U.S. Reports Contradictory Plane Signals : Iran Jet Transmitted on Civil and Military Bands, Pentagon Says

The Pentagon, providing new details that appeared to compound the mystery of the downing of an Iran Air jetliner by an American warship in the Persian Gulf on Sunday, asserted Tuesday that the plane was emitting contradictory radio signals, some identifying it as a civilian aircraft and some identifying it as military.

This revelation raised a host of new questions because Navy officials had said that the radio signals picked up by the U.S. cruiser Vincennes were among the critical factors that led the ship’s captain to believe that the Airbus A-300 was a hostile Iranian F-14 fighter and to order it shot down.

Pentagon spokesman Dan Howard, seeking to explain and justify the downing of Iran Air Flight 655, said that the Vincennes had received radio emissions from two transponders aboard the Iranian plane, one emitting military codes and one emitting civilian codes.

Further compounding the uncertainties, however, Howard conceded that a nearby U.S. guided missile frigate, the John H. Sides, picked up the civilian transponder signals from the aircraft but did not “hear” the military signals.

A transponder is a transmitter that responds to electronic questioning by air traffic controllers or other radar operators by emitting a code that identifies the aircraft.

In early briefings on the incident, military officials had refused to discuss details of the electronic signals picked up by the sophisticated Aegis-type cruiser, saying that such information is classified.

The plane, Howard said, was tracked from the minute it took off from the airfield at Bandar Abbas on Iran’s southern coast, a facility used by Iran for both civilian and military aircraft. American intelligence had, for the first time, detected F-14 activity in the area within the past few weeks, Howard said.

The Vincennes was in the Strait of Hormuz at the time, about 50 miles south of Bandar Abbas, Howard said. Radar operators aboard the Navy ship sent electronic queries to the unidentified aircraft, which responded with signals from both a civilian Mode 3 transponder and the exclusively military Mode 2 transponder.

U.S. military officials said Tuesday that they had never encountered an aircraft that was “squawking”--transmitting--on both Mode 3 and Mode 2.

An Iran Air pilot who flew Airbuses for the airline as recently as last fall questioned the new American account. He said that the planes never carried the transponder device needed to send the military code cited by U.S. officials.

12 Minutes After Gunfire

Howard also disclosed that the decision to bring the suspect aircraft down was made 12 minutes after the last shots were fired between U.S. warships and Iranian gunboats. Previous U.S. accounts had said that the missiles were fired while the crew of the Vincennes was still engaged in surface gunfire.

And Howard said that military officials could not explain discrepancies in reports of the doomed airliner’s altitude, nor could they account for why the Vincennes’ sophisticated radar showed the plane approaching at more than 500 miles an hour, nearly a physical impossibility for the Airbus at low altitude.

The Pentagon official said a six-member board of inquiry headed by Rear Adm. William M. Fogarty arrived aboard the Vincennes on Tuesday to begin to reconstruct the events leading to the tragedy. Howard stressed that whatever the investigation revealed, Capt. Will C. Rogers III of the Vincennes acted properly in what he believed was self-defense.

‘Very Crucial Decision’

“The commander had a very few minutes in which to make a very crucial decision that was certainly life or death for him and for his ship and for his crew,” Howard said. “And he had to make that decision based upon the information available to him at the time.”

Howard, discussing the radio signals detected by the Vincennes, said that the military Mode 2 transponder emissions detected by the Vincennes “were signals that we had previously identified or associated with an F-14. That was based on historical information in the gulf.”

The official said that the information revealed Tuesday was the first acknowledgment by U.S. forces that they were able to read another nation’s Mode 2 transponder signals.

Radiomen on the Vincennes and on the nearby U.S. guided-missile frigate John H. Sides sent a total of 12 warnings to the suspect aircraft, demanding that it identify itself and ordering it to change course, officials said. The plane continued at high speed on a course that would have taken it directly over the Vincennes.

Radar-Guided Missiles

Seven minutes after the jetliner took off, Capt. Rogers sent up two Standard SM-2 radar-guided missiles, at least one of which hit the Airbus and demolished it.

Mahmoud Vaziri, an ex-Iran Air pilot who flew Flight 655 until last October, challenged the U.S. account in an interview with The Times. He said the Iran Air Airbus A-300s he flew were never equipped to transmit over the military channel heard by the Vincennes.

“We don’t have the equipment to broadcast on anything but Mode Charlie,” he said, referring to the purely civilian channel the Pentagon calls Mode 3, known to many aviators as Mode C.

