DOC AIRBUS | AMM A320FMAIN GEAR - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The main landing gear (MLG) has two leg assemblies. The MLG legs, each with a twin-wheel assembly, are installed in the wings. They retract inboard into bays in the fuselage. The MLG supports the aircraft on the ground and (through the shock absorbers in the legs) absorbs the loads during landing, take-off and taxiing. When an MLG is extended, a side-stay assembly prevents sideways movement of the MLG and helps keep it extended.
** ON A/C NOT FOR ALL The main landing gear (MLG) has two leg assemblies. The MLG legs, each with a twin-wheel assembly, are installed in the wings. They retract inboard into bays in the fuselage. The MLG supports the aircraft on the ground and (through the shock absorbers in the legs) absorbs the loads during landing, take-off and taxiing. When an MLG is extended, a side-stay assembly prevents sideways movement of the MLG and helps keep it extended.
2. Component Location
** ON A/C NOT FOR ALL | FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C NOT FOR ALL | |||||
| 2505GM | SIDE STAY ASSY-MLG, L | 731 | 32-11-16 | ||
| ** ON A/C ALL | |||||
| 2501GM | LEG ASSY-MLG, L | 731 | 32-11-11 | ||
| 2502GM | LEG ASSY-MLG, R | 741 | 32-11-11 | ||
| 2506GM | SIDE STAY ASSY-MLG, R | 741 | 32-11-16 | ||
| ** ON A/C NOT FOR ALL | |||||
| 2505GM | SIDE STAY ASSY-MLG, L | 210 | 32-11-16 | ||
| ** ON A/C ALL | |||||
| 2823GM | DAMPER-TORQUE LINK, MLG L | 731 | 32-11-29 | ||
| 2824GM | DAMPER-TORQUE LINK, MLG R | 741 | 32-11-29 | ||
A. Main Landing Gear
Each MLG includes these components:
Each MLG includes these components:
- a MLG leg which includes a shock absorber
- torque links
- a side-stay assembly
- a retraction actuator
- electrical and hydraulic dressings.
B. Main Landing Gear Leg
Each MLG leg has two primary structural components, which are the main fitting and the sliding tube. Each of these components is a one-piece assembly and contains the shock absorber.
An axle, which is a part of the sliding tube, can contain a wheel-speed tachometer, a brake-cooling fan and/or a tire-pressure sensor for each wheel.
Each MLG leg has two primary structural components, which are the main fitting and the sliding tube. Each of these components is a one-piece assembly and contains the shock absorber.
An axle, which is a part of the sliding tube, can contain a wheel-speed tachometer, a brake-cooling fan and/or a tire-pressure sensor for each wheel.
C. Torque Links
The upper torque-link and the lower torque-link align the axle. They attach to the lugs at the front of the main fitting and the sliding tube. There is a torque-link damper at the interface of the upper and lower torque-links. The torque-link damper absorbs the vibrations that can occur during landing.
The upper torque-link and the lower torque-link align the axle. They attach to the lugs at the front of the main fitting and the sliding tube. There is a torque-link damper at the interface of the upper and lower torque-links. The torque-link damper absorbs the vibrations that can occur during landing.
D. Side-Stay Assembly
A two-piece side-stay assembly connects the MLG leg main-fitting and the wing structure. It prevents the movement of the landing-gear leg sideways. The side-stay assembly is locked in the down position by a two-piece lock-stay assembly.
A two-piece side-stay assembly connects the MLG leg main-fitting and the wing structure. It prevents the movement of the landing-gear leg sideways. The side-stay assembly is locked in the down position by a two-piece lock-stay assembly.
E. Retraction Actuator
A retraction actuating cylinder (Ref. AMM D/O 32-31-00-00) connects the wing structure and the landing-gear forward hinge-point. The retraction actuating cylinder retracts the MLG leg (sideways) into the fuselage.
A retraction actuating cylinder (Ref. AMM D/O 32-31-00-00) connects the wing structure and the landing-gear forward hinge-point. The retraction actuating cylinder retracts the MLG leg (sideways) into the fuselage.
F. Inflation Valve
The main fitting and the sliding tube each have an inflation valve. The valves are used to fill the shock absorber with hydraulic fluid and nitrogen.
The main fitting and the sliding tube each have an inflation valve. The valves are used to fill the shock absorber with hydraulic fluid and nitrogen.
G. Dressings
Between the main fitting and the sliding tube there is a slave link. It holds the electrical cables and the hydraulic pipes, to make sure they do not catch on the wheels.
A spare-seal activating-valve is on the main fitting. This operates if there is a hydraulic leak through the gland seals. It is only used until the gland seals can be examined/replaced.
