What happened
On March 12, 2024, a Bell 505 Jet Ranger X, registration HB-ZWC, was conducting a primary flight training mission near Egg, Switzerland. The flight, operated by a flight instructor and a student, involved various maneuvers including hovering exercises and reconnaissance of an off-airport landing site. After completing several hovering drills, the crew landed in a field and conducted a brief debriefing while the rotors were still turning.
During the subsequent takeoff attempt, the student pilot began to increase the collective pitch. Approximately ten seconds into the lift-off, the helicopter experienced a rapid and accelerating tilt to the right. The instructor attempted to intervene by quickly reducing the collective, but the movement could not be arrested. The aircraft entered a dynamic rollover, during which the main rotor blades struck the ground, causing the rotor mast to break and the tail boom to fracture. Both occupants sustained light injuries, and the aircraft was heavily damaged.
The investigation
Investigators examined the wreckage and the aircraft's maintenance records. The investigation focused on the condition of the landing gear, which was equipped with an optional high-skid gear and 'bear paws'—attachments designed to prevent the skids from sinking into soft ground.
At the crash site, the ground was found to be soft and saturated. While the left bear paw was slightly rotated, the right bear paw was found to be severely twisted inward, having been pressed into the earth. Inspection of the hardware revealed that the screw connections for the bear paws were loose, allowing the attachments to rotate around the skids with minimal force.
Findings
- The primary cause of the accident was a dynamic rollover that the pilot was unable to stop.
- Loose screw connections on the bear paws allowed the right attachment to rotate and become embedded in the soft ground, creating a pivot point for the rollover.
- Contributing environmental and mechanical factors included a combination of wind speeds near the transition to effective translational lift (ETL), wind from the front-left quadrant, the use of high-skid landing gear, and a high power margin due to the light weight of the aircraft.