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ASN Wikibase Occurrence # 134819
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Type:Silhouette image of generic EXEC model; specific model in this crash may look slightly different
RotorWay Exec 162F
Registration: N20539
MSN: 001
Fatalities:Fatalities: 0 / Occupants: 1
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Location:Coos Bay, OR -   United States of America
Phase: En route
Departure airport:North Bend, OR (OTH)
Destination airport:Norway, OR
Investigating agency: NTSB
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.

Probable Cause: 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.




Revision history:

21-Dec-2016 19:26 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
06-Dec-2017 08:01 ASN Update Bot Updated [Cn, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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