extension and improve free-fall ca-pability of the gear, a regenerative shuttle valveallows fluid to flow from the retract side of theactuators to the extend side.

Abnormal Main Gear ExtensionSystemTwo backup gear-extension systems are pro-vided in addition to normal gear extension:

• The T-handle operates a cable system tomechanically release the uplock hooksfrom the struts. The gear should free-fallinto position, aided by the pilot yawingthe aircraft.

NOTEIt may require an acceleration above150 KIAS to lock the nose landinggear into place.

• The round knob behind the T-handle re-leases pneumatic pressure (high-pres-sure nitrogen) from a bottle in the nosecompartment to pneumatically operatethe uplock actuators and release the up-lock hooks, then extend the gear actua-tors, which extend the gear.

Figure 14-5 displays the landing gear actuationduring abnormal/emergency extension. Oncethe uplock hooks are released, the pneumaticpressure is applied to ensure that the gear ac-tuators properly extend and lock the gear.Without using the pneumatic gear-extensionsystem, it is still possible to lock the gear downby yawing the aircraft to force the gear into po-sition. However, mechanical release and down-lock shou ld a lways be fo l lowed by thepneumatic extension procedure to ensure com-plete and proper extension of the gear.

Figure 14-3. Emergency Gear ReleaseHandle (Cover Removed)

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Main Gear Downlock MechanismEach main gear has a mechanical downlockmechanism (integral to the gear actuator),which locks the main landing gear in the downposition.

Applying hydraulic pressure is the only wayto release the downlocks; therefore, no blocksor external downlock pins are required.

Main Gear Retraction SystemFigure 14-6 shows landing gear actuation dur-ing retraction. The main gear retracts when hy-draulic pressure is applied to the retract sideof the actuators. This first releases the down-locks, then forces the actuators to retract,pulling the gear into the wheel wells. Beforethe wheels enter the wheel wells, an auto-matic braking feature (spindown) stops thewheels from spinning to prevent loose wheeltread or debris from striking the interior of thewheel well. When the gear is fully retractedinto the uplocks, a switch in each uplock de-tects that the main gear is up-and-locked.

Nose Gear SystemNose Gear Extension SystemNose gear extension is similar to the mainlanding gear. In the wheel well, the uplockhook is hydraulically retracted, releasing theuplock roller on the gear. The nosewheel ro-tates down and aft from the nose wheel well.The nose gear is mechanically locked in theextended position by a spring-actuated down-lock. A position switch on the drag brace in-dicates down-and-locked.

Whenever the nosewheel is extended, nose-wheel steering is engaged, regardless of whetherthe aircraft is in flight or on the ground.

Nose Gear Retraction SystemDuring nose gear retraction, a hydraulic actu-ator releases the nose gear downlock. The nosegear actuator extends, causing the nose gear toretract forward into the nosewheel well.

On takeoff, with weight off wheels, the nose-wheel steering remains engaged until retrac-tion. During retraction, nosegear steering isdisengaged and the nose gear is mechani-cally centered. In the wheel well, a spring-loaded mechanical uplock hook catches theuplock roller on the gear when it retracts. Aposition-sensor switch in the uplock indi-cates up-and-locked.

Nose Gear Door SystemNose gear movement actuates two doors to com-pletely enclose the nose gear and wheel at re-traction. The doors open during gear extensionand remain open after the gear is extended.

COMPONENTS

Main GearEach main gear assembly inc ludes (seeFigure 14-1):

• Trunnion

• Trailing link

• Oleo strut

• Main gea r ac tua to r s wi th in tegra ldownlocks

• Uplock assembly

• Main wheel tire and brake assembly

• Squat switch

TrunnionA trunnion is the main support (leg) for eachmain gear. It connects to the wheel through theoleo strut and the trailing link and is extendedor retracted by the main gear actuator. Duringextension, the trunnion (with the main gearcomponents attached) rotates down-and-out-board on pivots attached to the forward and aftwing spars.

Trailing LinkThe trailing link connects the trunnion to thewheel through a pivot and an oleo strut. It al-lows the wheel to simultaneously move up andaft when landing or during ground operations.

