Accident Overview
The aircraft was found two days after it failed to arrive. It had crashed during an autorotation in a rainforest. During the flare and touchdown, vegetation caught on a tundra pad on the left skid, causing the aircraft to roll over.
Examination Findings
Examination revealed that the lower Bendix coupling on the engine-to-transmission drive shaft (part number 369A4410) and the upper right engine mount (part number 369H8017) had failed. Metallurgical examination of the engine mount indicated low cyclic fatigue in the threaded rod area of the adjusting screw. The fracture area of the drive shaft was too badly damaged to determine the mode of failure.
Unapproved Modifications
Unapproved modifications and repairs had been made to both the drive shaft and the overlying cover panel. A steel reinforcing rod had been installed inside the cover panel. Due to pressure from the cargo, a large water bucket, the steel rod was forced onto the drive shaft. There was evidence of angular misalignment and subsequent failure of the drive shaft.
Registration and Inspection
The aircraft had previously operated in Canada with registration C-GVTJ. An annual inspection and U.S. airworthiness certificate had been issued despite the presence of unapproved modifications. The date of the modifications is unknown.