Landing gear

                  LANDING GEAR 

✈ATA32 

✈The landing gear consists of :

☂Two main landing gears that retract inboard(

⛑Each main gear has twin wheels and an oleopneumatic shock absorber. 

⛑Each main wheel has an antiskid brake.)

☂One nose landing gear that retracts forward. 

⛑The two-wheeled nose gear has an oleopneumatic shock strut and a nose wheel steering system.

☂Doors enclose the landing gear bays. 

☂Gear and doors are electrically controlled and hydraulically operated. 

☂The doors, are operated mechanically by the gear and close at the end of gear retraction. 

✈MAIN FITTING 
☂The main fitting includes:
⛑the main barrel,
⛑the drag stay,
⛑the cross tube,
⛑the aircraft attachment lugs.

☂It contains a diaphragm and tube assembly that forms the top of the shock absorber.  A pin connects the diaphragm and the tube assembly.  This pin is located in the two lateral holes in the main fitting, and contains the shock absorber upper charging valve.

☂SPARE-SEAL ACTIVATING-VALVE 
⛑A gland housing assembly, at the bottom end of the main fitting, seals the joint between the main fitting and the sliding tube.
⛑A spare-seal activating-valve can isolate the bottom gland seals if a leak occurs.

☂ACTUATING CYLINDER The MLG actuating cylinder is installed on the main fitting at the piston rod end.  Two lugs attach the body to the wing rear spar.  When it is hydraulically supplied:
⛑the piston rod extends to retract the MLG,
⛑the piston rod retracts to extend the MLG.
☂ SIDE STAY ASSEMBLY The main components of the side stay assembly are:
⛑a basic side stay,
⛑a lock stay,
⛑a lock stay actuator,
⛑two lock springs,
⛑ the proximity sensors and their related targets.
The lock springs move the lock stay to an over center position during the extension cycle.
☂LOCK STAY The lock stay provides an over center stop and a geometric lock of the L/G.
☂LOCK STAY ACTUATOR During MLG extension the two lock stay actuator ports are open to return; a restrictor controls the rate of MLG extension. It is pressurized to extend during MLG door closure until hydraulic pressure on the door close line is released. During MLG retraction, the hydraulic fluid retracts the piston which opens the over centered lock, to fold the side stay and the lock stay against the lock springs.
☂TORQUE LINKS/SLAVE LINK
 The torque links align the main fitting and the sliding tube, but let vertical movement between the parts occur.  The slave link is mounted at the rear.

☂TORQUE LINK DAMPER
The torque link damper is a spring-centered, two-way hydraulic unit, which has its own hydraulic reservoir. Its function is to decrease the landing vibrations through the torque links.  The hydraulic fluid contents of the damper are shown by the extension of the reservoir when it is pressurized.  When the contents are correct, the "FULL" and "REFILL" level indications are in view.

✈NLG
☂ACTUATING CYLINDER
The actuating cylinder operates the nose gear during retraction and extension sequences.
☂DRAG STRUT ASSEMBLY The drag strut assembly consists of a forestay at the top and a tubular arm at the bottom that are interconnected by a universal joint.  The uplock roller is installed on the upper hinge pin of the universal joint.
☂LOCKSTAY DOWNLOCK ACTUATOR
The downlock actuator locks and unlocks both brace assemblies of the lock stay. It is assisted by two springs.
☂SLIDING  TUBE The sliding tube includes the wheel axle. It is inclined 9 degrees forward; this design allows the wheels to return freely to the centered position and decrease the shimmy effect.  The towing lug is designed to shear if the towing load is more than the limit.  The two system proximity detectors provide signals for both gear extended and wheel centered positions.
☂ROTATING TUBE The rotating tube is inside the shock strut. It is equipped with a pinion that transmits steering orders from the steering actuating cylinder via the rotating tube and the torque link to the wheel axle.
☂TORQUE LINK The torque link is installed on the rear. It connects the sliding tube to the rotating tube.

☂LOCKSTAY ASSEMBLY
The lock stay assembly provides an over centered stop and a geometric lock of the nose gear. It includes both systems downlock proximity detectors. On the ground, a safety pin locks the two arms of the lock stay

✈SHOCK ABSORBER
☂The shock absorber is a telescopic oleo-pneumatic unit which includes the sliding tube.
☂It is installed in the main fitting to transmit the landing, take off and taxiing loads to the wing.
☂When the shock absorber is compressed, the load is transmitted to the hydraulic fluid and nitrogen gas.

