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Factory Direct
Accidents, Training, More Accidents
On March 3, 1991, United Airlines Flight 585 entered a right roll which eventually resulted in a steep nose-down attitude while on approach to Colorado Springs airport in Colorado. All the occupants of the aircraft perished. The NTSB struggled to discover the root cause, with the initial report stating: “...after an exhaustive investigation effort, [we cannot] identify conclusive evidence to explain the loss of the aircraft.” Eventually, the Board would amend the findings following a similar accident on USAir flight 427 (which resulted in the longest investigation in NTSB history at four and a half years).
The USAir accident was ultimately solved due to an incident that occurred on Eastwind Airlines flight 517. The pilots of flight 517 provided testimony to investiga- tors regarding uncommanded rudder inputs that they had encountered aloft (flight data recorders of the era did not capture details relating to rudder pedal position, so this information was not available to investigators for United 585 or USAir 427). All three events involved Boeing 737 aircraft, which had experienced a sudden yawing moment at relatively low airspeed. Flight telemetry from United 585 and USAir 427 suggested a full application of rudder had precipitated the loss of aircraft control. Investigators had been unable to exclude the pilots as the source of the offending input prior to the testimony provided by East- wind 517. In the end, the culprit was determined to be a bad rudder control valve. Most aircraft have a crossover speed where full rudder deflection will generate rolling inertia equal to maximum aileron authority. The rudder malfunctions of United 585 and USAir 427 occurred be- low the aileron crossover speed resulting in a wing-over descent and crash, while the malfunction experienced by Eastwind 517 occurred above crossover speed allowing the pilots to maintain control via copious amounts of aileron.
Anytime a series of high-profile accidents occur, a mas- sive response is sure to follow. While Boeing ultimately solved the problem by fixing the servo valve in the 737 rudder system, airline and cargo operators attempted to analyze how crews could more successfully respond to similar flight control issues in the future. Advanced maneuvering programs were developed with the noble intention of equipping pilots with the tools to respond to even the direst of flight control malfunctions. Some of these well-intended programs ultimately contributed to other accidents and incidents, as complex maneuvering theory was misappropriated by the occasional line pilot.
Even long-standing training techniques have proven capable of producing unintended consequences. The NTSB concluded that stall training was a factor in the Cogan Air 3407 accident. At the time, stall demonstrations required pilots to maintain altitude throughout the maneuver. The idea was that powerful aircraft have the performance to recover from a stall while maintaining level flight. Under the old system you could fail a checkride if you lost alti- tude during the recovery. This produced a strong desire to keep the nose up following a stall, which in hindsight
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