The SELCAL is designed to detect the four letter code attributed
to an individual aircraft, avoiding permanently monitoring the
receivers. When a call is identified for the aircraft, the
decoder actuates a signal indicator which may be a light, a chime,
or any combination of such crew alerting devices, and enables swift
and reliable answering of the call.
This system operates with existing HF and VHF ground-to-air
transmitters and receivers. As a standalone unit, Cobham's
SELCAL is well suited for upgrade programs in which function is not
included in the Audio Management Unit (AMU).