What happened
On June 1, 2020, an Eurocopter AS 365 N3 helicopter was performing a scramble takeoff from St. Peter-Ording airfield for an emergency medical mission. During the takeoff roll, the copilot noticed that the cyclic control stick was positioned unusually far forward and that the aircraft required excessive power to accelerate. Despite these anomalies, the crew proceeded with the takeoff, assuming the performance issues might be due to braking friction or recent changes in aircraft models.
As the helicopter transitioned into a hover, it suddenly pitched into a nose-up attitude. The pilot attempted to correct the pitch by lowering the collective, but the aircraft's tail struck the ground, followed by a hard landing on the main landing gear. There were no injuries among the four crew members, though the aircraft sustained light damage.
The investigation
Following the incident, the crew discovered that forward and aft inputs on the cyclic control stick had no effect on the rotor disc attitude. A subsequent inspection in the hangar revealed that the connection between the left control servo and the swashplate had failed. The connecting bolt, two washers, and a castellated nut were found lying on the gearbox deck.
Technical analysis conducted with assistance from the German Bundeswehr revealed that the castellated nut was a reused component that no longer met the required friction specifications. Furthermore, the bolt had been lubricated, contrary to manufacturer instructions, which facilitated the nut's loosening. The investigation also found that the maintenance records for the recent repair—which involved disconnecting this specific servo—were incomplete, lacked proper signatures, and failed to provide a clear audit trail of the work performed.