What happened
On May 31, 2009, a Dyn'Aero MCR 01 ULC, registration HB-WAK, was performing glider towing operations at the Courtelary airfield. After successfully releasing a Janus glider at an altitude of 1,400 meters, the pilot returned to the airfield for landing.
As the aircraft approached the runway threshold at a height of approximately 45 meters, the pilot heard a loud cracking sound and felt the rudder pedals suddenly move forward. The aircraft immediately entered a right-hand turn, and the pilot found the rudder controls to be inoperative. To maintain the runway centerline, the pilot performed a left-side slip. Upon touchdown, the aircraft continued to veer to the right despite braking efforts on the left side. The aircraft eventually exited the runway, striking a field approximately 10 meters from the edge. The nose of the aircraft struck the ground while the engine was still running at low power, causing heavy damage to the airframe, the nose gear, and the propeller. There were no injuries to the pilot.
The investigation
Investigators examined the flight control system and the physical condition of the rudder cables. They found that the left rudder control cable had snapped near the rear bulkhead of the fuselage. Technical analysis of the pulley and the surrounding structure revealed that the cable had been improperly positioned for some time.
Specifically, the cable was not seated correctly within the guide groove of the pulley. This misalignment caused the cable to rub continuously against the carbon fiber structure of the bulkhead (labeled as couple 12). This friction led to the gradual fraying and eventual breakage of the cable strands. The investigation also noted that while the aircraft had undergone various inspections, including a recent check by the Federal Office of Civil Aviation (FOCA) three days prior, the specific issue of the cable's path was not detected during routine daily or periodic maintenance.