What happened
A pilot conducting a 40-minute scenic flight released a sailplane from an airplane tow at 8,000 feet MSL. During the flight, the aircraft reached an altitude of approximately 14,000 feet MSL. Toward the end of the flight duration, the pilot descended through cloud cover, which resulted in the sailplane colliding with mountainous terrain at an elevation of approximately 6,000 feet MSL.
The investigation
An ocean/atmosphere scientist flying a glider in the same area near the time of the accident provided observations regarding the atmospheric conditions. The pilot noted that the day was characterized by powerful and rapidly changing lee wave systems within the coastal mountain ranges of the lower Southern California Bight. These systems produced updrafts and downdrafts ranging from 10 to 20 knots.
While lee wave structures are typically steady and reliable, this specific day was described as a rare occurrence, estimated at a 1 in 1,000 frequency, where the structure changed minute by minute. The witness reported encountering three separate instances of abrupt disintegration of well-ordered non-hydrostatic waves, which caused immediate altitude losses between 7,000 and 10,000 feet.