Definition

Selective Calling System.

Description

SELCAL is a signaling method which can alert an individual aircraft that a ground station wishes to communicate with it. SELCAL signals can be transmitted over either HF or VHF RTF. A SELCAL transmission consists of a combination of four preselected audio tones which takes approximately two seconds to transmit. The tones are generated by a SELCAL encoder at the ground stations and received by a decoder connected to the audio output of the aircraft receiver. SELCAL can relieve a flight crew from maintaining a listening watch on assigned frequencies, which can be especially helpful where ATC RTF still relies upon noisy HF channels.

Receipt of an assigned SELCAL code activates a flight deck call system which may be a light, an audible chime or both. On aircraft equipped with SELCAL, the flight crew can maintain a listening watch using either headsets or flight deck speaker.