PORTLAND — A small plane that crashed at the Portland International Jetport killing three people was functioning properly when it went down, a preliminary report by the National Transportation Safety Board says.

The report indicates the single-engine 172M Cessna plane had its wing flaps extended to the landing position and the propeller was rotating at impact when it crashed on Sept. 1.

Investigators are keeping the engine for further study. It is expected to be several months before the board rules on the cause of the crash.

The pilot, Diane W. Clark, 56, and her neighbor, Sally Leonard, both of Windham, were killed instantly.

Deborah Leonard-Prentice, 29, of Hooksett, N.H., was severely burned and died later that night at a Boston hospital.

Clark, who had logged more than 1,000 hours of flying time, had just taken off when she apparently ran into trouble. She was trying to land when the plane crashed.