Event Description
During flight, the aircraft began to vibrate severely. Subsequently, a loud bang was heard. The aircraft then began to descend with smoke present in the cabin. The engine out light and warning horn were activated. During the landing, the helicopter settled into the dirt, rocked forward, and then aft.
Pilot Statement
According to the pilot, the main rotor blades struck the tail boom due to low rotor rpm.
Examination Findings
Examination of the helicopter revealed that an overrunning clutch bearing had failed. A metallurgical examination was conducted but could not determine the cause of the failure because of the extent of damage. The bearing assembly and inner race (shaft) were exposed to temperatures greater than 1500 degrees Fahrenheit.
Maintenance History
The overrunning clutch was reportedly lubricated 7 hours prior to the accident, at the last 100-hour inspection. The inspection is also considered a 300-hour inspection. According to MDHC, at the 300-hour inspection the bearing is to be removed, cleaned, inspected, and repacked.