Enstrom 280 N282SH accident near Des Moines, Iowa

Probable cause

The partial loss of rotor and engine speed during approach for landing, which resulted in an autorotation and impact with terrain. The reason for the partial loss of rotor and engine speed could not be determined based on the available evidence. Contributing to the accident was the pilot’s improper execution of the autorotation.

NTSB analysis

The pilot of the personal flight stated that during a final approach for landing, the engine and rotor speeds decreased below the green arcs on their respective instruments, and the low-speed alarm sounded. The rotor speed and engine speed remained in synchronization and decreased at the same rate. The pilot stated he added throttle but neither the rotor speed nor the engine speed increased. He thought that the helicopter lost engine power and performed an autorotation, lowering the collective and initially pushing forward on the cyclic. The pilot stated he did not perform the autorotation perfectly and the outcome would have been better with a better execution of the autorotation. The proper entry into the autorotation utilizes aft cyclic inputs.

Postaccident examination of the helicopter confirmed flight control continuity. A postaccident engine run excluded the turbocharger system and used engine settings that were different than those of the original engine, which was insufficient to validate normal and original engine operation. The turbocharged engine was a supplemental type certificate installation, and those parameters were not provided and are unknown.

Text from the NTSB. Open the NTSB docket for CEN20LA261 for the full record.