The Stall Horn Fallacy of Stall Prevention
By Rod Machado
News flash! The Mona Lisa’s eyebrows are missing. That’s right. Gone! Some say they were scrubbed off during an early restoration. I suspect they were vaporized when Leonardo had Mona over for a pre-portrait barbecue and he took excessive liberty with the lighter fluid. While I didn’t attend a BBQ, my eyebrows are also missing. At least they appeared to disappear as they rose above my forehead in surprise at the FAA’s and ACS committee’s dumbing-down of standards for commercial pilot certification.
As you know, the FAA and ACS committee recently removed the requirement to demonstrate flight at minimum controllable airspeed (MCA) from the private and commercial checkride. Additionally, the requirement to enter and recover from a full stall was eliminated from the commercial pilot checkride. The most recent commercial pilot ACS only requires applicants to demonstrate stall recovery at the first indication of a stall (i.e., typically the stall horn or light as the FAA conceives it*). Removal of the MCA and full-stall requirements for commercial applicants supposedly prevents them from becoming desensitized to the stall horn, thus increasing the likelihood that they’ll reflexively apply stall recovery procedures at the first peep of the stall horn (or sight of the stall light). The FAA and ACS committee believe that this is all the evidence needed to be assured that these applicants will avoid real-life, unanticipated stalls. As I see it, this assumption is based on an incomplete and unrealistic understanding of what actually happens in the flight training environment. So let’s see why my eyebrows are missing.
One of Two Things Happen in a Stall
Generally speaking, in nearly all stall/spin accidents one of two things occur. Either the stall horn/light didn’t activate and the pilot stalled, or the stall horn/light activated but it didn’t influence the pilot’s behavior, who ultimately stalled.
I Didn’t Hear a Stall Warning
If a stall warning light or horn didn’t activate prior to a stall, then why didn’t the pilot recognize and respond to the all the other pre-stall clues so as to avoid the accident? Clearly, if pilots are taught to recover from the stall at the first indication of a horn or light, then it’s unlikely they’ll recognize, much less respond to, all the clues that precede an actual stall. However, if pilots are trained to recognize and react to all the additional pre-stall warning clues (not just the horn or light), then they are more likely to recognize and avoid the accidental stall irrespective of stall horn/light activation. In fact, the FAA even says as much in its Flight Training Handbook with the following phrase: Psychologists have also found that learning occurs most rapidly when information is received through more than one sense. Stimulating all of the senses (i.e., all pre-stall clue perceptions), not just one, results in more rapid behavior change. That means pilots experience a more permanent change in stall recognition and recovery behaviors for the amount of time they spend in stall training.
The Stall Warning Didn’t Affect Me
If the stall warning horn/light activated prior to a stall accident, why didn’t the pilot recognize and avoid the impending stall? The only logical answer here is that the pilot didn’t notice the stall warning or he noticed it but didn’t respond to it (we’ll just assume the stall warning is a horn from now on).
There are several reasons that this might occur. First, let’s consider that we’re not interested in the behavior of pilots who heard the stall horn and avoided stalling as a result. These individuals demonstrated the proper stall prevention behavior as pilots have been doing for the past 100 years. Instead, we’re concerned about pilots who don’t respond to the stall warning horn and stall as a result.
The principle of State Dependent Learning provides one explanation for this behavior. This principle says that pilots will respond most effectively to an event (i.e., stalling) based on the emotional state in which they initially learned about that event. If pilots learn stall recovery behaviors under relatively relaxed conditions, they’ll have the most immediate access to that information under relaxed conditions. If they learn stall recovery behaviors in the same mental state experienced during a real-life, unanticipated stall, they’ll have the most immediate access to that information in that mentally aroused condition. Unfortunately, most pilots don’t learn stall recovery behaviors in the mental state that replicates/simulates real-life stall conditions. That's why these same pilots often respond poorly when they accidentally stumble into a real-life, unanticipated stall experience. They might panic or freeze, perhaps even pulling the yoke full aft until impacting the ground (which is what happened in the Colgon crash where the captain held the yoke full aft in a stall for 37 seconds until impact).
