Chapter 14 Landing Gear and Brakes

CITATION MUSTANG OPERATING MANUAL CHAPTER 14 LANDING GEAR AND BRAKES

INTRODUCTION This chapter describes the landing gear, nosewheel steering, and brake system of the Citation Mustang.

GENERAL The Citation Mustang has retractable tricycle In the event of hydraulic gear extension sys- landing gear that is electrically controlled and tem failure, an independent mechanical uplock hydraulically actuated. Each gear is retracted release and pneumatic system provide for by its own hydraulic actuator. When retracted, emergency gear extension. the nose gear and the struts of the main gear are enclosed by mechanically actuated doors Nosewheel steering is mechanically actuated connected to the gear struts. The trailing-link through linkage from the rudder pedals. A fric- main gear wheels remain uncovered in the tion shimmy damper is contained within the wheel wells. Gear position and warning are nose gear strut. A bungee allows tighter turns provided by colored indicator lights and an with differential power and braking. The aircraft aural warning. is towed by connections on the nosewheel strut.

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

Crew alerting system (CAS) messages report the status of the braking and hydraulic systems and related systems. The rotary test switch tests all indications of the landing gear and brakes.

LANDING GEAR Figure 14-1. Left Main Landing Gear and Door DESCRIPTION The main landing gear struts are trailing-link struts, supporting the wheels with a trunnion and air-oil (oleo) strut, connected by a trail- ing link (Figure 14-1). The nose landing gear strut is a conventional air-oil (oleo) strut ex- tending from the trunnion (Figure 14-2).

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

It takes 6 seconds to extend the landing gear. At airspeeds between 100 and 160 KIAS, it takes 11Ð14 seconds to retract the landing gear. At airspeeds between 160 and185 KIAS, retraction takes 18Ð20 seconds.

Each inboard-retracting main gear uses two hy- draulic actuators (one for uplock release and one for gear actuation). Three more hydraulic actu- ators perform these duties for the forward-re- tracting nose gear. An electrically positioned Figure 14-2. Nose Landing Gear gear-control valve directs hydraulic pressure and Doors

14-2 510OM-00 CITATION MUSTANG OPERATING MANUAL for gear extension or retraction. If hydraulic free of the uplock roller, and the gear strut is extension fails, the emergency gear T-handle al- unlocked to start extension. lows the landing gear to mechanically release and free fall. A bottle of compressed nitrogen, Extension activated by the knob behind the T-handle, pro- vides pressure to ensure gear extension and When the uplock actuator is fully retracted, downlock (Figure 14-3). fluid passes through the uplock actuator to the gear-extend side of the gear actuator. Hydraulic pressure is then applied to the actuators, which extend until the gear is down- and-locked. To speed gear extension and improve free-fall ca- pability of the gear, a regenerative shuttle valve allows fluid to flow from the retract side of the actuators to the extend side.

Abnormal Main Gear Extension System Two backup gear-extension systems are pro- vided in addition to normal gear extension: ¥ The T-handle operates a cable system to mechanically release the uplock hooks from the struts. The gear should free-fall into position, aided by the pilot yawing the aircraft. NOTE It may require an acceleration above 150 KIAS to lock the nose landing gear into place. Figure 14-3. Emergency Gear Release Handle (Cover Removed) ¥ The round knob behind the T-handle re- leases pneumatic pressure (high-pres- sure nitrogen) from a bottle in the nose Main Gear System compartment to pneumatically operate the uplock actuators and release the up- Main Gear Extension System lock hooks, then extend the gear actua- Figure 14-4 displays the landing gear actu- tors, which extend the gear. ation during gear extension. Figure 14-5 displays the landing gear actuation during abnormal/emergency extension. Once Uplocks the uplock hooks are released, the pneumatic The main landing gear struts are mechanically pressure is applied to ensure that the gear ac- locked in the retracted position by a spring- tuators properly extend and lock the gear. loaded, hydraulically released uplock hook. Without using the pneumatic gear-extension system, it is still possible to lock the gear down In normal operation, to release a strut from its by yawing the aircraft to force the gear into po- uplock, the gear-control solenoid valve routes sition. However, mechanical release and down- fluid to the uplock hook actuator, retracting the lock should always be followed by the piston into the actuator. When the piston re- pneumatic extension procedure to ensure com- tracts completely, it pulls the uplock hook plete and proper extension of the gear.

