On July 23, 2008, about 1330 Pacific daylight time, a Glaser-Dirks Flugzeugbau DG-100G, N132S, experienced an uncommmanded release while being towed, and landed off the runway at Truckee-Tahoe Airport, Truckee, California. The pilot/owner was operating the glider under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot was not injured; the glider sustained substantial damage to the fuselage, both wings, and an aileron. The flight was departing at the time of the accident on a local flight. Visual meteorological conditions prevailed, and no flight plan had been filed.
The pilot reported that the lineman connected the tow rope, and gave it a tug prior to the takeoff, which commenced from runway 01. About 150 feet above ground level (agl), the pilot saw his end of the tow rope in front of him, and realized that the glider's release mechanism had activated without his command. He lowered the nose, regained airspeed, turned left, and landed in sagebrush. After 60 yards of ground run, the glider looped to the left, and traveled another 20 yards while rotating about 160 degrees. The fuselage sustained substantial damage about 2 feet aft of the wing trailing edge. The left wing tip, right wing root area, and the right aileron were damaged.
The tow pilot stated that he felt the glider release about 200 feet agl, and presumed that the tow rope had broken. After landing, he examined the tow rope, and found that it was intact with the proper fittings in place at each end.
During the post accident investigation, a Federal Aviation Administration (FAA) inspector was able to cause an uncommanded release of the tow rope an additional two times by tugging on it.
The Tost SH72, serial number 11633 SH, tow release was an original installation, which had been in service for 3,076 hours and 23 years. The manufacturer's recommended replacement interval for the tow release is 2,000 launches or 10,000 actuations. The annual condition inspection requirements in the airplane's operating limitations are to be in accordance with FAR 43 Appendix D. This FAR does not address compliance with manufacturer's service recommendations, which are not regulatory unless specifically written into the operating limitations for the airplane.