NTSB Identification: ANC92FA044.
The docket is stored on NTSB microfiche number 51122.
Accident occurred Friday, March 06, 1992 in HOBART BAY, AK
Probable Cause Approval Date: 12/09/1993
Aircraft: Bell 214B-1, registration: N314RM
Injuries: 2 Serious.

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.

THE HELICOPTER WAS HOVERING APPROX 200 FT ABOVE THE LOG WHICH WAS BEING ATTACHED TO THE CARGO HOOK. THE PILOTS HEARD A LOUD BANG FOLLOWED BY A LOSS OF ENGINE POWER. THE HELICOPTER AUTOROTATED INTO STEEP UNEVEN TERRAIN, THE ONLY AREA AVAILABLE. EXAMINATION OF THE ENGINE REVEALED FATIGUE FAILURE OF THE CENTRIFUGAL IMPELLER ENCOMPASSING A 60 DEG ARC. THIS SECTION SEPARATED FROM THE ENGINE AND HELICOPTER. ANALYSIS OF THE IMPELLER SHOWED THAT THE COOLING HOLES, ASSOCIATED ONLY WITH THE T5508D ENGINE, DID NOT HAVE THE PRESCRIBED RADIUS, AND CRACKS WERE FOUND EMANATING FROM THE OTHER COOLING HOLES. THE ENGINE RECORDS SHOW THAT THE IMPELLER HAD 5592.0 CYCLES WHEN INSTALLED IN THIS ENGINE IN APRIL 1991. THE COMPONENT SERVICE LIFE LIMIT OF THE IMPELLER IS 16,600 CYCLES.

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

FATIGUE FAILURE OF THE COMPRESSOR ASSEMBLY IMPELLER, AND INADEQUATE QUALITY CONTROL BY THE MANUFACTURER. A FACTOR WHICH CONTRIBUTED TO THE ACCIDENT WAS THE MOUNTAINOUS/HILLY TERRAIN.

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