510OM-00 14-3 CITATION MUSTANG OPERATING MANUAL GEAR ACTUATOR MAIN LANDING HYDRAULIC RESERVOIR ACCUMULATOR FROM BRAKES FROM NOSE GEAR UPLOCK ACTUATOR SHUTTLE VALVE CABIN AIR TO BRAKES TO UPLOCK ASSEMBLY ACTUATOR ACTUATOR ACCUMULATOR BLEED VALVE EXTEND LINE TO BRAKE TO METERING VALVE UPLOCK HOOK ACTUATOR GEAR CONTROL SOLENOID VALVE LINE RETRACT PNEUMATIC DUMP VALVE ACTUATOR NOSE DOWNLOCK NOSEGEAR RELEASE ACTUATOR UPLOCK ASSEMBLY ACTUATOR CONTROL MANIFOLD P P P VALVE GEAR SHUTTLE ACTUATOR EMERGENCY GEAR EXTENSION HANDLE MAIN LANDING REGENERATIVE Figure 14-4. Landing Gear Schematic—Extension LOW-PRESSURE SWITCH LOW-PRESSURE BOTTLE BLOWDOWN NORMAL-PRESSURE SWITCH EMERGENCY GEAR RETRACT PRESSURE SWITCH GEAR RETRACT SYSTEM PRESSURE RETURN STATIC NITROGEN CABIN AIR LEGEND

14-4 510OM-00 CITATION MUSTANG OPERATING MANUAL GEAR ACTUATOR MAIN LANDING HYDRAULIC RESERVOIR ACCUMULATOR FROM BRAKES FROM NOSE GEAR UPLOCK ACTUATOR SHUTTLE VALVE CABIN AIR TO BRAKES TO UPLOCK ASSEMBLY ACTUATOR ACCUMULATOR BLEED VALVE EXTEND LINE TO BRAKE TO METERING VALVE UPLOCK HOOK ACTUATOR GEAR CONTROL SOLENOID VALVE LINE RETRACT PNEUMATIC DUMP VALVE ACTUATOR NOSE DOWNLOCK NOSEGEAR RELEASE ACTUATOR UPLOCK ASSEMBLY ACTUATOR CONTROL MANIFOLD P P P VALVE GEAR SHUTTLE ACTUATOR EMERGENCY GEAR EXTENSION HANDLE MAIN LANDING REGENERATIVE Figure 14-5. Extension Landing Gear Emergency LOW-PRESSURE SWITCH LOW-PRESSURE BOTTLE BLOWDOWN NORMAL-PRESSURE SWITCH EMERGENCY GEAR RETRACT PRESSURE SWITCH GEAR RETRACT SYSTEM PRESSURE RETURN STATIC NITROGEN CABIN AIR LEGEND

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Main Gear Downlock Mechanism On takeoff, with weight off wheels, the nose- wheel steering remains engaged until retrac- Each main gear has a mechanical downlock tion. During retraction, nosegear steering is mechanism (integral to the gear actuator), disengaged and the nose gear is mechani- which locks the main landing gear in the down cally centered. In the wheel well, a spring- position. loaded mechanical uplock hook catches the uplock roller on the gear when it retracts. A Applying hydraulic pressure is the only way position-sensor switch in the uplock indi- to release the downlocks; therefore, no blocks cates up-and-locked. or external downlock pins are required.

Main Gear Retraction System Nose Gear Door System Nose gear movement actuates two doors to com- Figure 14-6 shows landing gear actuation dur- pletely enclose the nose gear and wheel at re- ing retraction. The main gear retracts when hy- traction. The doors open during gear extension draulic pressure is applied to the retract side and remain open after the gear is extended. of the actuators. This first releases the down- locks, then forces the actuators to retract, pulling the gear into the wheel wells. Before COMPONENTS the wheels enter the wheel wells, an auto- matic braking feature (spindown) stops the Main Gear wheels from spinning to prevent loose wheel tread or debris from striking the interior of the Each main gear assembly includes (see wheel well. When the gear is fully retracted Figure 14-1): into the uplocks, a switch in each uplock de- ¥ Trunnion tects that the main gear is up-and-locked. ¥ Trailing link Nose Gear System ¥ Oleo strut ¥ Main gear actuators with integral Nose Gear Extension System downlocks Nose gear extension is similar to the main ¥ Uplock assembly landing gear. In the wheel well, the uplock hook is hydraulically retracted, releasing the ¥ Main wheel tire and brake assembly uplock roller on the gear. The nosewheel ro- ¥ Squat switch tates down and aft from the nose wheel well. The nose gear is mechanically locked in the extended position by a spring-actuated down- Trunnion lock. A position switch on the drag brace in- A trunnion is the main support (leg) for each dicates down-and-locked. main gear. It connects to the wheel through the oleo strut and the trailing link and is extended Whenever the nosewheel is extended, nose- or retracted by the main gear actuator. During wheel steering is engaged, regardless of whether extension, the trunnion (with the main gear the aircraft is in flight or on the ground. components attached) rotates down-and-out- board on pivots attached to the forward and aft Nose Gear Retraction System wing spars. During nose gear retraction, a hydraulic actu- ator releases the nose gear downlock. The nose Trailing Link gear actuator extends, causing the nose gear to The trailing link connects the trunnion to the retract forward into the nosewheel well. wheel through a pivot and an oleo strut. It al- lows the wheel to simultaneously move up and aft when landing or during ground operations.

