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Aviation Accident

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NTSB Identification: WPR17IA198
14 CFR Part 91: General Aviation
Incident occurred Tuesday, August 22, 2017 in Glendale, AZ
Probable Cause Approval Date: 03/18/2019
Aircraft: ENSTROM F 28F, registration: N52PD
Injuries: 2 Uninjured.

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

The flight instructor and student pilot were practicing hovering autorotations when the cockpit filled with smoke. The helicopter had just touched down, so the flight instructor secured the cockpit and both he and the student egressed the helicopter with the engine still running. About 5 minutes later, the engine stopped. 
Postincident examination of the helicopter revealed no fire or other related damage. Maintenance personnel reported that the smoke appeared to have originated from the failure of an internal oil seal within the turbocharger-compressor that leaked oil into the turbocharger-compressor’s exhaust system. No further examination or repair was accomplished and the turbocharger was replaced.
Further examination revealed damage to the turbocharger-compressor v-clamp assembly that was installed on the exhaust. The strap portion of the v-clamp assembly contained cracks on the outer face that emanated from three of the four spot welds. The edge of the strap portion exhibited evidence of bending deformation on both sides of the assembly. In the deformed areas, the distance between the edge of the retainer and the edge of the strap was smaller when compared to other, non-deformed areas. Further, microscopic examination of the largest crack revealed a fatigue crack emanating from the outer surface of the v-clamp assembly strap. It is likely that the v-clamp assembly bolts were tightened to an extent that caused the deformation in the strap. The damage found to the v-clamp was not related to the source of the smoke.

The National Transportation Safety Board determines the probable cause(s) of this incident as follows:
  • An internal failure of the turbo-compressor, which resulted in oil leaking into the turbo-compressor’s exhaust.