If you’d like to see the effects of state dependent learning for yourself, try this experiment on a newly rated private pilot (this technique is known as induced panic and, despite the name, it's a perfectly legitimate technique to use in training). Have him/her start a power-off descent at 3,000 feet MSL (at least 3,000 feet above ground level) at approach speed. As the power is reduced to idle, tell him that, upon reaching 2,000 feet MSL, he is to hold his heading while maintaining altitude for 30 seconds without the use of power. Care to guess what will happen? In the majority of instances, this pilot will focus on the altimeter and the clock’s sweep second hand while completely ignoring the airplane’s stall horn. The airplane will most likely stall while this person sits there pulling the yoke full aft as if he’s trying to reel in the biggest fish in the ocean. What he won’t realize is that he’s the one on the hook at the other end of the line. This experiment demonstrates the effects of state dependent learning. It also demonstrates why unrealistic stall training prevents some pilots from developing the reflexive stall recognition and recovery behaviors needed for safe piloting.
Traditional Stall Training is Only Partially Effective
Traditional stall training typically doesn’t involve the highly aroused emotional state that inspires the fight, flight or freeze response. After all, flight instructors do their best to relax their students during stall recovery training. We speak of stalls in soft, gentle tones during the pre-flight stall briefing, avoiding terms such as near-death experience and the afterlife. Then we gently demonstrate stalls all the while ensuring that our students don’t become frightened and attempt to crawl underneath the front seat—the traditional “emotional destination of choice” for some students during stall practice. We go out of our way to make sure our students are relaxed during stall practice. Most of the time they are, so is it any wonder that a typical private pilot might be subject to the limitations of state-dependent learning? What we don’t do is complement our traditional stall training practice with techniques that incorporate the mental state of induced-panic. Yes, a competent, capable, mature and wise instructor can and should offer this type of training at the appropriate time during student development.
Even if students aren’t lucky enough to be offered stall training in realistic conditions, it’s still possible to train them to avoid most accidental stalls. How? The answer is repetition, repetition and more repetition. Any deficiency in state-dependent training can often be compensated for (to a great degree, at least) by increased exposure to the pre-stall environment and actual stall practice (i.e., repetitive full-stall practice, not imminent-stall practice). Think about this from the perspective of landing an airplane. A pilot’s basic pull-aft-to-flare elevator reflex doesn’t necessarily diminish with time (it might, however, need refinement over time). Why? Because pilots reinforce this reflex at least once on every flight. The continued reinforcement of basic landing skill ensures the permanence of this behavior. On the other hand, pilots don’t practice stalls on every flight. In fact, it’s doubtful that most pilots practice stalls after private pilot certification. If stalls are practiced, this usually occurs once every two years during the flight review. What makes matters worse is that most pilots seldom acquire sufficient stall recognition and recovery practice during private pilot certification. No, I’m not kidding. Read on.
How Much Stall Experience Do You Actually Have?
I’m sorry to say that a newly certificated private pilot might not have the quality or quantity of stall training needed to recognize and recover from an accidental stall. Oh sure, pilots will have the skill to recognize and recover from a stall in the highly choreographed environment of the practical checkride, but this demonstration has little if any relevance in terms of recognizing and recovering from real-life, unanticipated stalls. Recently, I conducted an examination of how much stall training pilots actually have. The results were not encouraging.
