What happened
Prior to departure, the aircraft experienced several loud backfires from the left engine during the startup sequence. Shortly after takeoff, observers near the runway noted unusual clattering sounds emanating from the plane. During the climb phase, the pilot declared an emergency due to a fire in the left engine. While operating under IFR conditions and being vectored toward Altus AFB, the aircraft descended into VFR visibility.
As the flight continued, witnesses observed smoke and flames trailing from the left engine area. The aircraft's nose pitched up, followed by a left roll, before the plane entered a steep, inverted, nose-down attitude. The aircraft subsequently crashed and caught fire. The accident resulted in two fatalities.
Findings
An investigation into the wreckage determined that the engine exhaust manifold header assembly had suffered a total failure. This failure was caused by advanced corrosion that allowed high-temperature exhaust gases to escape into the engine nacelle, where they ignited nearby fuel and oil lines.
Maintenance records indicated that while an advisory circular had requested general inspections of this component, there was no evidence that the part had been replaced during its 6,100 hours of service. The investigation also highlighted inadequate inspection procedures and insufficient oversight regarding the maintenance of the exhaust system.