Audio Control Panel (ACP)
Alternate–Normal (ALT–NORM) Switch

NORM (Normal) –

  • ACP operates normally.

ALT (Alternate) –

  • ACP operates in degraded mode.
In degraded mode only the following radios are available from
the respective ACP:

Captain's ACP in degraded mode : VHF–1

First Officer's  ACP in degraded mode : VHF–2

Observer's (Aft Overhead) ACP in degraded mode : VHF–1