The plot thickens … This is straight from the maintenance manual.
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CIDS Power Supply:
The service bus, the essential bus and the hot battery bus supply electrical power to the CIDS.
Depending on the available bus the CIDS operates in the:
- Normal mode or
- Emergency mode.
In the normal mode the service bus supplies 28VDC to the CIDS. All functions of the system operate fully.
In the emergency mode the essential bus supplies 28VDC to the CIDS. If the essential bus is not available then (if emerg lights are in arm or on) the hot battery bus supplies CIDS.
To conserve power the system operates with minimum functions.
The ACP’s and the AIP’s do not operate.
The remaining functions are:
- PA
- Cabin Interphone
- EVAC
- Smoke Detection
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So I guess it really depends on the failures your friend encountered in the SIM. If he had an ESS BUS fault when in Emergency Elec Config then the hot battery bus would supply those very basic CIDS functions - But no ACP 3.
Also, the AMU would not be powered so Cockpit Handset is all you would have.
If the ESS BUS fault occurred with power available then selecting the FO’s audio to 3 would transfer all of his audio equipment (including hand held mic) onto ACP 3.
Cockpit Handset would also be available.