On April 4, 1996, a Bell UH-1H (registration N6166R) was involved in an aviation accident near Rainier, WA. Investigators recorded the probable cause as: 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. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced engine failure while preparing to sling logs, forcing an autorotation landing that resulted in damage. Investigation revealed a disintegrated forward bearing in the turboshaft engine.
Incident Overview
While preparing to lift a load of logs, the pilot observed several changes in engine noise level. This was followed by two loud bangs and a total loss of power. The pilot executed an autorotation and landed in a small clearing directly beneath the rotorcraft, as no other suitable landing site was available. During the forced landing, the helicopter sustained damage.
Engine Examination
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 accumulated a total of 4202.4 operating hours, of which 199.4 hours were accrued after entering the civilian operating environment.
Service Bulletin Information
Nonmandatory Service Bulletin No. 0056 provided procedures for replacing the number 21 forward bearing with an improved bearing (P/N 1-300-082-03) within 400 hours after receipt of the bulletin.