Joined: 11 Dec 2005
|Posted: Wed Aug 08, 2012 4:58 am Post subject: Landing Gear and Brakes (Technical Notes)
|Nose Wheel Steering Tiller
• Turns the nose wheels up to 70 degrees in either direction
• Overrides rudder pedal steering
• Main gear aft axle steering is slaved to nose wheel steering. It automatically operates when the nose wheel steering angle exceeds 13 degrees to reduce tire scrubbing.
• turns the nose wheel up to 7 degrees in either direction
• does not activate main gear steering.
Alternate Gear (ALTN GEAR) Switch
Alternate extension may be selected with the landing gear lever in any position.
Gear Synoptic Display
• A relative value of wheel brake temperature is shown ranging from 0.0 to 9.9
• Blank box indicates any brake less than 3.0
• Solid white box indicates hottest brake on each main gear within range of 3.0 to 4.9
• Solid amber box indicates brake overheat condition on each wheel within range of 5.0 to 9.9
• Individual tire pressures, from 0 to 400 PSI, are displayed inside the individual wheel symbols on the GEAR synoptic display.
Semi-Levered Gear 777-300ER (AP-BHV, AP-BHW, AP-BID)
The semi-levered gear consists of an additional hydraulic actuator that connects the forward end of each main gear truck to the shock strut. During takeoff, the actuator locks to restrict rotation of the main gear truck and allow takeoff rotation about the aft wheel axle, thereby improving airplane performance capability. During landing, the actuator is unlocked to permit rotation of the main gear truck and provide additional damping.
Reserve Brakes and Steering
The fluid below the standpipe in the center hydraulic reservoir is used by the primary C1 pump as a reserve hydraulic source to power the alternate brakes and nose wheel steering.
The normal brake system provides each main gear wheel with individual antiskid protection.
The alternate brake system provides antiskid protection to tandem wheel pairs for the forward and middle axle wheels. The aft axle wheels remain individually controlled.
Antiskid protection is also provided when the brake system is being supplied pressure only from the brake accumulator.
EICAS ANTISKID message is displayed if:
- an antiskid fault affecting the brake system in use is detected
- the system is completely inoperative.
- the parking brake valve is not fully open with the parking brake released
Taxi Brake Release
During each taxi brake application, the antiskid system releases the brakes of one axle pair of each main landing gear (if wheel speeds are less than 45 knots). The system sequences through the axle pairs at each brake application, thereby reducing the number of brake applications by each brake. The taxi brake release system operates only with the normal brake system.
The system operates only when the normal brake system is functioning.
If MAX AUTO (for landing) is selected, deceleration is limited to the AUTOBRAKE 4 level until pitch angle is less than one degree, then deceleration is increased to the MAX AUTO level.
The deceleration level can be changed (without disarming the system) by rotating the selector.
Brake System Schematic