What happened
On October 17, 2021, a Robinson R44 Raven II helicopter departed from Herzogenaurach for a private flight. The aircraft was accompanied by two passengers. During the flight, the helicopter performed a maneuver near Schweinberg, circling an area of farmland. Shortly thereafter, the aircraft entered a period of rapid ascent and simultaneous deceleration.
Witnesses near Buchen observed the helicopter flying straight before a loud mechanical bang occurred, followed by the rotor blades folding upward. The aircraft appeared to deform and twist mid-air before entering a vertical descent into a nearby forest. The impact resulted in three fatalities, including the pilot and two passengers. One passenger was ejected from the aircraft during the flight and died upon impact, while the other two occupants were found near the wreckage.
The investigation
The BFU investigation focused on the flight path, the mechanical state of the aircraft, and the aerodynamic forces at play. Data recovered from the pilot's iPad (SkyDemon software) showed that in the final 60 seconds of flight, the aircraft climbed from approximately 1,930 ft to 2,130 ft AMSL while speed dropped from 105 kt to 83 kt.
The investigation examined the wreckage, finding that the rotor mast had broken below the swashplate and the rotor head had struck the mast. The investigation also included a metallurgical analysis of the pitch links by the Technical University of Braunschweig. While the analysis revealed significant material inhomogeneities and varying hardness levels in the pitch links, these were not determined to be the cause of the accident.
Findings
- The primary cause of the accident was a low-G maneuver that induced mast bumping.
- The sudden climb and drop in airspeed indicated an active, rapid forward control input, which created a low-G condition where the fuselage was momentarily unloaded from the rotor plane.
- This unloading caused the rotor head to strike the mast, leading to the structural failure of the rotor system and the subsequent disintegration of the aircraft in flight.
- The aircraft was in a good technical state, and no mechanical failures or engine issues were identified as contributing factors.
- While water was found in the fuel filter, it was not considered a cause of the crash.