What happened
During a cargo flight, a fire broke out in the vicinity of the number three engine. In response to the emergency, the flight crew initiated procedures to manage the fire, which included pulling the fire handle and feathering the engine. Despite these efforts, the fire remained active. While the Douglas aircraft was maneuvering in the traffic pattern to land at a nearby rural airstrip, observers noted flames emanating from the engine area. During this phase, the right wing of the aircraft buckled upward, resulting in a crash.
Findings
An investigation of the wreckage identified a failure of the master rod within the front bank of cylinders of the number three engine. Metallurgical analysis showed that corrosion pits had created a crack at the top of the master rod head. Additionally, the master rod head was found to be out of round, and the shank of the rod had suffered a fatigue fracture.
Analysis of the cockpit voice recorder indicated that the crew performed emergency actions in the incorrect sequence. While both the operator's training and the manufacturer's checklist required the propeller to be feathered before activating the fire extinguishing system, the crew pulled the fire handle first. This incorrect sequence of emergency procedures reduced the effectiveness of the fire suppression system.