Hypoxia Contributed to Fatal Caravan Crash
Cessna 208B Caravan, Naches, Wash., Oct. 7, 2007–The Board attributed the
fatal crash to the pilot’s failure to maintain adequate airspeed to avoid a stall while maneuvering. Contributing factors were the pilot’s impaired state due to hypoxia, his inadequate pre-flight weather evaluation and his attempted flight into known adverse weather. The pilot’s inadvertent flight into IMC with turbulence at night was listed as an additional cause.
The single-engine turboprop, operated by Kapowsin Air Sports, was destroyed and the commercial pilot and nine passengers killed when the Caravan crashed into terrain during a night flight from Star, Idaho, to Shelton, Wash. The flight was carrying a group of skydivers to their home base after a weekend of
skydiving. The day of the accident, the pilot flew several jump flights and stopped early in the afternoon to prepare the aircraft for the return flight.
The flight was planned into an area of cloud, turbulence and icing, which
the pilot had researched. He delayed the departure until he decided he could complete the flight under VFR in compliance with company policy, which did
not permit IFR flights. Recorded radar data of the more than two-hour flight indicated that the pilot was likely attempting to avoid adverse weather while trying to maintain VFR.
The aircraft was turning when it departed from controlled flight, and a performance study showed a rapidly increasing angle of attack consistent with an aerodynamic stall. Weather radar showed the aircraft likely entered cloud during the final three minutes of flight.
The unpressurized aircraft had been flying at more than 14,000 feet for more than an hour and reached 15,000 feet just before the crash.
The pilot did not use supplemental oxygen. The owner of the airplane stated
that since oxygen was never used, it did not service the system, although there were two masks in the airplane. FAR 91.211 states that the required minimum flight crew must be provided with and use supplemental oxygen for any part of a flight that is longer than 30 minutes duration at cabin pressure altitudes above 12,500 feet msl up to and including 14,000 feet msl. At cabin pressure altitudes above 14,000 feet msl, the required minimum flight crew must be provided with and use supplemental oxygen.
The airplane owner also indicated that it was not company policy to fly into known icing conditions, and that the Caravan was placarded with “not approved for known icing.” Numerous pilot reports indicated icing conditions present in the region above 10,000 feet through 18,000 feet at the time of the accident.