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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.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

Nose Wheel Steering Schematic
Figure 2 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 4.  Rudder Pedal Steering Mechanism
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 A.  The rudder pedal steering mechanism consists of a steering crank, a clutch arm, a cable drum, an eccentric mounted in the clutch crank, and a rudder pedal steering quadrant (Fig. 3). This mechanism connects the rudder pedals to the nose wheel steering and is actuated by the weight of the airplane compressing the nose gear shock strut. The compression of the shock strut actuates the squat switch which causes an electric motor (actuator) to reposition the clutch crank so that stops, mounted on the clutch crank, do not contact the clutch arm. In this position, the clutch arm contacts the stops on the steering crank and any movement of the rudder pedals is transmitted from the steering crank to the rudder pedal steering quadrant (Fig. 4, condition 1). This quadrant is connected to the nose wheel steering cables and is free to move with the cables whenever nose wheel steering is used, or drive the cables when positioned by the rudder pedal steering mechanism (Fig. 4, condition 2).
 B.  When the nose gear is extended, the squat switch/electric actuator system positions the eccentric to move the stops mounted on the clutch crank into contact with the clutch arm. This prevents any movement of the rudder pedals from reaching the clutch arm and moving the quadrant (Fig. 4, condition 3).
 C.  A time delay circuit delays the disengagement of the nose wheel steering system for ten seconds after the nose landing gear strut is fully extended. This prevents rudder pedal steering disengagement during takeoff on rough runways.
 5.  Steering System Cables
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 A.  The nose wheel steering cable system consists of two sets of 3/32 inch diameter cable with tin-coated corrosion-resisting steel terminals. The first set of cables, designated NWSA and NWSB, is used to actuate the steering metering valve by turning the steering wheel. The second set of cables, designated NGPPA and NGPPB, makes up the squat switch/electric actuator system to engage rudder pedal steering.
 B.  The steering cables, NWSA and NWSB, begin at the steering wheel drum and terminate on the steering collar at the back of the nose gear shock strut. Movement of the steering wheel puts one cable under tension and the steering control crank mounted on the nose gear is displaced moving the control piston in the steering metering valve. Movement of the control piston directs fluid under pressure to the steering cylinder which moves the steering collar. The steering collar moves in the desired direction of turn and, as the amount of turn is reached, the tension in the cable is reduced by the follow-up action and the control piston is returned to the centered position. The wheel must be held throughout the turn or the system will return to center by action of the centering spring in the rudder pedal steering mechanism.
 C.  NGPPA and NGPPB system cables are driven by an electric actuator. When the torsion links are compressed by nose gear action, the squat switch energizes the actuator and the NGPP cables reposition stops in the rudder pedal steering mechanism to allow rudder pedal steering.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
CABLE NWSA  ARM CLUTCH NWSB CABLE  QUADRANT STEERING RUDDER PEDAL  WHEEL STEERING  ARM STEERING PEDAL RUDDER 
CONTROL CRANK VALVE  VALVE METERING STEERING ROTARY ACTUATOR  SHOCK STRUT COMPRESSED CRANK CLUTCH NGPPA CABLE NGPPB CABLE STOPS  CRANK STEERING PEDALS TO RUDDER 
NOSE GEAR 
SHOCK STRUT EXTENDED ECCENTRIC DRUM AND STOPS FEATURE WITH SHEAR ROD ASSEMBLY CONTROL 
Figure 3 Rudder Pedal Steering Mechanism 
　
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