Iran Air Flight 655 - Radio Communication

Radio Communication

Throughout its final flight, IR655 was in radio contact with various air traffic control services using standard civil aviation frequencies, and had spoken in English to Bandar Abbas Approach Control seconds before the Vincennes launched its missiles. According to the U.S. Navy investigation the Vincennes at that time had no equipment suitable for monitoring civil aviation frequencies, other than the International Air Distress frequency. Subsequently U.S. Navy warships in the area were equipped with dialable VHF radios, and access to flight plan information was sought, to better track commercial airliners.

The official ICAO report stated that ten attempts were made to contact Iran Air flight 655: seven on military frequencies and three on commercial frequencies, addressed to an "unidentified Iranian aircraft" and giving its speed as 350 knots (650 km/h), which was the ground speed of the aircraft their radar reported. The crew of the Iran Air 655, however, would have seen a speed of 300 knots (560 km/h) on their controls, which was their relative airspeed, possibly leading them to conclude that the Vincennes was talking to another aircraft. Both Sides and Vincennes tried contacting flight 655 on several civilian and military frequencies.

International investigations concluded that the crew of IR655 assumed that the three calls that they received before the missiles struck must have been directed at an Iranian P-3 Orion (see below).