☂The shock absorber is a 2 stage unit and contains four chambers:
⛑a first stage gas chamber contains gas at a low pressure and hydraulic fluid,
⛑ a recoil chamber that contains hydraulic fluid,
⛑a compression chamber that contains hydraulic fluid,
⛑a 2nd  stage gas chamber that contains gas at a high pressure.

☂Primary control of the shock absorber recoil is:
⛑the fluid flow from the recoil chamber into the gas chamber,
⛑the fluid flow from the gas chamber into the compression chamber.

☂MAIN DOOR
⛑The main door is attached to the fuselage structure by two hinges and is operated by a hydraulic actuator.   
⛑Two ramps are installed on the inside of the main door.  These ramps make sure that the gear does not catch on the main door during a free-fall extension.
⛑Two proximity sensors and targets send the door open position signal of the main door to the Landing Gear Control and Interface Units (LGCIUs).
☂MLG DOOR UPLOCk
The MLG door uplock is closed mechanically, locking the door in the closed position and hydraulically opened, releasing the door during normal extension and retraction sequences.  The uplock can also be opened mechanically in free-fall extension and ground door opening.
☂HINGED FAIRING
The hinged fairing is attached to the wing skin by a single hinge and to the L/G by an adjustable tie-rod.  The adjustable tie-rod causes the hinged fairing to follow the L/G during the L/G extension and retraction.
☂FIXED FAIRING
 The fix fairing is attached to the gear on 5 points and is fully adjustable in vertical and horizontal directions.

✈EXTENSION/RETRACTION SYSTEM 

☂Landing Gear Control and Interface Units (LGCIU) 1 and 2 electrically control the gear and door sequencing.(hyd. operated)  

☂The LGCIU in control is the active unit and the other is the standby unit.    

☂The two systems are electrically segregated with different connections on the related selector valves. 

☂In case of failure, the gear can be mechanically extended from the cockpit by means of a gravity extension crank handle. 

(After free fall extension, the L/G doors stay open and the L/G is locked down by the lockstays and springs.) 

✈The green hydraulic system actuates all gear and doors.

✈When the aircraft is flying 

☂faster than 260 kt, a safety valve automatically cuts off hydraulic supply to the landing gear system

☂Below 260 kt, the hydraulic supply remains cut off as long as the landing gear lever is up.

✈LANDING FLAPS INFORMATION 

☂The  LGCIUs process the signals from four flap disconnect proximity switches, then send them to the Slat/Flap Control Computers (SFCCs). 

☂The  LGCIUs do not monitor failures in the  SFCC  system.

✈L/G INDICATOR PANEL
☂This panel is connected to  LGCIU1, which receives signals from proximity detectors.
⛑ ▿ light: comes on green if the gear is locked down.
⛑UNLK light  : comes on red if the gear is not locked in the selected position.
☂ If one  UNLK  indication remains on, the landing gear position can be confirmed using the WHEEL  SD page  (information from  LGCIU  1 & 2).

✈Only One green triangle on each landing gear is sufficient to confirm that the landing gear is downlocked.

✈LANDING GEAR SELECTOR LEVER
☂A two-position selector lever sends electrical signals to the two  LGCIUs. (These control the green hydraulic supply to the landing gear system by means of selector valves.)
☂The flight crew must always move the L/G lever in one continuous movement (i.e. with no stop between both positions).
☂When the flight crew selects  UP  or DOWN (and if the airspeed is below  260 kt):
⛑All landing gear doors open
⛑Each landing gear moves to the selected position
⛑All landing gear doors close.

✈L/G LEVER UP : This position selects landing gear retraction. While the landing gear doors are opening,
☂the normal brake system brakes the wheels of the main landing gear automatically.
☂A brake band in the nose landing gear well brakes the nose landing gear wheels as the doors close (for aircraft equipped with nose landing gear rubbing strips).
✈ L/G DOWN: This position selects landing gear extension.
☂An interlock mechanism prevents anyone from accidentally retracting the gear while the aircraft is on the ground.
⛑It does so by locking the lever in DOWN position when the shock absorber on either main gear is compressed (aircraft on ground) or
⛑ the nose wheel steering is not centered. ✈The landing gear hydraulic system remains pressurized as long as the landing gear is extended (if green hydraulic pressure is available).

✈RED ARROW This red arrow lights up if the landing gear is not locked down when the aircraft is in the landing configuration, and a red warning appears on  ECAM.

✈LANDING GEAR GRAVITY EXTENSION
☂To put the landing gear down by gravity, the flight crew must pull the gear crank out, then turn it clockwise for 3 turns.
☂When the flight crew operates the crank handle, the cutout valve shuts off hydraulic pressure to the landing gear system and depressurizes it.

