NTSB Identification: ANC90LA170.
The docket is stored on NTSB microfiche number 43181.
Accident occurred Sunday, September 09, 1990 in KOKHANOK, AK
Probable Cause Approval Date: 12/08/1992
Aircraft: Bell 206B, registration: N385EH
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

THE PILOT EXPERIENCED A SPOOL DOWN ON THE TURBINE ENGINE. EXAMINATION OF THE ENGINE REVEALED THAT THE AIR COMPRESSOR SCROLL TO TEE TUBE ASSEMBLY COMPRESSOR END FITTING HAD BROKEN. METALLURGICAL EXAMINATION OF THE PART SHOWED THAT THERE WERE NO MATERIAL IRREGULARITIES, THAT THE TUBE BEND DEVELOPMENT AND LINEAR MEASUREMENTS VARIED FROM THE ENGINEERING DRAWINGS, AND THAT THE TUBE ASSEMBLY FAILED IN A FATIGUE MODE. THE ORIGIN WAS ON THE TUBE O.D. APPROXIMATELY 0.020 INCH BELOW THE 'B' END FLARE RADIUS.

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

THE FAILURE OF THE COMPRESSOR END OF THE AIR COMPRESSOR SCROLL TO TEE TUBE ASSEMBLY CAUSING THE ENGINE TO SPOOL DOWN. THE FORCED LANDING IN ENEVEN, UNPREPARED, AND LIGHTLY FORESTED TERRAIN WERE FACTORS.

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