Witnesses saw a twin-engine airplane spinning slowly, smoke wafting from its wings, before it crashed moments after taking off Aug. 7, killing both seasoned pilots aboard and destroying the house it struck in rural Westmoreland County.

A preliminary report released Friday by the National Transportation Safety Board said witnesses also heard "abnormal engine sounds" from the Beech Baron BE-58 after it took off that morning from Arnold Palmer Regional Airport near Latrobe. The agency will not issue a final report for at least a year, but preliminary findings suggest mechanical issues may have played a role in the crash.

Edward Francis Sobota, 65, of Unity, who had recently purchased the plane, and Theodore P. Kokolis, 66, of Moon, a flight instructor, were killed instantly when the plane slammed into a house off Route 286 in Bell, near Saltsburg and the Westmoreland-Indiana county boundary.

Mr. Kokolis, who had logged 23,250 hours of flight time, was observing a "checkride" flight by Mr. Sobota, a commercial pilot who previously owned the plane in the 1980s. They crashed about 14 nautical miles from the airport, just 12 minutes after they radioed that they were planning "some airwork," lifted off from the airport's runway 23 and headed northwest.

Homeowner Steve Yanko and his dog escaped unharmed, but the house was destroyed by the fire that erupted after the crash of the fuel-laden plane. His wife was not home at the time.

In their report, NTSB investigators said one witness told of hearing the plane's engine quit and restart several times, then "rev up loudly after the third restart." Several witnesses described the plane's descent as spinning or spiraling down and said they saw smoke or vapor trailing from it, according to the report.

The report also notes that the plane had passed an annual inspection on March 8. Federal Aviation Administration records showed both pilots aboard had no records for past enforcement action or previous accidents or incidents.

Mr. Yanko told investigators he'd been asleep on a couch in his basement when he was awakened by a "violent noise." The fire that consumed his house "burned incredibly fast," he told investigators, but he was able to distinguish a portion of the plane's wing beyond the edge of his roof and "a chrome propeller."

In the days after the crash, investigators who searched through the wreckage retrieved both of the plane's engines and propellers; one of its cargo doors; an 11-foot portion of its left wing; its avionics system; and portions of its seats, control column and landing gear, fuel and flap systems. Those pieces of the plane are being examined for additional clues about the cause of the crash.

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