The hydraulic pipes and the electrical harness are in rigid and flexible conduits. The conduit routing gives:
Between the main fitting and the sliding tube there is a slave link. It holds the electrical cables and the hydraulic pipes, to make sure they do not catch on the wheels.
A spare-seal activating-valve is on the main fitting. This operates if there is a hydraulic leak through the gland seals. It is only used until the gland seals can be examined/replaced.
The hydraulic pipes and the electrical harness are in rigid and flexible conduits. The conduit routing gives:
- protection from runway debris, birdstrikes and flailing tire treads
- maximum separation of the two systems.
4. Power Supply
Not Applicable.
** ON A/C NOT FOR ALL Not Applicable.
** ON A/C NOT FOR ALL
6. Component Description
The MLG leg has a main fitting and a sliding tube, which together make the shock absorber. The torque-links align the main fitting and sliding tube, but lets vertical movement between the parts occur. A torque link damper decreases the landing vibrations through the torque links.
A MLG retraction actuating cylinder extends and retracts the MLG (Ref. AMM D/O 32-31-00-00).
The MLG leg has a main fitting and a sliding tube, which together make the shock absorber. The torque-links align the main fitting and sliding tube, but lets vertical movement between the parts occur. A torque link damper decreases the landing vibrations through the torque links.
A MLG retraction actuating cylinder extends and retracts the MLG (Ref. AMM D/O 32-31-00-00).
A. Main Fitting
The main fitting is made of die-forged ultra-high-tensile steel, and includes:
To prevent possible stress points, the main fitting does not have screw-threads or screw-thread inserts.
The external lugs and brackets on the main fitting hold these parts:
A hollow cross-tube at the top of the main fitting has two attachment-fittings that connect the MLG to the airframe. The aft attachment-fitting has a machined lug that holds the rear spherical bearing. The forward attachment-fitting has a cylindrical lug that connects to the forward spherical bearing. A pintle pin connects the aft attachment-fitting of the MLG gear to RIB5. The pintle pin has greasers to lubricate the attachment fitting with grease. A seal assembly and locking ring, on the forward attachment fitting has greasers to lubricate the spherical bearing.
A drag stay between the main fitting and the forward end of the hollow tube holds the MLG retraction actuator. A machined lug on the drag stay connects the lock stay.
The forward and the aft fitting assemblies transmit vertical loads (and small drag loads caused by friction) to the airframe.
The main fitting is made of die-forged ultra-high-tensile steel, and includes:
- the main barrel
- the drag stay
- the cross tube
- the aircraft interface attachment-lugs.
To prevent possible stress points, the main fitting does not have screw-threads or screw-thread inserts.
The external lugs and brackets on the main fitting hold these parts:
- the MLG retraction-actuating-cylinder
- the lock stay
- the brake manifold
- the fixed fairing
- the uplock pin
- the side-stay assembly
- the upper torque-link
- the spare-seal activating-valve
- the upper slave-link
- a beam (to install or remove the MLG during maintenance).
A hollow cross-tube at the top of the main fitting has two attachment-fittings that connect the MLG to the airframe. The aft attachment-fitting has a machined lug that holds the rear spherical bearing. The forward attachment-fitting has a cylindrical lug that connects to the forward spherical bearing. A pintle pin connects the aft attachment-fitting of the MLG gear to RIB5. The pintle pin has greasers to lubricate the attachment fitting with grease. A seal assembly and locking ring, on the forward attachment fitting has greasers to lubricate the spherical bearing.
A drag stay between the main fitting and the forward end of the hollow tube holds the MLG retraction actuator. A machined lug on the drag stay connects the lock stay.
The forward and the aft fitting assemblies transmit vertical loads (and small drag loads caused by friction) to the airframe.
B. Sliding Tube
MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL
MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL
The sliding tube, which is ultra-high tensile-steel, moves in the main fitting and is a primary component of the shock absorber. The sliding tube has a chromed external face.
The axle and sliding tube are a one-piece item. The shock-absorber (main fitting) lower-bearing is put as low as possible to stop bend of the sliding tube. It also makes the structure lighter.
The internal diameter of the barrel of the sliding tube is reduced to engage the lower diaphragm of the shock absorber. The diaphragm is held in the sliding tube with a tube which screws into the jacking dome below the axle.
The sliding tube, which is ultra-high tensile-steel, moves in the main fitting and is a primary component of the shock absorber. The sliding tube has a chromed external face.
The axle and sliding tube are a one-piece item. The shock-absorber (main fitting) lower-bearing is put as low as possible to reduce the bending moments on the sliding tube. It also makes the structure lighter.