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Oleo StrutThe oleo (air-oil) strut is a sealed hydraulic pis-ton and cylinder that uses compressed nitrogento absorb landing and taxiing shocks. It absorbsshocks between the trailing link (attached tothe wheel) and the trunnion (attached to the air-craft). On the ground, the oleo struts support theweight of the aircraft.

Main Gear ActuatorsInboard of (and attached to) each main geartrunnion is a fluid-driven actuator, which ex-tends or retracts the main landing gear. Themain gear actuators are normally driven hy-draulically but can be extended pneumaticallyfor emergency gear extension.

Each main landing gear actuator includes its ownintegral mechanical locking system to lock theactuator in place when it is fully extended,thereby locking the gear down. Hydraulic retrac-tion pressure retracts the locking system and per-mits gear retraction.

Uplock AssemblyIn each wheel well, a spring-loaded mechani-cal uplock hook catches the uplock roller on thegear when it retracts. (During preflight, checkthat the rollers rotate.) This locks the gear in theup position. A switch in the uplock assembly de-tects when the trunnion uplock roller is in thelock (gear is up-and-locked). At the start ofgear extension, a hydraulic uplock-sequencingvalve/actuator unit retracts the uplock hook,releasing the main landing gear, then passeshydraulic fluid to the gear actuator. In case ofan emergency gear extension, pressurized nitro-gen gas retracts the uplock hook.

Main Wheel, Tire, and WheelAssemblyEach main gear assembly includes a singlewheel with tire and a fluid-actuated multiple-disc brake assembly. Each main wheel has threefusible plugs that melt to deflate the tire if ex-cessive temperature is generated by an over-heated brake. Inflate with dry nitrogen to 85 ±5 psi (586 KPa ± 34 KPa) unloaded. Maximumtire ground speed is 160 knots.

Squat SwitchA squat switch on the bottom of each trunniondetects whether or not the aircraf t is onground/weight -on-wheels (WOW) or inflight/weight-off-wheels. The squat switch pro-vides this information to aircraft systems thatuse this information (including engine/FADEC,windshield anti-ice, pressurization, landinggear control, antiskid braking, power distribu-tion, and air conditioning). Refer to Chapter17—“Miscellaneous” for more informationabout squat switches.

If the left and right squat switches have dif-ferent WOW signal indications for longer than2 seconds, the amber WOW MISCOMPAREmessage appears. This advises that any aircraftsystems relying on WOW signals may be in-operative or may operate unpredictably.

Main Gear Door and FairingEach main landing gear strut has a gear doormechanically attached to the trunnion assem-bly of the gear. When the gear is operated, thedoor moves up and down with the gear itselfand is not separate from the gear in its oper-ation. The door will cover the gear strut but thetire is partially exposed.

Nose GearThe nose gear assembly supports the nose sec-tion of the aircraft while on the ground and pro-vides steering and a linkage for towing. Thenose gear assembly (see Figure 14-2) includes:

• Strut

• Shimmy damper

• Drag brace and downlock

• Uplock assembly

• Gear actuator

• Single wheel and tire assembly

StrutThe nose gear strut includes the trunnion (at-tached to pivots and moved by the gear actuator), the shock strut, and the nosewheel

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fork. The integral oleo (air-oil) shock strut ab-sorbs landing impact and other shocks. Thelower end of the shock strut attaches to thenosewheel fork, which holds the nosewheelassembly.

A folding torque link holds the shock strut cylin-der and nosewheel fork piston together andkeeps them aligned with each other.

Shimmy DamperTo reduce nose gear shimmy during takeoff,landing, and taxiing, the nose gear has ashimmy damper. It is a friction band aroundthe center of the shock strut cylinder. It rubsagainst the inside of the trunnion using fric-tion to reduce nosewheel shimmy.

Drag Brace and DownlockIn the down (gear-extended) position, the gearis mechanically locked down by an integral lock-ing mechanism in the drag brace. A positionswitch on the drag brace signals when the nosegear is down-and-locked. During extension, thedownlock is spring-actuated to lock mechani-cally. During retraction, the downlock is re-leased by a hydraulic actuator on the drag brace.

