Nose Gear Extension and Retraction Component Location
Figure 1

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A

737-300/400/500MAINTENANCE MANUAL
SNUB VALVE SLEEVE
OUTER CYLINDER
SNUB VALVE
GEAR DOWN PORT
METERED
ORIFICE

GEAR UP
NOSE GEAR EXTENDED
PORT
(SNUB VALVE CLOSED)
NOSE GEAR IN TRANSIT
(SNUB VALVE OPEN)

NOSE GEAR RETRACTED
(SNUB VALVE CLOSED)

Nose Gear Actuator
Figure 2

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A 737-300/400/500MAINTENANCE MANUAL
 3.  Nose Gear Lock Mechanism
________________________
 A.  The nose gear lock mechanism locks the gear in the gear up and the gear down positions. The mechanism also releases the lock just before gear retraction or extension. The mechanism includes a lock actuator, lock spring bungees, and a lock strut consisting of a lock link and a lock brace assembly (Fig. 3). The lock strut is between structure and the drag brace. When the gear is extended, the lock strut prevents the drag strut from folding when forces tending to retract the gear are applied. When the gear is retracted, the lock strut and the upper drag brace form a pair of shear legs from which the gear hangs by the lower drag brace. In up or down positions, the hinge of the lock strut is overcenter to lock the gear in position. The lock actuator moves the lock strut across the overcenter position to release the gear. The bungee springs are under tension when the lock strut is in locked position, holding the hinge overcenter even when the lock actuator is depressurized. A pin inserted through holes drilled through the lock strut hinge provides a ground lock to prevent inadvertent gear retraction during ground operations.
 4.  Nose Gear Lock Actuator
_______________________
 A.  The nose gear lock actuator locks and unlocks the nose gear in either up or down position (Fig. 4). The actuator is a hydraulic piston type and is mounted on the forward face of the aft bulkhead in the wheel well. The actuator retracts to move the lock strut over center, start the drag brace folding, and so begin the retraction cycle. For gear extension, the lock actuator extends to unlock the gears. At the end of gear retraction or extension, the actuator forces the lock strut into the overcenter locked position against the tension of the lock spring bungees.
 5.  Nose Gear Lock Spring Bungee
____________________________
 A.  The nose gear lock spring bungees are arranged to apply a load to hold the lock strut in overcenter position. Bungees consist of tension springs, with one end attached to the lock brace pivot on structure, and the other end to a lock link lug beyond the lock strut hinge. Bungees are tensioned to keep gear locked when hydraulic pressure is off the actuators.
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737-300/400/500MAINTENANCE MANUAL
SEE A
BRACE UPPER DRAG  BRACE LOCK  BUNGEE LOCK SPRING 
DRAG BRACE LOWER  1 LOCK LINK BRACKET STRUCTURE BRACKET ON PIN HOLE GROUND LOCK  ACTUATOR LOCK 
(UNLOCKED) A 
INDICATOR VISUAL LOCK 

(LOCKED)
1 NOT ON ALL AIRPLANES  A
Nose Gear Lock Mechanism Figure 3
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