A lip in the sliding tube engages the head of a cylinder, to make a second stage chamber. The jacking dome is at the bottom of the cylinder.
The lower torque-link attachment-lugs are at the front of the sliding tube. The lower slave-link attachment lug is at the rear of the sliding tube.
The debogging lugs are on the rear face of the slave-link bracket. (It is not necessary to remove the components of the main leg to use the debogging lugs).
The axle has sleeves, which give the axle protection. Brake mounting-flanges are machined as part of the axle, to hold each brake unit. The brake unit connects to the flange by nine dowels and three bolts. The positions of the dowels and bolts prevent incorrect assembly.
MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL The axle and sliding tube are a one-piece item. The shock-absorber (main fitting) lower-bearing is put as low as possible to stop bend of the sliding tube. It also makes the structure lighter.
The internal diameter of the barrel of the sliding tube is reduced to engage the lower diaphragm of the shock absorber. The diaphragm is held in the sliding tube with a tube which screws into the jacking dome below the axle.
The sliding tube, which is ultra-high tensile-steel, moves in the main fitting and is a primary component of the shock absorber. The sliding tube has a chromed external face.
The axle and sliding tube are a one-piece item. The shock-absorber (main fitting) lower-bearing is put as low as possible to reduce the bending moments on the sliding tube. It also makes the structure lighter.
A lip in the sliding tube engages the head of a cylinder, to make a second stage chamber. The jacking dome is at the bottom of the cylinder.
The lower torque-link attachment-lugs are at the front of the sliding tube. The lower slave-link attachment lug is at the rear of the sliding tube.
The debogging lugs are on the rear face of the slave-link bracket. (It is not necessary to remove the components of the main leg to use the debogging lugs).
The axle has sleeves, which give the axle protection. Brake mounting-flanges are machined as part of the axle, to hold each brake unit. The brake unit connects to the flange by nine dowels and three bolts. The positions of the dowels and bolts prevent incorrect assembly.
C. Shock Absorber
MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL
MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL
The shock absorber is a telescopic oleo-pneumatic unit which includes the sliding tube. It is in the main fitting to transmit the landing, take-off and taxiing loads to the wing.
When the shock absorber compresses, the load transmits to the hydraulic fluid and nitrogen gas. The recoil stroke is slow to make sure that the aircraft does not become airborne again.
The shock absorber is a two stage unit and contains four chambers:
The damping tube, which contains the first stage orifice, attaches to the head of the 2nd stage cylinder and has a fluid connection. The movement of the damping tube through the orifice block decreases the fluid flow in the 1st stage damping. This increases the damping effect. A floating piston in the 2nd stage cylinder separates the hydraulic fluid of the compression chamber and the gas of the 2nd stage chamber. During a compression stroke, the floating piston does not move down until the gas pressures of the 1st and the 2nd stage chambers are equal.
MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL MLG Shock Absorber - Sectional View ** ON A/C NOT FOR ALL When the shock absorber compresses, the load transmits to the hydraulic fluid and nitrogen gas. The recoil stroke is slow to make sure that the aircraft does not become airborne again.
The shock absorber is a two stage unit and contains four chambers:
- a 1st stage gas chamber contains an LP gas pressure and some hydraulic fluid
- a recoil chamber that contains hydraulic fluid
- a compression chamber that contains hydraulic fluid
- a 2nd stage gas chamber that contains a HP gas pressure.
- the fluid flow from the recoil chamber into the gas chamber
- the fluid flow from the gas chamber into the compression chamber.
The damping tube, which contains the first stage orifice, attaches to the head of the 2nd stage cylinder and has a fluid connection. The movement of the damping tube through the orifice block decreases the fluid flow in the 1st stage damping. This increases the damping effect. A floating piston in the 2nd stage cylinder separates the hydraulic fluid of the compression chamber and the gas of the 2nd stage chamber. During a compression stroke, the floating piston does not move down until the gas pressures of the 1st and the 2nd stage chambers are equal.
(1) Upper Bearing
The sliding tube connects to the main fitting by a bearing and a bearing housing. A recoil valve assembly (on the bearing housing) has a recoil-orifice-plate and recoil chamber to control the flow of fluid. An annular travel-stop inside the sliding tube is attached by the dowels which hold the bearing housing. The travel-stop touches the center tube flange when the unit is fully extended, and holds the sliding tube.
The sliding tube connects to the main fitting by a bearing and a bearing housing. A recoil valve assembly (on the bearing housing) has a recoil-orifice-plate and recoil chamber to control the flow of fluid. An annular travel-stop inside the sliding tube is attached by the dowels which hold the bearing housing. The travel-stop touches the center tube flange when the unit is fully extended, and holds the sliding tube.
