What happened
On September 8, 2007, a Robinson R22 Beta helicopter departed from Karlsruhe/Baden-Baden airfield for a demonstration flight as part of a flight school training camp. The flight included a passenger who was being given instructions to assist in controlling the aircraft.
Shortly after departure, witnesses near Kuppenheim observed the helicopter performing unusual maneuvers, including steep climbs and nose-down movements, accompanied by a loss of altitude and lateral rolling. As the aircraft continued its flight, witnesses noted an unusually loud, pulsating engine noise and a high-frequency sound similar to a lawnmower.
While flying near Weitenung, witnesses observed the helicopter exhibiting unstable yaw oscillations, with the tail striking sideways. During this period, structural components began to detach from the aircraft. The tail boom suddenly snapped in the middle, causing the helicopter to enter a rapid spin around its vertical axis. After several rotations, the aircraft lost further altitude and plummeted vertically onto the A5 motorway at approximately 15:52 local time. The impact was high-energy and nearly vertical, resulting in two fatalities and the total destruction of the aircraft.
The investigation
The BFU examined the wreckage, radar data, and witness statements. The investigation focused on the structural failure of the tail boom and the condition of the tail rotor shaft. Radar data indicated that the transponder signal ceased approximately two minutes before the crash, and radio communications became unintelligible shortly before the impact, suggesting a potential electrical issue.
Physical examination of the wreckage revealed that the tail rotor shaft was S-shapedly deformed. The tail boom had split into three pieces at the 4th and 6th frames, with all rivets missing at these junctions. The investigation also found that the anti-collision light (ACL) cable had been severed and wrapped around the rotating shaft, contributing to the torsion and deformation of the shaft.
Findings
- The primary cause of the structural failure was a tail rotor shaft oscillation caused by an overspeed condition.
- The high-frequency vibrations from the oscillating shaft weakened the tail boom structure, causing it to snap.
- The loss of the tail boom and subsequent loss of control rendered the aircraft unrecoverable.
- The pilot's flight experience was considered low, particularly given the time elapsed since his last period of active flying.
- While an overspeed was the likely trigger, the exact cause—whether a pilot error, a mechanical defect, or an electrical failure affecting engine RPM indicators—remains undetermined.