The flight interphone is to talk and listen to the flight deck. When the flight crew is using their headsets to communicate with each other and you're plugged into the flight int, you can talk and listen to them.
The service interphone is for maintenance. A switch in the flight deck has to be switched from flight to service interphone. This lets the amt's to communicate with others that are plugged into the plane. There are service int outlets located all over the plane, in the wheel well, mec, engines, tail, etc.
If the switch is in the flight position, only the flight outlet is active. If the switch is in the service position, both are active.
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The flight interphone is to talk and listen to the flight deck. When the flight crew is using their headsets to communicate with each other and you're plugged into the flight int, you can talk and listen to them.
The service interphone is for maintenance. A switch in the flight deck has to be switched from flight to service interphone. This lets the amt's to communicate with others that are plugged into the plane. There are service int outlets located all over the plane, in the wheel well, mec, engines, tail, etc.
If the switch is in the flight position, only the flight outlet is active. If the switch is in the service position, both are active.
I believe that Flight is for calls to someone on the ground, while Service is for communication within the aircraft.