Selcal SC-04

• alternative name: TMC

The SELCAL or Selective Calling system used in aviation is a radio communication system by which the ground-based radio operator can send a signal to the aircraft with which it wants to establish communication. This is helpful on oceanic routes, where the use of HF (high frequency) causes too much background noise, and pilots prefer to lower the volume of that “selective call”.

To identify each aircraft, they are assigned a SELCAL letter code. This is made up of two letter pairs and each has a different assigned frequency. So when the operator chooses the aircraft to speak with, 4 tones are sent with the four different frequencies, and the aircraft that corresponds to that code alerts the crew with a blue light and a bling-blong type acoustic signal!

The letters used are from A to S, except I and O.

Usually, the only aircraft equipped with a SELCAL warning system are those that operate ocean routes (and therefore use HF frequencies). ARINC (Aeronautical Radio Inc.) issues these codes in the United States.

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