What happened
On the morning of the accident, an aircraft departed from Paris-Le Bourget Airport at 07:50 local time. The purpose of the flight was to conduct performance tests on a newly installed air scoop design. To facilitate comparative data collection, the modification was applied to only one engine.
Shortly after takeoff, the aircraft reached 4,300 feet. At 07:59, the crew deactivated the starboard engine to begin the testing sequence, climbing on the single port engine with the cooling gills in the open position. The second phase of the test began at 08:11 while at 6,980 feet, involving a change in the gill position to the trail setting. By 08:22, the aircraft had leveled off at 7,900 feet with the cooling gills closed.
Approximately one hour later, while operating at a relatively low airspeed, the aircraft became uncontrollable and entered a spin. During this sequence, the empennage separated from the airframe. The aircraft subsequently crashed into a field in Moisville. The impact resulted in the destruction of the aircraft and five fatalities among the crew.
Findings
Investigations into the flight conditions and the mechanical state of the aircraft found no evidence of an initial mechanical failure. Instead, it was determined that the crew encountered difficulties maintaining normal flight while operating on two engines. This situation likely involved overspeed, a reduction in pitch, or challenges restarting the engine, which led to a stall during asymmetrical flight. The resulting aerodynamic stresses and buffeting exceeded the structural design limits, causing the loss of the tail-plane.