General

When you tune an ILS frequency on the NAV control panels, discrete signals go to the DEUs to tell if the frequency is an ILS or VOR frequency. Each NAV control panel sends the discrete signal to the DEU 1 and DEU 2.

The FCCs send an ILS tune inhibit to the ILS function of the MMRs during the approach (APP) mode of operation. The ILS receiver will not accept another tune frequency during this mode.

The PSEU sends air/ground discrete signals to the MMRs to set the flight leg count in the internal memory, and also inhibit test in the air.

The MMRs send ILS ground station audio to the REU. The REU sends the audio to the flight compartment.