Accident Sequence
Shortly after departure and level off, the pilot reported an engine malfunction and initiated a return to the airport. About two minutes later, he reported an engine fire and declared an emergency. Approximately one minute thereafter, the right wing separated from the aircraft and the plane crashed.
Wreckage Examination
Examination of the wreckage revealed extensive inflight fire damage in the area of the wing separation. A 2.5 by 3 inches hole was found in the right inboard exhaust tube, part number 0850712-6. The hole was oriented toward the accessory compartment, where numerous fuel and oil lines were fire damaged and charred. Much of the engine support structure and wing spar were melted in that area. The exhaust tube walls were thin, brittle, and discolored in the area of the rupture, and several areas of cracks and small holes were found.
Maintenance Records
The exhaust tube had accumulated 5,862 hours of total service and 1,762 hours since it was overhauled. Records showed that Airworthiness Directive 75-23-08 had been complied with during the last inspection, which occurred 25 flight hours prior to the accident.
Probable Cause
The official probable cause findings include a corroded exhaust manifold/pipe that failed totally and leaked, due to inadequate maintenance by company personnel, inadequate manufacturer procedure, and inadequate FAA surveillance. This led to a partial loss of engine power, an inflight fire, and ultimately the total failure and separation of the wing, resulting in an uncontrolled descent into terrain. The pilot, who was the sole occupant, was killed.