NTSB Identification: LAX98FA095.
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Accident occurred Monday, February 23, 1998 in SAN GORGONIO MO, CA
Probable Cause Approval Date: 08/13/2001
Aircraft: Beech A36, registration: N3103W
Injuries: 2 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 airplane collided with mountainous terrain about 11.3 nautical miles south-southeast of the departure airport. The departure airport's automated weather observation system was reporting skies clear to 12,000 feet above ground level (agl), with winds from 220 degrees at 14 knots gusting to 26 knots at the estimated time of departure. The pilot received a weather briefing 1 hour 46 minutes prior to departure. He was informed that the winds at 9,000 feet mean sea level (msl) over the area were 210 degrees at 50 knots, and that conditions would get worse by 1100. The briefing also contained AIRMETS for mountain obscuration, moderate turbulence, and moderate rime and mixed icing above the freezing level. The accident site elevation was approximately 10,300 feet msl. The airplane approached the accident site on a heading of approximately 240 degrees. This would have placed the airplane on the lee side of a high ridgeline with winds exceeding 50 knots. There was a valley extending towards the southwest directly in front of and 90 degrees to the ridgeline on which the airplane crashed. This valley may have produced a funneling effect, which would have significantly accelerated the wind flow over the ridge. Satellite imagery of the site at the time of the accident showed high clouds above the mountains. The cloud tops were estimated to be 13,000 feet. Additionally, rotor clouds could be seen southwest of the crash site. Studies have shown that severe turbulence, wind shear, and downdrafts are commonly found on the downwind side of high mountainous terrain when high wind conditions exist. The maximum climb rate for the airplane at 9,000 feet under static conditions was calculated to be 900 feet per minute. No preimpact mechanical malfunctions were found during examination of the wreckage.

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

The pilot's inability to maintain altitude due to an encounter with adverse winds and downdrafts on the lee side of a mountain. Also causal was the pilot's inadequate weather evaluation, which precipitated his intentional flight into an area of known adverse weather in high mountainous terrain. Factors include terrain induced turbulence and downdrafts as a result of high wind conditions.

Full narrative available

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