N/A Airport
Aircraft Accident/Incident Report

Clines Corner, New Mexico 87070
Sunday, April 29, 2012 13:00 MDT

While in soaring flight, the pilot heard a loud metallic sound come from the area near the rudder pedals and subsequently lost contact between his feet and the pedals, which resulted in a temporary loss of glider control. Although the pilot regained control of the glider, it was descending. When the glider had descended to about 10,000 feet mean sea level, the pilot chose to bail out with a parachute due to the descent rate and the unfavorable terrain for landing. The glider subsequently impacted a mesa and sustained substantial damage. Subsequent examination of the adjustable rudder pedal system revealed that the right rudder cable had fractured at the forward opening of the S-tube on the right rudder pedal. Examination of the rudder pedal design configuration revealed that full-forward deflection of the rudder pedal forced the cable to sharply bend at the point where it exited the forward opening of the S-tube, which was confirmed by a corresponding wear pattern on the accident glider’s S-tube. The repeated bending during normal operation resulted in the fatigue failure of 92 percent of the individual right rudder cable wires and, subsequently, final overstress failure of the remaining wires. After the accident, the owner of another glider of the same design examined the rudder cable on his glider and found similar damage to the cable. Subsequently, he conducted ground testing, which confirmed that repeated operation of the rudder pedals resulted in further damage to the rudder cables, indicating a progressive failure. Therefore, it is likely that the right rudder cable failed during the flight and resulted in the loss of rudder control. The glider manufacturer subsequently issued service bulletins and service letters to address the rudder pedal system deficiencies discovered during the accident investigation. Flight testing conducted by the manufacturer in an exemplar glider confirmed that the glider would have been controllable if the pilot had not chosen to bail. However, the flight testing was conducted under controlled conditions, and the test pilot was fully aware of the modifications made to the exemplar glider to simulate the cable failure. Further, despite these modifications, the test pilot was still able to fully control the rudder, if necessary, during the flight test. Since the accident pilot did not have knowledge of the nature of the control problem and did not have the ability to gain full rudder control, his decision to bail out of the airplane was understandable.

The fatigue failure of the rudder cable due to the inadequate design of the rudder pedal system.