14-6 510OM-00 CITATION MUSTANG OPERATING MANUAL GEAR ACTUATOR MAIN LANDING HYDRAULIC RESERVOIR ACCUMULATOR FROM BRAKES FROM NOSE GEAR UPLOCK ACTUATOR SHUTTLE VALVE CABIN AIR TO BRAKES TO UPLOCK ASSEMBLY ACTUATOR ACTUATOR ACCUMULATOR BLEED VALVE EXTEND LINE TO BRAKE TO METERING VALVE UPLOCK HOOK ACTUATOR GEAR CONTROL SOLENOID VALVE LINE RETRACT PNEUMATIC DUMP VALVE ACTUATOR NOSE DOWNLOCK NOSEGEAR RELEASE ACTUATOR UPLOCK ASSEMBLY ACTUATOR CONTROL MANIFOLD P P P VALVE GEAR SHUTTLE ACTUATOR EMERGENCY GEAR EXTENSION HANDLE MAIN LANDING REGENERATIVE Figure 14-6. Landing Gear Schematic—Retraction LOW-PRESSURE SWITCH LOW-PRESSURE BOTTLE BLOWDOWN NORMAL-PRESSURE SWITCH EMERGENCY GEAR RETRACT PRESSURE SWITCH GEAR RETRACT SYSTEM PRESSURE RETURN STATIC NITROGEN CABIN AIR LEGEND

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Oleo Strut Squat Switch The oleo (air-oil) strut is a sealed hydraulic pis- A squat switch on the bottom of each trunnion ton and cylinder that uses compressed nitrogen detects whether or not the aircraft is on to absorb landing and taxiing shocks. It absorbs ground/weight-on-wheels (WOW) or in shocks between the trailing link (attached to flight/weight-off-wheels. The squat switch pro- the wheel) and the trunnion (attached to the air- vides this information to aircraft systems that craft). On the ground, the oleo struts support the use this information (including engine/FADEC, weight of the aircraft. windshield anti-ice, pressurization, landing gear control, antiskid braking, power distribu- Main Gear Actuators tion, and air conditioning). Refer to Chapter 17—“Miscellaneous” for more information Inboard of (and attached to) each main gear about squat switches. trunnion is a fluid-driven actuator, which ex- tends or retracts the main landing gear. The If the left and right squat switches have dif- main gear actuators are normally driven hy- ferent WOW signal indications for longer than draulically but can be extended pneumatically 2 seconds, the amber WOW MISCOMPARE for emergency gear extension. message appears. This advises that any aircraft systems relying on WOW signals may be in- Each main landing gear actuator includes its own operative or may operate unpredictably. integral mechanical locking system to lock the actuator in place when it is fully extended, thereby locking the gear down. Hydraulic retrac- Main Gear Door and Fairing tion pressure retracts the locking system and per- Each main landing gear strut has a gear door mits gear retraction. mechanically attached to the trunnion assem- bly of the gear. When the gear is operated, the Uplock Assembly door moves up and down with the gear itself and is not separate from the gear in its oper- In each wheel well, a spring-loaded mechani- ation. The door will cover the gear strut but the cal uplock hook catches the uplock roller on the tire is partially exposed. gear when it retracts. (During preflight, check that the rollers rotate.) This locks the gear in the up position. A switch in the uplock assembly de- Nose Gear tects when the trunnion uplock roller is in the The nose gear assembly supports the nose sec- lock (gear is up-and-locked). At the start of tion of the aircraft while on the ground and pro- gear extension, a hydraulic uplock-sequencing vides steering and a linkage for towing. The valve/actuator unit retracts the uplock hook, nose gear assembly (see Figure 14-2) includes: releasing the main landing gear, then passes hydraulic fluid to the gear actuator. In case of ¥ Strut an emergency gear extension, pressurized nitro- ¥ Shimmy damper gen gas retracts the uplock hook. ¥ Drag brace and downlock Main Wheel, Tire, and Wheel ¥ Uplock assembly Assembly ¥ Gear actuator Each main gear assembly includes a single wheel with tire and a fluid-actuated multiple- ¥ Single wheel and tire assembly disc brake assembly. Each main wheel has three fusible plugs that melt to deflate the tire if ex- Strut cessive temperature is generated by an over- The nose gear strut includes the trunnion (at- heated brake. Inflate with dry nitrogen to 85 ± tached to pivots and moved by the gear 5 psi (586 KPa ± 34 KPa) unloaded. Maximum actuator), the shock strut, and the nosewheel tire ground speed is 160 knots.

