What happened
On December 8, 2013, at approximately 14:15 local time, a Robinson R44 Raven II helicopter was attempting to depart from the Landshut-Ellermühle airfield (EDML) for a flight to Mühldorf am Inn (EDMY). The aircraft had been positioned on the taxiway in front of hangars four and five, aligned with the wind.
As the pilot initiated the takeoff, the aircraft lifted to a height of between 10 and 40 cm before suddenly and uncontrollably began rotating to the left (counter-clockwise) around its vertical axis. The pilot attempted to immediately land the aircraft back on the ground to regain control. During this maneuver, the helicopter continued to rotate while on the ground and subsequently capsized to the right. The airfield manager noted an unusual rotation but did not witness the initial liftoff. There were no injuries to the pilot, though the aircraft sustained heavy damage.
The investigation
The BFU examined the aircraft and the site of the occurrence. Physical evidence at the scene included skid marks on the taxiway and impact marks from the main rotor in the grass. The investigation of the Robinson R44 Raven II revealed significant structural damage: one rotor blade had detached near the rotor head, while the other had struck the tail boom. The rotor mast was bent to the left, control rods to the rotor head were broken, and the tail rotor and horizontal stabilizer were damaged. The fuselage exhibited multiple dents and impacts.
Findings
- The aircraft experienced an uncontrolled rotation in the direction of the main rotor's rotation.
- While such rotations are typically caused by improper pedal input (excessive left pedal pressure) leading to torque-induced spinning once ground friction is reduced, the BFU noted that a rotation in this specific direction (left) was previously unknown in similar investigations.
- The manufacturer reported two similar historical incidents where no technical malfunctions were found, suggesting that excessive left pedal application prior to liftoff is the most likely cause of such uncontrolled rotations when ground friction decreases.