BACKUP ICS MODE
Each audio panel has a backup mode that can be selected when one of the
Audio Panels fail via the BKUP pop-up control knob.
The backup mode permits the pilot headset to be connected directly to the
on-side VHF COMM (Backup radio audio line) and cross-side audio panel
ICS for intercommunication (Backup interphone line). Both lines are analog
audio lines.
In case the Audio Panel failure depends on the loss of input power (ICS PLT
or ICS CPLT circuit breaker tripped), power to operate the Audio Panel in
Backup mode comes from the cross-side Audio Panel.
In Backup mode, switching between intercomunication and radio
transmission is performed by an external relay controlled by the Radio PTT
button.
In Backup mode, the BKUP pop-up control knob on the Audio Panel controls
both the ICS and COM audio volumes. In this case the ICS and COM audio
volumes cannot be adjusted separately.
BACKUP RADIO TUNING
In case the normal radio tuning is not available (i.e. NIM failure, MAU failure)
a BKUP RADIO page is available in the MCDU to permit limited control of
the on-side main radios, only.
A dedicated backup radio tuning line (ARINC 429 digital bus) between each
MCDU and the on-side MRC allows each pilot only to retur the on-side VHF
COM and VHF NAV radios and to control the on-side transponder.
The DME will automatically be retuned to the VHF NAV paired frequency (no
DME Hold function is available in backup mode).
In case of MAU failure:
• The BKUP RADIO page is automatically selected on the on-side
MCDU
• Normal tuning using the CCD and the PFD is still available via the
cross-side MAU.