14-8 510OM-00 CITATION MUSTANG OPERATING MANUAL fork. The integral oleo (air-oil) shock strut ab- Single Wheel and Tire Assembly sorbs landing impact and other shocks. The lower end of the shock strut attaches to the The nosewheel assembly includes a wheel and nosewheel fork, which holds the nosewheel tire. The nose gear tire has chines to deflect assembly. water and slush. The tire must be inflated to 120 ± 5 psi or 827 KPa (± 34 KPa). Maximum A folding torque link holds the shock strut cylin- tire limit speed is 160 knots. der and nosewheel fork piston together and keeps them aligned with each other. Gear Control Solenoid Valve The gear control solenoid valve regulates the Shimmy Damper flow of hydraulic fluid to the gear actuators, up- To reduce nose gear shimmy during takeoff, lock-release actuators, and nose gear down- landing, and taxiing, the nose gear has a lock-release actuator. It is an electrically driven shimmy damper. It is a friction band around solenoid valve, actuated by two opposing sole- the center of the shock strut cylinder. It rubs noids that respond to electrical commands from against the inside of the trunnion using fric- the LANDING GEAR handle. tion to reduce nosewheel shimmy. When the LANDING GEAR handle is com- manded DOWN, the gear-extend solenoid on Drag Brace and Downlock the valve moves the valve to the gear-extend In the down (gear-extended) position, the gear position, routing fluid pressure to the uplock- is mechanically locked down by an integral lock- release actuators and then to the gear-extend ing mechanism in the drag brace. A position side of the gear actuators (see Figure 14-4). switch on the drag brace signals when the nose gear is down-and-locked. During extension, the When the LANDING GEAR handle is com- downlock is spring-actuated to lock mechani- manded UP, the gear-retract solenoid on the cally. During retraction, the downlock is re- valve moves the valve to the gear-retract posi- leased by a hydraulic actuator on the drag brace. tion, which routes fluid to the nose gear down- lock release actuator and the gear-retract side Uplock Assembly of all three gear actuators (see Figure 14-6). A mechanical latching system (uplock hook) similar to the main gear system is attached to Without DC power, the valve centers, releas- the airframe in the nose wheel well. It locks ing pressure from the gear-extend side of the the nose gear in the up (gear-retracted) posi- system. This permits emergency extension of tion. During gear extension, a fluid the gear using mechanical and pneumatic ac- actuator/valve unit releases the hook and then tuation (see Figure 14-5). DC power can be dis- passes hydraulic fluid (or pressurized nitro- connected from the gear control solenoid valve gen in an emergency) to the gear actuator. On by pulling the LDG GEAR CONTROL cir- gear retraction, the uplock latch catches a cuit breaker on the SYSTEMS panel of the roller on the rising nosewheel fork to lock the left CB panel. gear in the up position. (During preflight, check that the roller rotates.) A switch in the CONTROLS AND INDICATIONS uplock hook mechanism detects whether or not the gear is up-and-locked. LANDING GEAR Control Handle Gear Actuator The LANDING GEAR control handle is on The fluid-driven nose gear actuator retracts to the left side of the center tilt panel (Figure extend the nose gear. It also triggers nose gear 14-7) and controls the normal landing gear re- door operation through linkages. traction and extension procedure. The handle

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

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

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

Figure 14-7. Landing Gear Control Panel Never attempt to pull the gear handle up dur- ing taxi. actuates switches to complete circuits to the extend or retract side of the gear control so- Before energizing the aircraft electrical system, lenoid valve. The gear handle must be pulled ensure that the gear handle is in the down po- out of a detent prior to movement to either the sition to prevent inadvertent gear retraction. GEAR UP or GEAR DOWN position. In particular, if the squat switches do not agree On the ground, to keep the gear handle in the (as indicated on the EICAS by an amber WOW GEAR DOWN position, the left and right main MISCOMPARE message), it is possible to gear squat switch deenergizes a locking-sole- raise the gear handle, possibly resulting in noid in the instrument panel to extend a spring- gear retraction on the ground. Circuit Breakers PLUNGER Circuit breakers provide protection for the components and wiring of the landing gear system. Specific components are: RETRACT SWITCH ¥ LH ELE #1 EXTEND ¡ HYD PUMP 2 SWITCH ¡ LDG GEAR CTL 2 ¥ LH ELE EMERG LOCKING SOLENOID LDG GEAR MONITOR 2 FWD ¡ Gear Position Indicators Figure 14-8. Landing Gear Handle One red and three green position indicators Locking Solenoid and on the landing gear control panel provide Switches gear position indication. In addition, an aural

