Incident Overview
A pilot was conducting a post-annual inspection and maintenance test flight in a helicopter. After completing one steep approach, the pilot initiated another. During the second approach at approximately 400 feet above ground level, the helicopter seemed to mush and feel sluggish. Recalling minor issues noted during preflight hydraulic checks, the pilot decided to abort the steep approach and proceed to a landing spot on a taxiway. The pilot aimed to increase airspeed to get the aircraft on the ground as soon as possible. No visual or auditory warning indications from the helicopter instruments indicated a problem, but an unusual noise persisted from behind.
The pilot elected to perform a run-on landing instead of a flare to a quick stop arrival. Witnesses reported that the helicopter porpoised, hitting the ground nose first, then the tail rotor, followed by the helicopter sliding on its side before stopping in the grassy area of the infield.
Examination Findings
An examination of the helicopter wreckage revealed no abnormalities with the engine, airframe, and its systems, except for the air conditioner compressor. The compressor, located in the aft lower portion of the engine compartment, was found with its belt off the pulley. The belt exhibited damage consistent with chafing against the nuts on the driveshaft Thomas coupling. The pulleys were misaligned, and the support bracket for the compressor was loose with missing rivets.
Maintenance History
The helicopter's maintenance records indicated that during the annual inspection, the air conditioner compressor had a belt change and the base plate was re-shimmed to realign the driveshaft and the compressor.