What happened
On August 2, 2014, a private MINI-50/500 helicopter, registration HB-YJS, was involved in a loss of control accident at the Yverdon-les-Bains aerodrome (LSGY). The flight began after the engine initially failed to remain running following a startup attempt at the parking position. After a successful second start, the pilot proceeded with a flight consisting of a hover and subsequent low-altitude translational flight within ground effect, maintaining an altitude between 1 and 2 meters.
While performing a wide 180-degree turn approximately 50 meters from the threshold of runway 05, the aircraft encountered a tailwind at an altitude of 3 meters. During this maneuver, the pilot observed a decrease in rotor RPM and attempted an immediate landing. As the aircraft descended to a height of approximately 30 cm, the rotor speed dropped to 80%. The helicopter then experienced a 90-degree yaw to the left, struck the ground, and continued to pivot an additional 25 degrees before coming to a rest on its skids.
The investigation
The investigation focused on the sequence of events leading to the loss of control and the mechanical state of the aircraft. Investigators examined the engine's initial failure to stay running, the subsequent flight profile, and the specific conditions during the turn. The assessment included the impact of the tailwind and the observed reduction in rotor RPM during the final descent.
Findings
- The aircraft sustained significant damage to the rotor blades, fuselage, tail boom, and tail rotor.
- The pilot remained uninjured during the incident.
- A primary contributing factor was the decrease in rotor RPM to 80% during the low-altitude maneuver, which occurred while the aircraft was operating in a tailwind.