✈WHEEL SD PAGE
☂(1) The landing gear positions are indicated by 2 triangles for each gear. The indications are as follow:
⛑Green triangle indicates that one  LGCIU  detects a landing gear downlocked
⛑Red triangle indicates that one  LGCIU  detects a landing gear in transit
⛑No triangle indicates that one  LGCIU  detects a landing gear uplocked
⛑Amber crosses will replace the right triangle to indicate that  LGCIU  1 or  LGCIU  2 has failed.

(2) Landing gear door position indication

(3) UP LOCK This legend appears amber along with a caution on the  ECAM  if the landing gear uplock is engaged when the landing gear is down locked.

(4)L/G CTL This legend appears amber along with an  ECAM  caution if the landing gear lever and the landing gear position do not agree. This legend only appears when the landing gear is moving to the selected position

FLT L/G DOWN : This memo appears in green if the aircraft is operated in ferry flight conditions with landing gear down.

✈NOSE L/G - Description
☂A hydraulic actuating cylinder steers the nose wheel.
☂The yellow hydraulic system supplies pressure to the cylinder, and electric signals from the Brake and Steering Control Unit (BSCU) control it.

☂The  BSCU  receives orders from:
⛑Captain's,
⛑First Officer’s steering hand wheels (orders added algebraically),
⛑Rudder pedals,
⛑Autopilot.

☂The steering system receives actuating hydraulic pressure when:
⛑A/SKID  & N/W  STRG  switch is ON
⛑Towing control lever is in normal position
⛑At least one engine is running
⛑Aircraft is on ground.
☂The handwheel can turn the nosewheel up to  75 °  in either direction. A lever, on the towing electrical box (on nose landing gear),
☂enables ground crew to deactivate the steering system for towing. Then the wheel can be turned  95 °  in either direction.

☂SIDE CONSOLES
As per above figure ....
⛑(1) Steering handwheels
Note: The steering system centers the nose wheel automatically after liftoff.
⛑(2) Rudder PEDALS DISC pb Pressing this button on either handwheel removes control of nose wheel steering from the rudder pedals until the button is released.

☂MEMO DISPLAY
NW STRG DISC : This memo appears, when the nose wheel steering selector is in the towing position and with engines not running.
NW STRG DISC : This memo appears, when the nose wheel steering selector is in the towing position and if at least one engine is running.

✈ SAFETY PRECAUTIONS
☂ wheel chocks are in place,
☂the hydraulic system is depressurized,
☂safety sleeves and safety pins are fitted on the L/G and L/G doors,
☂ground door opening handles are in the open position.
☂MLG or NLG & DOOR SAFETY DEVICES Installation of the safety devices on the MLG and MLG doors.



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Hydraulic system

           HYDRAULIC SYSTEM'S

✈The word hydraulics is based on the Greek word for water, and originally meant the study of physical
behavior of water at rest and in motion.

✈BASIC COMPONENTS
☂The basic components of any hydraulic system are reservoirs, filters, and pumps (hand or power-driven).
☂The reservoir holds the fluid supply for the system and helps cool the fluid.
☂Filters are used to ensure
that no contamination reaches the components in a hydraulic system.
☂The pleated micronic filter is the
most common.

✈Hydraulic fluid & Quantity
- (EXXON HYJET5-SKYDROLLD4)

✈The aircraft has three independent hydraulic systems:- (FOR A320)
☂green
☂yellow
☂blue.
✈Each system has its own hydraulic reservoir 
✈Power supply
☂The three hydraulic systems supply Normal hydraulic power at 3000 psi to the users:- 
  ⛑Flight controls
 ⛑Landing gear
 ⛑Brakes
 ⛑Nose wheel steering
 ⛑Cargo doors
 ⛑Thrust reverser operation
 ⛑Constant Speed Motor / Generator (CSM/G).

☂In an emergency, the blue system can be pressurized by the Ram  Air Turbine (RAT).    ⛑The RAT is deployed automatically or              manually.
  ⛑It pressurizes the blue hydraulic                  system at 2500 psi.

✈Hydraulic fluid cannot be transferred from one system to another.

✈System pressurization source
 ⛑WHY?:- A reservoir in each hydraulic system is pressurized with air to prevent cavitation.

☂Green System :- Two Source
     ⛑Engine Driven Pump(1)
     ⛑Power Transfer Unit (PTU)

☂Yellow System:- four source
     ⛑Engine Driven Pump(2)
     ⛑Electric Pump
     ⛑Hand Pump for cargo door OPS.
     ⛑Power Transfer Unit (PTU).
☠ Yellow system mainly used on ground for maintenance and cargo door operation.

