Bell 206 N119SP accident near Arden Hills, Minnesota

Probable cause

A partial loss of engine power for reasons that could not be determined based on the available evidence

NTSB analysis

The purpose of the flight was to simulate elevated close-quarter operations with firemen mounting and dismounting the helicopter skids following a pinnacle approach and landing to a shipping container at a training facility. The pilot stated that he made a “stable” straight-in approach to the shipping container and that, shortly after landing, he heard a “bang” and a “thunk.” The pilot stated that the helicopter “felt loose” and that he was having difficulty keeping it in position on top of the shipping container, so he decided to abort the landing and climb away from the shipping container. He increased collective to establish a climb, but quickly realized that the helicopter was not climbing as intended. The pilot briefly lowered collective to gain main rotor rpm, then increased the collective to reduce the helicopter’s rate of descent before a hard landing between shipping containers. The pilot remembered hearing an engine-out warning and possibly a low rotor speed alarm in the cockpit, but he could not recall exactly when he heard the warning and/or alarm. He also did not recall seeing any master warning indicator lights, but he stated that his attention was focused outside of the helicopter during the final moments of the flight.

A review of video footage from a camera mounted to one of the firefighter’s helmets indicated that, after the pilot aborted the landing on the shipping container, the helicopter rotated slightly left as it climbed about 10 to 15 ft before it rotated about 90° to the right and descended to a dirt road between three shipping containers. As the helicopter descended, there was an audible decrease in engine speed and main rotor speed. The helicopter landed hard upright, which deflected the landing skids and fractured the tail boom aft of the fuselage. The helicopter sustained substantial damage to the lower fuselage, tail boom, and the tail rotor driveshaft during the hard landing.

Postaccident examination and testing of the engine did not reveal any anomalies that would have precluded normal operation. The engine successfully ran at ground idle, flight idle, takeoff power, and maximum continuous power. Additionally, the engine was rapidly cycled between flight idle and maximum power numerous times with no observed hesitation or surging in engine operation. The engine exceeded the expected power output for a new-production engine at low cruise, normal cruise, and maximum takeoff power settings. Functional testing of the fuel control unit and power turbine governor revealed no anomalies that would have precluded normal engine operation. Additionally, the helicopter had ample fuel available at the time of the accident. The reason for the loss of engine power could not be determined based on the available information.

Text from the NTSB. Open the NTSB docket for CEN16LA156 for the full record.