WPR09FA089 · Glaser-Dirks DG-400

The pilot was attempting to set an altitude record over the big island of Hawaii. The glider was towed to 12,600 feet mean sea level (msl) and released about 1028. Around 1245, the pilot radioed that he was in the primary wave, climbing at 1,000 feet per minute, and was at 28,000 feet (msl). He then stated that he was going to crossover to Mauna Loa. The next day search aircraft identified widely scatted debris at 10,000 feet on the southwest face of the Mauna Loa Volcano. The glider was equipped with a flight data recorder, which depicted that the glider climbed to 20,375 feet msl near the town of Holualoa, flew east-northeast and rose to 30,116 feet msl over Mauna Kea, then proceeded south-southwest to Mauna Loa and climbed to 36,846 feet msl. Three minutes and twelve seconds from the end of the recording, at 38,630 feet, the track abruptly became linear from a constant-rate turn headed in a southwest direction, with the rate of descent rapidly increasing over the next 16 seconds to 24,000 feet per minute. At the beginning of the descent, the track exhibited a pitch oscillation before the descent rate accelerated. Fifty-six seconds from the end of the recording the track suddenly reversed course 180 degrees and descended almost vertically until the end of the data. The sudden course reversal can be associated with the structural failure of the airframe from very high aerodynamic loads. A large section of the left wing was located 3.4 miles downwind from the main wreckage, indicating that the left wing separated from the airframe at a high altitude. The spar cap fractures were consistent with a negative overload of the wing. Between 1315:23 and 1315:43, the true airspeed was calculated to increase from 60 knots to 120 knots, back to 103 knots, then 180 knots, and finally 241 knots. The operating limitation section of the glider’s flight manual lists 146 knots (270 km/h) as the red line airspeed. At 20,000 feet indicated airspeed is limited to 117 knots for flutter prevention. The manufacturer stated that the airspeed limitation can be extrapolated linearly to 40,000 feet. Due to the extensive fragmentation of the airframe, the possibility of a flight control malfunction could not be ruled out.

Verbatim NTSB analysis and probable cause from the NTSB dataset