NTSB Identification: SEA05LA058.
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Accident occurred Thursday, March 10, 2005 in Coos Bay, OR
Probable Cause Approval Date: 09/13/2005
Aircraft: Rotorway Exec 162F, registration: N20539
Injuries: 1 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
While in cruise flight, the pilot detected a burning rubber smell and heard "strange loud noises" just as both the engine and rotor rpm began to fluctuate. Soon thereafter, the engine began to lose power, and the pilot elected to make an autorotational landing. He headed for a nearby opening, which turned out to be a cemetery, and as he touched down among the gravestones with zero forward speed, the aircraft rolled over onto its right side. Immediately after it rolled to the side, flames appeared in the cockpit, but the pilot was able to escape out of the left side of the helicopter. A post-accident teardown inspection of the engine and drive assembly revealed that the upper main drive pulley bearing, a double ball bearing assembly, had partially disintegrated, leading to the decoupling of the main rotor shaft drive from the engine output drive shaft. The upper ball bearings were loose in the assembly, and their retaining cage had been destroyed. All of the subject bearings displayed excessive wear, flat spots, and significant thermal damage. Although there was very little grease remaining in the assembly, and the lower drive belt sheave grease passage set screw was found backed half way out, it could not be positively determined whether a lack of lubrication initiated the sequence of events leading to the failure of the bearing assembly, or whether the grease had been consumed by the heat generated by an internal failure resulting from other factors. According to the pilot/builder of the helicopter, he had adhered to the required 25 hour grease service intervals since the aircraft had been built, approximately 115 hours prior to the accident.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The disintegration, for undetermined reasons, of the upper main drive pulley assembly bearing, while in cruise flight, leading to the decoupling of the main rotor drive assembly from the engine drive assembly. Factors include the absence of any suitable forced landing area, leading to a landing between the gravestones of a cemetery. Full narrative available
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