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737-300/400/500MAINTENANCE MANUAL
 LANDING GEAR CONTROL SYSTEM - DESCRIPTION AND OPERATION
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General
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 A.  The landing gear control system is operated by moving a control lever projecting from the pilots' instrument panel (Fig. 1). A cable system transmits the control lever movement to a selector valve in the left wheel well. When positioned by the control lever, the selector valve directs hydraulic pressure to the actuators for gear retraction and extension. The control lever is provided with a lock to prevent the lever from being moved into UP position when the airplane is supported on the gear. An override trigger in the control lever may be used to bypass the lock for testing or if the lock system should lose electrical power.
Landing Gear Selector Valve
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 A.  The landing gear selector valve directs hydraulic pressure to the landing gear up and down lines (Fig. 2). Return fluid from the landing gear system passes back through the selector valve and on to the hydraulic system A reservoir. The selector valve is bolted to the ceiling of the left main wheel well. Linkage connects the selector valve to the control cable system. When the landing gear control handle is operated, motion from the handle is transferred through the cable system to a shaft passing through the wheel well ceiling. An arm on the end of shaft below the ceiling positions the selector valve through an adjustable link.
Landing Gear Control Cable System
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 A.  The landing gear control cable system transfers movement from the control lever to the landing gear selector valve (Fig. 1). The control cable system consists of four cables, two short and two long. Short cables run forward and down from the control lever drum, then aft under the control cabin floor. Long cables run forward from the selector valve control drum to meet the control lever cables at a point under the control cabin floor where the cables are joined by turnbuckles.
Landing Gear Control Lever
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 A.  The landing gear control lever runs in a guide as the lever is moved up or down. The guide has detents to hold the control lever in any one of three positions, UP, OFF, or DN. To change the control lever position, it is necessary to pull out the lever to release a roller on the inner end from the detent.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
LANDING GEAR LANDING GEAR SELECTOR VALVE CONTROL LEVER
CONTROL CABLES 
GEAR UP CONTROL CABLE LGVA 
TURNBUCKLES  QUADRANT 
GEAR DOWN CONTROL CABLE LGVB 
TURNBUCKLE  QUADRANT SUPPORT BRACKET 
GEAR UP DETENT  CONTROL LEVER POSITION SWITCH  GEAR OFF DETENT CONTROL LEVER DRUM  PRESSURE PORT RETURN PORT  DOWN PORT UP PORT 
GEAR DOWN CONTROL CABLE LGVB  CONTROL LEVER LOCK  OVERRIDE TRIGGER  CONTROL LEVER (GEAR DOWN POSITION) LANDING GEAR  LANDING GEAR SELECTOR VALVE 
GEAR UP CONTROL CABLE LGVA  LOCK SOLENOID 
Figure 1 Landing Gear Control Component Location 

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
DOWN LINE UP LINE

RETURN LINE PRESSURE LINE
OFF POSITION

GEAR UP

Landing Gear Selector Valve Schematic
Figure 2

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A
737-300/400/500MAINTENANCE MANUAL
 B.  The lock override mechanism enables the inner end of the control lever to be pulled clear of the lock stop when the control lever lock is engaged. The override feature is obtained by making the control lever shaft in two parts, one sliding inside the other. A trigger connected to the inner part projects through a slot in the underside of the outer shaft. A compression spring between a flange on the inner shaft and the control handle quadrant holds the trigger against the bottom of the slot (Fig. 3). When the control lever is pulled, both the inner and outer shafts move together through the quadrant until the inner end clears the detent. At this point, a stop prevents further movement. To retract the inner end of the lever far enough to pass the lock stop, the trigger must be operated. Pulling the trigger telescopes the inner shaft into the lever, the additional retraction of the control lever inner end thus obtained, allows the lever to clear the lock stop.
　
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