☠If No electric power is available, a hand pump in the yellow system can be used to operate the cargo doors.
☂Blue System :- Two source
     ⛑Electric Pump
     ⛑Ram Air Turbine(RAT) - In emergency            only

☠Blue Electric Pump operates all the time in-flight and on the ground when at least one engine is operating.

☠The RAT and Yellow electric pumps do not normally run during flight( used on ground only).

✈PUMP
☂The heart of any hydraulic system is the pump which converts mechanical energy into hydraulic energy.
☂The source of mechanical energy is
⛑electric motor
⛑engine driven
⛑the operator's muscle.

Pumps powered by muscle are called hand pumps.


✈POWER TRANSFER UNIT (PTU)

☂A bidirectional power transfer unit enables the yellow system to pressurize the green system and viceversa.

☂The power transfer unit (PTU) comes into action automatically when the differential pressure between the green and the yellow systems is greater than 500 PSI.

☂The PTU therefore allows the green system to be pressurized on the ground when the engines are stopped.

☂PTU is able to transfer the power but not fluid.

✈RAM AIR TURBINE (RAT)

☂RAT is a small unit having to small aerofoil shaped blade which installed in it.
☂ it is deployed to the incoming airstream,
the blades rotate at high speed providing
emergency drive for the blue hydraulic system pressure pump.
☂RAT is automatically deployed
 if it senses
⛑ Both hydraulic system EDPs failed and           loss of pressure
⛑ Failure of both AC bus 1 and 2.
⛑ Aircraft speed is above 100 knots.

✈It can be deployed manually from the overhead panel. It can be stowed only when the aircraft is on the ground.

The RAT hydraulic pump is for emergency use only and will only deploy manually for hydraulic problems.
☂ For electrical problems it will deploy automatically above 100 kts. with loss of all AC bus.
☂Note: Min RAT speed is 140 kts. with A319/321 and modified A320 RATs stalling at less than 125 kts.
☂This speed limit is for electrical power and the RAT will continue to supply hydraulic power to much slower speeds.

✈SYSTEM ACCUMULATOR'S
☂An accumulator in each system helps to maintain a constant pressure by covering transient demands during normal operation.

☂Three system accumulators are pressurized with N2 to a pressure 
of 1950 psi.
☂The brake accumulator is pressurized to 1200 psi pressure.

✈PRIORITY VALVE 
☂Priority valves cut off hydraulic power to heavy load users if hydraulic pressure in a system gets low.

✈FIRE SHUTOFF VALVE'S
☂Each of the green and yellow systems has a fire shutoff valve in its line upstream of its engine-driven pump.
☂The flight crew can close it by pushing the ENG 1(2) FIRE pushbutton.

✈LEAK MEASUREMENTS VALVE'S
☂Each system has a leak measurement valve upstream of the primary flight controls.
☂These valves, which measure the leakage in each circuit, are closed by operation of the LEAKMEASUREMENT VALVES pushbutton switch on the maintenance panel.

✈Leakage limitation

✈FILTERS
☂Filters clean the hydraulic fluid as follows ☂HP filters on each system and on the reservoir filling system and the normal braking system
☂return line filters on each line
☂Case drain filters on engine pumps and the blue electric pump (which permit maintenance crew to monitor pump wear by inspecting the filters for the presence of metallic particles).

✈RESERVOIR PRESSURIZATION
☂Normally,  HP  bleed air from engine 1 pressurizes the hydraulic reservoirs automatically.
☂If the bleed air pressure is too low, the system takes bleed air pressure from the crossbleed duct.
☂The systems maintain a high enough pressure to prevent their pumps from cavitating.

✈OVERHEAD PANEL discussion
ENG 1 (2) PUMP pb
⛑On : - The pump pressurizes the system when the engine is running.
⛑OFF:- The pump is depressurized. The generation of hydraulic power stops.
⛑ FAULT lt :-This amber light comes on, and the  ECAM  caution appears, if :‐
☠The reservoir level is low
☠The reservoir overheats
☠The reservoir air pressure is low
☠The pump pressure is low (inhibited on the ground, when the engine is stopped).

☂This light goes out, when the crew selects OFF, except during an overheat. (The light stays on as long as the overheat lasts).

✈ BLUE ELEC PUMP pb (guarded) 
☂AUTO : If AC power is available, the electric pump operates :
⛑In flight‐On the ground
⛑if one engine is running or
⛑ if the crew has pressed the BLUE PUMP OVRD pushbutton on the maintenance panel.
☂OFF : The pump is de-energized.
☂FAULT lt : This amber light comes on, and a caution appears on the  ECAM.

