What happened
On 16 August 2015, an MX Aircraft MX2, registration N88MX, was performing a training flight near Châteauneuf sur Cher, France. The pilot, an experienced aerobatic flyer, was preparing for the World Aerobatic Championships. After completing a 10-minute program, the pilot initiated a pull-out maneuver at approximately 8 g to perform a final fly-pass for the public.
During this maneuver, the pilot reported hearing a loud explosion. The aircraft suffered a sudden structural failure: the engine and its mount separated from the airframe, and the right wing broke mid-span. The pilot successfully evacuated the aircraft using a parachute, landing safely in a nearby field.
The investigation
The investigation focused on the structural integrity of the wings, the engine mount, and the firewall attachment points. Technical examinations of the wings at the Nantes CETIM revealed that the composite construction, including the carbon fiber platen and epoxy resin, met manufacturer specifications and showed no signs of fatigue or impact damage. The wing failure was determined to be the result of extreme overloading.
Examination of the engine and propeller showed no signs of imbalance or mechanical failure that could have transmitted abnormal loads to the airframe. However, analysis of the engine mount revealed significant deformation. While the upper right support bracket showed evidence of fatigue, the remaining three brackets exhibited damage consistent with sudden overloading.
Detailed microscopic analysis of the upper right support bracket identified fatigue striations in the resin. This was traced to a bonding defect and a design flaw where the washer of the bolted fastener was in direct contact with the composite material, causing local stress concentrations and crushing the composite surface.
Findings
- The primary cause of the accident was the fatigue failure of the upper right support bracket attaching the engine mount to the fuselage.
- This initial failure caused the remaining three support brackets to fail instantaneously due to extreme overload, leading to the separation of the firewall and the engine.
- The loss of the engine caused an immediate shift in the aircraft's center of gravity, resulting in an abrupt pitch-up. This sudden change in attitude subjected the right wing to loads exceeding its structural limits, causing it to break.
- Contributing factors included a bonding defect in the bracket and a non-optimal design that placed the bolted fastener in a direction that did not leverage the maximum tensile strength of the composite material.