TETERBORO, NJ, USA
N73LM
BELL 206 B3
THE PILOT WAS HOVERING WHEN HE HEARD A WHINE IN THE ENGINE THAT INCREASED IN INTENSITY. HE SAW TORQUE FLUCTUATIONS, HEARD AN EXPLOSION, AND AUTOROTATED TO THE RAMP. INVESTIGATION SHOWED THE POWER TURBINE INNER SHAFT FAILED IN TORSION DUE TO CORROSION ON THE INNER SURFACE AND THIS ALLOWED THE THIRD STAGE TURBINE WHEEL TO GO INTO OVERSPEED AND FAIL. ALLISON ISSUED THREE SERVICE BULLETINS ON THE POWER TURBINE INNER SHAFT. NONE OF THEM USED CALENDAR TIME FOR COMPLIANCE, ONLY ENGINE TOTAL TIME. THE HELICOPTER WAS 11 YEARS OLD WITH 2146 HRS TT AIRFRAME AND ENGINE. THE FIRST SCHEDULED WORK ON THE POWER TURBINE OCCURS AT 3550 HRS.
FAILED POWER TURBINE SHAFT. FACTORS IN THE ACCIDENT WERE CORROSION ON THE POWER TURBINE SHAFT AND INADEQUATE MANUFACTURER'S SERVICE BULLETINS.
Source: NTSB Aviation Accident Database
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