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The nose wheel steering system is armed from a switch on the landing gear control panel in the flight compartment. It is activated once the WOW signal and nose landing gear down-and-locked signals are present. Steering commands are input to the Electronic Control Unit ( ECU) through the pilot’s hand wheel (full authority ± 75°) and/or the rudder pedals (limited authority ± 7.5°). NOTE If handwheel and rudder pedal input commands are received at the same time, the ECU will sum these inputs to a maximum of ± 75°. Nose wheel position feedback is provided to the SCU by 2 transducers mounted on the steering actuators. The Steering Control Unit (SCU) controls an electro-hydraulic servo-valve in the hydraulic manifold (mounted on the nose gear assembly), which ports hydraulic pressure to each of the steering actuators as required. The steering actuators (mounted on the main fitting of the nose gear) operate in a push/pull manner to rotate the steering collar. Mechanical torque links are provided to transmit the movement of the steering collar to the nose wheels. The steering commands are processed by the SCU and No. 3 hydraulic system pressure is routed through the system, when the landing gear is selected down. In the air mode, the nose wheel is centered electrically by the SCU and mechanically by centering cams as the shock strut extends under its own weight. When the steering system is disarmed or with no WOW signal, the nose wheel steering will revert to free caster and shimmy damping to ensure stability within the nose wheel circuit. In the free caster mode of operation, steering is accomplished only through differential braking and differential thrust. The SCU continuously monitors the nose wheel steering system and any fault within the system will be displayed as a caution message. Fault detection will result in nosewheel steering system shut down and the system will then operate in free caster mode of operation. Rev 2A, Apr 11, 2005 Flight Crew Operating Manual Volume 2 LANDING GEAR NOSE WHEEL STEERING SCHEMATIC STEERING ACTUATORS P NOSE WHEEL ASSEMBLY NO.3 HYDRAULIC SYSTEM STEERING MANIFOLD NOSE LANDING GEAR DOWN AND LOCKED WOW LGECU ELECTRONIC CONTROL UNIT TO EICAS NOSE STEER GF1510_033 LANDING GEAR PARK/EMER BRAKE ON |
