Aircraft Radio System (Cabin Interphone)

Cabin Interphone

The cabin interphone is a miniature automatic telephone exchange servicing several subscribers:

the cabin attendants and the captain. In addition the system interfaces with the PA to allow announcementt so be made. Numbers a redialled by push buttons on the telephone type hand sensor on the pilot's control unit. Eleven two-figure numbers are allocated to the subscribers plus additional
numbers for PA in various or all compartments an 'all-attendantsc' all and an 'all-call'. Two dialling codes consist of letters: P-P is used by an attendant to alert the pilot (call light flashes on control unit and chime sounds once) while PA-PA is used by the pilot to gain absolute priority over all other users of the PA system. The directory is listed on the push-to-talks witch incorporated in each hand set to minimize ambient noise.

All dialling coded ecoding and the necessary trunk switching is carried out in the central switching unit. CSU (automatic exchange). The CSU also contains three amplifiers one of which is permanently

allocated to the pilot on what is effectively a private trunk. Of the five other available trunks, two are

allocated to the attendants, two to the PA system and

one for dialling. (Note a trunk is simply a circuit which can connect two subscribers.) The cabin interphone and service in terphone systems may be combined into a common network by appropriates election on the flight engineer's interphone switch panel, captain's ASP and cabin interphone control unit. Any handset may then be lifted and connected in to the network (dial'all-call'). In a similar way the flight interphone circuits may be used to make specific calls over.the cabin interphone system.