Accident Sequence
While maneuvering at low altitude, the pilot heard a series of compressor stalls, accompanied by a rapid decay of rotor rpm. The helicopter subsequently struck the ground, spun around, and rolled over onto its right side.
Engine Examination
Functional testing of the engine revealed it was 20 horsepower below overhaul specifications. The compressor exhibited repeated stalls. Disassembly of the compressor disclosed erosion of the case liner, most noticeably at the 5th and 6th stages. Additionally, the rotating labyrinth seal was missing.
Resolution
After replacing the missing labyrinth seal and installing a slave compressor module, the engine tested to normal operational parameters.