What happened
On October 11, 2014, a Robinson R22 Beta helicopter departed from a private helipad in Wiedergertingen, Germany, for a sightseeing flight. The flight proceeded toward the northern edge of the Alps, passing near the towns of Wertach and Jungholz. While circling the "Schönkahler" mountain peak near the German-Austrian border, the aircraft experienced a loss of engine power and a subsequent decay in main rotor RPM.
During the second circuit of the peak, the pilot attempted to climb, but noticed a sudden drop in performance. The aircraft's airspeed decreased, and the rotor RPM warning horn and light were activated. The pilot reported that the aircraft became unresponsive to control inputs. Attempting to fly away from the nearby slope proved unsuccessful, prompting the pilot to attempt an emergency landing. During the landing, a skid became entangled with the terrain, causing the helicopter to flip forward and to the side.
The passenger, a qualified commercial pilot, was focused on taking photographs and did not intervene during the flight. He noted that the aircraft began to lose altitude and slow down just as the warnings activated, and the impact occurred before he could take any corrective action.
The investigation
The BFU investigation examined the aircraft, the flight path, and the environmental conditions at the time of the accident. Radar tracking from the German military and civil air traffic control confirmed the flight path until the aircraft's position near the accident site at approximately 18:15 local time.
Physical examination of the Robinson R22 Beta revealed significant structural damage. The tail boom was broken near the vertical fin, both tail rotor blades were lost, and the main rotor blades were severely bent and twisted. The landing gear sustained damage, with the left skid broken and detached from its cross-tube. The cockpit glazing was destroyed, and the nose of the fuselage was crushed.
Investigators found that the engine appeared externally intact, and the spark plugs showed a normal combustion pattern. The fuel filter was clean, and fuel was present in both the filter and the carburetor, though the fuel tank was empty due to a rupture at the rear corner of the tank. The aircraft's weight and balance were within limits at takeoff, with a total takeoff mass of approximately 595 kg.
Findings
- The primary cause of the accident was overpitching, characterized by a loss of engine power or insufficient power to maintain the intended flight path, leading to a decay in main rotor RPM.
- The aircraft was operating at a high density altitude of approximately 6,500 ft AMSL.
- At altitudes above 4,000 ft, the manufacturer's warnings note that the governor becomes less effective and the carburetor is frequently fully open, requiring precise manual control of the rotor RPM via the collective lever.
- The pilot's attempt to climb during the maneuver induced the power deficiency that led to the rotor RPM decay.