COMMUNICATION PROCEDURE
As by ICAO Documentation 9432 – manual of radiotelephony, a callsign shall be one of the following types:
- The characters corresponding to the registration marking of the aircraft.
- The telephony designator of the aircraft operating company or agency, followed by the last four characters of the registration marking of the aircraft.
- The telephony designator of the aircraft operating company or agency, followed by the flight identification
On initial contact, pilot must spell his complete callsign, usually at the end of his message. Always pronounce each digit separately.
A pilot shall use his abbreviated callsign only after air traffic controller has taken the initiative.