14-10 510OM-00 CITATION MUSTANG OPERATING MANUAL warning sounds if gear is up when the com- cates the need to prepare for emergency brak- bination of throttle position, flap position, and ing. Refer to the “Brakes” section of this chap- airspeed indicate landing configuration. ter. For more information, refer to Chapter 13—“Hydraulic System.” The green NOSEÐLHÐRH lights on the LDG GEAR control panel indicate gear down and locked. As each gear locks down, its respec- Aural Warning tive green light illuminates. The warning/caution advisory system pro- vides a landing gear aural warning if one or The red landing gear UNLOCK light indicates more gear are not locked down and either of an unsafe gear condition. It illuminates when the following situations occurs: the gear handle is moved out of GEAR UP de- tent and remains on until all three gear are ¥ One or both throttles are retarded below down and locked. At retraction, the light illu- approximately 85% N2 and airspeed is minates when the gear handle is moved out of below 130 KIAS. Pressing the HORN SI- the down position and remains visible until all LENCEÐPUSH button on the gear con- three gear are up and locked. trol panel (see Figure 14-7) silences this warning. Normal indication with the gear down is three ¥ Flaps are extended beyond the TAKE green lights visible. With the gear retracted, OFF AND APPROACH setting. In this all lights extinguish and the red UNLOCK situation, the aural warning cannot be si- light extinguishes. lenced with the HORN SILENCEÐ PUSH button. Figure 14-9 shows indicator displays for var- ious gear positions. Test the landing gear in- Aural warning is DC-powered. Circuit protec- dicator lights and warning horn by positioning tion for the aural warning system and position the rotary TEST knob to LANDING GEAR. lights is on the right CB panel labeled WARN LIGHT within the lights grouping. CAS Messages Rotary TEST Knob HYD PRESS LO The rotary TEST knob is at the top of the copi- The amber HYD PRESS LO message indi- lot panel. This knob is used to test the land- cates low hydraulic system pressure. During ing gear and antiskid warning systems. extension, if this message appears and gear is not indicating down and locked within 6 sec- onds, refer to the checklist for landing gear OPERATION emergency extension. This message also in- dicates the need to prepare for emergency Preflight braking. Refer to the “Brakes” section of this During preflight, inspect the pressure gauge chapter. For more information, refer to for the emergency landing gear extension Chapter 13—“Hydraulic System.” pneumatic bottle. It is in the nose baggage compartment, on the right side of the aft wall. HYD PUMP ON Determine the current temperature, and then The amber HYD PUMP ON message indicates compare the gauge pressure indication to the that the hydraulic pump has been operating pressures listed on the placard next to the for more than a minute. See the Airplane Flight gauge to determine if the pneumatic pressure Manual (AFM) procedure for responding to is appropriate. this message, and prepare for emergency land- ing gear extension. This message also indi-

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DOWN AND LOCKED UP AND LOCKED

NOSE GEAR NOT ONE OR MORE GEAR NOT DOWN AND LOCKED UP AND LOCKED

Figure 14-9. Landing Gear Position Indications

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Retraction and Extension is interrupted and the valve returns to the neu- tral position. With pressure no longer applied Moving the LANDING GEAR handle to the to the gear actuator, three actions occur: GEAR DOWN position energizes the gear control solenoid valve. The DC power for the 1. The internal locking mechanism within landing gear control circuit is from the left bus each main gear actuator assumes the through the LDG GEAR CONTROL circuit downlocked position. breaker in the SYSTEMS section of the pilot CB panel. 2. The spring-loaded nose gear mechani- cal downlock latches.

Retraction 3. Downlock switches illuminate the green Placing the LANDING GEAR handle in the NOSEÐLHÐRH position indicators on GEAR UP position energizes the retract sole- the gear control panel. noid of the gear control valve. The gear con- trol valve is positioned to direct pressure to: EMERGENCY/ABNORMAL ¥ The nose gear downlock-release actua- tor to release the nose gear downlock For specific information on the emergency/ab- normal procedures, refer to the appropriate ¥ The gear-retract side of each gear actu- FAA-approved abbreviated checklist or the ator (also releases downlocks inside the AFM. main gear actuators) ¥ The extend side of the uplock actuators, which position the uplock hooks to catch NOSEWHEEL STEERING the rising gear All downlocks are released and retraction be- DESCRIPTION AND gins (see Figure 14-6). OPERATION As each gear reaches the fully retracted posi- Mechanical linkage from the rudder pedals tion, a spring-loaded uplock hook catches it and mechanically actuates the nosewheel steer- an uplock microswitch actuates. When all three ing system (Figure 14-10). uplock microswitches actuate, the gear control solenoid valve circuit is interrupted and the Whenever the nosewheel is extended, nose- valve returns to the neutral position. All posi- wheel steering is engaged regardless of tion indicators on the control panel extinguish. whether the aircraft is in flight or on the ground. During retraction, nosewheel steer- Extension ing is disengaged and the nose gear is me- Placing the landing gear handle in the GEAR chanically centered. DOWN position energizes the gear control solenoid valve to the extend position. The gear Rudder pedals mechanically steer the nose control solenoid valve is positioned to route gear to 20¡ either side of center. A spring pressure to the uplock actuators, which re- linkage provides an additional 55¡ of nose- leases the gear uplocks (see Figure 14-4). wheel deflection (±75¡ total) via castering accomplished with application of differen- When the spring-loaded uplocks release, pres- tial engine power or braking. sure continues to the gear-extend side of the gear actuators. As each gear reaches the fully ex- For towing, ensure that the rudder (gust) tended position, a downlock microswitch ac- lock is disengaged and do not exceed 75¡ tuates. When all three downlock switches nosewheel deflection. If 75¡ is exceeded, actuate, the gear control solenoid valve circuit the steering system or airframe structure will

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STEERING BUNGEE OUTPUT WARNING SPRING LEVER If damage to nosewheel steering is suspected or crewmembers detect ab- STEERING normal steering system action, do not PIN attempt to fly the aircraft. If the sys- tem is damaged, the crew does not have full steering control of the air- craft on takeoff or landing. If the air- craft flies, even if the gear remains extended after takeoff, the nosewheel may not remain centered, and may not be controllable. CENTERING FITTING CAUTION

