Enstrom Helicopter Corp 280C N5699N accident near Ogden, Utah

Probable cause

The pilot's improper use of the helicopter's collective both during the takeoff sequence and while attempting remedial action in response to an engine over-boost condition, which resulted in a hard precautionary landing.

NTSB analysis

The pilot reported that just after passing through takeoff translational lift, he noticed that the reciprocating engine was being over-boosted and that the main rotor blade RPM was drooping. He therefore lowered the collective in an attempt to lower the boost and to regain main rotor rpm, but the helicopter began to sink at a rate that made it necessary for him to immediately transition to a landing. After touching down on the ground, the skids partially collapsed, the helicopter pitched forward, and the main rotor blades flexed downward far enough to sever the tail boom. According to the pilot, the engine seemed to be running strong and smooth, and there did not appear to be any problems with the flight control system. No anomalies were found during a post-accident inspection of the airframe, nor during the engine test run.

Text from the NTSB. Open the NTSB docket for WPR09LA261 for the full record.