WPR17IA198

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.

On August 22, 2017, about 0904 mountain standard time, an Enstrom F-28F helicopter, N52PD, experienced smoke coming from the engine cowling area after touchdown at the Glendale Municipal Airport (GEU) Glendale, Arizona. The certified flight instructor and student pilot were not injured, and the helicopter was not damaged. The helicopter was registered to and operated by Airwest Aviation Academy LLC under the provisions of Title 14 Code of Federal Regulations Part 91, as an instructional flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight departed GEU about 0820. The flight instructor reported that at the time of the incident, the student was practicing hovering autorotations. Several had been accomplished without incident. During the last one, the engine appeared to have stalled, but sounded as if it were running rough when the cockpit filled with smoke. The helicopter was on the ground and the flight instructor secured the cockpit and both he and the student evacuated the helicopter with the engine still running and smoke coming out of the right side air scoop. About five minutes later, the engine stopped running. Postincident examination of the helicopter revealed that no fire or other related damage was present. Maintenance personnel reported that the source of 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 identified that the V-clamp assembly that was installed on the turbo-compressor exhaust was damaged. The V-clamp assembly was removed and sent to the National Transportation Safety Board Material Laboratory, Washington DC for further examination. The examination of the V-clamp assembly revealed that the strap portion of the assembly contained cracks on three of the four spot welds that emanated from the outer face of the strap. 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, were smaller when compared to other non-deformed areas. Microscopic examination of the longest crack revealed that a fatigue crack emanated from the outer surface of the strap. The damage to the V-clamp was unrelated to the source of the smoke.