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NTSB Report
July 14, 1990 · Bell 206L-1 · N300AH
Farewell, AK
Overview
Report Status
Probable Cause
Event Type
Accident
Date
July 14, 1990
Injury Outcomes
5 injuries (5 serious injuries)
Location
Farewell, AK
Aircraft
Bell 206L-1
Tail Number
N300AH
Operator
Alaska Helicopters
Injuries
Serious
Aircraft Damage
Substantial
NTSB Number
ANC90FA117
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.
NTSB Probable Cause
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.
Full Narrative
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.
Flight
Event TypeAccident
Event Time09:00 AKDT
Nearest Airport0nm N
Runway0
Flight Plan FiledCvfr
Aircraft FireGrd
Aircraft ExplosionNo
Aircraft
AircraftBell 206L-1
Tail NumberN300AH
Aircraft CategoryHeli
DamageSubstantial
OperatorAlaska Helicopters
Operating RulePart 135
Engines1
Engine TypeTurboshaft
Engine DetailsAllison · 250-C28B · Turboshaft · 500
Seats7
People & Injuries
Injury Summary5 injuries (5 serious injuries)
Fatal0
Serious5
Minor0
Uninjured0
Total5
Crew 1Age 50 · Second Class
Conditions
ConditionsVMC
LightDaylight
WindCalm
Visibility40 sm
CeilingOvercast 6500 ft
Temperature / Dew Point52 / 48
Altimeter30.00 inHg
Observation Time11:00
Weather SourceWFAC