CDU
The left and right CDUs supply alternate tune inputs directly to the DME interrogators if the AIMS tune inputs fail. The left CDU alternate tunes the left interrogator and the right CDU alternate tunes the right interrogator.
DME Outputs
Each DME interrogator has two output buses. The output buses supply data to both AIMS cabinets.
Each DME interrogator sends data to both AIMS cabinet to display DME data on the PFDs and NDs. The interrogators also send test status and fault reports.
AIMS
The left AIMS cabinet sends test commands and flight legs data to the DME interrogators on the left and right CMC buses.
The right AIMS cabinet sends manual or automatic tune inputs to the DME interogators on the left and right tune buses.
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777 AIRCRAFT MAINTENANCE MANUAL
DME SYSTEM -ARINC 429 INTERFACES
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DME SYSTEM -INTERROGATOR
General
The DME interrogator scans 252 channels and calculates distance information for all channels in the DME range. There are 200 DME channels paired with the VHF NAV frequencies. The other 52 channels are for military TACAN facilities. The DME receive frequency is 63 MHz above or below the transmit frequency.
Purpose
The purpose of the DME interrogator is to:
*
Interrogate DME stations
*
Receive the station replys
*
Receive audio identifiers
*
Calculate slant range distances.
Frequencies
The DME interrogator uses these L-Band frequencies:
*
1025 MHz to 1150 MHz (transmit)
*
962 MHz to 1215 MHz (receive).
These DME tuning frequencies are in the VHF band:
*
108.00 to 117.95 MHz paired VOR or ILS
*
133.30 to 135.95 MHz unpaired.
Front Panel
The front panel of the DME interrogator has these features:
*
LED status indicators
*
Self test switch.
Training Information Point
The maintenance manual and the fault isolation manual do not have a task for the line maintenance technician to do a test from the front panel of the DME interrogator. You must do all tests for the DME interrogator from the MAT or a PMAT.
Many LRUs on the 777 are compatible with other model airplanes that do not have a central maintenance computing system (CMCS). For that reason these LRUs have a front panel test feature.
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DME SYSTEM -INTERROGATOR
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DME SYSTEM -ANTENNA
General
The DME l-band antenna transmits the interrogator output signal and receives the ground station reply signals.
Physical Description
The antenna has an O-ring moisture seal and attaches to the airplane by four screws. The DME and ATC antennas are the same and are interchangeable.
Training Information Point
WARNING: EXTRA FORCE ON THE ANTENNA BASE MAY BE REQUIRED TO BREAK THE WEATHERPROOFING SEAL. TO PREVENT DAMAGE TO AIRPLANE SKIN OR ELECTRICAL CABLE AT THE ANTENNA BASE, CAREFULLY PRY AROUND THE ANTENNA WITH A SEALANT REMOVAL TOOL.
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DME SYSTEM -ANTENNA
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DME SYSTEM -TUNING
General
These are the three ways to tune the DME interrogators:
*
Manually by the left, right, or center CDU
*
Automatically by the FMCF in the AIMS cabinets
*
By the CDUs as an alternate tune source.
Manual Tune
You manually tune the DME interrogators from the left or right control display units (CDUs). The center CDU can tune the interrogators if the left or right CDU fails. Manual tune inputs from the CDUs go through the left and right systems ARINC 629 buses, then to the left and right AIMS cabinets. Manual tune inputs from the left or right AIMS cabinet comes from the right AIMS cabinet and goes to the DME interrogators.
AIMS Autotune
The flight manangement computing function (FMCF) of the left or right AIMS cabinet can automatically tune (autotune) the DME interrogators. Autotune inputs from the left or right AIMS cabinets go through the right AIMS cabinet, then to the DME interrogators.
Alternate Tune
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