✈NOTE- Same as green or blue pump in yellow

✈PTU PB SWITCH:-
⛑AUTO-The power transfer unit runs automatically when the differential pressure between the green and yellow systems is more than  500 PSI.
Note: OFF : The  PTU  is inhibited during the first engine start and automatically tested during the second engine start.
⛑OFF-Both the green and the yellow  PTU  electrohydraulic valves close. Power transfer stops
⛑FAULT- a this amber light comes on , when CAUTION appears on the ECAM.

✈RAT MAN ON pb
☂The flight crew may extend the  RAT  at any time by pressing the RAT MAN ON pushbutton.
☂Note: The  RAT  extends automatically if AC BUS 1 and AC BUS 2 are lost.

✈MAINTENANCE PANEL
☂BLUE PUMP OVRD pb sw (guarded)
⛑ON : The blue electric pump is on if the ELEC PUMP pushbutton switch on the  HYD  panel is at AUTO.
⛑Off : The blue electric pump is off.

☂LEAK MEASUREMENT VALVES pb sw (guarded)
⛑OFF: The corresponding electrohydraulic valve closes and shuts off hydraulic supply to the primary flight controls.
⛑On : The corresponding electrohydraulic valve opens to go back to normal hydraulic supply.

✈ECAM HYD PAGE

(1) Reservoir quantity- It is in green, unless the fluid level goes below the warning level, in which case it becomes amber
(2) Reservoir LO AIR PRESS-This appears in amber, and a caution appears on  ECAM, if the air pressure for the indicated reservoir drops below normal.

(3) Reservoir OVHT This appears in amber, and a caution appears on  ECAM, if the temperature of returning hydraulic fluid temperature at the inlet to its reservoir is above normal.
(4)FIRE VALVE
Cross line -Amber: The valve is fully closed.
In line - Green :The valve is not fully closed. (5)OVHT -This appears in amber if the electric pump for that system (blue or yellow) overheats.
(6)RAT
RAT  -White :- RAT is Stowed
RAT - Green :-RAT is not stowed
RAT  -Amber :Pressure for stowing the  RAT  has been applied, or the  RAT  pump is not available.
(7)ELEC -This legend, normally white, becomes amber if the associated power supply fails.
(8) YELLOW ELEC PUMP control
White : The electric pump is off.
Green : The electric pump is ON.
(9)PTU  control

1)⛑Green :PTU pushbutton switch is in AUTO and the  PTU  is not transferring pressure.
⛑Amber: The  PTU pb-sw  is OFF.
2)⛑Green : The  PTU  is supplying the green hydraulic system.
3)Green : The  PTU  is supplying the yellow hydraulic system.
(10) ENG PUMP control and low pressure indication
⛑In line (Green) : The pushbutton switch for the designated PUMP is on and hydraulic pressure is normal.
⛑Cross line (Amber) : The pushbutton switch for the designated PUMP is OFF.
⛑ “LO” (Amber) : The pushbutton switch for the designated PUMP is on and hydraulic pressure is LOW.

(11)SYSTEM LABEL-
⛑Pressure >1450psi - green or white
⛑pressure <1450psi - amber
(12) System pressure
(13) PUMP This legend, normally white, becomes amber when N2 is below idle.

✈HYD PTU : This memo appears in green, when the power transfer unit is running.

✈RAT OUT : This memo appears in green, if the Ram Air Turbine is not fully stowed. The color changes to amber during flight phases 1 and 2.

✈SAFETY PRECAUTIONS
☂make sure that you obey all the  AMM safety procedures.
☂ Make sure that the hydraulic system you work on is isolated before you pressurize the other hydraulic systems.
☂Make sure that the travel ranges of the flight controls are clear. (Movement can cause injury to persons and/or damage to the aircraft).

☂Do not get hydraulic fluid or hot gas from hydraulic reservoir on your body.(Use protective clothing to prevent risk of poisoning and burns.)
☂ Use solvents, cleaning agents, sealants and other special materials in a ventilated area.
☂ To prevent inadvertent breathing or contact with your body, use applicable gloves, eye protections and face mask.
☂Install safety devices and warning before working on or near landing gear and related doors.

✈HYD SYSTEM MAINTENANCE TYPE'S
☂Air in hydraulic system
☂Hydraulic reservoir servicing
☂Hydraulic fluid sampling
☂External leaks.

✈Dispatch with hydraulic leak

✈Necessary tools for hydraulic system

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