Accident Overview
A six-engine seaplane prototype was conducting a test flight to evaluate the aircraft's controls following severe vibrations experienced on the engines. While cruising at an altitude of 1,200 meters, a part separated from the right wing. The aircraft subsequently went out of control and crashed into the sea approximately one kilometer northwest of Le Cap Ferret.
Rescue and Recovery
Following the crash, the crew of a trawler and a French Marine boat recovered some debris floating on the water. All 12 individuals on board were killed.
Crew and Occupants
The flight crew included Robert Boissard, Chief Pilot; mechanics Kléber Coulé, Henri Faugère, and Mr. Dumonteil; radio operator Alexandre Lepêcheur; technical directors Mr. Renaud and Mr. Bouchery; technician Mr. Remaury; Adj Grezel; engineers Mr. Malpot, Mr. Martin, and Mr. Brolin.
Official Probable Cause
According to the inquiry, the probable cause of the accident was a fatigue failure of the aileron control couplings. This failure resulted from the simultaneous occurrence of several vibratory phenomena: the cruising speed of the propeller with a 7/16 reducing gear resonated with the critical vibratory frequencies of the wing and the aileron, with excitation amplified by propeller cuffs; and the occurrence of extreme aileron flutter, aerodynamically induced due to failure of the linkage between the aileron and the slat. Under these conditions, it was impossible for the crew to detect these phenomena before their effects became irreparable.