What happened
During the takeoff phase, approximately 400 feet above the ground, the crew of the aircraft noted a discrepancy in the left engine manifold pressure, accompanied by a slight hesitation and a mild backfire. This was followed by an observable oil leak from the front nose section of the engine, resulting in a decrease in both RPM and manifold pressure. Air traffic controllers reported seeing smoke emanating from the left engine. As the aircraft struggled to maintain altitude, the left engine's propeller failed to feather.
The aircraft subsequently impacted trees and vehicles, and the right wing struck a residential building before the plane came to a rest on a road. A fire broke out immediately upon impact. While all occupants managed to exit the aircraft without assistance, the fire caused the fuselage to melt from the cockpit to the tail section. The left wing separated from the aircraft approximately 12 feet from the outboard section, and the engine detached from the firewall. The cargo, which consisted of granite weighing approximately 3,140 lbs, was also part of the wreckage.
Findings
Post-accident examinations of the left engine revealed that the ten bolts securing the nose dome section flange to the stationary reduction gear had fractured, despite the safety wires remaining intact. Metallurgical analysis indicated that the bolts failed due to fatigue caused by reversed bending.
Furthermore, investigators discovered that the chamber for the propeller feathering oil system was not properly secured to the plate sections, which allowed oil to bypass the necessary process for propeller feathering. The investigation also identified significant internal engine damage, including metal flakes found in the oil breather screen, main oil screen, and oil filter housing. These findings were consistent with the catastrophic failure of the silver-plated master rod bearing, which was in an advanced stage of deterioration.