The American-trained Iran Air pilot said he doubts whether Iran’s Civil Aviation Organization would have bought the transponders since he left Iran last October.

“They’re short of cash,” he said. “They’re having a hard enough time getting equipment as it is--it has to be paid for with hard currency. Why would they want to buy such unnecessary equipment?”

Both Are Civilian Sets

Vaziri said that while Iran Air jetliners carry two transponders, both are solely Mode 3 civilian sets, and they cannot transmit at the same time.

The Iranian pilot said that Amir Razvani, whom he identified as the pilot of the downed airliner, would not have allowed Iranian authorities to put a military transponder aboard an Airbus loaded with 290 passengers and crew. Vaziri said he had known Razvani for several years, flown with him many times and considered him a friend.

“Why would you want to have a transponder operating in military mode going toward a (U.S.) Navy ship?” he asked. “You’ve got enough on your mind just flying in Iran and in the Persian Gulf. You don’t go looking for trouble.”

Vaziri described Razvani as “very conservative. . . . If he had the slightest idea there was something out there, he would have delayed. He wasn’t radical or religious. He didn’t want to die. Nobody wants to die.”

No Speculation on Source

Vaziri’s account left open the possibility that the Mode 2 emissions were coming from a second airplane or a source on the ground. But Pentagon officials said that they had no evidence that a second plane was in the air and refused to speculate on the source of the radio signals.

Another new piece of information added to the puzzle was the exact timing of the end of surface gunfire and the takeoff of the Iranian Airbus. Briefing reporters after the incident Sunday, Adm. William J. Crowe Jr., chairman of the Joint Chiefs of Staff, said that the decision to attack the plane was made in an intense burst of activity while Capt. Rogers of the Vincennes was “engaged already in surface action” against three small Iranian gunboats.

But according to details released Tuesday, the shooting stopped at 10:42 a.m. local time, while the jetliner did not leave the ground until 10:47 a.m. Because of the jetliner’s ambiguous transponder data, its apparently threatening flight path and its refusal to respond to radio warnings, the plane was declared hostile, and the missiles were fired at 10:54.

Captain ‘Very Prudent’

But Howard said that the Vincennes’ captain was “very prudent” in considering the approach of the unknown aircraft a threat related to the recently completed firefight.

Howard acknowledged that Pentagon officials could not explain conflicting reports on the plane’s altitude. The Vincennes reported the plane as flying at about 9,000 feet; the Sides reported it at above 12,000 feet, and air traffic control in Dubai, the plane’s destination in the United Arab Emirates, pegged it at 7,800 feet.

In addition, sailors on the Vincennes said that the plane was descending and gaining speed as it approached the warship, while radar operators on the Sides said it was maintaining a steady altitude.

It is not yet known whether this conflicting data was available to the commander of the Vincennes when he made the decision to shoot the jetliner down.

Howard said that one assertion not yet in question was the plane’s speed as it headed toward the warship. The Vincennes said it was flying at between 450 and 455 knots, about 520 miles an hour. But the Iranian pilot--with support from the authoritative Jane’s All the World’s Aircraft--said that the plane is structurally incapable of such speed at altitudes below 25,000 feet.

Data Recorder Sought

The investigative panel will try to determine the speed of the aircraft from computer tapes on the Vincennes and from the plane’s flight data recorder, if Iranian authorities recover it from the wreckage and share it with American investigators, Howard said.

Other Pentagon officials have attributed anomalies in radar data to thick haze and humidity in the region. One official intimately familiar with the Vincennes’ Aegis radar system said that “the environment in the gulf changes dramatically from day to day” and that the Navy cannot precisely calibrate the radar to correspond to atmospheric conditions each day.

But, he said, the Vincennes’ SPY-1 radar “is the most accurate the Navy has. It’s never let me down.”

AWACS in Northern Gulf

Howard, the Pentagon spokesman, also revealed that a Saudi Arabian AWACS radar surveillance plane was flying in coordination with a U.S.-escorted merchant ship convoy at the far northern end of the gulf at the time of the encounter in the Strait of Hormuz. A U.S. guided-missile frigate was escorting the tanker Sea Isle City under AWACS radar cover Sunday morning, but the plane’s orbit did not allow it to track the action at the other end of the gulf, some 500 miles away.

Military experts said that the “look-down” radar capabilities of the AWACS would have made it much more likely that the Iran Air jetliner would have been identified as innocent and that the disaster would have been prevented.

“All things being equal,” Howard said, “it’s desirable to have AWACS and Aegis working together everywhere in every situation, but the fact is that those resources don’t exist. You cannot do it everywhere at every time.”