Uplock AssemblyA mechanical latching system (uplock hook)similar to the main gear system is attached tothe airframe in the nose wheel well. It locksthe nose gear in the up (gear-retracted) posi-t i on . Dur ing gea r ex t ens ion , a f l u idactuator/valve unit releases the hook and thenpasses hydraulic fluid (or pressurized nitro-gen in an emergency) to the gear actuator. Ongear retraction, the uplock latch catches aroller on the rising nosewheel fork to lock thegear in the up position. (During preflight,check that the roller rotates.) A switch in theuplock hook mechanism detects whether or notthe gear is up-and-locked.

Gear ActuatorThe fluid-driven nose gear actuator retracts toextend the nose gear. It also triggers nose geardoor operation through linkages.

Single Wheel and Tire AssemblyThe nosewheel assembly includes a wheel andtire. The nose gear tire has chines to deflectwater and slush. The tire must be inflated to120 ± 5 psi or 827 KPa (± 34 KPa). Maximumtire limit speed is 160 knots.

Gear Control Solenoid ValveThe gear control solenoid valve regulates theflow of hydraulic fluid to the gear actuators, up-lock-release actuators, and nose gear down-lock-release actuator. It is an electrically drivensolenoid valve, actuated by two opposing sole-noids that respond to electrical commands fromthe LANDING GEAR handle.

When the LANDING GEAR handle is com-manded DOWN, the gear-extend solenoid onthe valve moves the valve to the gear-extendposition, routing fluid pressure to the uplock-release actuators and then to the gear-extendside of the gear actuators (see Figure 14-4).

When the LANDING GEAR handle is com-manded UP, the gear-retract solenoid on thevalve moves the valve to the gear-retract posi-tion, which routes fluid to the nose gear down-lock release actuator and the gear-retract sideof all three gear actuators (see Figure 14-6).

Without DC power, the valve centers, releas-ing pressure from the gear-extend side of thesystem. This permits emergency extension ofthe gear using mechanical and pneumatic ac-tuation (see Figure 14-5). DC power can be dis-connected from the gear control solenoid valveby pulling the LDG GEAR CONTROL cir-cuit breaker on the SYSTEMS panel of theleft CB panel.

CONTROLS AND INDICATIONS

LANDING GEAR ControlHandleThe LANDING GEAR control handle is onthe left side of the center tilt panel (Figure14-7) and controls the normal landing gear re-traction and extension procedure. The handle

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actuates switches to complete circuits to theextend or retract side of the gear control so-lenoid valve. The gear handle must be pulledout of a detent prior to movement to either theGEAR UP or GEAR DOWN position.

On the ground, to keep the gear handle in theGEAR DOWN position, the left and right maingear squat switch deenergizes a locking-sole-noid in the instrument panel to extend a spring-

loaded plunger into the gear handle path. Thisprevents inadvertent movement of the handleto the GEAR UP position (Figure 14-8).

Airborne, with the left and right main gearsquat switches in the in-flight position, thelanding gear handle locking solenoid ener-gizes to retract the plunger. This frees thehandle for movement to the GEAR UP posi-tion. This safety feature cannot be overrid-den. If the solenoid fails or electrical poweris lost, the gear handle cannot be moved tothe GEAR UP position.

When the gear handle is up, if the locking-so-lenoid plunger deenergizes and extends (dueto DC power failure or another cause), theplunger does not prevent moving the gear han-dle to the down position.

Never attempt to pull the gear handle up dur-ing taxi.

Before energizing the aircraft electrical system,ensure that the gear handle is in the down po-sition to prevent inadvertent gear retraction.

In particular, if the squat switches do not agree(as indicated on the EICAS by an amber WOWMISCOMPARE message), it is possible toraise the gear handle, possibly resulting ingear retraction on the ground.

Circuit BreakersCircuit breakers provide protection for thecomponents and wiring of the landing gearsystem. Specific components are:

• LH ELE #1

° HYD PUMP 2

° LDG GEAR CTL 2

• LH ELE EMERG

° LDG GEAR MONITOR 2

Gear Position IndicatorsOne red and three green position indicatorson the landing gear control panel providegear position indication. In addition, an aural

PLUNGER

RETRACTSWITCH

EXTENDSWITCH

LOCKINGSOLENOID

FWD

Figure 14-8. Landing Gear HandleLocking Solenoid andSwitches

Figure 14-7. Landing Gear Control Panel

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warning sounds if gear is up when the com-bination of throttle position, flap position, andairspeed indicate landing configuration.

