F-15s Tried Identifying Copters Electronically : Mideast: But Pentagon says they got ‘no friendly response’ from transponder devices before firing.

The pilots of two U.S. F-15C jet fighters tried to identify a pair of Blackhawk helicopters electronically before firing their missiles, but they did not receive the proper signal in return before they mistakenly shot the choppers down, the Pentagon said Friday.

Gen. John M. Shalikashvili, chairman of the Joint Chiefs of Staff, said that the F-15Cs used their IFF equipment--for Identification, Friend or Foe--to “interrogate” the helicopters but received “no friendly response” from the Blackhawks’ transponder devices.

Although more information is expected from an Air Force investigation now under way, officials said the failure of the helicopters’ transponders to identify them as U.S. aircraft could have been a principal cause of Thursday’s tragedy.

Officials also said there was no communication--by radio or by other electronic devices--between the helicopters and the Airborne Warning and Control System (AWACS) command plane that was flying nearby.

The AWACS plane knew in advance that both sets of aircraft would be in the area, and its controllers were supposed to have coordinated their movements and to have helped prevent any misidentification, officials said.

Friday’s disclosure shed a potentially important light on the tragedy, in which two U.S. F-15Cs mistakenly shot down a pair of U.S. UH-60 Blackhawk helicopters over northern Iraq, killing 26 people, including 15 Americans.

But those knowledgeable about IFF procedures cautioned that they can be complex and that a failure of the helicopters’ transponders to identify them definitively as American might not by itself have provided justification for the F-15C pilots to shoot them down.

They said the choppers’ transponders also might have been turned off for a recent landing--a common practice to prevent the “burnout” of IFF equipment. If so, the devices would not have replied automatically to the F-15Cs’ signals.

The transponders could also have been set for a different code than was expected by the F-15Cs’ IFF gear or they could have been malfunctioning, knowledgeable officials said.

The disclosures underscored the complexity of the situation--and the continued bafflement of officials trying to find out how the incident could have happened in the face of a battery of fail-safe procedures that had been established to prevent just such accidents.

Pentagon officials declined to answer other questions about the case, pending completion of a high-level investigation being conducted at the crash site near the village of Irbil in northern Iraq and at Ramstein Air Base in Germany.

But, in a hint that some human error was responsible, Defense Secretary William J. Perry specifically told reporters that the investigation was intended “to determine personal culpability, if any, whether systems failures or inadequacies existed and whether procedures were adequate.”

“If our procedures need change, we will change them, and we will change them immediately,” Perry said. “If individuals are found to be culpable, we will discipline them. But we do not--we will not rush to judgment.”

He said that he had suspended all U.S. patrol flights over northern Iraq for a day to give investigators time to visit the crash site and gather any evidence that might be available. But he said normal operations are expected to resume this morning.

As an added safeguard, he said, he had tightened the rules of engagement--the procedures for determining when a fighter pilot may fire at a potential target over northern Iraq.

Although neither Perry nor Shalikashvili would say so publicly, defense officials said that pilots now will be required to obtain clearance from AWACS controllers before firing at another aircraft and no longer will be allowed to shoot solely after identifying them visually.

Under rules in force Thursday, the F-15C pilots could decide to fire on their own once they had identified the helicopters--even though they had mistaken them for Iraqi aircraft.

The Clinton Administration on Friday also disclosed the names of four of the 15 Americans killed in the crash--Army Col. Richard A. Mulhern, Air Force 2nd Lt. Laura Ashley Piper, Army Warrant Officer John W. Garrett and Barbara L. Schell, a Foreign Service officer.

Mulhern had been on his way to take command of an allied military coordination center in Zakhu; it is assigned to provide military advice and intelligence to the Kurds in northern Iraq. Schell was a policy adviser there.

Piper was an intelligence officer assigned to the allied air base in Ramstein, Germany, and Garrett was a helicopter pilot. It was not known whether he was flying or was a passenger. The names of others killed were being withheld until their families are notified.

Perry and Shalikashvili also made these points in their news conference:

* The helicopters apparently did not notify the AWACS plane when they took off after their previous stop at an Iraqi village, and the AWACS controllers did not radio the helicopters to warn them that the F-15Cs were in the area. “Had that procedure worked, there should not have been this accident,” Perry said.

* The pilots of the two F-15Cs did not try to contact the helicopter pilots by radio after making visual identification--a procedure that might have avoided the tragedy. Such contact apparently is not required but often is done as a precaution.

* Officials do not know yet whether the pilots of the F-15Cs asked the AWACS controllers to confirm whether the helicopters were friendly or whether the AWACS crew authorized the shootings. “The investigation will have to determine that,” Shalikashvili said.

Perry also listed other questions he has asked the investigators to look into: Had the helicopters filed a flight plan? If so, had they deviated from their outlined route?

“These are all very good questions, and we do not have definitive answers . . . at this time,” he said. But he added: “We will have . . . very shortly. That is what our investigation is all about.”

The failure of the helicopters’ IFF gear to signal the F-15Cs was puzzling to military officers. Had everything been operating properly, the signals should have been transmitted automatically and the accident could have been averted.

Shalikashvili told reporters that the operation had been carefully and correctly planned and all involved had been properly briefed about it. But, he added, “what actually then happened, I cannot speculate on.”

And Perry lamented that “there are half a dozen procedures that we have in place, any one of which . . . could have prevented this. . . . They didn’t all have to operate,” he said. “Just one of them had to operate and this . . . would not have happened.”

A Search for Answers

Defense Secretary William J. Perry says military investigators will try to get answers to the following questions to explain why U.S. warplanes shot down two American helicopters in Iraq:

* Were the helicopters in contact with the airborne warning and control (AWACS) command plane controlling allied air operations?

* Did the AWACS attempt to contact the helicopters?

* Were the helicopters’ IFF (Identification, Friend or Foe) systems working?

* Did the F-15Cs ask the AWACS for confirmation before firing?

* Had the helicopters filed a flight plan? If yes, were they flying the planned route or had they deviated from the filed route?

* Were the AWACS and F-15Cs aware that two U.S. helicopters were in the area?

* Did the F-15Cs attempt to make radio contact with the helicopters? If not, why not?