Federal investigators wound up their field work at the site of last week's Delta air crash Sunday, refusing to comment on speculation that double engine failure might have led to the disaster.

The Dallas Morning News, quoting anonymous sources close to the investigation, reported Sunday that investigators are trying to determine whether two of the three engines on the Boeing 727 failed in the seconds before Wednesday's crash."When someone says engine failure, there are a whole host of things that might mean," Lee Dickinson, a member of the National Transportation Safety Board (NTSB),said at a briefing Sunday. "One of the things I will not do is speculate on anything."

Some pilots said the fact that the wing flaps on the jet were apparently retracted at the time of the crash, when they ordinarily would have been extended for takeoff, may have been a sign the pilots were trying to fly the plane on one engine, not a cause of the crash, newspapers reported.

Thirteen people were killed when Flight 1141 en route to Salt Lake City crashed and burned seconds after takeoff at Dallas-Fort Worth International Airport. Ninety-five people survived.

A recording of cockpit crew members showed they mentioned engine failure. Two loud pops were then heard, which could have indicated a "compressor stall." But Dickinson said a compressor stall, which occurs when an engine is starving for air, is not critical. "Keep in mind, compressor stall is not serious, it's a hiccup."

At the site Sunday, investigators sealed the cockpit in a blue tarp. It will be taken to Delta headquarters in Atlanta where it will be dismantled and studied.

Workers used power saws to remove the landing gear beneath the 727 and also bored into the ground beneath the left wing to determine the amount of fuel that may have spilled during the crash.

Two surviving flight attendants were taken to the wreckage and questioned by investigators, Dickinson said. He said he had no immediate information on what they said.

Dickinson said he planned to leave Dallas later Sunday, and only a few investigators would remain as the center of the inquiry moves to Washington.

The role of the wing flaps, which are extended during takeoff to provide added lift, continued to be discussed.

Flight Engineer Stephen Judd has told investigators that the wing flaps were extended in the proper position upon takeoff. But evidence collected from the wreckage indicates the flaps were completely or almost completely retracted.