NTSB Identification: WPR11FA302
14 CFR Part 91: General Aviation
Accident occurred Saturday, July 02, 2011 in Lone Pine, CA
Probable Cause Approval Date: 07/18/2012
Aircraft: SCHLEICHER ASW-20, registration: N838KS
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The pilot intended to fly along the ridgeline of a mountain range that runs south to north, accented by mountainous terrain to the west and a wide desert valley to the east. The mountain ridgeline rises between 8,000 and 12,000 feet mean sea level (msl). The glider’s datalogger recorded the glider’s position and altitude every 6 seconds as the pilot flew north along the ridgeline. The flight lasted 1 hour 12 minutes; during the last half of the flight, the glider was flying below the ridgeline and within one or two wingspans of the terrain slope. One minute before the final data point was recorded, the glider reversed course and proceeded south. The change in ground speed from 90 knots before the course reversal to 60 knots after the course reversal indicates that the glider turned into a strong southerly wind. The glider impacted the slope in a nose-low attitude and with wings parallel to the 65-degree terrain slope at 7,478-feet msl. The angle of impact is consistent with the glider being in a left turn (away from terrain) at the time of impact. No preaccident mechanical malfunctions or failures were found that would have precluded normal operation of the glider.

Weather observations between two locations, one at the south end of the valley and one at the north end of the valley, indicated clear skies and warming surface temperatures. Wind magnitudes increased dramatically at the surface the hour before the accident at the northern weather observation station due to the warming surface temperatures and the developing valley breeze circulation. Typical daily orographic turbulence was most likely present near the mountainous terrain.

Toxicology test results from cavity blood samples taken from the pilot revealed positive results for temazepam (sedative). The identified level of temazepam is considered to be in the therapeutic range for this medication. While it is possible that the results are reflective of the true blood level and that the pilot could have experienced some level of impairment from this medication, the investigation was unable to conlude that the pilot was impaired because the possibility of post-mortem redistribution of drugs can make the assessment of cavity blood difficult when trying to determine true blood level and impairment.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The glider encountered a strong downward orographic wind flow and turbulence that forced it into terrain. Also causal was the pilot’s decision to operate the glider very close to the terrain.

Full narrative available

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