What happened
On July 19, 2010, a Dynaéro MCR Sportster, registration F-PFDE, departed from the Royan-Médis airfield for a flight to Blois, with a passenger on board. Shortly after takeoff, radar tracking recorded a left turn during the climb between 20 and 400 feet, followed by a second left turn during a descent at approximately 200 feet. The aircraft's radar signal was lost while on a magnetic heading of approximately 300°.
The aircraft was subsequently located crashed approximately 300 meters north of the threshold of runway 28, roughly 700 meters from the last radar detection point. The wreckage showed the aircraft struck the ground at high speed with a left bank. The investigation confirmed that the pilot and passenger were killed, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and found that the flaperon actuation was asymmetric. Specifically, the left flaperon maneuvering screw was sliding freely within its threaded sleeve. Technical analysis of the screws and sleeves revealed that the thread wear was a progressive process occurring well before the accident.
Detailed metallurgical testing showed that the left master screw was manufactured from metal with a sulfur content five times higher than the maximum allowed by European standards (NF EN ISO 898-1). Additionally, the protective zinc layer was absent from the design documents and showed significant degradation. The investigation also identified a galvanic corrosion risk: the contact between the zinc-coated screw and the bronze sleeve, in the presence of moisture, likely caused electrolysis of the bronze. Furthermore, the wear patterns on the right and left components were interchanged, indicating the parts had been swapped.
Findings
- The primary cause of the accident was a loss of roll control during a precautionary landing attempt, triggered by the asymmetric retraction of the flaperons following takeoff.
- The materials used in the manufacturing of the flight control components were inadequate for primary flight controls. The high sulfur content in the screw and the incompatible contact between zinc and bronze facilitated rapid degradation of the threads.
- The pilot, who performed his own maintenance, had likely detected the defect during a recent 50-hour inspection. To continue flying while awaiting the delivery of new actuators, the pilot had swapped the master screws between the left and right carriages to keep the axial play within tolerable limits. This action did not prevent the eventual failure of the left actuator.