Accident Overview
On 19 May 2011 at 11:51 local time, a Eurocopter AS 350 B2, registered as HB-ZAM, was involved in an accident at Niederösch, Bern, Switzerland. The helicopter was conducting a training flight under visual flight rules (VFR) when it lost control during an approach exercise without hydraulic assistance, resulting in a rollover. The three occupants were uninjured, but the helicopter sustained severe damage.
Aircraft and Occupants
The helicopter, a Eurocopter AS 350 B2 (Ecureuil), was owned by Kunert Aircraft Asset GbR and operated by Mountain Flyers 80 Ltd. On board were two pilots and one observer. The pilot in command (instructor) held a German commercial pilot license (CPL(H)) with type ratings on the AS350/350B3 and instructor (TRI) and examiner (TRE) privileges. He had 1,586 total flight hours, 291 on type. The student pilot held a CPL(H) with 267 total hours, 95 on type. The observer, also a flight instructor, had 2,923 total hours, 386 on type, and was seated in the rear.
Sequence of Events
Following a pre-flight briefing covering the planned exercises—including hydraulic-off procedures, autorotation, and tail rotor failure—the helicopter departed Bern-Belp at 11:28 with three persons and about 260 liters of fuel. After leaving the control zone, the crew performed practice approaches and an autorotation exercise. Subsequently, while westbound near Koppigen, the instructor briefed the hydraulic-off exercise. He reminded the student to reduce speed upon activation of the hydraulic warning and to maintain a constant forward speed before landing.
The instructor selected a mowed field south of a forest as the landing area. He activated the hydraulic test switch (ACCU TST pushbutton), reduced speed, and switched off the hydraulic system using the hydraulic cut-off switch on the collective. The test switch was then deactivated.
During the final approach at about 60 kt, the helicopter was positioned on a base leg relative to the field. The student, in the instructor's view, did not turn onto a short final approach. The instructor momentarily intervened, verbally pointing out the field, then released control. As the helicopter descended in a turn, it lost forward speed at 10–15 m above ground. The instructor took control again but could not reduce the helicopter's attitude despite full muscular effort. The helicopter moved backwards with a left yaw of about 30°. The crew managed to lower the nose, but the helicopter continued drifting right. After a final attempt to control direction, the right skid contacted the ground and the helicopter rolled onto its right side.
The cabin remained largely intact. The crew shut down the engine using the emergency cut-off and electrical system before exiting uninjured. The emergency locator transmitter was deactivated and rescue services alerted.
Meteorological Conditions
MeteoSwiss reported a flat pressure distribution over continental Europe with weak southwesterly winds aloft. No further details were provided.
Cause and Contributing Factors
The Swiss Accident Investigation Board (SAIB) determined the cause of the accident to be a landing with a lateral component, resulting in the helicopter overturning after a loss of control during an approach exercise without hydraulic assistance. Contributing factors were a short final approach in a turn at too low translational speed and a late takeover by the instructor.