The green NOSE–LH–RH lights on the LDGGEAR control panel indicate gear down andlocked. As each gear locks down, its respec-tive green light illuminates.

The red landing gear UNLOCK light indicatesan unsafe gear condition. It illuminates whenthe gear handle is moved out of GEAR UP de-tent and remains on until all three gear aredown and locked. At retraction, the light illu-minates when the gear handle is moved out ofthe down position and remains visible until allthree gear are up and locked.

Normal indication with the gear down is threegreen lights visible. With the gear retracted,all lights extinguish and the red UNLOCKlight extinguishes.

Figure 14-9 shows indicator displays for var-ious gear positions. Test the landing gear in-dicator lights and warning horn by positioningthe rotary TEST knob to LANDING GEAR.

CAS MessagesHYD PRESS LOThe amber HYD PRESS LO message indi-cates low hydraulic system pressure. Duringextension, if this message appears and gear isnot indicating down and locked within 6 sec-onds, refer to the checklist for landing gearemergency extension. This message also in-dicates the need to prepare for emergencybraking. Refer to the “Brakes” section of thischapter. For more informat ion , refer toChapter 13—“Hydraulic System.”

HYD PUMP ONThe amber HYD PUMP ON message indicatesthat the hydraulic pump has been operatingfor more than a minute. See the Airplane FlightManual (AFM) procedure for responding tothis message, and prepare for emergency land-ing gear extension. This message also indi-

cates the need to prepare for emergency brak-ing. Refer to the “Brakes” section of this chap-ter. For more information, refer to Chapter13—“Hydraulic System.”

Aural WarningThe warning/caution advisory system pro-vides a landing gear aural warning if one ormore gear are not locked down and either ofthe following situations occurs:

• One or both throttles are retarded belowapproximately 85% N2 and airspeed isbelow 130 KIAS. Pressing the HORN SI-LENCE–PUSH button on the gear con-trol panel (see Figure 14-7) silences thiswarning.

• Flaps are extended beyond the TAKEOFF AND APPROACH setting. In thissituation, the aural warning cannot be si-lenced wi th the HORN SILENCE–PUSH button.

Aural warning is DC-powered. Circuit protec-tion for the aural warning system and positionlights is on the right CB panel labeled WARNLIGHT within the lights grouping.

Rotary TEST KnobThe rotary TEST knob is at the top of the copi-lot panel. This knob is used to test the land-ing gear and antiskid warning systems.

OPERATION

PreflightDuring preflight, inspect the pressure gaugefor the emergency landing gear extensionpneumatic bottle. It is in the nose baggagecompartment, on the right side of the aft wall.Determine the current temperature, and thencompare the gauge pressure indication to thepressures listed on the placard next to thegauge to determine if the pneumatic pressureis appropriate.


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DOWN AND LOCKED UP AND LOCKED

NOSE GEAR NOTDOWN AND LOCKED

ONE OR MORE GEAR NOTUP AND LOCKED

Figure 14-9. Landing Gear Position Indications

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Retraction and ExtensionMoving the LANDING GEAR handle to theGEAR DOWN position energizes the gearcontrol solenoid valve. The DC power for thelanding gear control circuit is from the left busthrough the LDG GEAR CONTROL circuitbreaker in the SYSTEMS section of the pilotCB panel.

RetractionPlacing the LANDING GEAR handle in theGEAR UP position energizes the retract sole-noid of the gear control valve. The gear con-trol valve is positioned to direct pressure to:

• The nose gear downlock-release actua-tor to release the nose gear downlock

• The gear-retract side of each gear actu-ator (also releases downlocks inside themain gear actuators)

• The extend side of the uplock actuators,which position the uplock hooks to catchthe rising gear

All downlocks are released and retraction be-gins (see Figure 14-6).

As each gear reaches the fully retracted posi-tion, a spring-loaded uplock hook catches it andan uplock microswitch actuates. When all threeuplock microswitches actuate, the gear controlsolenoid valve circuit is interrupted and thevalve returns to the neutral position. All posi-tion indicators on the control panel extinguish.

ExtensionPlacing the landing gear handle in the GEARDOWN position energizes the gear controlsolenoid valve to the extend position. The gearcontrol solenoid valve is positioned to routepressure to the uplock actuators, which re-leases the gear uplocks (see Figure 14-4).

