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A
737-300/400/500MAINTENANCE MANUAL
B. Extension
(1) When the control lever is moved to DN position, hydraulic pressure is directed to the main gear actuator, the lock port of the downlock actuator, and to the modular package. After passing through the modular package, pressure reaches the unlock port of the uplock actuator. Pressure to and from the uplock actuator is unrestricted and the actuator moves quickly to unlock the gear. After retraction, as soon as retraction pressure leaves the main actuator, the full weight of the gear hangs on the uplock hook. To prevent the possibility of main actuator extension force further loading the hook, and so causing noisy disengagement of the uplock, the transfer cylinder goes into action. On the first surge of pressure in the main actuator down line, the cylinder transfers pressure to the main actuator up line. Loss of transfer cylinder pressure from the up line is delayed by the flow limiting valve in the modular package. For a moment, pressure is equal on both ends of the main actuator, and the piston differential area creates an up force. The uplock actuator extends to unlock the hook during the up force period and the gear extends. On extension, locking pressure on the downlock actuator pulls the lock strut into the overcenter locked position. Spring bungees apply a force to keep the strut in locked position.
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A
737-300/400/500MAINTENANCE MANUAL
MAIN LANDING GEAR EXTENSION AND RETRACTION - TROUBLE SHOOTING
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1. General_______
A. Trouble shooting the main gear retraction mechanism requires the airplane to be jacked for gear retraction per Chapter 7, Airplane Jacking. External hydraulic power from a test bench capable of a varying flow rate and electrical power must be provided. Three men are required. One stationed in the control cabin to operate the landing gear control lever, one stationed at the hydraulic test bench to vary retraction speed or stop the gear in an intermediate position, and one stationed at the wheel well to observe the gear action. The control cable system must be correctly rigged and hydraulic reservoirs filled to correct level. Close observation of the gear action should reveal the cause of the trouble.
2. Trouble Shooting Charts
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A 737-300/400/500MAINTENANCE MANUAL
Insert inline pressure gage at unlock part of downlock actuator. Pressurize hydraulic system. Check inline gage pressure and compare with cabin hydrau-lic gage pressure. IF -
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