What happened
On June 12, 2018, an Enstrom 280C helicopter was conducting flight proficiency checks near Ganderkesee, Germany. The flight, which included several simulated engine failures and autorotations, was part of a scheduled training session for a pilot undergoing evaluation.
At approximately 13:40 local time, the crew climbed to an altitude of roughly 2,000 ft AMSL to practice a 180-degree autorotation north of Ganderkesee. Immediately after the pilot reduced the collective pitch to initiate the maneuver, the engine failed. While the pilot in command took control of the aircraft, the second pilot attempted to restart the engine, but the attempt was unsuccessful. The crew proceeded to perform an autorotative landing in a pre-selected field near the town of Berne.
During the landing, the helicopter slid across the field, causing the aircraft to tilt forward and rotate slightly to the left. The main rotor blades struck the tail boom, causing significant structural damage to the airframe and the tail rotor assembly. Both occupants escaped the no injuries.
The investigation
The BFU examined the wreckage and the engine performance. The investigation included a ground run of the engine with the main rotor blades removed. During testing, the engine started normally and operated without any visible leaks or external damage. However, investigators noted that a sudden reduction in RPM from 2,95 and 950 RPM caused the engine to stabilize after a few seconds.
The investigation also reviewed manufacturer service information regarding turbocharged engines. This documentation notes that rapid power changes—specifically "power chops" or rapid reductions in power—can cause transient RPM decay and engine instability in turbocharged models like the Enstrom 280C.