When the spring-loaded uplocks release, pres-sure continues to the gear-extend side of the gearactuators. As each gear reaches the fully ex-tended position, a downlock microswitch ac-tuates. When all three downlock switchesactuate, the gear control solenoid valve circuit

is interrupted and the valve returns to the neu-tral position. With pressure no longer appliedto the gear actuator, three actions occur:

1. The internal locking mechanism withineach main gear actuator assumes thedownlocked position.

2. The spring-loaded nose gear mechani-cal downlock latches.

3. Downlock switches illuminate the greenNOSE–LH–RH position indicators onthe gear control panel.

EMERGENCY/ABNORMALFor specific information on the emergency/ab-normal procedures, refer to the appropriateFAA-approved abbreviated checklist or theAFM.

NOSEWHEEL STEERING

DESCRIPTION ANDOPERATIONMechanical linkage from the rudder pedalsmechanically actuates the nosewheel steer-ing system (Figure 14-10).

Whenever the nosewheel is extended, nose-wheel s teer ing is engaged regardless ofwhether the aircraft is in flight or on theground. During retraction, nosewheel steer-ing is disengaged and the nose gear is me-chanically centered.

Rudder pedals mechanically steer the nosegear to 20° either side of center. A springlinkage provides an additional 55° of nose-wheel deflection (±75° total) via casteringaccomplished with application of differen-tial engine power or braking.

For towing, ensure that the rudder (gust)lock is disengaged and do not exceed 75°nosewheel deflection. If 75° is exceeded,the steering system or airframe structure will

510OM-0014-14

be damaged. If the rudder (gust) lock is en-gaged, towing beyond 55° may cause struc-tural and/or steering system damage.

During preflight, check that the stop bolts arepresent and intact (Figure 14-11). If they areno t , t he s t e e r i ng sy s t em i s damaged .Maintenance is required before flight.

If damage to nosewheel steering issuspected or crewmembers detect ab-normal steering system action, do notattempt to fly the aircraft. If the sys-tem is damaged, the crew does nothave full steering control of the air-craft on takeoff or landing. If the air-craft flies, even if the gear remainsextended after takeoff, the nosewheelmay not remain centered, and maynot be controllable.

Anytime the gear is extended, thenosewheel deflects with rudder pedalmovement. During a crosswind land-ing, center the pedals immediatelybefore nosewheel touchdown.

BRAKES

DESCRIPTIONDisc brakes are on the main gear assemblies.The aircraft hydraulic system provides normalpower braking with a pneumatic (pressurizednitrogen) system for backup (Figure 14-12). Thehydraulic system automatically maintains con-stant pressure for brake operation.

The brakes are normally used as antiskid powerbrakes but can operate as power brakes with-out antiskid protection. In the event that brakesystem hydraulic pressure is lost, emergencybraking is available.

The crew initiates braking by pressing on thetops of the rudder pedals. The pedals connectby cables to actuate the brake metering valve.If both the pilot and copilot apply brakes si-multaneously, the one applying the greaterforce on the rudder pedals has control.

CAUTION

WARNING


CENTERINGFITTING

STEERINGOUTPUT

LEVERBUNGEESPRING

STEERINGPIN

Figure 14-10. Nosewheel Steering

STOP BOLTS

Figure 14-11. Stop Bolt Location

510OM-00 14-15


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510OM-0014-16


Antiskid SystemWith the ANTI SKID switch in the up (on) po-sition, the antiskid system provides maximumbraking efficiency on all runway surfaces. Theantiskid control system can only reduce pres-sure; the applied pressure can never be morethan that commanded by the crew.

A wheel speed transducer on each wheel elec-tronically transmits wheel-speed signals tothe antiskid control box as a variable fre-quency. If the control box detects sudden de-celeration of a wheel (impending skid) itcommands the antiskid valve to reduce pres-sure to that specific wheel/brake. When theslow wheel catches up to the fast wheel andthe transducer signal returns to normal, brak-ing pressure is restored to the brakes.

