What happened
On 7 March 2023, a PIPER - PA18 “Super Cub” amphibious aircraft, registered F-HYHB, was conducting a local instruction flight at the Biscarrosse - Parentis seaplam base in France. The flight, operated by Aquitaine Hydravions, involved a pilot in training and an instructor working toward a seaplane rating.
Following an initial water landing that the instructor attributed to a minor piloting error, the crew attempted a second takeoff. During this second approach, the pilot noticed a slight vibration that went unnoticed by the instructor. Upon contacting the water, the aircraft swerved violently to the left. The right wing struck the surface, causing the aircraft to rotate right and nose down. This sudden movement resulted in the rupture of the float struts and the landing gear structure. The two occupants successfully evacuated the cockpit and waited on the floats for emergency services.
The investigation
The BEA examined the wreckage and found that the four brackets for the horizontal float interconnecting struts had ruptured. Specifically, the forward right-hand bracket had failed at the attachment point, while the other three brackets experienced failures at the float attachment site.
Metallurgical analysis via optical and scanning electron microscopy revealed that the forward right-hand bracket had suffered from fatigue cracking initiated at a bore hole. The examination also showed signs of fretting and an out-of-round hole, suggesting the part had been subjected to repeated upward bending loads, typical of maneuvers on choppy water or during high-speed taxiing on the step. The remaining sections of the brackets showed evidence of ductile failure, indicating they were unable to withstand the extreme loads applied during the final impact.
Findings
- The primary cause of the structural failure was fatigue cracking in the forward right-hand mounting bracket, which progressed over time during service.
- The final rupture of the remaining brackets was caused by the intense, sudden loads (overloading) experienced during the uncontrolled water landing.
- The manufacturer's maintenance program for the floats did not specifically account for the high-intensity usage of a training organization, which performs a high volume of water landing cycles.
- Routine visual inspections were insufficient to detect internal crack growth within the struts.
- The instructor did not identify the pilot's reported vibration as a mechanical issue, and the pilot did not report the vibration to the instructor during the takeoff run.