-
a L/G uplock

 -
a L/G door uplock

 -
a L/G downlock.

 The L/G uplocks are installed in each L/G bay to lock the L/G in the retracted position. The MLG uplocks have spring struts which keep the uplock in a set position. They also decrease the loads on the airframe structure when the MLG uplock pin goes into the lock.
 The L/G door uplock locks the L/G doors in the closed position. The L/G doors can be opened for maintenance on the ground (Ref. 32-12-00) and (Ref. 32-22-00).
 The lockstay locks the L/G in the extended position (Ref. 32-11-00) and (Ref. 32-21-00). The lockstay holds the L/G in the extended position because of its geometric (overcenter) position.
 4. Power Supply____________
 A. Electrical Power Supply
 (Ref. Fig. 013)

 B. Hydraulic Power Supply
 The Green Main Hydraulic-Power System (Ref. 29-11-00) supplies hydraulic power to operate the system.
 6. Interface_________ (Ref. Fig. 014)
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 Normal Extension and Retraction - Block Diagram
 Figure 013

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 Normal Extension and Retraction System - Interface Figure 014
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 7. Component Description_____________________
 A. L/G Control Lever (6GA)
 (Ref. Fig. 008)
 The L/G control lever is installed on the First Officers side of the center instrument panel to control the L/G extension and retraction (normal extension and retraction mode). The front face of the unit has a control lever and two arrows identified 'UP' and 'DOWN'.
 The control lever has a knurled wheel on the end of an arm. The arm moves in a slot in the face of the unit. Internal locks in the unit keep the arm in the fully UP or the fully DOWN position. The arm moves switches inside the unit, which supply electrical signals to the LGCIU's. A solenoid-operated baulk mechanism prevents an UP selection if the L/G shock absorbers are not fully extended. The LGCIU's supply 28V DC to energize the baulk solenoid and release the mechanism, when the shock absorbers are fully extended. Internal white lighting shows through the UP and DOWN legends and the outline of the two arrows.
 To operate the L/G control lever, you pull it away from the face of the unit. Then move it to the UP or DOWN position. The lower part of the DOWN arrow shows red when the aircraft is in a landing configuration (but the L/G is not locked down).
 B. L/G Isolation Safety Valve 49GA
 (Ref. Fig. 009, 015)
 The primary components of the valve are:
 -
a valve body

 -
a solenoid and electrical connector

 -
a pilot valve.

 The safety valve is installed on a manifold in the RH MLG bay.
 The pilot valve is a spool valve that is connected to the main valve body by two screws.
 The safety valve body has three ports that are identified A, B and C. The valve body has holes to connect the ports and faces to install the solenoid and connector.
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 Safety Valve - Schematic Figure 015
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 The safety valve is an electrically-operated, two-position valve that isolates the Green hydraulic supply to the L/G system. When the computed airspeed is more than 264 kts the safety valve closes (solenoid de-energized). The safety valve opens (solenoid energized) when the computed airspeed is less than 260 kts and the L/G control-lever is selected DOWN.
 A signal from LGCIU-1 (5GA1) keeps the safety valve open during maintentance. The LGCIU sends this signal when the LH and RH MLGs are compressed or, when ground power is connected to the aircraft.
 The safety valve gets its electrical supply from the essential busbar (401PP), during maintenance it can be supplied from the ground service busbar (601PP).
 With the solenoid energized the pressure inlet A is connected to the supply outlet C and the return outlet B is closed. This connects the Green hydraulic system to the L/G system.
 With the solenoid de-energized the pressure inlet A is closed and the supply outlet C is connected to the return outlet B. This isolates the Green hydraulic system from the L/G system.
 C. Selector-Valve Manifold-Assembly (2524GM)
 (Ref. Fig. 016, 017)
 **ON A/C 301-399,
 (Ref. Fig. 018, 019)
 **ON A/C ALL
 The selector valve manifold assembly is an electrically-operated hydraulic unit that controls the flow of hydraulic fluid to and from the L/G hydraulic components. The primary components of the unit are:
　
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