Plain English Meaning

Private phone lines that controllers use to talk to each other and to other facilities. They are not the radios that pilots hear.

Full Definition

Dedicated, hard-wired voice communication circuits that connect ATC facilities, sectors, and controllers to one another and to other agencies, separate from the air-to-ground radio frequencies used to talk to pilots.

Context Anchor

Seen in air traffic control and radio outage procedures, including cases where a center frequency is not working normally.

Derivation

From 'inter-' (between) and 'phone' (voice/sound). It originally referred to internal telephone systems within ships, aircraft, and buildings — voice links between people inside the same operation rather than calls to the outside world.