The antiskid system includes “touchdown pro-tection,” which prevents landing with thebrakes locked. Any time both squat switchesindicate that the aircraft is in the air and thegear is extended, the antiskid unit dumps brakepressure (except during gear retraction whenbraking is applied to spindown the wheels).Upon landing, this dump continues for 3 sec-onds after weight-on-wheels or until wheelspinup (whichever occurs first), before brakepressure is enabled.

During high-speed ground movement, “locked-wheel crossover protection” prevents suddenyawing due to differential braking. If the an-tiskid controller senses a 70% difference inspeed between left and right brakes, it reducesbrake pressure to both wheels. At low speeds(approximately 12 knots), this feature is dis-abled to permit tight turns during taxiing.

Parking BrakesParking brakes are a locked configuration of thebrakes. Brakes are locked when the parkingbrake valve traps hydraulic fluid in the brakelines. The valve (and hence the parking brakes)can only be set by pulling on the PARKINGBRAKE knob on the right lower side of thepilot instrument panel (Figure 14-13) whilepressing on the brake pedals.

Emergency BrakesIf the hydraulic brake system fails, a pneumaticbrake system is available to actuate the wheelbrakes (Figure 14-14). The system uses nitro-gen pressure from a pneumatic bottle independ-ent of emergency landing gear extension system.

Pulling on the EMERGENCY BRAKE handle(under the center of the pilot left tilt panel) ac-tuates the emergency brake system. Pull outand hold the handle aft to apply and modulateemergency braking pressure. The lever has a stopto prevent locking the brakes and blowing thetires. The emergency brakes are effective for sixpulls on the handle. No electrical power is re-quired for the emergency brakes.

COMPONENTS

Brake PedalsBrakes are normally actuated by the pilot orcopilot pressing on the tops of one or moreof the rudder pedals. Each pedal is mechan-ically linked to the brake metering valve andto the corresponding pedal. Both pilot andcopilot foot forces are transmitted to thebrake metering valve by cables. For eachwheel, the pilot applying the greater force tothe corresponding pedal determines brake

Figure 14-13. PARKING BRAKE Knob

510OM-00 14-17

pressure to that wheel, and the position of thecorresponding pedal for the other pilot. Thepilot and copilot pedals move together.

Brake Metering ValveThe brake metering valve regulates left orright brake pressure according to brake pedalinputs as commanded by the crew.

Wheel Speed TransducersOne transducer is in each main gear axle. Adrive clip on the wheel hubcap spins the innerrotor of the transducer. Wheel speed data isprovided directly to the antiskid control unit.

Antiskid Control ValveTo prevent skids, the antiskid control valve reg-ulates the distribution of brake pressure, as re-quired to prevent the skid. The antiskid controlvalve is electrically controlled by the ASCU.

Antiskid Control UnitA digital ASCU monitors wheel speed to pro-vide wheel skid protection and optimum brak-ing efficiency on all runway surfaces. Basedon wheel speed inputs, the control unit reducesbrake pressure as required to prevent the skid.

Parking Brake ValveThe parking brake valve is in the brake linesbetween the antiskid control valve and thebrake assemblies. When a crewmember pullsthe PARKING BRAKE knob and depressesthe brake pedals, the valve engages checkvalves to trap brake fluid pressure in the brakelines. To relieve pressure due to fluid expan-sion when the parking brake is engaged shortlyafter heavy braking, 1,200-psi thermal reliefvalves are in the parking brake valve.


POWER BRAKE SYSTEM

SHUTTLE VALVE SHUTTLE VALVE

EMERGENCYBRAKE VALVE

EMERGENCY BRAKENITROGEN BOTTLE

LEGENDNITROGEN PRESSURE

METERED BRAKE FLUID

MECHANICAL

OVERBOARDVENT LINE

Figure 14-14. Emergency Brake System

510OM-0014-18


Emergency Brake ValveThe emergency brake valve is lever operatedto provide metered pneumatic pressure fromthe emergency nitrogen bottle directly to thebrake assemblies. The emergency brake valveconnects through a cable to the emergencybrake lever, which is under the instrumentpanel near the right knee of the pilot.

Brakes and Shuttle ValvesDisc brakes are in each main gear assembly.The brakes respond to hydraulic or pneumaticpressure. Normally, fluid from the brake meter-ing valve hydraulically actuates the left andright brakes separately as commanded by thecrew and/or the antiskid control unit. However,a shuttle valve at each brake allows high-pres-sure nitrogen from the emergency brake valveto bypass hydraulic flow and apply pressure di-rectly to both brakes evenly.

