What happened
On June 21, 2014, a PS-28 Cruiser, registration HB-WXC, was conducting a flight training exercise over Lake Neuchâtel, near the commune of Cudrefin. The flight, operated by the Groupe de vol à Moteur de Neuchâtel, was intended to be a difference training session for a new aircraft recently delivered to the club.
During the flight, the crew initiated a low-speed maneuver at an altitude of approximately 2,000 feet above the water. While reducing power to idle to maintain a low airspeed of approximately 42 knots, the aircraft began to lose altitude and entered a left turn. This quickly transitioned into a descending spiral. Flight data indicates that the aircraft's descent rate accelerated significantly, reaching 6,500 feet per minute, with G-forces increasing to 2.5g. During this spiral, the aircraft's pitch became unstable, and it eventually struck the surface of the lake at 9:21 AM. Both occupants of the aircraft sustained fatal injuries, and the aircraft was destroyed upon impact.
The investigation
Investigators from the Swiss Transportation Safety Investigation Board (SUST) analyzed secondary radar data, onboard flight recordings, and statements from witnesses and pilots. The investigation focused on the aerodynamic behavior of the aircraft during the low-speed phase and the physical state of the crew.
Technical analysis of the flight data revealed that the aircraft entered a high-G stall (dynamic stall). The data showed that while the aircraft was in the descending spiral, a significant and continuous pull on the elevator was applied. This suggests a reactive attempt by one of the crew members to recover the aircraft from the dive. However, the maneuver was performed at a low altitude over water, where a lack of visual references likely contributed to an excessive and ineffective control input.
Medical examinations of the crew did not reveal specific pathologies that would definitively explain a sudden loss of consciousness, though investigators noted that certain conditions, such as transient cardiac arrhythmias or epilepsy, might not leave detectable traces during post-mortem examinations.
Findings
- The primary cause of the accident was the loss of control during a low-speed flight exercise, leading to a collision with the water.
- A sudden incapacitation of one crew member may have contributed to the occurrence of the accident.
- The aircraft was operating at a takeoff mass that exceeded the manufacturer's prescribed limits; historical data showed that a significant percentage of previous flights with this aircraft had been performed overweight.
- No technical defects or unexpected aerodynamic behaviors were found in the aircraft or its systems.
- The impact was severe enough to tear the shoulder harness attachment points from the cockpit structure.