Incident Details
The pilot of a helicopter was conducting a sightseeing flight when, approximately 10 minutes after departure at an altitude of 400 to 500 feet in cruise flight, he heard a noise similar to a shotgun blast. The aircraft subsequently experienced vibration, uncommanded yaw, and low rotor and engine rpm. The pilot regained control and executed a successful autorotation.
Postcrash Examination
Postcrash examination of the helicopter revealed shrapnel damage to the drive train, framework, and fuel tank. The damage originated from a failed transmission forward main driveshaft yoke. The failed yoke was examined by the NTSB Materials Laboratory, which identified a cracked weld that had originated during manufacture.
Probable Cause
A cracked weld in the transmission forward main driveshaft yoke that originated during manufacture.