DAYTON, Ohio — A wing walker and aerobatic pilot killed in a fiery crash at an Ohio air show practiced their performance the previous day and reported no mechanical problems with the plane, according to preliminary report released Thursday by federal investigators.

Thousands of horrified spectators witnessed the June 22 crash and explosion at the Vectren Air Show near Dayton. The plane was turned upside-down and positioned to cross in front of the crowd when the nose pitched slightly and the aircraft abruptly rolled and struck ground, according to the accident report from the National Transportation Safety Board.

The crash, captured on video and in photos by, left a debris field 145 feet long, according the report.

The preliminary report does not address the cause of the crash. The safety board is expected to take months to issue a final report.

The preliminary report was based on information including spectators' videos and photos and initial statements collected by federal investigators. Those statements indicated no mechanical malfunctions were reported after the June 21 practice session by the pilot and the wing walker, the report said.

Some witnesses said they knew something was amiss because the plane was flying too low and slow.

Fairfield resident Thanh Tran said he saw a look of concern on the wing walker's face just before the impact.

"She looked very scared," he said. "Then the airplane crashed on the ground."

Federal Aviation Administration records showed clean safety records for the 64-year-old pilot, Charlie Schwenker of Oakton, Va., and 44-year-old performer Jane Wicker, of Bristow, Va.

Wicker was the third wing walker to die in two years. She was a mother of two teenage boys and was recently engaged to a pilot whom she planned to marry atop a plane.

Schwenker's wife of nine years described him as an exacting pilot who took no unmeasured risks.