CONTROLS AND INDICATIONS

ANTI SKID SwitchThe ANTI SKID switch (see Figure 14-12) ison the LANDING GEAR control panel and isnormally in the up (on) position. In the OFF(down) position, the antiskid system deacti-vates; brake operation remains the same ex-cept that antiskid protection is not available.Before turning the antiskid system off, en-sure that brake pressure is released. Beforeturning the antiskid system on, ensure thatthe wheels are not rotating.

Circuit BreakersThe power brake and antiskid systems receiveDC power from the left electrical bus.

The HYD PUMP circuit breaker is in the SYS-TEM section of the left CB panel. Disengagingthe HYD PUMP circuit breaker electricallydisables the hydraulic pump. This action re-duces or eliminates hydraulic system pressure.This results in limited or improper function-ing of the power brake system or completelyeliminates the power brake system.

The SKID CONTROL circuit breaker is alsoin the SYSTEM section of the left CB panel.Disengaging the SKID CONTROL circuitbreaker disables the antiskid system and touch-down protection.

CAS MessagesANTISKID FAILIf a fault develops in the antiskid system, theamber ANTISKID FAIL message appears, andthe system must be deactivated (select ANTI-SKID switch to OFF). When the message is vis-ible, leaving the antiskid system on can resultin unpredictable braking system performance.

The ANTISKID FAIL message indicates thatan internal test routine has failed or there areelectrical problems. Electrical problems mayinclude DC power that is off or below opera-tional levels, or shorts or opens in the antiskidsystem wiring.

This message also appears when the rotaryTEST knob is selected to ANTI SKID.

HYD PRESS LOWhen brake system pressure drops below op-erational levels, the amber HYD PRESS LOmessage appears. Use of the emergency brakesystem for braking is required after the land-ing gear is extended manually. The HYDPRESS LO message also incorporates a 15-sec-ond delay in flight.

HYD PUMP ONThe HYD PUMP ON message indicates thatthe hydraulic pump has been operating formore than a minute. See the AFM procedurefor responding to this message, and prepare touse the emergency brake handle for braking.(This message also indicates the need to pre-pare for emergency gear extension; refer to the“Landing Gear” section of this chapter). Formore information, refer to Chapter 13—“Hydraulic System.”

510OM-00 14-19


NO TIRE SPINDOWNTen seconds after gear retraction begins, ifeither tire is spinning above 10 knots, thewhite NO TIRE SPINDOWN message ap-pears, indicating failure of the tire spindownfunction of the antiskid system. This couldcause damage to the wheel wells from loosetire tread and debris.

This message also appears when the rotaryTEST knob is selected to ANTI SKID.

Rotary TEST KnobThe rotary TEST knob is at the top of the copi-lot panel. This knob tests the antiskid system.

OPERATION

Antiskid Touchdown ProtectionDuring landing, the antiskid system “touch-down protection” feature prevents the aircraftfrom touching down with locked brakes.Touchdown protection mode is active anytimeall three of the following conditions exist:

• The ANTI SKID switch is ON.

• Both squat switches indicate that theaircraft is in flight.

• The gear is extended.

Under these conditions (regardless of pilotor copilot pedal position), the touchdownprotection mode releases all brake pressurefrom the brakes.

To ensure adequate wheel spinup on contami-nated runways, the touchdown protection modestays active for 3 seconds after the first wheeltouches down (either left or right squat switchindicates weight-on-wheels).

Under normal conditions, the wheels spinupalmost immediately; therefore, a spinup over-ride feature is incorporated. Anytime wheelspeed is above 50 knots (regardless of squatswitch position), touchdown protection isoverridden and normal antiskid braking isavailable.

Power Braking (Antiskid ON)For normal operation of the power brake andantiskid system, all three of the followingconditions must exist:

• The ANTI SKID switch is up (on).

• Both wheels are rotating at aircraftgroundspeed.

• Either squat switch (left wheel or rightwheel) senses weight on wheel.

Maximum braking technique is obtained by:

1. Lowering the nose to the ground

2. Firmly applying and holding the brakesuntil the desired speed has been reached

3. Extending the speedbrakes while apply-ing the wheel brakes

NOTEDo not pump the brakes.

