✔️📘✏️SELCAL a selective-calling radio system that can alert an aircraft's crew that a ground radio station wishes to communicate with the aircraft.
✔️📘✏️Aircraft operating on long/transoceanic routes are out of VHF coverage area for a major part of their flights. Maintaining a listening watch on the en-route frequencies (HF) is mandatory for such flights.
✔️📘✏️Since HF channels are high in static noise, it will be very annoying for the flight crew to continuously monitor these channels. To avoid this SELCAL system is installed on the aircraft. With the help of SELCAL, a ground station calls a particular aircraft.
✔️📘✏️The system can function with both HF and VHF communication systems. In India, SELCAL facility is available only with HF system.
✔️📘✏️Each aircraft being assigned a different four letter SELCAL code, which is selected on the decoder. A ground station that desire to call a particular aircraft transmits a SELCAL code signal on the appropriate HF channel.
✔️📘✏️The aircraft on which the decoder is set to the code that matches the received code will give the pilot a visual (a blinking lamp in the cockpit) and audio (chime in the headset) indication. This alerts the pilot about the call.
✔️📘✏️Transmission of SELCAL coded signal is possible only from the ground to air and no vice versa.