What happened
Shortly after departing and reaching cruising altitude, the pilot reported an engine malfunction and decided to return to the airport. Approximately two minutes later, he announced an engine fire and declared an emergency. About one minute after that, the right wing detached from the fuselage, and the aircraft crashed.
The investigation
Examination of the wreckage revealed extensive in-flight fire damage concentrated in the area where the wing had separated. Investigators located a 2.5 by 3-inch hole in the right inboard exhaust tube, part number 0850712-6. This rupture was oriented toward the accessory compartment, which contained numerous fuel and oil lines that were severely fire-damaged and charred.
Much of the engine support structure and the wing spar were melted in this area. Further inspection of the exhaust tube showed that its walls were thin, brittle, and discolored near the rupture site. Several areas of cracks and small holes were also found along the component. The tube had accumulated 5,862 hours of total service time, with 1,762 hours since it was last overhauled. Records confirmed that Airworthiness Directive 75-23-08 had been complied with during the last inspection, which occurred just 25 flight hours prior to the accident.