What happened
On June 24, 2005, a Bell 47G-4A helicopter was conducting sightseeing flights as part of a large-scale maritime event in the Kieler Förde. During a scheduled passenger exchange, the helicopter landed on the water alongside a small inflatable boat. At the time of the incident, one passenger had already transferred to the boat, while a second passenger, a child, was being lifted onto the right-side float to board the aircraft.
As the transfer was underway, waves generated by a nearby passing vessel reached the aircraft. This caused the right float to submerge deeper into the water while the left float lifted. The pilot attempted to stabilize the helicopter by applying left cyclic input to the mechanical stop and increasing power via the collective pitch. However, these actions increased the lateral rotor thrust vector to the right. The right float, acting as a pivot point due to the weight of the passenger and the fact that ground crew members in the inflatable boat were holding onto it, caused the aircraft to roll. The helicopter eventually struck the water with its rotor blades, causing it to flip and submerge upside down. The impact destroyed the aircraft, but all seven people involved were rescued by nearby emergency vessels.
The investigation
The BFU examined the wreckage and determined that there were no technical defects contributing to the accident. The investigation focused on the sequence of events during the passenger transfer and the pilot's corrective actions. The wreckage showed extensive damage, including broken rotor blades, severed control rods, and the separation of the tail rotor shaft and engine assembly from the fuselage. The investigation also reviewed the operational procedures for the passenger exchange and the environmental conditions at the landing site.
Findings
- The primary cause of the accident was a dynamic rollover.
- The passenger transfer was conducted without direct supervision or instruction from ground personnel.
- The pilot's decision to increase power during the initial tilting motion contributed to the roll.
- The landing area was not sufficiently protected from the wake of passing vessels.
- The inflatable boat used for the transfer was undersized for the number of personnel it was carrying.