777 AIRCRAFT MAINTENANCE MANUAL
DME SYSTEM -GENERAL DESCRIPTION
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DME SYSTEM -COMPONENT LOCATIONS -FLIGHT DECK
DME Component locations -Flight Deck
These are the components on the flight deck that interface with DME:
*
Left and right EFIS Control Panel (CP)
*
Captain and first officer primary flight displays (PFDs) and navigation displays (NDs)
*
Left and right control display units (CDUs)
*
Audio control panels (ACPs).
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DME SYSTEM -COMPONENT LOCATIONS -FLIGHT DECK
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DME SYSTEM -COMPONENT LOCATION -MAIN EQUIPMENT CENTER AND ANTENNAS
DME Component Locations
These components are in the main equipment center:
*
Left DME interrogator
*
Right DME interrogator
*
DME/ATC/TCAS suppression splitter
*
left and right resistor assemblies.
These components are on the exterior of the airplane:
*
Left DME antenna
*
Right DME antenna.
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DME SYSTEM -COMPONENT LOCATION -MAIN EQUIPMENT CENTER AND ANTENNAS
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DME SYSTEM -POWER, ANALOG, AND DISCRETE INTERFACE
Power and Antenna Interface
Each DME interrogator receives 115v ac from its circuit breaker.
Air/Ground Relay
The air/ground relays supply discrete inputs to the DME interrogators for these functions:
*
Set flight legs (as alternate source, primary is from the CMCF of AIMS)
*
Inhibit test commands in the air.
CDU
The CDUs send a frequency source select discrete to cause the interrogator to select the tune input from either the CDU or the AIMS cabinets. The resistor assemblies pull up the discretes to 28v dc. The left CDU sends a ground discrete to the left interrogator when the discrete is true. The right CDU sends a ground discrete to the right interrogator when the discrete is true.
DME Antenna
The DME antennas transmit and receive DME signals. The antenna transmits signal pulse pairs to the ground stations then receive the reply signal pulse pairs from the DME ground station and sends them to the interrogator.
DME/ATC/TCAS Suppression
The DME system, the air traffic control (ATC) system, and the traffic alert and collision avoidance system (TCAS) operate in the same frequency band. When a DME interrogator, an ATC transponder or a TCAS computer transmits, it sends a suppression pulse through the suppression splitter. This pulse inhibits reception of the other four units. This prevents damage to the receiver circuits of the other LRUs.
DME Audio
The DME interrogator sends the DME station audio identifier to the audio management unit (AMU). The AMU combines the DME audio with VOR or ILS audio. The audio goes to the headsets and the flight interphone speakers.
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DME SYSTEM -POWER, ANALOG, AND DISCRETE INTERFACE
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DME SYSTEM -ARINC 429 INTERFACES
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