(2) Upper Bearing
The sliding tube connects to the main fitting by a bearing and a bearing housing. A recoil valve assembly (on the bearing housing) has a recoil-orifice-plate and recoil chamber to control the flow of fluid. The upper -bearing housing threads are engaged onto the sliding piston.
The sliding tube connects to the main fitting by a bearing and a bearing housing. A recoil valve assembly (on the bearing housing) has a recoil-orifice-plate and recoil chamber to control the flow of fluid. The upper -bearing housing threads are engaged onto the sliding piston.
(3) Upper Diaphragm and Tube Sub-assembly
The upper diaphragm and tube sub-assembly is connected to the main fitting by a lateral pin. The lateral pin has the 1st stage charging-valve which fills the shock absorber with hydraulic fluid or nitrogen gas. An oil-level tube goes through the diaphragm into the gas chamber. This gives the correct level of fluid in the shock absorber during the maintenance procedures.
The tube of the diaphragm and tube sub-assembly goes into the open top of the sliding tube. The top part of the tube has four holes in the area of the gas chamber. These holes permit fast separation of the fluid and the gas when the MLG leg goes from the retracted to the extended position.
A diaphragm with a baffle, is at the bottom of the diaphragm and tube sub-assembly. The baffle causes the defusion of the fluid that goes through it, to decrease the quantity of absorbed gas. The diaphragm has a compression-orifice-plate that lets full flow during the compression, but decreases the flow during the recoil. A damping tube, on the lower diaphragm, moves through the baffle. It has a set of four radially-aligned holes that give the two-stage damping effect of the shock absorber.
You can remove the shock absorber from the main fitting while it is on the aircraft. You must remove the lateral retaining pin and the main-gland lower-bearing assembly first. (To get the sufficient ground clearance, it is necessary to increase the jacked height of the aircraft).
The upper diaphragm and tube sub-assembly is connected to the main fitting by a lateral pin. The lateral pin has the 1st stage charging-valve which fills the shock absorber with hydraulic fluid or nitrogen gas. An oil-level tube goes through the diaphragm into the gas chamber. This gives the correct level of fluid in the shock absorber during the maintenance procedures.
The tube of the diaphragm and tube sub-assembly goes into the open top of the sliding tube. The top part of the tube has four holes in the area of the gas chamber. These holes permit fast separation of the fluid and the gas when the MLG leg goes from the retracted to the extended position.
A diaphragm with a baffle, is at the bottom of the diaphragm and tube sub-assembly. The baffle causes the defusion of the fluid that goes through it, to decrease the quantity of absorbed gas. The diaphragm has a compression-orifice-plate that lets full flow during the compression, but decreases the flow during the recoil. A damping tube, on the lower diaphragm, moves through the baffle. It has a set of four radially-aligned holes that give the two-stage damping effect of the shock absorber.
You can remove the shock absorber from the main fitting while it is on the aircraft. You must remove the lateral retaining pin and the main-gland lower-bearing assembly first. (To get the sufficient ground clearance, it is necessary to increase the jacked height of the aircraft).
(4) Gland-Housing Assembly
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL
A gland-housing assembly, at the bottom end of the main-fitting barrel, seals the joint between the barrel and the sliding tube. This assembly has:
Three threaded pins attach the gland housing and the bearing to the barrel of the main fitting. The threaded pins have greasers to lubricate the bearing.
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL - a gland housing, that holds the top (spare) and the bottom (main) gland seals
- a bearing, that keeps the sliding tube correctly aligned
- a wiper ring, that keeps the unwanted material out of the shock absorber.
Three threaded pins attach the gland housing and the bearing to the barrel of the main fitting. The threaded pins have greasers to lubricate the bearing.
(5) Spare-Seal Activating Valve
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL
Each main fitting has a spare-seal activating-valve. This valve can isolate the bottom gland seals if a leak occurs. The activating valve is on the barrel of the main fitting, adjacent to the gland-housing assembly. When the activating valve closes, it isolates the bottom set of seals (from the fluid pressure).
The spare seal operates when you remove the cap screw and turn the threaded valve-stem in. This puts the ball valve on its seat, which isolates the bottom gland seals and causes the top gland seals to seal the joint.
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL MLG Shock Absorber - Gland Housing Sub-Assembly and Spare Seal Activating-Valve ** ON A/C NOT FOR ALL The spare seal operates when you remove the cap screw and turn the threaded valve-stem in. This puts the ball valve on its seat, which isolates the bottom gland seals and causes the top gland seals to seal the joint.
