DENVER -- Fuel-control equipment for one of the engines on an airplane that crashed at Centennial Airport in December might have restricted fuel flow before the crash, which killed all three people on board, the National Transportation Safety Board reported Tuesday.

The report said NTSB analysts could not determine whether both engines on the 37-year-old Cessna 421 were running shortly before the crash, when the pilot reported engine trouble.

The Dec. 17 crash killed Nadia Barghelame, 20, of Fort Collins; Craig Markley, 72, of Fort Collins; and Roy Crain, 60, of Taylor, Mich. All three were commercial pilots.

The report, called a "factual report" that is typically released before the NTSB makes a final determination of the cause of a crash, said autopsies showed none of the three had used illegal drugs or alcohol.

Witnesses told investigators after takeoff, the plane flew low over the runway and drifted across a median and another runway before it rolled sharply to the right and dived into the ground. Witnesses said it appeared the pilot had the rudder in the full-right position, apparently to compensate for the nose veering to the right.

Mechanical problems that could have restricted fuel flow to the left engine probably were there before the crash, the engine's manufacturer told the NTSB.

The plane had taken off from the Fort Collins-Loveland airport that morning and was on its return flight when it crashed. The report said witnesses told investigators the pilot had trouble starting the engines before both flights. One witness at Centennial told investigators she saw a puff of black smoke while the plane was taxiing to the runway.

Barleghame's father told investigators his daughter had called him from Centennial and told him the plane was having engine or fuel problems, and that something had been "hooked up backwards" during a recent repair, the report said. It said repair technicians in Fort Collins said they had recently replaced some fuel-control equipment for the left engine. They said it was a simple repair and that it was impossible for anything to be hooked up backwards, the report said.

The report also said the sound of only one propeller could be identified in an audio analysis of a tape recording of communications between the plane and control tower shortly before the crash.

"It is not known if two propellers rotating at the same speed caused the observed frequency or if it was only one propeller creating the (sound) signature," the report said. "No background aircraft warning tones or alarms were heard."

A week before the crash, on Dec. 10, Paul Krysiak of Aurora and James Presba of Lone Tree were killed when their plane crashed south of the airport just after takeoff.

The N.T.S.B. found no connection between the two accidents.