What happened
On December 29, 2012, a pilot attempted a scenic flight from the Mellensee helipad near Rehagen, accompanied by a passenger. After starting the engine of the Eurocopter AS 350B, the pilot performed checks on the hydraulic system. During this process, the pilot encountered issues with the radio and intercom system, which required checking headset connections.
Once the engine reached flight power, the pilot set the friction brake on the control stick. However, upon releasing the pitch lock and pulling the pitch, the helicopter suddenly yawed to the left. Fearing a collision with a nearby hangar, the pilot increased power to climb over the structure. During this maneuver, the pilot found that directional control around the vertical axis was nearly impossible; the flight pedals were extremely stiff and the control stick was difficult to move. The helicopter performed several rotations at an altitude of approximately 10 meters before the pilot managed to bring the aircraft down to the ground about 50 meters from the takeoff point.
The AS 350B struck the ground heavily at approximately 13:40 local time. The impact caused the front left skid to break, and the aircraft overturned. The pilot immediately shut down the engine, all electrical consumers, and the master switch. Both the pilot and the passenger sustained two minor injuries to their hands but were able to exit the overturned aircraft independently.
The investigation
The BFU examined the wreckage and the circumstances of the flight. The investigation focused on the sudden loss of control and the mechanical state of the hydraulic system. The aircraft, a 1984 model, had been in operation for approximately 32 hours since its last 100-hour inspection. The BFU inspected the hydraulic pump, the control rods, and the tail rotor assembly. The investigation also reviewed the pilot's training, the aircraft's maintenance history, and the procedures for hydraulic system testing.
Findings
While the on-site inspection of the aircraft did not reveal any evidence of a technical defect prior to the accident, the investigation highlighted a critical operational risk. The pilot experienced a sudden loss of yaw control and extreme stiffness in the flight controls, which is characteristic of hydraulic system issues.
Historically, the manufacturer has noted several instances where the unintended takeoff of the aircraft occurred due to the hydraulic cut-off switch being engaged while the pitch lock was released. The investigation noted that the unintended release of the pitch lock during the hydraulic test procedure can lead to such loss of control. Furthermore, the investigation emphasized the importance of clear, concise, and easily accessible checklists to prevent human error during complex pre-flight procedures, particularly in single-pilot operations.