*
AIMS -airplane information management system
*
CMCF -central maintenance computing function
*
GPWC -ground proximity warning computer
*
PFC -primary flight computer
*
PWS -predictive windshear
*
RA -radio altitude
*
TCAS -traffic alert and collision avoidance system
*
WXR -weather radar
*
xcvr -transceiver
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777 AIRCRAFT MAINTENANCE MANUAL
RADIO ALTIMETER SYSTEM -INTRODUCTION
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RA SYSTEM -GENERAL DESCRIPTION
General
The system has three transceivers (xcvr). Each xcvr has a transmit and a receive antenna.
The transceivers get discrete inputs from the air ground relays and from the AIMS cabinets.
Radio altitude data goes on ARINC 429 data buses to the these components:
*
Airplane information management system (AIMS) cabinets
*
Autopilot flight director computers (AFDCs)
*
Traffic alert and collision avoidance system (TCAS) computer
*
Weather radar receiver-transmitters
*
Ground proximity warning computer (GPWC).
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777 AIRCRAFT MAINTENANCE MANUAL
RA SYSTEM -GENERAL DESCRIPTION
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RA SYSTEM -COMPONENT LOCATION -1
General
These are the RA system components in the E5 rack in the forward cargo compartment:
*
Right RA transceiver (xcvr)
*
Center RA xcvr
*
Left RA xcvr.
These are the RA system components on the bottom of the fuselage:
*
Left RA receive antenna
*
Center RA receive antenna
*
Right RA receive antenna
*
Left RA transmit antenna
*
Center RA transmit antenna
*
Right RA transmit antenna.
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777 AIRCRAFT MAINTENANCE MANUAL
RA SYSTEM -COMPONENT LOCATION -1
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RA SYSTEM -COMPONENT LOCATION -2
General
These are the RA system components and components that interface with the RA system in the flight deck:
*
Primary flight displays (PFD)
*
Left and right EFIS control panels
*
Left and right control display units (CDU).
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RA SYSTEM -COMPONENT LOCATION -2
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RA SYSTEM -POWER, ANTENNA, AND DISCRETE INPUTS
Power
Power for the RA xcvrs is 115v ac from:
*
115v ac left transfer bus (left RA)
*
115v ac standby bus (center RA)
*
115v ac right transfer bus (right RA).
Antenna Interfaces
The transmit antennas send radio frequency (RF) signals to the ground. The receive antennas send reflected RF signals to the receiver circuits of the RA xcvr.
AIMS Discrete
The primary flight control computers (PFCs) supply a test inhibit signal to the RA xcvr through the airplane information management system (AIMS) cabinets. This signal prevents a RA test when the primary flight computers detect a ground speed more than 40 knots, or the airplane is in the air.
Air/Ground Discrete
The RA xcvr stores internal faults in a nonvolatile fault memory. The RA xcvr stores these faults by flight segments. The central maintenance computing function (CMCF) of the AIMS supplies the primary flight leg start times. The air/ground relay is an alternate way to detect the air/ground condition.
Input Program Pins
The RA xcvr program pins are:
*
Continuous data
*
Aircraft installation delay (AID) of 80 feet
*
System select.
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RA SYSTEM -POWER, ANTENNA, AND DISCRETE INPUTS
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RA SYSTEM -DATA BUS OUTPUTS, RADIO MINIMUMS INTERFACE
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