Power Interface

The NAV control panel uses 115v ac power for operation. It also uses 28v dc for an internal monitor. The NAV control panel uses 5v ac from the master dim and test for panel lights.

Arinc 429 Interfaces

Frequency tune inputs and test commands from the NAV control panel go to the MMR on an ARINC 429 bus.

When you tune an ILS frequency, the frequency tune circuits operate switches in the NAV control panel that send these discrete signals:

• Open discrete to the REU

• Ground discrete to the DEUs

• 28v dc to the FCCs

• 28v dc to the LOC antenna switches.

Discrete Interfaces

The REU uses the open discrete to select ILS audio. The DEUs use the ground discrete to set the ILS displays. The NAV control panel sends the 28v dc to the FCCs when an ILS frequency is active. It also sends 28v dc to the LOC antenna switches when an ILS frequency is active for switch operation.

The on-side FCC supplies a discrete during an AFDS approach mode. The discrete causes the MMR to not accept any frequency changes. The discrete also goes to the NAV control panel. When the discrete is set, It prevents any frequency change to the output data word that goes to the MMR. The MMR uses the air/ground discrete for flight leg count.

Rf Interfaces

RF signals from the VOR/LOC antenna or localizer antenna in the nose radome, go to the localizer receiver circuits in the MMR. RF signals from the glideslope antenna in the nose radome go to the glideslope receiver circuits in the MMR.

ILS - FUNCTIONAL DESCRIPTION

Receiver Functional Description

All inputs to the receiver go through a high intensity radiated frequency (HIRF) filter. This filter provides protection to internal circuits.

Tune inputs from the NAV control panel go to the main processor. The processor sends the tune frequency to the frequency synthesizer circuits. The frequency synthesizer circuits tune the localizer receiver and glideslope receiver.

The receiver circuits send the RF signal inputs from the

antennas to the main processor. The processor computes

localizer deviation and glideslope deviation.

ILS data goes out on two ARINC 429 buses.

Output 1 goes to FCC A and FCC B.

Output 2 goes to these LRUs:

• FDAU

• Standby attitude indicator

• GPWC

• FMC

• DEUs.

The A/D function of the receiver converts the audio from the localizer ground station from an analog to a digital format. The audio then goes to the main processor. The main processor sends the audio to the REU. The processor also detects any morse code station identifier and sends it out on the data buses. When there is a station identifier on the data bus, the DEUs replace the frequency display with the four letter station identifier.

Test

To start an ILS test, push the NAV control panel test switch when there is an ILS frequency active or push the front panel test switch. When the processor receives a test signal, it does a test of operation and receiver condition. Test results show on the front panel LED status indicators. The LRU status LED shows red for test faults or green if there are no faults. The control fail LED comes on red if there is no tuning input data from the control panel. The control fail LED will show green for valid tune inputs.

ILS - CONTROLS