(6) Spare-Seal Activating Valve
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL
Each main fitting has a spare-seal activating valve. This valve can isolate the bottom gland seals if a leak occurs. The activating valve is on the barrel of the main fitting, adjacent to the gland-housing assembly. When the activating valve closes, it isolates the bottom set of seals (from the fluid pressure).
The spare seal operates when you turn the threaded valve-stem in. This puts the ball valve on its seat, which isolates the bottom gland seals and causes the top gland seals to seal the joint.
MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL MLG Shock Absorber - Gland Housing Sub-Assembly and Spare-Seal Activating Valve ** ON A/C NOT FOR ALL The spare seal operates when you turn the threaded valve-stem in. This puts the ball valve on its seat, which isolates the bottom gland seals and causes the top gland seals to seal the joint.
D. Torque Link Damper
The torque-link-damper is a spring-centered, two-way hydraulic unit, which has its own (pressurized) hydraulic reservoir. Its function is to decrease the landing vibrations through the torque links.
The torque-link damper has a damper body with a reservoir at the top and a check valve at the bottom. A bleed screw and a bleed plug are installed in the top of the reservoir. The torque-link damper is on the bottom of the upper torque-link and operates through the apex bolt from the lower torque link.
The hydraulic fluid contents of the damper are shown by the extension of the reservoir when it is pressurized. When the damper is filled and pressurized with hydraulic fluid, the reservoir piston moves through the barrel. At the same time the cage moves to compress the spring. When the cage moves to the correct position along the barrel, the word FULL shows. If the quantity of hydraulic fluid in the damper is less than the sufficient quantity, the word REFILL shows.
The torque-link-damper is a spring-centered, two-way hydraulic unit, which has its own (pressurized) hydraulic reservoir. Its function is to decrease the landing vibrations through the torque links.
The torque-link damper has a damper body with a reservoir at the top and a check valve at the bottom. A bleed screw and a bleed plug are installed in the top of the reservoir. The torque-link damper is on the bottom of the upper torque-link and operates through the apex bolt from the lower torque link.
The hydraulic fluid contents of the damper are shown by the extension of the reservoir when it is pressurized. When the damper is filled and pressurized with hydraulic fluid, the reservoir piston moves through the barrel. At the same time the cage moves to compress the spring. When the cage moves to the correct position along the barrel, the word FULL shows. If the quantity of hydraulic fluid in the damper is less than the sufficient quantity, the word REFILL shows.
E. Side Stay Assembly 2505GM (2506GM)
MLG Side Stay - Lower Cardan Joint ** ON A/C NOT FOR ALL
MLG Side Stay - Lower Cardan Joint ** ON A/C NOT FOR ALL
The side stay assembly is between the rear spar of the wing and the main fitting of the MLG leg. A cardan (universal) joint connects the side stay assembly at each position. These joints let each connection point turn around two axes.
The primary components of the side stay assembly are:
MLG Side Stay - Lower Cardan Joint ** ON A/C NOT FOR ALL MLG Side Stay - Lower Cardan Joint ** ON A/C NOT FOR ALL The primary components of the side stay assembly are:
- a basic side stay
- a lock stay
- a lock-stay actuator
- two hydraulic hoses (from the Green hydraulic system to the lock-stay actuator)
- two lock springs
- the proximity sensors and their related targets.
(1) Basic Side Stay
The basic side stay has two links with a central pivot pin. The upper link is an 'H' section member that has bushed lugs. These attach to the lock-stay actuator, the lock springs and the lock stay. The lower link is also 'H' section, that has forked ends. The cardan joints connect the side-stay to the wing structure and the main fitting.
The basic side stay has two links with a central pivot pin. The upper link is an 'H' section member that has bushed lugs. These attach to the lock-stay actuator, the lock springs and the lock stay. The lower link is also 'H' section, that has forked ends. The cardan joints connect the side-stay to the wing structure and the main fitting.
(2) Lock Stay
The lock stay gives the mechanical downlock for the main landing gear. It has two 'H' section links that move around a central pin. The forked ends attach the lock stay to the basic side-stay and to the main fitting.
The lower link of the lock stay has bushed lugs for the connection of the downlock actuator. The two pairs of lugs extend from the end of the lower link that connects to, and operates, the lock springs.
The upper link of the lock stay continues below the center pivot to give an overcenter stop. This gives an overcenter, geometric lock if there is a failure of the internal stop of the downlock actuator.
Two proximity sensors and their related targets are on the brackets. Other brackets on the upper link hold the electrical harnesses that connect to these proximity sensors.
The lock stay gives the mechanical downlock for the main landing gear. It has two 'H' section links that move around a central pin. The forked ends attach the lock stay to the basic side-stay and to the main fitting.
