JEAN, NV, USA
N98NL
Glaser-Dirks DG-800B
The glider impacted terrain and the pilot reported that he lost elevator control. The bolt connecting the pushrod to the elevator was found, but the attaching nut was not found. The European production glider had a total time of 4 hours since manufacture. The metallurgist who examined the bolt reported the first three threads of the accident bolt did not have debris in the roots; however, proper engagement of the locknut would cause six threads to be free of debris. An exemplar locknut in the hand-tightened only position (without engaging the blue plastic lining of the locknut) caused the nut threads to wipe material from the roots of the first three bolt threads
On June 21, 1998, at 1130 hours Pacific daylight time, a Glaser-Dirks DG-800B, N98NL, crashed short of the runway at the Jean, Nevada, airport. The glider sustained substantial damage. The commercial pilot, the sole occupant, suffered serious injuries. The personal flight was returning to the airport at the time and no flight plan was filed. Visual meteorological conditions prevailed. Witnesses reported that the aircraft was very low on the final approach and was oscillating. The aircraft impacted the terrain short of the runway in a level attitude. The cockpit was crushed and the pilot was removed by paramedics. The pilot reported that he lost elevator control. A Federal Aviation Administration inspector from the Las Vegas, Nevada, Flight Standards District Office examined the aircraft. He reported that the bolt connecting the pushrod to the elevator was found in the fuselage, but the attaching nut was not found. The European production aircraft had a total time since manufacture of 4 hours. The bolt and exemplar parts were examined with an optical microscope at Seal Laboratories in Los Angeles, California, on July 31, 1998, in the presence of the Safety Board. A copy of the laboratory report is appended to this file. According to the metallurgist, the first three threads of the accident bolt did not have debris in the roots, and installation of an exemplar locknut in the hand-tightened position would cause the nut threads to wipe material from the roots of the first three bolt threads. For proper tightening of the locknut, the threads must be engaged over the full height of 6 mm (six turns) so that the blue plastic lining which provides thread locking is deformed. This would require three more turns than are indicated by the lack of debris in the thread roots. The metallurgist concluded that a nut was installed on the bolt but not fully tightened.
The disconnection of the elevator control attachment nut due to improper installation by the manufacturer, which resulted in the pilot's loss of control.
Source: NTSB Aviation Accident Database
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