Degraded Audio System Operation
If the remote electronics unit or ACP malfunctions, the ACP cannot control the remote
electronics unit. Audio system operation can be switched to a degraded mode by
placing the ALT–NORM switch to ALT. In this mode, the ACP at that station is
inoperative and the crewmember can only communicate on one radio.
The ACP transmitter selectors are not functional. The transmitter selector for the
usable radio illuminates when a station is operating in the degraded mode. The
receiver switches are not functional, and only the usable radio is heard at a preset
volume, through the headset. The speaker and speaker switch are not functional at
that station. In addition, the flight interphone and service interphone cannot be used.
The control wheel PTT switch INT position and the ACP PTT switch I/C position are
not functional since the flight interphone is not functional.
The mask and boom microphones can be used for transmission on the usable radio.
The MASK–BOOM switch works normally in the degraded mode. The mask and boom
microphones can be keyed with the control wheel PTT switch MIC position or the ACP
PTT switch R/T position. The hand microphone is not usable in the degraded mode of
operation.
Note: Audio warnings for altitude alert, GPWS, and windshear are not heard on an
audio system operating in the degraded mode.
An audio system operating in the degraded mode cannot access the passenger
address system through the ACP. The crewmember can still use the service
interphone handset and PA microphone if they are installed on the control stand.
