This August 2008 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Lancair ES. Injuries: 2 Fatal. Location: Cliffdell, Wash. Aircraft damage: Destroyed.
What reportedly happened: During the IFR flight at 11,000 feet MSL in mountainous terrain, the pilot’s last transmission to air traffic control confirmed his altimeter setting. Shortly thereafter, radar data indicated that the airplane started a descending right-hand turn. The final radar return was at 9,700 feet MSL. The airplane wreckage was located about one mile west of the final radar return, at an elevation of 3,830 feet. The debris field was consistent with an in-flight breakup, with wreckage distributed over a distance of half a mile. A study of the meteorology in the vicinity at the time of the accident indicated that a broken to overcast ceiling existed between 5,000 to 6,000 feet MSL and extended up to 14,000 feet. Satellite imagery depicted cloud top temperatures of -1° to -3° between 11,000 and 12,000 feet MSL. The location of the last radar return was immediately downwind of Mt. Rainier and the sounding wind profile indicated favorable conditions for mountain wave formation. Digital photos of Mt. Rainier taken a few minutes before the accident were recovered from a camera onboard the airplane. The images depict a clear view of clouds surrounding Mt. Rainier and that the airplane was operating immediately above a broken-to-overcast cloud layer. The radar track combined with weather radar imagery and satellite imagery indicated that the airplane entered IMC at the time it entered the descending right turn, which escalated into a spiral descent. Flight performance data recovered from cockpit instrumentation indicate that five minutes prior to the accident the airplane experienced continuous turbulence ranging from 0.77 to 1.5 vertical g’s, consistent with a mountain wave encounter. During the last few seconds of flight the airplane was oriented 88.6° nose down, 113° angle of bank, and 290 knots. Upon exiting the bottom of the cloud layer, at 6,135 MSL, the airplane experienced a rapid onset of g’s that exceeded the strength of the airplane. The sudden onset of g-load is constant with the pilot’s attempt to recover from the rapid descent and unusual attitude.
Probable cause: The pilot’s failure to maintain aircraft control while in cruise flight due to spatial disorientation.
For more information: NTSB.gov