The lower link of the lock stay has bushed lugs for the connection of the downlock actuator. The two pairs of lugs extend from the end of the lower link that connects to, and operates, the lock springs.
The upper link of the lock stay continues below the center pivot to give an overcenter stop. This gives an overcenter, geometric lock if there is a failure of the internal stop of the downlock actuator.
Two proximity sensors and their related targets are on the brackets. Other brackets on the upper link hold the electrical harnesses that connect to these proximity sensors.
(3) Lock Springs
A pair of tension springs are in the bottom channel of the upper side stay. They attach between the upper end of the basic side stay and the lugs of the lock stay. The lock springs have an eye-end fitting at each end with a plain bush. The bushes turn on the attachment pins at each end. During the extension cycle the lock springs move the lock stay to an overcenter position (and keep it there).
A pair of tension springs are in the bottom channel of the upper side stay. They attach between the upper end of the basic side stay and the lugs of the lock stay. The lock springs have an eye-end fitting at each end with a plain bush. The bushes turn on the attachment pins at each end. During the extension cycle the lock springs move the lock stay to an overcenter position (and keep it there).
(4) Lock-Stay Actuator
During the MLG extension, the two lock-stay actuator ports are open to return. The fluid from Port A passes through a restrictor, which controls the rate of MLG extension. When the main landing gear extends, the two lock springs push the side stay and the lock stay to make them straight. The lock springs also pull the lock stay to an overcenter position. When the main door starts to close, the full area side of the lock stay actuator is pressurized (Port B). This makes sure that the lock stay is in the overcenter position.
During the MLG retraction, the hydraulic fluid from port A goes through a restrictor and onto the actuator annular-end. The piston rod retracts, and breaks the overcenter lock, to fold the side-stay and the lock stay against the lock springs tension.
The lock stay actuator pulls against the lock spring forces at a very low pressure. This makes sure that the lock stay starts to fold before the high pressure is transmitted to the retraction actuator. A pressure relief-valve is in the valve-housing to keep the pressure level in the lock-stay actuator. to a specified limit. If a high pressure does occur, the pressure relief-valve opens to let the fluid go through Port A, to return.
The manufacturer sets the lock-stay actuator to a specified length. No adjustment is necessary when it is on the landing-gear leg.
You can install a split sleeve on the piston rod of the lock-stay actuator to give a strong ground lock.
During the MLG extension, the two lock-stay actuator ports are open to return. The fluid from Port A passes through a restrictor, which controls the rate of MLG extension. When the main landing gear extends, the two lock springs push the side stay and the lock stay to make them straight. The lock springs also pull the lock stay to an overcenter position. When the main door starts to close, the full area side of the lock stay actuator is pressurized (Port B). This makes sure that the lock stay is in the overcenter position.
During the MLG retraction, the hydraulic fluid from port A goes through a restrictor and onto the actuator annular-end. The piston rod retracts, and breaks the overcenter lock, to fold the side-stay and the lock stay against the lock springs tension.
The lock stay actuator pulls against the lock spring forces at a very low pressure. This makes sure that the lock stay starts to fold before the high pressure is transmitted to the retraction actuator. A pressure relief-valve is in the valve-housing to keep the pressure level in the lock-stay actuator. to a specified limit. If a high pressure does occur, the pressure relief-valve opens to let the fluid go through Port A, to return.
The manufacturer sets the lock-stay actuator to a specified length. No adjustment is necessary when it is on the landing-gear leg.
You can install a split sleeve on the piston rod of the lock-stay actuator to give a strong ground lock.
F. Dressings
The MLG dressings are the hydraulic lines and the electrical wiring (and the parts that attach, hold and prevent damage to them). The routing of the dressings gives maximum separation for the systems and protection from possible damage.
The dressings are flexible conduits or rigid conduits and pipes. The parts that do not need to move are rigid and the parts that are at joints (such as the wing/gear interface, across the torque and slave links, and the wheel brakes) are flexible.
The MLG dressings are the hydraulic lines and the electrical wiring (and the parts that attach, hold and prevent damage to them). The routing of the dressings gives maximum separation for the systems and protection from possible damage.
The dressings are flexible conduits or rigid conduits and pipes. The parts that do not need to move are rigid and the parts that are at joints (such as the wing/gear interface, across the torque and slave links, and the wheel brakes) are flexible.
(1) Hydraulic Dressings
The hydraulic dressings on the MLG complete the hydraulic circuits for:
The hydraulic dressings on the MLG complete the hydraulic circuits for:
- the MLG retraction actuator
- the lock-stay actuator
- the normal and alternate braking systems.