Anytime the gear is extended, the nosewheel deflects with rudder pedal movement. During a crosswind land- Figure 14-10. Nosewheel Steering ing, center the pedals immediately before nosewheel touchdown. be damaged. If the rudder (gust) lock is en- gaged, towing beyond 55¡ may cause struc- tural and/or steering system damage. BRAKES During preflight, check that the stop bolts are DESCRIPTION present and intact (Figure 14-11). If they are not, the steering system is damaged. Disc brakes are on the main gear assemblies. Maintenance is required before flight. The aircraft hydraulic system provides normal power braking with a pneumatic (pressurized nitrogen) system for backup (Figure 14-12). The hydraulic system automatically maintains con- stant pressure for brake operation.

STOP BOLTS The brakes are normally used as antiskid power brakes but can operate as power brakes with- out antiskid protection. In the event that brake system hydraulic pressure is lost, emergency braking is available.

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

Figure 14-11. Stop Bolt Location

14-14 510OM-00 CITATION MUSTANG OPERATING MANUAL SYSTEM PRESSURE RETURN METERED PRESSURE NITROGEN CABIN AIR EXHAUST NITROGEN HYD PRESS LO ON HYD PUMP ANTISKID FAIL NO TIRE SPINDOWN LEGEND PARKING BRAKE PARKING ACCUMULATOR TO GEAR RETRACT TO GEAR EXTEND TO P DIGITAL ANTISKID P CONTROL UNIT CONTROL EMERGENCY BRAKE HANDLE P CONTROL MANIFOLD MANUAL HYDRAULIC SYSTEM RESERVOIR FROM GEAR RETRACT FROM PRESSURE LINE (FOR TIRE SPINDOWN) 29-VDC PUMP HYDRAULIC BLEED VALVE ACCUMULATOR PARKING BRAKE PARKING VALVE VENT LINE VALVE BRAKE OVERBOARD CABIN AIR ANTISKID METERING SHUTTLE VALVES CONTROL VALVE CONTROL Figure 14-12. Brake and Digital Antiskid System Power NITROGEN BOTTLE NITROGEN EMERGENCY BRAKE EMERGENCY BRAKE VALVE PILOT/COPILOT RUDDER PEDALS RUDDER PILOT/COPILOT

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Antiskid System With the ANTI SKID switch in the up (on) po- sition, the antiskid system provides maximum braking efficiency on all runway surfaces. The antiskid control system can only reduce pres- sure; the applied pressure can never be more than that commanded by the crew.

A wheel speed transducer on each wheel elec- tronically transmits wheel-speed signals to the antiskid control box as a variable fre- quency. If the control box detects sudden de- celeration of a wheel (impending skid) it commands the antiskid valve to reduce pres- sure to that specific wheel/brake. When the slow wheel catches up to the fast wheel and the transducer signal returns to normal, brak- ing pressure is restored to the brakes. Figure 14-13. PARKING BRAKE Knob The antiskid system includes “touchdown pro- Emergency Brakes tection,” which prevents landing with the brakes locked. Any time both squat switches If the hydraulic brake system fails, a pneumatic indicate that the aircraft is in the air and the brake system is available to actuate the wheel gear is extended, the antiskid unit dumps brake brakes (Figure 14-14). The system uses nitro- pressure (except during gear retraction when gen pressure from a pneumatic bottle independ- braking is applied to spindown the wheels). ent of emergency landing gear extension system. Upon landing, this dump continues for 3 sec- onds after weight-on-wheels or until wheel Pulling on the EMERGENCY BRAKE handle spinup (whichever occurs first), before brake (under the center of the pilot left tilt panel) ac- pressure is enabled. tuates the emergency brake system. Pull out and hold the handle aft to apply and modulate During high-speed ground movement, “locked- emergency braking pressure. The lever has a stop wheel crossover protection” prevents sudden to prevent locking the brakes and blowing the yawing due to differential braking. If the an- tires. The emergency brakes are effective for six tiskid controller senses a 70% difference in pulls on the handle. No electrical power is re- speed between left and right brakes, it reduces quired for the emergency brakes. brake pressure to both wheels. At low speeds (approximately 12 knots), this feature is dis- COMPONENTS abled to permit tight turns during taxiing. Brake Pedals Parking Brakes Brakes are normally actuated by the pilot or Parking brakes are a locked configuration of the copilot pressing on the tops of one or more brakes. Brakes are locked when the parking of the rudder pedals. Each pedal is mechan- brake valve traps hydraulic fluid in the brake ically linked to the brake metering valve and lines. The valve (and hence the parking brakes) to the corresponding pedal. Both pilot and can only be set by pulling on the PARKING copilot foot forces are transmitted to the BRAKE knob on the right lower side of the brake metering valve by cables. For each pilot instrument panel (Figure 14-13) while wheel, the pilot applying the greater force to pressing on the brake pedals. the corresponding pedal determines brake

