History of Flight
On April 29, 2012, at about 1300 mountain daylight time, a Jonker Sailplanes JS-1B glider, registration N555AP, collided with terrain following an in-flight loss of control near Clines Corner, New Mexico. The pilot bailed out of the glider and received minor injuries during his parachute landing. The glider sustained damage to the fuselage and both wings. The aircraft was registered to and operated by the pilot under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and the flight was not operated on a flight plan. The flight originated from Moriarty Airport (0E0), Moriarty, New Mexico, about 1230.
The pilot reported that while in flight at about 11,300 feet mean sea level (msl), he heard a loud metallic noise from the area near the rudder pedals and lost contact between his feet and the rudder pedals. He attempted to adjust the pedals using the adjustment handle, but it had no tension and did not retract as designed. He maintained partial control using aileron and elevator, but the glider descended in a right yaw condition. When the glider descended to about 10,000 feet msl, the pilot elected to bail out because the surrounding terrain was unfavorable for a forced landing.
Data from the Clear Nav GPS receiver showed the glider's trajectory: it made a climbing left turn of about 360 degrees, then a descending right turn, followed by an abrupt descent to the ground. The pilot stated the glider was in a right turn at the mishap, but GPS data showed a left turn; the pilot could not explain the discrepancy.
Personnel Information
The 68-year-old pilot held a commercial pilot certificate with airplane single-engine land, multi-engine land, instrument airplane, and glider ratings. He reported 7,000 total flight hours, including 100 hours in the accident glider. His most recent flight review was completed on March 20, 2011. He was issued a third-class medical certificate with a restriction for corrective lenses on January 12, 2012.
Aircraft Information
The accident glider was a Jonker Sailplanes JS-1B, serial number 24, a single-seat, high-performance sailplane constructed mainly of composite materials. It was manufactured in 2011 and issued an airworthiness certificate on July 27, 2011. The airframe had accumulated about 100 hours total time in service at the time of the accident.
Meteorological Information
Weather conditions recorded at 0E0 AWOS at 1255: wind from 230 degrees at 6 knots, visibility 10 miles, scattered clouds at 7,500 feet agl, temperature 21°C, dew point 1°C, altimeter 30.04 inches of mercury.
Wreckage and Impact Information
The glider impacted a mesa in rural New Mexico, 23 miles and 23 degrees from 0E0. The empennage was partially separated from the tail boom near the leading edge of the vertical stabilizer. The tail boom had a longitudinal split from the separation point forward toward the cockpit. The forward fuselage had crushing damage in the cockpit area. The wings were mostly intact; the left wing had a split in the bottom skin from the removable wing tip joint running inboard. The control system was intact except for a break in the right rudder cable at the forward exit of the S-tube on the adjustable rudder pedals.
Additional Information
Examination of the rudder pedal design revealed that the pedals were retained by an acorn-style nut without internal locking capability. The NTSB Materials Laboratory found the right rudder cable severed; 8% of wires showed overstress failure and 92% showed fatigue failure due to bending stress. The left rudder cable had 22 broken wires, all similar fatigue fractures. The S-tube exit had wear damage consistent with the cable's diameter and position. A mockup showed that with full rudder deflection, the cable made a sharp bend at the S-tube exit.
An owner of an exemplar glider (N60VR) found similar cable damage and conducted ground tests. Cycling the rudder pedals for five minutes nearly severed the right rudder cable; the securing nut on the pedal shaft had backed off, allowing lateral movement. The glider manufacturer conducted flight tests with a simulated right rudder cable break by removing the pedal return spring. The tests included spin evaluations; the glider was controllable with minimal difficulty, and a traffic pattern was flown using rudder only during final landing due to crosswinds.
Following the accident, Jonker Sailplanes issued Service Bulletin SB.JS-007 and Technical Notes TN.JS-009, TN.JS-010, and TN.JS-011 addressing rudder cable inspection, replacement, and a refined S-tube design to reduce cable wear.