To close and lock the L/G doors, the L/G door selector-valve is energized. Hydraulic pressure is supplied through Port B, to make sure that the piston is fully released. The NLG doors close and when the door pin strikes the upper hook jaw, it causes the hook to pivot to the closed position. The lock-lever return-spring causes the lock-lever to pivot and engage the hook cam, which locks the hook in the closed position.

 (c)
 Proximity Sensors

 During the operation of the locking mechanism, the target to proximity sensor position changes. This positional change causes an uplock 'locked' or 'unlocked' signal to be supplied to the LGCIU's.
R 1EFF : ALL 1 32-31-00Page 79 1 1 May 01/05 1 1 1CES 1 (d) Hydraulic Failure

 When the hydraulic system is not available, the door uplock is released by the mechanical operation of the free-fall release-cam. When the free-fall extension-handle is rotated, it rotates the cam shaft. Rotation of the cam shaft causes the release cam to disengage the lock lever from the hook cam. The hook pivots open due to the return spring and door pin forces.
 The reset of the free-fall release-cam (free-fall system) resets the uplock to its 'normal' open position.
 (e) Ground Door Opening
 The ground door opening system uses a separate release cam which operates in the same way as the free-fall release cam.
 N. MLG Lockstay Actuator
 **ON A/C 301-399,
 (Ref. Fig. 040)
 **ON A/C ALL
 The lockstay actuator is a hydraulic unit with rate control devices. The main components of the actuator are:
 -
a cylinder

 -
a piston

 -
a two way restrictor valve

 -
a pressure relief valve.

 The lockstay, that moves to an overcenter position, locks the L/G in the fully extended position.
 A more detailed description and operation is given in (Ref. 32-11-00).
 P. NLG Downlock Release Actuator
 (Ref. Fig. 041)
 **ON A/C 301-399,
 (Ref. Fig. 042)
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 MLG Lockstay Actuator
 Figure 040
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 NLG Downlock Release Actuator Figure 041
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 NLG Downlock Release Actuator - Schematic
 Figure 042 
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 **ON A/C ALL
 (1) Description
 The lockstay actuator is a double acting hydraulic actuator.
 The lockstay, that moves to an overcenter position, locks the NLG in the fully extended position.
 (2) Operation
 (a)
 NLG Extension

 When you extend the NLG , the two lockstay-actuator hydraulic-ports (A and B), are open to return. As the NLG extends, the two lock springs force the lockstay and drag strut to straighten. The lockstay is pulled to an overcenter position by the lock springs. When the NLG doors start to close, the full area of the lockstay actuator is pressurised, through port B. This makes sure that the lockstay is in the overcenter position. After the NLG has extended, the pressure remains to keep it in the locked position (if the landing-gear control-lever is in the DOWN position).

 (b)
 NLG Retraction

 When you retract the NLG, hydraulic pressure acts on the annular face of the piston, through port A. The actuator then retracts. As the actuator retracts, it breaks the overcenter lock, the lockstay and side stay fold into position against the tension of the locksprings.

 (c)
 Restrictor Valve

 The restrictor valve is installed in the actuator assembly , and decreases the speed of operation of the downlock actuator. This causes a decrease in the speed of operation of the lockstay and the NLG.

 (d)
 Proximity Sensors

 During the operation of the lockstay assembly, the related position of the target and proximity sensor changes. This change causes a NLG 'locked' or 'unlocked' signal to be supplied to the LGCIU's.
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 Q. In-line Check Valves
 (Ref. Fig. 043)
 (1) General
 There are five in-line check-valves installed in the L/G hydraulic system.
 The check-valves have a cylindrical body, made of stainless steel or aluminium alloy, which contains a poppet and a spring. There are threaded hydraulic connections (of different dimensions) at each end of the body, that connect the check valve to the hydraulic system. An internal poppet is held against the valve seat (in the closed position) by a spring to make a metal-to-metal seal.
　
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