What happened
The pilot was conducting an agricultural operation, specifically spraying cotton, when the aircraft began experiencing severe vibration throughout the airframe. Recognizing the severity of the situation, the pilot elected to execute a forced landing. During the flare phase of the approach, the pilot advanced the throttle in an attempt to raise the nose and gain altitude or control. However, the engine had completely failed, rendering the throttle input ineffective.
The aircraft touched down and subsequently flipped onto its back (inverted position). The pilot was not injured in the crash.
The investigation
A mechanical examination of the engine was conducted to determine the cause of the failure. The inspection revealed that the crankshaft assembly, identified by part number 270458, had failed at the through bolt location of the front crankshaft cheek.
Findings
The investigation determined that the engine failure was caused by a structural fracture in the crankshaft assembly. This mechanical failure occurred during the critical phase of flight when the pilot was attempting to execute a forced landing following the onset of severe vibrations.