TIRE PRESSURE INDICATION SYSTEM -TIRE PRESSURE MONITOR UNIT
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TIRE PRESSURE INDICATION SYSTEM -FUNCTIONAL DESCRIPTION
Power Supply
The left 28 v dc MAIN bus supplies the electrical power to operate the tire pressure indication system.
TPMU -Tire Pressure Sensor
The TPMU supplies an excitation signal to each of the 14 wheel interface units.
The wheel interface unit sends the signal across the rotating interface of the wheel to the tire pressure sensor.
Tire Pressure Sensor -TPMU Signal
The tire pressure sensor sends a dc voltage signal that is in proportion to the tire pressure.
The wheel interface unit transmits the signal across the rotating interface of the wheel back to TPMU.
TPMU Operation
The TPMU gets the tire pressure signals and sends them to AIMS for flight deck display.
The TPMU also calculates non-normal tire pressure conditions and shows these EICAS messages:
* TIRE PRESS (Advisory) -non-normal tire pressure conditions
* TIRE PRESS (Status) -non-normal tire pressure conditions.
Non-normal tire pressure conditions include:
*
Tire pressure below 100 psi
*
Main gear tire pressure different from average tire pressure by 18 percent (the TPMU calculates average tire pressure by discarding the three highest and the three lowest tire pressures and averaging the middle six tire pressures)
*
More than 25 percent difference in pressure between main gear tires on the same axle
*
More than 12 percent difference between the nose gear tire pressures.
A fault monitor in the TPMU monitors TPIS components and interfaces for faults. The status message TIRE PRESS SYS shows if there is a fault.
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TIRE PRESSURE INDICATION SYSTEM -FUNCTIONAL DESCRIPTION
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TIRE PRESSURE INDICATION SYSTEM -INDICATIONS
General
Tire pressure indication, shows in psi on the landing gear synoptic display and the brake and steering maintenance page.
Tire Pressure Indication
The landing gear synoptic display and the brake and steering maintenance page show normal tire pressure in white.
The tire pressure display changes to amber to show non-normal pressure conditions.
Non-normal conditions also cause a message to show on the EICAS display.
The tire display will go out of view if there is a Loss of pressure data or if the pressure data is invalid.
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TIRE PRESSURE INDICATION SYSTEM -INDICATIONS
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777 AIRCRAFT MAINTENANCE MANUAL
THIS PAGE IS INTENTIONALLY LEFT BLANK
32-50-00
Page 1 D633W101-BEJ Jan 05/2002
BOEING PROPRIETARY -Copyright # -Unpublished Work -See title page for details.
STEERING -INTRODUCTION
Purpose
The nose gear steering (NGS) system and the main gear steering system (MGSS) supply directional control of the airplane on the ground.
The MGSS also decreases tire scrub and the U-turn radius.
You make steering inputs through two steering tillers and the rudder pedals.
Nose Gear Steering
The nose gear steering system is a hydro-mechanical system that moves the nose landing gear up to 70 degrees left or right.
Main Gear Steering
The main gear steering operates when the nose gear turns more than 13 degrees.
The aft axles on each main gear truck move up to 8 degrees in each direction.
The main gear steering system gets position inputs from the NGS. A main gear steering control unit (MGSCU) controls the main gear steering system.
Abbreviations and Acronyms
* AIMS -airplane information management system
*
ARINC -Aeronautical Radio, Inc.
*
EHSV -electrohydraulic servovalve
*
F/O -first officer
*
LVDT -linear variable differential transformer
*
MGSCU -main gear steering control unit
*
MGSS -main gear steering system
*
MLG -main landing gear
*
MFD -multi-function display
*
NG -nose gear
*
NGS -nose gear steering
*
NLG -nose landing gear
