Hughes 369 N58251 accident near Honolulu, Hawaii

Probable cause

A partial loss of engine power due to an obstructed fuel line as a result of the separation of the circlip from the pin used on the fuel start pump. The reason for the circlip separation could not be determined based on the available evidence.

NTSB analysis

During longline operations, the helicopter lost partial power and the main rotor rpm decreased. The pilot jettisoned the external load and the helicopter impacted trees, resulting in substantial damage. The engine continued to run after impact, and the pilot performed an emergency engine shutdown.

Examination revealed that the start fuel pump was damaged. The circlip and pin that held the flapper valve in place in the bypass inlet were missing, and the flapper valve was wedged against the sidewall of the bypass inlet, obstructing about 50% of the discharge port. The pin was located in the fuel line between the start fuel pump and the engine-driven fuel pump; the circlip was not found.

No other mechanical malfunctions were found that would have precluded normal operation.

The pin found in the fuel line and obstruction from the flapper valve located in the start fuel pump likely induced restricted fuel flow from the engine-driven fuel pump to the engine, which resulted in a partial loss of engine power.

Based on the available evidence, the reason for the separation of the circlip from the pin could not be determined.

Text from the NTSB. Open the NTSB docket for ANC21LA003 for the full record.