Enstrom F-28C N5688R accident near Anchorage, Alaska

Probable cause

The pilot’s failure to maintain main rotor rpm on takeoff, which resulted in a forced run-on landing.

NTSB analysis

The pilot reported that the helicopter preflight and engine runup were normal; however, he could not maintain main rotor rpm on departure and the engine lost partial power. The pilot made a run-on landing to a snow-covered lake, which resulted in substantial damage to the tail boom.

Postaccident examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

Since there were no mechanical anomalies with the helicopter, it is likely the pilot allowed the main rotor rpm to decrease and exceeded the available engine power to recover from the low main rotor rpm condition. When the main rotor rpm decreases, the amount of power the engine can produce also decreases, which is likely the reason the pilot perceived a partial loss of engine power. In addition, the obstacles along the departure path prevented the pilot from lowering the collective to regain main rotor rpm, which resulted in the pilot electing to perform a run-on landing.

Text from the NTSB. Open the NTSB docket for ANC23LA024 for the full record.