Operation
The NAV control panels have an active frequency display window and a standby frequency display window. The frequency that shows in the active frequency display window is the frequency that the navigation radios use for operation. The standby frequency display window shows the next frequency you will use.
The transfer switch is a momentary action switch. It transfers the frequency in the standby frequency display window to the active frequency display window. When you push the switch, the frequency that is in the active frequency display window transfers to the standby frequency display window.
The frequency select control is a continuous rotary knob. There is an inner knob and an outer knob. The outer knob sets the tens and ones. The inner knob sets the tenth and one hundreth numbers.
At power up, the frequency displays show the last frequency entry before power down.
The NAV control panel continuous BITE function monitors the operation. The NAV control panel shows FAIL in the active and the standby frequency display windows when there is a failure. The monitor in the NAV control panel monitors the 28v dc input. If the monitor does not get the 28v dc, the frequency display windows are blank.
Test
When you push the test switch, the NAV control panel sends a test command out on it’s output bus. If a VOR frequency shows in the active frequency window, the test command goes to the VOR receiver. IF an ILS frequency shows in the active frequency window, the control panel sends a test command to the ILS receivers. If there is a DME frequency that is paired with the VOR or ILS frequency, a test command also goes to the DME interrogators.
When you do a test of the master dim and test system, the NAV control panel shows 188.88. The display shows for two seconds on then one second off until the test is complete.
DME SYSTEM - OPERATION - CONTROLS
General
The audio control panels (ACP) permit the crew to hear the DME station identification signals. The identification signals are 1350 Hz.
The EFIS control Panel mode selector switch selects the NAV display modes that show DME distance.
Audio Controls
Set these controls on the audio control panel to listen to DME audio:
Push ON the NAV receiver volume control (NAV 1 for DME 1 and NAV 2 for DME 2)
Select B (both) or R (range) on the voice range filter switch
Set the NAV receiver volume control.
The voice/range selector permits you to hear DME audio. You will hear the DME audio when the voice/range selector is in the R or B position.
EFIS Controls
The EFIS control panel mode selector switch must be in the VOR/ILS position to show DME distance on the top right of the ND.
You put the VOR/ADF 1 switch to VOR 1 to show DME 1 in the lower left corner of the ND. DME 2 shows in the lower right corner of the ND when the VOR/ADF 2 switch is put to VOR 2.
DME SYSTEM - DISPLAY
Normal PFD Display
The left PFD shows DME 1 data. The right PFD shows the DME 2 data. The DME distance display shows in white letters and numbers.
Normal RDMI Display
The radio distance magnetic indication (RDMI) on the captain’s primary electronic flight instrument (EFIS) display shows DME distance. The first officer’s RDMI on the secondary EFIS shows the DME distance.
The RDMI show DME 1 distance above the DME1 legend on the left side and DME 2 distance on the right side above the DME2 legend.
The DME distance display shows in white letters and numbers.
Normal ND Display
DME distance shows on the top right corner of these ND displays:
Expanded and centered VOR
Expanded and centered ILS.
The DME also shows in the lower left (VOR 1) and the lower right (VOR 2) corner of the ND if you select VOR on the EFIS control panel.
DME NCD or Failed Displays
Amber dashes replace numbers when the DME distance is no computed data (NCD). If the DME has a failure, an amber DME flag replaces the DME distance. The NCD and fail flag show in amber.
DME NCD and Fail Displays
White dashes replace the DME distance when the DME distance data is no computed data (NCD). If the DME has a failure, the DME amber flag replaces the DME distance.
DME SYSTEM - FUNCTIONAL DESCRIPTION
Normal Tune Input
The navigation control panel is the normal source for tune inputs. The flight management computer (FMC) sends up to four channels of auto tune signals to the navigation control panel. The navigation control panel adds one manual channel and sends five tune channels to the DME interrogator.
Alternate Tune Input
If the navigation control panel has a failure, the FMC sends auto signals directly to the DME interrogator.
Discrete Inputs
When the navigation control panel has a failure, it grounds a source select discrete to the DME central processing unit (CPU). The CPU changes the input from the navigation control panel to the FMC.
The proximity switch electronics unit (PSEU)supplies an air/ ground discrete to prevent a DME test when the aircraft is in the air. The discrete also supplies flight leg data.
Operation
The CPU uses tune inputs to tune the frequency synthesizer. The CPU give a signal to the transmitter to send interrogation pulses. The transmit pulses go through a circulator then to the DME antenna.
The transmitter sends a signal to the suppression circuits. During a transmission, the suppression circuit in the DME 1 interrogator sends a suppression pulse to these units:
DME 2 interrogator
ATC 1 and 2 transponders (XPNDR)
TCAS computer.
The suppression pulse stops receiver operation in the other LRUs to prevent damage to internal circuits.
Receive
The circulator sends the RF pulse pairs it receives from the antenna to the receiver. The receiver sends the pulse pair to the CPU. The CPU calculates the slant range distance. It uses the time it takes to transmit pulse pairs and get a reply from the ground station. When another L-band system transmits, a suppression pulse stops the receiver operation.
Interrogator Output
After the CPU calculates slant range distance, the CPU sends it to two ARINC 429 transmitters. One ARINC 429 transmitter sends the range data to the DEUs for the flight deck displays and to other systems. A second ARINC 429 transmitter sends range data to the flight control computer. The CPU sends the pulse pairs to the pulse pair decoder. The decoder sends the DME audio to the REU.
Bite Module
The built-in test equipment (BITE) in the CPU monitors the circuits in the DME interrogator for faults. The fault memory in the DME keeps the number of faults per flight. Shop personnel can read the fault memory contents.
Test
The CPU does a test of the interrogator when it receives a test command from the navigation control panel. You can also push the test switch on the front panel of the interrogator. The LEDs on the front panel of the interrogator do not show during the navigation control panel test.
DME SYSTEM - SELF TEST
Self Test
Push the test switch on the DME interrogator to start a DME selftest.
Front Panel Displays
The LED status indicators go through this sequence:
The LRU status and control fail LEDs come on red for two seconds.
The LRU status LED changes to green.
All LEDs go off for two seconds.
The applicable LEDs come on to show the LRU status.
The red CONTROL FAIL LED shows when the tuning source is invalid.
The LRU STATUS LED shows interrogator test results. The LRU STATUS LED shows green for a good test or it shows red for a test failure.
