The largest cause of commercial aviation fatalities is loss-of-control-in-flight (LOC-I). Following high-profile accidents including Flight 3407 and Flight 447, several working groups helped the International Civil Aviation Organization (ICAO) develop the soon-to-be-released Manual of Aeroplane Upset Prevention and Recovery Training—a major step toward implementing a mitigation strategy that targets LOC-I.
Unlike controlled-flight-into-terrain accidents, which were reduced through implementation of enhanced ground proximity warning systems, LOC-I cannot be resolved through technology alone. It requires better awareness, recognition and avoidance, and recovery training. In today's cockpit, the pilot's training is the final safety net to prevent LOC-I.
LOC-I is often the result of aerodynamic stalls. Whether a stall is initially due to crew mismanagement of energy, inattention, inaccurate flight path monitoring or weather-induced events, it is critical for flight crews to reduce back pressure. In addition to flight-envelope protection (if available), an aircraft will provide warning signs as the angle-of-attack approaches the critical level, after which a stall occurs. There are rapid increases in aerodynamic buffet, reduced control effectiveness and stability, and possible “roll off” as one of the wings loses lift sooner or more abruptly than the other. It is particularly that last action that seems to catch pilots off guard and tempt inappropriate actions, and for which training needs to be reconsidered.
The recently released Stall Recovery Template provides the memory items for pilots to use in recovering from an impending or existing stall: disengage the autopilot and auto-thrust, apply forward pressure and nose-down trim as needed, level the wings, apply thrust as appropriate, retract speed brakes/spoilers and return to the desired flight path.
These maneuvers are being taught in what is known as an “Approach-to-Stall,” where the training exercise exposes pilots to an impending stall, typically in a pre-announced manner, asking them to “recover now” and thereby demonstrate their ability to follow that template. Because the recovery action from an approach-to-stall and an actual stall is the same (basically, reduce angle-of-attack to regain control), teaching the maneuvers should reduce the resulting control losses.
It all seems so easy. Unfortunately, there is one subtle difference in most LOC-I events: It's called startle. It can lead to “brain stall.”
When pilots face an unexpected event—and with the impressive levels of reliability these days, these are indeed very rare—often there is a cognitive freezing that causes confusion or reversion to reactions developed earlier. Even the most seasoned pilot may end up acting inappropriately.
A recentstudy showed that one-quarter of pilots exposed to an unexpected stall applied the template correctly. This study, intended to assess the training effectiveness of varying levels of stall representation in full-flight simulator math models, found that several of the line pilots who had previously been trained/briefed on this procedure, fought against the aerodynamics, exacerbating the stall.
There is no simple reason why this occurs, but there are some possibilities: previous training emphasizing “minimum altitude loss” following a stall; the lack of scenario-based stall recovery training programs within airline curricula; and the lack of proper simulation models that reasonably represent the characteristics of stalls in swept-wing aircraft. Limited practice of even approach-to-stall recoveries during the already tight training sessions also may be a factor. Regardless, we have a sky filled with pilots who should sharpen these skills and understand startle management.
We need to improve both stall prevention and recovery training. Stalls should not catch a pilot off guard, and attention must focus on recovery that includes sacrificing altitude for kinetic energy. We need to continue to improve our simulator models, understand simulator limitations and create that critical element of surprise in the simulator. Presenting startling conditions with proper instruction in high-performance light airplanes also appears to enhance awareness by pilots. Finally, proper instruction ties it all together.
Most of all, we need to generate awareness of the problem. Stalls don't just happen. Basic airmanship, manual handling skills and thorough academic knowledge are the foundations of aviation safety. And when the threat prevails, we must maintain the three most important tenets: fly the plane, fly the plane and fly the plane.
Advani, an aerospace engineer and pilot, is the owner and president of International Development Technology; he has chaired an international team on upset prevention and recovery.