Probably all flight crews, but especially post-maintenance flight crews, and maintenance controllers should be trained to know the warning signs of a malfunctioning stall warning and/or stick-pusher system, and know when the inoperative component should be repaired prior to the next flight rather than deferred. This information should be contained in ground training, and probably reinforced in the simulator.

Notably, in September 2009, Transport Canada Airworthiness Directive CF-2009-36 states: “There have been several stick-pusher capstan shaft failures causing severe degradation of the stick-pusher function. This directive is issued to revise the first flight of the day check of the stall protection system to detect degradation of the stick-pusher function. It also introduces a new repetitive maintenance task to limit exposure to dormant failure of the stick-pusher capstan shaft. Dormant loss or severe degradation of the stick-pusher function could result in reduced controllability of the airplane.”

Among the ASRS data were numerous reports in which the stick shaker and/or stick pusher activated when other cockpit indications revealed the aircraft was at a safe flight condition. When these false warnings and activations occurred during benign phases of flight, the crews were invariably startled and then perplexed, both of which were distractions. In some cases the pilots found little guidance in their Quick Reference Manuals to deal with the false indications. In one case, the AOA vane had actually fallen off the aircraft after it left the ramp. In all these false alarms, the flight crews performed the most important task — that is they kept flying their aircraft at a known pitch and power setting.

One report in which an aircraft was placed in severe jeopardy by an errant stick-pusher activation occurred in an MD-83 at 50 ft. AGL during the landing flare. The pilots instinctively yanked (probably with plenty of adrenaline to boost their power) as the stick pusher wrongly nosed the aircraft toward the ground.

The FAA's Advisory Circular encourages trainers to develop realistic scenarios such as the forgoing push-over that could be encountered in operational conditions. That helps, to be sure, but preventing stall accidents will require a multi-layered methodology that includes procedures that optimize cross-checking and monitoring, thorough flight testing of icing protection systems, MELs that eschew the easy deferral of vital components without full consideration of the effects on flight safety, more informed ground school instruction and improved simulator fidelity, particularly near the edges of the aircraft's performance envelope. BCA