Monitor and Test

The test switch starts a test of the VOR/MB receiver. The built-in test equipment (BITE) circuits do a test of the VOR/MB receiver. The test results show on the common display, light emitting diodes (LEDs), and through the flight interphone speakers and headsets.

During the test, a self-test frequency generator gives a 75 MHz RF signal that has 400 Hz, 1300 Hz, and 3000 Hz audio signals. The bandpass filters find the audio signals and send them to the audio amplifier. The audio amplifier sends the audio signals to the REU. The REU sends the audio signals to the flight interphone speakers and headsets in the flight deck.

The BITE circuits monitor the condition of the output data of the VOR/MB receiver.

The VOR/MB receiver gets an air/ground discrete signal from the proximity switch electronics unit (PSEU). The VOR/MB receiver uses this signal to prevent a test in the air.

An internal nonvolatile fault memory (NVM) in the BITE circuits use the air/ground discrete signal. The NVM uses this signal to calculate flight legs.