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Airbus Says Iran Air Jetliner Equipped with Two Transponders With AM-Airliner Rdp, Bjt

July 6, 1988

TOULOUSE, France (AP) _ One possibility emerging Tuesday to explain the downing of an Iranian passenger jet was that the plane could have been signaling, but the U.S. warship that shot it down got the wrong message.

The Airbus A300 involved was delivered to Iran Air six years ago with two transponders aboard that should have responded to identification requests from the USS Vincennes, Airbus spokesman David Velupillai said in this southern French town.

In Washington, chief Pentagon spokesman Dan Howard said Tuesday that the aircraft had been broadcasting a radio identification signal on a frequency used only by military aircraft, leading the Vincennes captain to believe he faced attack.

A U.S. expert said the jetliner could have installed its own transponder, ″to work with their own (Iranian) air defense system.″

Iranian airliner pilots, however, denied that Flight 655 would have been sending on a military channel.

The Vincennes sent electronic identification requests and voice warnings to change course, beamed over civilian and military radio channels, U.S. military officials said. The plane, mistaken for an F-14 fighter, was shot down Sunday and all 290 aboard died.

Electronic identification signals are received by transponders, electronic devices that are standard equipment on Airbus planes, said Velupillai.

He said the make of transponders on Airbus planes is up to the individual customer and he did not know the manufacturer of the transponders on the Iran Air jet.

Velupillai did not know if the original transponders delivered with the plane had been changed or how many transponders, if any, had been on board.

All transponders, regardless of make, work to international standards on a system called Secondary Surveillance Radar. A civilian ground station sends a pulse to which the plane automatically responds with data on the height of the aircraft, its bearing and - if the pilot has dialed in a code given by the air traffic controller - the identification code of the plane.

Iran’s U.N. ambassador, Mohammad Ja’afar Mahallati, told a news conference at U.N. headquarters in New York on Tuesday that Iranian air force commander Brig. Gen. Sallari, not further identified, informed him:

″The plane ... for 14 minutes ... was disseminating the normal signals of all civilian planes ... which proves to any radar that this is a civilian plane.″

Howard said at the Pentagon that the Iranian aircraft was broadcasting over a radio transmitter known as Identify Friend or Foe ″in two modes. It was squawking on Mode-3, which is ... a common identifier for both military and civilian aircraft, used in air traffic control.″

″It was also sending signals on a military mode, Mode-2. And the signals that ... the Vincennes was receiving from that aircraft, were signals that we had previously identified or associated with an F-14 ... No commercial airliners use Mode-2.″

Bill Reed, a spokesman at Allied-Signal Inc.’s Bendix Communications divison in Towson, Md., said Tuesday that one of the two transponders with which jetliners are normally equipped is a backup.

He confirmed that when an air traffic controller or other transmitter sends an interrogatory signal, the device transmits a response, or transponds, with the plane’s altitude and identity.

Reed said that in the case of an aircraft approaching a Navy ship in a combat area, the ship probably would send signals, trying to trigger transponder response, in every possible civilian and military mode. ″They probably were hitting them with every mode they had,″ Reed said.

He said most civilian airliners respond only in civilian modes, but equipment can be added.

″They may have put their own transponder in there to work with their own air defense system,″ Reed said.

In London on Tuesday, Capt. Massoud Razavi, a senior Iran Air pilot, denied U.S. claims that the downed A300 was transmitting on two transponders, including a frequency used previously for military information.

He told a news conference at the Iranian Embassy: ″The transponder we are using is the standard transponder and we use ‘mode A’ which is the civilian code. The code is given by Dubai (a United Arab Emirates member, 150 miles south of Bandar Abbas) and it is preset into the transponder before takeoff.″

Capt. Mehroujan Gharib, an Iran Air Boeing 747 supervisory pilot and safety officer, replied ″No″ at the same conference when asked if Iran Air civilian planes sometimes used a military frequency.

Both Iranian pilots indicated it was hard to believe the pilot of Flight 655, bound from Bandar Abbas to Dubai, would not have responded to U.S. Navy challenges.

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