The evidence indicates that most pilots have less than two hours of actual stall practice (defined as the time beginning with the aft draw on the elevator to initiate a stall, and recovering back to a non-stalled attitude, and doesn’t include the time for clearing turns and setting up the stall). And I'm being quite generous with the time estimate here. I suspect it's more like 45 to 60 minutes instead of two hours of stall practice. Furthermore, the time a primary student spends recognizing the first hint of a stall warning (i.e., horn/light) and responding with a release of yoke pressure, accounts for about 5-10 minutes of a newly rated private pilot’s total stall experience. Yep, this is the time actually spent in a stalled or near-stalled condition and it isn’t much! Despite our natural tendency to overestimate our stall training experience, most careful readers will admit that they didn’t have much more stall training experience than that listed here immediately after private pilot certification.
Given the small amount of actual stall training that private pilots receive, they aren’t likely to have the repetition necessary to build strong stall recognition and recovery reflexes. This deficiency becomes even more obvious when you consider that during the 70 hours of typical training it takes to earn a private pilot certificate, flight instructors can still be heard to say, “More right rudder!” Isn’t that interesting? In 70 hours of actual practice, students still have a hard time building the rudder and aileron coordination reflex. It requires a real stretch of the imagination to assume that pilots can be conditioned to recognize and avoid the accidental stall at the first peep of the stall horn with less than two hours of actual stall practice and less than 5-10 minutes associating the stall horn with the need for reducing the angle of attack. Your hair gets more conditioning than this.
So What Does All This Mean?
The FAA and ACS committee presided over the removal of the ACS requirement to demonstrate flight at minimum controllable airspeed from both the private and commercial practical test. They did so to prevent the stall horn (or light) from being associated with anything other than the need to apply stall recovery procedures. The FAA believes that pilots who are trained to apply stall recovery procedures at the first peep of a stall horn are better prepared to avoid real-world unanticipated stalls. With limited stall training times and the highly around mental states associated with unanticipated stalls, the FAA and ACS committee’s assumption betrays a very deep misunderstanding of how pilots learn to recognize and recovery from accidental stalls.
Let’s also remember that the FAA and ACS committee removed the “full stall” requirement from the commercial pilot Airman Certification Standards (I have no doubt that this will eventually occur at the private pilot level, too). This suggests that average commercial pilot trained today might not have performed a full stall since his/her certification as a private pilot. How would you like to be sitting in the back of an airplane with someone at the flight controls who was trained to these “FAA and ACS-committee endorsed” standards? I know I wouldn’t. Without experiencing all the basic pre-stall clues associated with full stalls, most commercial pilot applicants will be less likely to recognize the onset of a full stall much less apply appropriate recovery procedures should one wing stall before the other (the onset of a spin).
Of course, the reflexive response offered by the FAA and ACS committee to these musings is that flight instructors can still teach full stalls to their commercial students irrespective of what the ACS requires. Unfortunately, this statement also betrays a deep misunderstanding of human nature and is the "ultimate cop-out" for having to deal with flight training concepts that are harmful to aviation. While it’s true that CFIs can provide this additional training, this doesn’t mean they will. In fact, most instructors teach only what the ACS requires them to teach (this is especially true given that the ACS not only looks like a syllabus, it's also being used as a syllabus—instead of only a "testing" standard). The fact is that many instructors are not voluntarily teaching essential skills beyond the ACS. Were this not true, then 40%-50% of all aviation accidents wouldn’t be based on a lack of stick and rudder skills (skills CFIs are clearly not teaching or at least teaching adequately). Please remember that the FAA removed steep spirals from the Commercial Practical Test Standards for a period of over 10 years, then reinstated the maneuver. Upon reinstatement, very few instructors remembered how to perform this maneuver (and it’s an essential maneuver for all pilots to learn whether or not it is on the practical exam).
Perhaps the ultimate irony here is that the FAA (as per FAR 121.423) is now requiring airline pilots to do full stalls during initial and recurrent training, while not requiring commercial pilot applicants to demonstrate full stalls on their practical checkride. All I can say is, “I think I’ll miss my eyebrows?”
*The first peep of the stall horn, as you know by now, doesn’t represent a stall. It represents the airplane’s proximity to a stall. Nevertheless, the FAA speaks of the horn as a “stall warning.”