S 094-028
 WARNING:_______REFER TO AMM 32-00-30/201 FOR THE LOCK REMOVAL PROCEDURE. THE FAST MOVEMENT OF THE DOORS CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
 (20) Remove the door lock of the nose landing gear (AMM 32-00-30/201).
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 ALL  ú ú 01 Page 409 ú Oct 10/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 BODY GEAR STEERING SYSTEM - DESCRIPTION AND OPERATION
_____________________________________________________
 1.  General (Fig. 1)_______
 A.  Body gear steering supplements nose gear steering for directional control during towing and taxiing of the aircraft. Body gear steering also reduces tire scrubbing when maneuvering on the ground. A switch, actuated by a cam that is mechanically driven from the nose gear steering tiller, arms the body gear steering system. The system is controlled by a closed loop servo system which modulates hydraulic pressure to a pair of steering actuators on each body gear. As the nose gear turns in one direction, the body gear turns smaller proportional angles in the other direction. The body gear steering arming circuit is deactivated whenever the gear is in tilted position, or when wheel speed is greater than 20 knots (Fig. 2). Back lash within the system creates a difference in nose wheel position for the arm and disarm functions. When the angle of nose wheel steering increases, the system is armed at 21 degrees. When the angle of nose wheel steering decreases, the system is disarmed at 20 degrees.
 B.  The system is pressurized by hydraulic system No. 1. The body gear steering actuators are pressurized only when the landing gear handle is in the down position and the arming switch on the rudder interconnect quadrant is actuated. Each actuator has an internal mechanical lock and two lock-operated switches. The switches will cause a BODY GEAR STRG message to be displayed on the EICAS system when primary and alternate systems both indicate body gear steering actuator unlocked or pressurized when not commanded.
 C.  The feedback transducer is an integral part of the steering actuator. Amplifiers and valves which receive signals from the nose gear tiller are mounted in a separate module in the wheel well. The major equipment comprising steering installation are four identical steering actuators and two hydraulic control modules. Each module includes the amplifier which provides position signal to operate the servo valve.
 D.  An electrical interlock prevents both actuators on each gear from being unlocked at the same time.
 E.  A check valve in the return port of each body gear steering control module prevents possible unlocking of body gear steering actuators due to high return line pressures during gear retraction or alternate extend landings.
 2.  Command Transducer (Fig. 1)__________________
 A.  The command transducer gives a signal to move the body gear truck to a defined position. The electrical signal is amplified through the electronic control unit which in turn operates the servo valve installed in the control module.
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 ALL  ú ú 01 Page 1 ú Oct 10/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 747-400 MAINTENANCE MANUAL 
SEE  A  BODY GR STRG ARM DC BODY GR STRG ARM AC (OVERHEAD CIRCUIT BREAKER PANEL, P7)  ELECTRONICS CONTROL (FORWARD BG STRG ARM EICAS DISPLAY PANEL, P9) 
SEE  B 
SEE  C 
BODY GEAR DSEE 
FLIGHT COMPARTMENT 
FLOOR (REF) EQUIPMENT CENTER ELECTRONIC MAIN ELECTRICAL/  A 
TRANSDUCER COMMAND  ARMING SWITCH BODY GEAR STEERING  MECHANISM INTERCONNECT STEERING RUDDER PEDAL
B 

INTERCONNECT ACTUATORS
C
Body Gear Steering System Component Location Figure 1 (Sheet 1)
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