Bell 206-L4 N154MW accident near Birmingham, Alabama

Probable cause

A total loss of engine power for undetermined reasons.

NTSB analysis

The helicopter pilot reported that, following a maintenance test flight to verify that a newly installed power turbine governor was accurately set, he flew over the anticipated landing area and entered the downwind leg of the traffic pattern. While turning to the base leg of the traffic pattern, about 500 feet above ground level and at 40 to 50 knots, he reported that he heard a loud bang and that the airframe “lurched.” He entered an autorotation and located a vacant parking garage deck within gliding range. The engine-out audio warning sounded and segment lights illuminated. The pilot landed the helicopter and it skidded about 15 feet. A test run determined that the engine operated below the normal specifications for new engines. The pneumatic line from the power turbine governor was found to be leaking and was removed and sent to the NTSB's Materials Laboratory for further examination. That examination revealed superficial longitudinal tool marks that did not extend to the interior surfaces of the flared ends. The interior surface of the flared ends exhibited some localized fretting damage on one side, consistent with damage that could have been caused by inadequate torque at the connection; however, no other anomalies were noted. According to the engine manufacturer, the leak would not have caused the engine to operate below the normal specification. The postaccident examination revealed no preimpact mechanical malfunctions or failures with the helicopter or engine that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for ERA11LA175 for the full record.