(2) Electrical Dressings
The electrical dressings on the MLG complete the electrical circuits to these systems/components:
The electrical dressings on the MLG complete the electrical circuits to these systems/components:
- the normal braking system (Ref. AMM D/O 32-42-00-00)
- the alternate braking systems (Ref. AMM D/O 32-43-00-00), (Ref. AMM D/O 32-44-00-00) and (Ref. AMM D/O 32-45-00-00)
- the brake temperature-monitoring system (Ref. AMM D/O 32-47-00-00)
- the brake cooling system (Ref. AMM D/O 32-48-00-00) (if installed)
- the TPIS (tire pressure indicating system) (Ref. AMM D/O 32-49-00-00) (if installed)
- the proximity switches (Ref. AMM D/O 32-31-00-00).
(3) Electrical Harnesses
The 1M and 2M electrical harnesses have cables which supply the electrical connection to the:
The disconnection point for the 1M harness is at the MLG disconnection box (Ref. 32-11-46). For the 2M harness, the disconnection point is outboard of the gear rib 5.
The 1M and 2M electrical harnesses have cables which supply the electrical connection to the:
- braking and anti-skid systems (Ref. AMM D/O 32-42-00-00), (Ref. AMM D/O 32-43-00-00), (Ref. AMM D/O 32-44-00-00) and (Ref. AMM D/O 32-47-00-00)
- position and warning systems (Ref. AMM D/O 32-60-00-00) and (Ref. AMM D/O 32-62-00-00)
- indicating and warning systems (Ref. AMM D/O 32-61-00-00).
The disconnection point for the 1M harness is at the MLG disconnection box (Ref. 32-11-46). For the 2M harness, the disconnection point is outboard of the gear rib 5.
(4) Electrical Harnesses
The 1M and 2M electrical harnesses have cables which supply the electrical connection to the:
The disconnection point for the 1M harness is at the MLG disconnection box (Ref. 32-11-46). For the 2M harness, the disconnection point is outboard of the gear rib 5.
The 1M and 2M electrical harnesses have cables which supply the electrical connection to the:
- braking and anti-skid systems (Ref. AMM D/O 32-42-00-00), (Ref. AMM D/O 32-43-00-00), (Ref. AMM D/O 32-44-00-00) and (Ref. AMM D/O 32-47-00-00)
- brake cooling system (Ref. AMM D/O 32-48-00-00)
- position and warning systems (Ref. AMM D/O 32-60-00-00) and (Ref. AMM D/O 32-62-00-00)
- indicating and warning systems (Ref. AMM D/O 32-61-00-00).
The disconnection point for the 1M harness is at the MLG disconnection box (Ref. 32-11-46). For the 2M harness, the disconnection point is outboard of the gear rib 5.
(5) Proximity Sensors
The proximity sensors and targets attach to the MLG in specified locations. They send position/status data to the Landing Gear Control and Interface Units (LGCIU's) (Ref. AMM D/O 32-31-00-00). These units use the data to:
The proximity sensors and targets attach to the MLG in specified locations. They send position/status data to the Landing Gear Control and Interface Units (LGCIU's) (Ref. AMM D/O 32-31-00-00). These units use the data to:
- control the retraction and extension sequences of the landing gear
- supply the indication/failure data of the MLG to the indication and warning systems in the cockpit.
7. Operation/Control and Indicating
MLG - Extension and Retraction Positions
MLG - Extension and Retraction Positions
A. Main Landing Gear
(1) Retraction
When you set the L/G control lever to UP, the hydraulic pressure goes to each MLG actuator and lock-stay actuator. Because the lock-stay actuator is more lightly loaded, it retracts first to release the overcenter lock of the lock stay. The lock stay folds against the tension of the lock springs. The retraction actuator then extends, to retract the MLG. The cardan joints of the lock stay and the side-stay let these units retract in different planes from that of the MLG.
The retraction cycle is:
When you set the L/G control lever to UP, the hydraulic pressure goes to each MLG actuator and lock-stay actuator. Because the lock-stay actuator is more lightly loaded, it retracts first to release the overcenter lock of the lock stay. The lock stay folds against the tension of the lock springs. The retraction actuator then extends, to retract the MLG. The cardan joints of the lock stay and the side-stay let these units retract in different planes from that of the MLG.
The retraction cycle is:
- the MLG doors open
- the MLG retracts
- the MLG doors close.
(2) Extension
When you set the L/G control lever to DOWN, the hydraulic pressure goes to:
The uplock actuator opens quickly (to keep a minimum load-time on the uplock hook). The tension in the lock springs and its own weight help to extend the MLG.