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POWER BRAKE SYSTEM

SHUTTLE VALVE SHUTTLE VALVE

EMERGENCY BRAKE VALVE

LEGEND OVERBOARD NITROGEN PRESSURE VENT LINE METERED BRAKE FLUID MECHANICAL

EMERGENCY BRAKE NITROGEN BOTTLE Figure 14-14. Emergency Brake System pressure to that wheel, and the position of the Antiskid Control Unit corresponding pedal for the other pilot. The pilot and copilot pedals move together. A digital ASCU monitors wheel speed to pro- vide wheel skid protection and optimum brak- ing efficiency on all runway surfaces. Based Brake Metering Valve on wheel speed inputs, the control unit reduces The brake metering valve regulates left or brake pressure as required to prevent the skid. right brake pressure according to brake pedal inputs as commanded by the crew. Parking Brake Valve The parking brake valve is in the brake lines Wheel Speed Transducers between the antiskid control valve and the One transducer is in each main gear axle. A brake assemblies. When a crewmember pulls drive clip on the wheel hubcap spins the inner the PARKING BRAKE knob and depresses rotor of the transducer. Wheel speed data is the brake pedals, the valve engages check provided directly to the antiskid control unit. valves to trap brake fluid pressure in the brake lines. To relieve pressure due to fluid expan- sion when the parking brake is engaged shortly Antiskid Control Valve after heavy braking, 1,200-psi thermal relief valves are in the parking brake valve. To prevent skids, the antiskid control valve reg- ulates the distribution of brake pressure, as re- quired to prevent the skid. The antiskid control valve is electrically controlled by the ASCU.

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Emergency Brake Valve The SKID CONTROL circuit breaker is also in the SYSTEM section of the left CB panel. The emergency brake valve is lever operated Disengaging the SKID CONTROL circuit to provide metered pneumatic pressure from breaker disables the antiskid system and touch- the emergency nitrogen bottle directly to the down protection. brake assemblies. The emergency brake valve connects through a cable to the emergency brake lever, which is under the instrument CAS Messages panel near the right knee of the pilot. ANTISKID FAIL If a fault develops in the antiskid system, the Brakes and Shuttle Valves amber ANTISKID FAIL message appears, and Disc brakes are in each main gear assembly. the system must be deactivated (select ANTI- The brakes respond to hydraulic or pneumatic SKID switch to OFF). When the message is vis- pressure. Normally, fluid from the brake meter- ible, leaving the antiskid system on can result ing valve hydraulically actuates the left and in unpredictable braking system performance. right brakes separately as commanded by the crew and/or the antiskid control unit. However, The ANTISKID FAIL message indicates that a shuttle valve at each brake allows high-pres- an internal test routine has failed or there are sure nitrogen from the emergency brake valve electrical problems. Electrical problems may to bypass hydraulic flow and apply pressure di- include DC power that is off or below opera- rectly to both brakes evenly. tional levels, or shorts or opens in the antiskid system wiring.

CONTROLS AND INDICATIONS This message also appears when the rotary TEST knob is selected to ANTI SKID. ANTI SKID Switch The ANTI SKID switch (see Figure 14-12) is HYD PRESS LO on the LANDING GEAR control panel and is normally in the up (on) position. In the OFF When brake system pressure drops below op- (down) position, the antiskid system deacti- erational levels, the amber HYD PRESS LO vates; brake operation remains the same ex- message appears. Use of the emergency brake cept that antiskid protection is not available. system for braking is required after the land- Before turning the antiskid system off, en- ing gear is extended manually. The HYD sure that brake pressure is released. Before PRESS LO message also incorporates a 15-sec- turning the antiskid system on, ensure that ond delay in flight. the wheels are not rotating. HYD PUMP ON Circuit Breakers The HYD PUMP ON message indicates that the hydraulic pump has been operating for The power brake and antiskid systems receive more than a minute. See the AFM procedure DC power from the left electrical bus. for responding to this message, and prepare to use the emergency brake handle for braking. The HYD PUMP circuit breaker is in the SYS- (This message also indicates the need to pre- TEM section of the left CB panel. Disengaging pare for emergency gear extension; refer to the the HYD PUMP circuit breaker electrically “Landing Gear” section of this chapter). For disables the hydraulic pump. This action re- more information, refer to Chapter 13— duces or eliminates hydraulic system pressure. “Hydraulic System.” This results in limited or improper function- ing of the power brake system or completely eliminates the power brake system.

