NTSB Identification: SEA96FA076.
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Accident occurred Thursday, April 04, 1996 in RAINIER, WA
Probable Cause Approval Date: 02/28/1997
Aircraft: Bell UH-1H, registration: N6166R
Injuries: 1 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

While preparing to sling a load of logs, the pilot noticed several changes in engine noise level followed by two loud bangs and a total loss of power. He executed an autorotation/landing into a small clearing directly beneath the rotorcraft as no other suitable site was available. During the forced landing, the helicopter was damaged. Disassembly of the ex-military, Allied Signal (Lycoming) T53-L-13BA turboshaft engine revealed that the number 21 forward bearing (P/N 1-300-082-01B) had disintegrated. The engine had a total of 4202.4 operating hours of which 199.4 were accrued since entering the civilian operating environment. Nonmandatory Service Bulletin No. 0056 provided procedures for replacing this bearing with an improved bearing (P/N 1-300-082-03), within 400 hours after receipt of the bulletin.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

failure of the forward power shaft (number 21) bearing. A factor relating to the accident was: the lack of suitable, unobstructed terrain for an emergency landing.

Full narrative available

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