NOTEThe antiskid system is not operativeduring emergency braking.

Depressing the brake pedals moves cables at-tached to the power brake metering valve,which meters hydraulic pressure to the brakeassemblies in direct proportion to pedal force.

With the ANTI SKID switch on and a groundspeed of at least 12 knots, maximum brakingwith skid protection is available. Any ten-dency of a wheel to rapidly decelerate (skid)is detected by the wheel speed transducer, andthe antiskid control valve is signaled to mo-mentarily dump pressure from affected brakes.As wheel speed returns to normal, dumpingceases and pressure is once again increased inthe brake assemblies. When wheel speed dropsbelow approximately 12 knots, the antiskidfunction disengages.

510OM-0014-20

Braking on each main wheel is controlled bythe corresponding pedal; therefore, differen-tial braking is available.

Power Braking (Antiskid OFF)The ANTI SKID switch is normally in the up(on) position. In the OFF position, the antiskidsystem deactivates and the amber ANTISKIDFAIL message appears. The power brakes,powered by the hydraulic system, still func-tion without the assistance of the antiskid sys-tem. With the loss of the antiskid system,touchdown protection and tire spin-down areinoperable.

Parking BrakesTo set the parking brakes, apply the brakes inthe normal manner, then pull out the PARK-ING BRAKE knob (see Figure 14-13). Thismechanically actuates the parking brake valveand traps fluid in the brakes. To release theparking brakes, depress the brake pedals, thenpush in the PARKING BRAKE knob. One-way check valves allow setting increasedtrapped pressure once the brakes are set by sim-ply depressing the brake pedals harder.

Do not use parking brakes after using emer-gency brakes. Hold emergency brakes untilthe aircraft can be secured.

Parking brakes can hold the aircraft for onlya limited time. They are not intended to securean unattended aircraft. Parking brakes are atemporary function, to be used only until theaircraft can be secured.

NOTEIf brakes are suspected of being hot,do not set the parking brake.

Antiskid TestThe antiskid system is checked as part of thero t a ry t e s t p rocedu re i n t he Cockp i tPreparation checklist. This same test can beconducted in flight if a problem is suspected.

With the antiskid switch ON (up), the antiskidcontrol unit is continuously conducting in-tegrity checks of the system. If any faults aredetected, an amber ANTISKID FAIL messageappears in the CAS window.

To ground test the antiskid system:

• Rotate the rotary TEST knob to the ANTISKID test position.

• The ANTISKID FAIL and NO TIRESPINDOWN messages f l a sh fo r 6seconds.

• Test is valid if the ANTISKID FAIL andNO TIRE SPINDOWN messages areconfirmed extinguished after 6 seconds.

• Test is failed if the ANTISKID FAILand/or NO TIRE SPINDOWN messagesremain illuminated after more than 6seconds.

Emergency BrakesPulling the red EMERGENCY BRAKE han-dle aft actuates the emergency brake valvemechanically (see Figure 14-14). The valvemeters nitrogen pressure through shuttle valveson the brake assemblies in direct proportionto the amount of lever movement.

Since nitrogen pressure is applied to both brakessimultaneously, differential braking is not pos-sible. Returning the lever to its original positionreleases pressure from the brakes and vents itoverboard, which releases the brakes.

Apply the emergency brakes only enough toobtain the desired rate of deceleration, thenhold them until the aircraft stops.

Best performance can be obtained using asmooth, steady, continuous pull of the handleto obtain the desired deceleration rate. Multiplepulls and releases of the handle deplete the ni-trogen charge.

Do not depress the brake pedals while apply-ing emergency airbrakes. Shuttle valve actionmay deplete nitrogen pressure, reducing avail-able braking power.


510OM-00 14-21

Repeated applications deplete nitrogen pres-sure. If the emergency nitrogen bottle is full,six applications are available for emergencybraking.

Antiskid protection is not available duringemergency braking. Do not attempt to taxiafter clearing the runway when using the emer-gency brakes. Maintenance action is requiredsubsequent to emergency braking.

EMERGENCY/ABNORMALFor specific information on emergency/abnor-mal procedures, refer to the appropriate abbre-viated checklists or the FAA-approved AFM.


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