What happened
On 23 November 2021, a PIPER - PA18 “SUPER CUB”, registration F-GNMD, was performing local water landing exercises on Lake Biscarrosse Parentis. The pilot, accompanied by one passenger, had been conducting a series of short circuits and landings. During the ninth water landing of the day, the pilot initiated the flare at an estimated height of five to ten meters with a slight nose-up attitude.
As the pilot reduced power to idle, the right wing suddenly sank, causing the aircraft to pitch nose-down and enter a right turn. Despite the pilot applying left aileron inputs and increasing power, control could not be regained. Upon contact with the water, the floats ruptured, and the aeroplane destroyed itself as it quickly sank. The two occupants managed to evacuate the aircraft and inflate their life jackets, eventually being rescued by another seaplane and emergency services.
The investigation
The investigation examined the wreckage, the aircraft's weight and balance, and the pilot's recent flight history. Examination of the wreckage revealed that the right float's horizontal struts had been torn off and the wing struts had perforated the float. Significant damage was also noted on the left wing and fuselage, likely occurring during the recovery process.
Regarding the aircraft's weight, investigators determined that the aircraft was approximately 39 kg over its maximum landing weight at the time of the accident. The investigation also reviewed the pilot's experience, noting that while he held a valid SEP(sea) rating, he had not flown a seaplane for 33 months prior to the accident. Furthermore, the investigation looked into the pilot's adherence to the operator's fuel loading instructions and the impact of repetitive flight exercises on pilot vigilance.
Findings
- The primary cause of the accident was an asymmetric stall during the flare phase.
- This stall was likely triggered by the premature adoption of a nose-up attitude combined with a total reduction of engine power to idle.
- The aircraft was operating in an overloaded state, exceeding the maximum landing weight by approximately 39 kg.
- The repetitive nature of the landing exercises, paired with the pilot's lack of recent seaplane experience, likely contributed to a reduction in vigilance regarding flight parameters.