Incident Overview
An instructor pilot reported that after leveling at cruise altitude, a burning odor was detected in the cockpit. A forced landing to a hayfield was initiated. During the descent, oil covered the windscreen, and the engine subsequently seized. While on the landing roll, the nose landing gear sheared.
Post-Accident Examination
Subsequent examination of the engine revealed that a plug, which had been inserted into one of the vacant engine component drive gear openings, had not been safety wired. The plug was found at the bottom of the engine cowling. Investigators determined that the engine oil had drained out of the drive opening when the plug fell out, which resulted in the seizure of the engine.
Conclusions
The investigation established that the engine failure was caused by complete oil loss due to the migration of an unsafety-wired plug from a vacant drive gear opening. No further factors were identified or stated in the source material.