What happened
While performing cruise flight at 6,000 feet, the pilot notified air traffic control of an engine fire and requested an immediate landing. Following this report, the left wing of the aircraft separated while in flight, resulting in an uncontrolled descent and a crash.
The investigation
Investigators determined that the number six cylinder on the left engine had detached during the flight. A metallurgical examination of the cylinder identified a fatigue fracture. This fatigue was found to have originated at a corrosion pit located between the cooling fins of the cylinder.
Evidence indicated that the fire spread from the engine to the left wing fuel tank, which caused the wing to separate from the aircraft. Additionally, investigators observed heat streaking on both the left horizontal stabilizer and the left engine cowling. Aircraft maintenance records indicated that the engine had completed 1,682 flight hours since its last overhaul, which occurred on May 19, 1975.