Business aviation needs “to focus on high-altitude stalls” in upset prevention and recovery training (UPRT), due to the effect reduced air density has on aircraft performance and aerodynamics, according to John Cox, CEO of Safety Operating Systems. Speaking at the Flight Safety Foundation’s Business Aviation Safety Summit in early May, he told delegates that the industry is not adequately addressing flight instability at high altitudes. He maintained that many pilots have no experience hand-flying aircraft at high altitudes due to RVSM mandates on using autopilots above FL290.
The loss-of-control accident in January over the Arabian Sea involving a Bombardier Challenger 604 at FL340 underscores the need for renewed focus on UPRT, Cox said. Following a wake encounter with an A380, the Challenger rolled several times and reportedly lost 10,000 feet of altitude before recovery, resulting in serious injuries to passengers and the permanent grounding of the aircraft due to damage from exceeding operating limitations.
According to the interim report on the wake vortex encounter, the A380 was flying in the opposite direction and was 1,000 feet overhead and slightly to the right of the Challenger. Approximately a minute after the two aircraft passed each other, the Challenger hit turbulence from the A380’s wake and quickly went out of control. Before the crew regained control at FL240, the aircraft had exceeded several design load limits, rolled several times, dropped 8,700 feet, lost vital avionics (including attitude displays) and the left engine had to be caged. The pilot-flying explained that since the sky and the ocean were almost the same blue color, he had been able to recognize the aircraft's flight attitude only “with the help of the clouds.”
After the crew regained control, they declared an emergency and diverted to an alternate airport, where they made a normal landing. Although no external damage could be seen (in contrast to that in the cabin), Bombardier determined that the airframe structure could not be restored to airworthy condition. Two passengers were severely injured and one passenger and the flight attendant sustained minor injuries.
When properly executed, “high-altitude recoveries are slow and gentle,” Cox said. BJ Ransbury, president of UPRT provider Aviation Performance Solutions, who has discussed the accident with Bombardier investigators, told attendees they declined to say whether the Challenger crew had undergone upset training.