At the same time, the movement of the MLG causes the side-stay and the lock stay to open, until they go to their overcenter position. These movements help the hydraulic pressure in the lock-stay actuator to mechanically extend it. The lock-stay actuator then makes sure that the lock stay is overcenter. Also, it helps the lock springs keep the MLG in the locked down position, when the MLG doors close.
The extension cycle is:
When you set the L/G control lever to DOWN, the hydraulic pressure goes to:
- the uplock actuator
- the annular side of the retraction actuator
- the full area side of the lock-stay actuator.
The uplock actuator opens quickly (to keep a minimum load-time on the uplock hook). The tension in the lock springs and its own weight help to extend the MLG.
At the same time, the movement of the MLG causes the side-stay and the lock stay to open, until they go to their overcenter position. These movements help the hydraulic pressure in the lock-stay actuator to mechanically extend it. The lock-stay actuator then makes sure that the lock stay is overcenter. Also, it helps the lock springs keep the MLG in the locked down position, when the MLG doors close.
The extension cycle is:
- the MLG doors open
- the MLG extends
- the MLG doors close.
(1) Compression
During the compression, the sliding tube goes into the barrel of the main fitting. The capacity of the shock absorber reduces, which compresses the gas. The fluid goes through the damping head and lifts the compression-orifice plate off its seat, to let the fluid flow fully.
Initially, the fluid also flows from the compression chamber to the 1st stage gas chamber, through the first-stage orifices of the damping tube. While the shock absorber compresses, the damping tube and the first-stage orifices go through the damping head. The flow through the first-stage orifices stops, and the flow limits to that through the compression-orifice plate. This produces a two-stage damping effect. The gas compression in the 2nd stage chamber, pushes on the floating piston to help the damping. It also helps to make the damping effect and the compression effect of the oleo smooth.
At the same time, the fluid goes from the 1st stage gas chamber into the recoil chamber, through the openings in the upper bearing. This flow of fluid moves the recoil-orifice plate against the flange of a retaining ring, to let the fluid flow fully. The gas compression and the fluid transfer absorb the shock-loads from the MLG.
During the compression, the sliding tube goes into the barrel of the main fitting. The capacity of the shock absorber reduces, which compresses the gas. The fluid goes through the damping head and lifts the compression-orifice plate off its seat, to let the fluid flow fully.
Initially, the fluid also flows from the compression chamber to the 1st stage gas chamber, through the first-stage orifices of the damping tube. While the shock absorber compresses, the damping tube and the first-stage orifices go through the damping head. The flow through the first-stage orifices stops, and the flow limits to that through the compression-orifice plate. This produces a two-stage damping effect. The gas compression in the 2nd stage chamber, pushes on the floating piston to help the damping. It also helps to make the damping effect and the compression effect of the oleo smooth.
At the same time, the fluid goes from the 1st stage gas chamber into the recoil chamber, through the openings in the upper bearing. This flow of fluid moves the recoil-orifice plate against the flange of a retaining ring, to let the fluid flow fully. The gas compression and the fluid transfer absorb the shock-loads from the MLG.
(2) Recoil
The energy in the gas, which is in the 1st stage and the 2nd stage gas chambers, starts the recoil travel. The fluid goes through the recoil-orifice and the compression-orifice plates. The flow of fluid moves these plates to their almost closed position, so that the fluid movement is slow. This decreases the speed of the recoil travel.
A flow of fluid through the first-stage orifices in the damping tube only occurs if the recoil-orifice and the compression-orifice plates go into the compression chamber again. The gas in the 2nd stage chamber helps to make the extension effect of the shock absorber smooth.
The energy in the gas, which is in the 1st stage and the 2nd stage gas chambers, starts the recoil travel. The fluid goes through the recoil-orifice and the compression-orifice plates. The flow of fluid moves these plates to their almost closed position, so that the fluid movement is slow. This decreases the speed of the recoil travel.
A flow of fluid through the first-stage orifices in the damping tube only occurs if the recoil-orifice and the compression-orifice plates go into the compression chamber again. The gas in the 2nd stage chamber helps to make the extension effect of the shock absorber smooth.
(3) Compression and Recoil - 2nd Stage Gas Chamber
The compression and the expansion of the gas in the 2nd stage gas chamber helps to make the effect of the shock absorber smooth. This is transmitted through the floating piston to the oil and then to the remaining parts of the shock absorber assembly. This procedure helps to make a smooth landing.
The compression and the expansion of the gas in the 2nd stage gas chamber helps to make the effect of the shock absorber smooth. This is transmitted through the floating piston to the oil and then to the remaining parts of the shock absorber assembly. This procedure helps to make a smooth landing.