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NO TIRE SPINDOWN Power Braking (Antiskid ON) Ten seconds after gear retraction begins, if For normal operation of the power brake and either tire is spinning above 10 knots, the antiskid system, all three of the following white NO TIRE SPINDOWN message ap- conditions must exist: pears, indicating failure of the tire spindown function of the antiskid system. This could ¥ The ANTI SKID switch is up (on). cause damage to the wheel wells from loose ¥ Both wheels are rotating at aircraft tire tread and debris. groundspeed. This message also appears when the rotary ¥ Either squat switch (left wheel or right TEST knob is selected to ANTI SKID. wheel) senses weight on wheel. Maximum braking technique is obtained by: Rotary TEST Knob 1. Lowering the nose to the ground The rotary TEST knob is at the top of the copi- lot panel. This knob tests the antiskid system. 2. Firmly applying and holding the brakes until the desired speed has been reached

OPERATION 3. Extending the speedbrakes while apply- ing the wheel brakes Antiskid Touchdown Protection During landing, the antiskid system “touch- NOTE down protection” feature prevents the aircraft from touching down with locked brakes. Do not pump the brakes. Touchdown protection mode is active anytime all three of the following conditions exist: NOTE ¥ The ANTI SKID switch is ON. The antiskid system is not operative ¥ Both squat switches indicate that the during emergency braking. aircraft is in flight. ¥ The gear is extended. Depressing the brake pedals moves cables at- tached to the power brake metering valve, Under these conditions (regardless of pilot which meters hydraulic pressure to the brake or copilot pedal position), the touchdown assemblies in direct proportion to pedal force. protection mode releases all brake pressure from the brakes. With the ANTI SKID switch on and a ground speed of at least 12 knots, maximum braking To ensure adequate wheel spinup on contami- with skid protection is available. Any ten- nated runways, the touchdown protection mode dency of a wheel to rapidly decelerate (skid) stays active for 3 seconds after the first wheel is detected by the wheel speed transducer, and touches down (either left or right squat switch the antiskid control valve is signaled to mo- indicates weight-on-wheels). mentarily dump pressure from affected brakes. As wheel speed returns to normal, dumping Under normal conditions, the wheels spinup ceases and pressure is once again increased in almost immediately; therefore, a spinup over- the brake assemblies. When wheel speed drops ride feature is incorporated. Anytime wheel below approximately 12 knots, the antiskid speed is above 50 knots (regardless of squat function disengages. switch position), touchdown protection is overridden and normal antiskid braking is available.

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Braking on each main wheel is controlled by With the antiskid switch ON (up), the antiskid the corresponding pedal; therefore, differen- control unit is continuously conducting in- tial braking is available. tegrity checks of the system. If any faults are detected, an amber ANTISKID FAIL message Power Braking (Antiskid OFF) appears in the CAS window. The ANTI SKID switch is normally in the up To ground test the antiskid system: (on) position. In the OFF position, the antiskid ¥ Rotate the rotary TEST knob to the ANTI system deactivates and the amber ANTISKID SKID test position. FAIL message appears. The power brakes, powered by the hydraulic system, still func- ¥ The ANTISKID FAIL and NO TIRE tion without the assistance of the antiskid sys- SPINDOWN messages flash for 6 tem. With the loss of the antiskid system, seconds. touchdown protection and tire spin-down are ¥ Test is valid if the ANTISKID FAIL and inoperable. NO TIRE SPINDOWN messages are confirmed extinguished after 6 seconds. Parking Brakes ¥ Test is failed if the ANTISKID FAIL and/or NO TIRE SPINDOWN messages To set the parking brakes, apply the brakes in remain illuminated after more than 6 the normal manner, then pull out the PARK- seconds. ING BRAKE knob (see Figure 14-13). This mechanically actuates the parking brake valve and traps fluid in the brakes. To release the Emergency Brakes parking brakes, depress the brake pedals, then Pulling the red EMERGENCY BRAKE han- push in the PARKING BRAKE knob. One- dle aft actuates the emergency brake valve way check valves allow setting increased mechanically (see Figure 14-14). The valve trapped pressure once the brakes are set by sim- meters nitrogen pressure through shuttle valves ply depressing the brake pedals harder. on the brake assemblies in direct proportion to the amount of lever movement. Do not use parking brakes after using emer- gency brakes. Hold emergency brakes until Since nitrogen pressure is applied to both brakes the aircraft can be secured. simultaneously, differential braking is not pos- sible. Returning the lever to its original position Parking brakes can hold the aircraft for only releases pressure from the brakes and vents it a limited time. They are not intended to secure overboard, which releases the brakes. an unattended aircraft. Parking brakes are a temporary function, to be used only until the Apply the emergency brakes only enough to aircraft can be secured. obtain the desired rate of deceleration, then hold them until the aircraft stops. NOTE Best performance can be obtained using a If brakes are suspected of being hot, smooth, steady, continuous pull of the handle do not set the parking brake. to obtain the desired deceleration rate. Multiple pulls and releases of the handle deplete the ni- Antiskid Test trogen charge. The antiskid system is checked as part of the Do not depress the brake pedals while apply- rotary test procedure in the Cockpit ing emergency airbrakes. Shuttle valve action Preparation checklist. This same test can be may deplete nitrogen pressure, reducing avail- conducted in flight if a problem is suspected. able braking power.

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

Antiskid protection is not available during emergency braking. Do not attempt to taxi after clearing the runway when using the emer- gency brakes. Maintenance action is required subsequent to emergency braking. EMERGENCY/ABNORMAL For specific information on emergency/abnor- mal procedures, refer to the appropriate abbre- viated checklists or the FAA-approved AFM.

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