Bell 206B N43CM accident near Taylors Island, Maryland

Probable cause

A partial loss of engine power during cruise flight for reasons that could not be determined because postaccident examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation.

NTSB analysis

The commercial pilot reported that the helicopter was in cruise flight when he heard a "loud bang," which was followed by a partial loss of engine power. He performed an autorotation to shallow water near a shore, where the tailboom sustained substantial damage. A postaccident examination of the airframe and engine, which included an engine operational check, revealed no evidence of any mechanical malfunctions or failures that would have precluded normal operation. The loss of engine power that occurred during the accident flight could not be duplicated during a test run. Following the engine test run, the fuel control unit (FCU) was removed and tested separately. Tests revealed that the FCU operated erratically due to a bellow anomaly. However, because this condition was discovered only after the engine had successfully completed its test cell runs, a direct correlation could not be drawn between the condition of the FCU and the reported loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA15LA179 for the full record.