Incident Overview
On August 22, 2017, at approximately 0904 mountain standard time, an Enstrom F-28F helicopter, registered as N52PD, experienced smoke emanating from the engine cowling area after touchdown at Glendale Municipal Airport (GEU) in Glendale, Arizona. The helicopter was on an instructional flight under Title 14 Code of Federal Regulations Part 91, operated by Airwest Aviation Academy LLC. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight had departed GEU at about 0820.
Sequence of Events
The certified flight instructor reported that the student pilot was practicing hovering autorotations. Several had been completed without incident. During the final autorotation, the engine appeared to stall and then ran rough, as the cockpit filled with smoke. The helicopter was on the ground, and the flight instructor secured the cockpit. Both occupants evacuated the helicopter while the engine remained running and smoke continued from the right side air scoop. Approximately five minutes later, the engine stopped.
Postincident Examination
Examination of the helicopter revealed no fire or other related damage. Maintenance personnel determined that the smoke originated from a failure of an internal oil seal within the turbocharger-compressor, which allowed oil to leak into the turbocharger-compressor's exhaust system. No further examination or repair was performed; the turbocharger was replaced.
During the examination, a damaged V-clamp assembly on the turbo-compressor exhaust was identified. The assembly was sent to the National Transportation Safety Board Material Laboratory in Washington, DC, for analysis. The examination revealed cracks in three of the four spot welds on the strap portion, emanating from the outer face. The strap edge showed bending deformation on both sides, with reduced distance between the retainer edge and strap edge in deformed areas compared to non-deformed areas. Microscopic examination of the longest crack confirmed a fatigue crack originating from the outer surface. The damage to the V-clamp was determined to be unrelated to the smoke source.