NTSB Identification: ANC90FA117.
The docket is stored on NTSB microfiche number 42876.
Nonscheduled 14 CFR
Accident occurred Saturday, July 14, 1990 in FAREWELL, AK
Probable Cause Approval Date: 05/10/1993
Aircraft: BELL 206L-1, registration: N300AH
Injuries: 5 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.

WHILE APPROACHING A REMOTE MOUNTAINTOP SITE TO LAND, AT ABOUT 100 FT AGL AND 40 MPH, THE ENGINE LOST ALL POWER AS A RESULT OF A CONTAINED ENGINE FAILURE, AND THE HELICOPTER MADE A HARD LANDING. ENGINE TEARDOWN REVEALED THAT THE 1ST STAGE TURBINE WHEEL HAD FAILED DUE TO THERMAL FATIGUE WHICH ORIGINATED ON THE TRAILING EDGE O.D. RIM SURFACE. IN ADDITION, BOTH THE 1ST AND 2ND STAGE TURBINE WHEEL AIRFOILS EXHIBITED EVIDENCE OF OVERTEMPERATURE OPERATION. THE FUEL CONTROL WAS PROPERLY SET. THERE WAS NO EVIDENCE OF AN INTERNAL ENGINE OIL FIRE. FAST ENGINE SHUTDOWNS CAN ALSO RESULT IN OVERTEMPERATURES IF SUFFICIENT COOL DOWN TIME AT IDLE POWER IS NOT ALLOWED BEFORE THE ENGINE IS SHUTDOWN. THE TURBINE OUTLET TEMPERATURE GAUGE DID NOT INCORPORATE THE 'OVERTEMPERATURE LIGHT' FEATURE.

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

AN INTERNAL ENGINE FAILURE DUE TO A THERMAL FATIGUE FAILURE OF THE 1ST STAGE TURBINE WHEEL AS A RESULT OF OVERTEMPERATURE. THE HIGH ROUGH/UNEVEN TERRAIN PREVENTED A SUCCESSFUL AUTOROTATION.

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