DME SYSTEM - ARINC 429 INTERFACES

Navigation Control Panel

The navigation control panels supply a manual tune frequency input to the DME interrogator. They also send four auto tune frequency inputs from the Flight Management Computer (FMC). The control panels send tune and test data on two output data buses. One output data bus goes to the MMR receiver and one output data bus goes to both the DME interrogator and VOR receiver.

DME Outputs

Each DME interrogator has two output buses. One output bus supplies data to the on-side flight control computer (FCC). DME 1 sends data to FCC A and DME 2 sends data to FCC B. the other Output bus supplies data to these units:

· Flight management computer system (FMCS).

· Display electronics units 1 and 2

· Flight data acquisition unit (FDAU).

The FMCS uses DME distance to calculate position updates.

The DEUs use DME distance for displays.

The FDAU receives DME distance and formats it for the flight data recorder.

Flight Management Computer

The FMC supplies auto tune commands through the navigation control panel to the DME interrogator. If the navigation control panel has a failure, the DME gets auto tune signals directly from the FMC.

 

 

 

DME SYSTEM - POWER, ANTENNA, ANALOG, AND DISCRETE INTERFACE

Power Interface

Each DME interrogator receives 115v ac from the DME circuit breakers.

DME Antenna Interface

The DME antennas transmit and receive DME signals. The antennas transmit signals to the ground stations. They then receive the reply signals from the DME ground station and send them to the interrogator.

Source Select Discrete

The source select discrete controls the ARINC 429 receive ports in the DME interrogator. With the source select open, the DME interrogator gets manual and auto tune commands from the navigation control panel. If the navigation control panel has a failure, the source select discrete goes to ground. The DME then gets auto tune signals directly from the FMC.

PSEU

The proximity switch electronics unit (PSEU), supplies an air/ ground discrete inputs to the DME interrogators to set flight leg count. The air/ground discrete also goes to the navigation control panels to inhibit test commands in the air.

Default Scan Inhibit Discrete

The default scan inhibit discrete locks the DME interrogator so it can not make a scan of all the DME frequencies. It tunes to five channels controlled by the navigation control panel and the flight management computer.

DME/ATC/TCAS Suppression

These systems operate in the same frequency band:

· DME

· Air traffic control (ATC)

· Traffic alert and collision avoidance system (TCAS).

When a DME interrogator, an ATC transponder, or the TCAS computer transmits, it sends a suppression pulse through the suppression lines. This pulse stops the 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 remote electronics unit (REU). The audio goes to the headsets and the flight interphone speakers.

 

 

 

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