MANSFIELD - Federal investigators have attributed a fatal plane crash at Mansfield Municipal Airport last year to pilot error and an overweight plane.

The pilot and a passenger were killed in the Sept. 8, 2007, crash and two other passengers were seriously injured.

The National Transportation Safety Board determined the probable cause of the accident was the pilot's improper use of wing flaps soon after takeoff, which affected the ability of the plane to climb and subsequently caused it to stall.

The plane was overloaded by 64 pounds, which contributed to the crash, according to the findings of the NTSB.

Killed in the crash were the pilot, Lawrence Mann, 38, of Portland, Maine, and another passenger, Cabott Squire, 29, also of Portland. Mathew Kramer, 30, of Mansfield, and Jared Lamey, 30, of Saco, Maine, were seriously injured.

The 10:30 a.m. crash of the Cessna 172 occurred the day of an annual aviator "fly-in," but was not related to the gathering. The occupants of the plane were believed to be headed to Cape Cod for a day of golfing.

The NTSB said a video recording of the accident showed the airplane wavering during its climb in a nose-high attitude, and beginning a turn to the left.

The airplane reached an altitude of about 100 feet before increasing the turn to approximately 60 degrees. The airplane then appeared to pitch nose down, with a sharp roll to the left, and hit the ground, according to the agency's findings.

The NTSB was assisted in the investigation by the Federal Aviation Administration and the Massachusetts Aeronautics Commission.