Several high-altitude/high-Mach accidents reveal deficiencies in pilot handling of the aircraft. The NTSB has pointed out several times the glaring lapses in training curriculum to adequately prepare pilots for flight in this environment.

To help determine if there are any consistent aircraft handling mistakes that pilots make in this environment, we queried instructors Zach McCarley and David Culbertson at Calspan’s Upset Recovery Training program (their notable credentials are outlined in the adjoining sidebar). The Calspan program includes a high-altitude scenario in its specially modified variable-stability fly-by-wire (FBW) Learjet 25. The FBW software programming allows the instructors to simulate a conventional (not fly-by-wire) regional jet’s handling qualities at high altitude while the aircraft is actually at 15,000 ft. The instructors introduce a pitch upset mimicking an autopilot failure or kicked off with a mild transient trim.

One of the consistent mistakes Culbertson notices is that pilots have been so ingrained to remain at their assigned altitude that they have a tendency to try to stay there regardless of warnings of more important concerns. He has also noticed a tendency of trainees to pull too hard on the yoke, saying, “We routinely see very experienced pilots over-controlling the aircraft.”

Over-controlling is a distinct threat at high altitude. For the same control surface movement at constant airspeed, an airplane at 40,000 ft. experiences a higher pitch rate than one at 5,000 ft. because there is less aerodynamic damping. Therefore, the change in angle of attack (AOA) is greater, creating more lift and a higher load factor. It takes less force to generate the same load factor as altitude increases. Thus, it’s imperative to not overreact with large and drastic inputs.

Unfortunately, the flight crew of a China Eastern Airlines MD-11 did just that when the leading edge wing slats inadvertently deployed while in cruise 950 mi. south of Shemya, Alaska, on April 6, 1993. The autopilot disconnected and the captain attempted manual control. The airplane progressed through several violent pitch oscillations that killed two passengers and injured 149 others. The NTSB determined that given the reduced longitudinal stability and associated light control force characteristics the captain’s attempt to recover led to the violent pitch oscillations. The Safety Board said contributing factors included the lack of specific pilot training in recovery from high-altitude upsets.

Unintentional autopilot disengagement at high altitude is key in many Aviation Safety Reporting System (ASRS) flights. One of business aviation’s deadliest accidents occurred Sept. 14, 1999, when the autopilot on a Falcon 900 disconnected at high speed during a flight from Athens to Bucharest, Romania. The aircraft was descending when the pilot flying (PF) moved the control wheel to level off at FL 150 and the autopilot disconnected, resulting in several pitch oscillations exceeding the aircraft’s flight load factor limits. Seven passengers were killed.

The Romanian Civil Aviation Inspectorate’s final report on the accident said one of the possible explanations for the PF’s attempt to manually override the autopilot was that he was employing a technique appropriate for the Boeing 737-400, in which both pilots had received a proficiency check just months prior. Neither pilot had received a proficiency check in the Falcon.

A similar misuse of the autopilot led to a serious upset over the U.S. a month later when another Falcon 900 was descending to land at Grand Rapids, Michigan. The first officer manually applied elevator control input to level the aircraft at 11,000 ft. without disengaging the autopilot. Several pitch oscillations occurred. The peak vertical accelerations during the upset were +3.3 and -1.2. The flight attendant somehow escaped serious injury. All other aircraft occupants were seated and buckled at the time of the upset.

When a pilot elects to disconnect the autopilot, smooth control inputs avoiding abrupt control actions are necessary. This advice applies as well when the disconnect is unintentional. The latter is especially challenging because of the startle factor and a pilot’s instinctive rush to quickly grab the yoke to regain control. B&CA