35
$\begingroup$

Is the correct stall recovery action somehow counter-intuitive? I've read about crashes like Colgan Air 3407 where pilots experiencing a stall have done the exact wrong thing and pitching the nose up. It makes me wonder if pitching down does not feel right to a person.

Not being a pilot I can only relate it to driving a car. You're taught that to recover from a skid you should steer into it. An inexperienced driver will be in a turn, feel a skid and turn the wheel further into the turn resulting in loss of control. You have to teach yourself to overcome that instinctive reaction and remember what you were trained to do.

Is the reaction to a stall similar? When you feel the a/c lose lift and start dropping is it an instinctive reaction to try to climb? You're going down and you want to go up so you pull back. Do you have to teach yourself to overcome a reflex to use proper recovery technique?

If so do airline pilots practice stall recovery in a simulator? I know it took me a bit of practice in an icy parking lot to make skid recovery come naturally.

$\endgroup$
  • 4
    $\begingroup$ "You're taught that to recover from a skid you should steer into it"... really? AFAIK not so in Italy. Safe driving is not taught in order to take the driving license. They just teach you how to accelerate/brake, turn, change gears, park. Hopefully pilots do more training than that. $\endgroup$ – Bakuriu Jun 10 '15 at 11:29
  • 3
    $\begingroup$ No one teaches you that when taking driving lessons. Just if you go for an advanced driving course, that's the action they teach you there. $\endgroup$ – Alexus Jun 30 '15 at 23:22
30
$\begingroup$

The correct way to recover from a stall is counter intuitive, not because pilots are trying to climb, but because the nose of the airplane drops due to the loss of lift and aircraft design. 99.999% of the time (when the aircraft is not in a stall), if the nose drops, you simply pull back in order to raise it and this muscle memory is built over time.

Unfortunately, if the aircraft has stalled, pulling back will only worsen the situation and you need to push forward in order to gain sufficient airspeed for a recovery.

Yes, stall recovery is taught in both primary training, and during simulator training for pilots, although not typically to a full stall in the simulator. Instead, the aircraft is slowed to the first indication of a stall which may be a stall warning system instead. At this point they are expected to apply the correct stall recovery techniques recommended by the manufacturer / their SOP's.

There is a fairly large difference between recovering from a stall in a training environment because you know that it is coming and already know what you are going to do when it happens. A large part of stall training is for stall recognition so that hopefully if it were to happen outside the training environment, the pilot will recognize the warning signs before it happens and can apply the proper stall recover technique before the aircraft enters a full stall.

Unfortunately, out "in the real world" most unplanned stalls that occur happen because the pilot is distracted by something else and they aren't expecting it. That lack of anticipation sometimes causes them to fall back on muscle memory and pull up just because the nose fell without realizing what happened. This can be more likely when the stall doesn't happen quite like it does in training. In some situations there may be fewer warning signs, or a component of the stall warning system isn't working as expected and can delay the realization that they are in a stall.

For more information on what a stall is and why pilots practice them, see another question that was asked before here: What happens when an airplane stalls and why do pilots practice it?

$\endgroup$
  • $\begingroup$ Apologies for possible a dumb question, but are you sure that pilots in training are told what simulation they are going through before it occurs? That seems ridiculous. $\endgroup$ – Scott Jun 9 '15 at 22:25
  • 4
    $\begingroup$ @scott yes. Stalls in sim training are purposeful, briefed maneuvers demonstrated to show proficiency. The only other way they would happen is accidentally through pilot error and in the sim environment that is a ticket to more training. To be clear, the sim instructor / APD will say e.g. "show me a right turning stall" and you will demonstrate that maneuver (or whatever variation he asks for). $\endgroup$ – casey Jun 10 '15 at 2:15
  • $\begingroup$ Is it possible in a simulator to accurately simulate what a stall feels like? Some of the answers here are saying they simulate an 'impending' stall, such as warning horns. I doubt if very many pilots have experienced an actual stall in an airliner. It appears that the AF 447 crew were in a stall for 4 minutes with the stall warning going most of the time but never recognized what was happening. They disregarded the warning system. Apparently their training in stall recognition failed them. $\endgroup$ – TomMcW Jun 10 '15 at 4:22
  • 1
    $\begingroup$ @TomMcW: Simulator can't accurately simulate the drop when the aircraft accelerates downward because of loss of lift, since inertial forces can't be simulated. But it can simulate the buffeting that precedes it and the stall warning and it can simulate any changes in attitude. $\endgroup$ – Jan Hudec Jun 10 '15 at 6:42
  • 1
    $\begingroup$ @TomMcW Actually, one of the contributing factors in the AF 447 accident is that the stall warning was NOT going most of the time, and was inhibited due to the extremely slow airspeed (it was a design decision made because an airliner "can't" be flying at such a slow airspeed). It came on in the beginning but then went off, and was one aspect that led to the confusion among the pilots. $\endgroup$ – Lnafziger Jun 10 '15 at 15:27
17
$\begingroup$

There are a few issues. First off everyone that has a pilots license (in the US at least) has stalled an aircraft (generally a trainer), its a requirement for obtaining the license. Commercial pilots also receive spin awareness and recovery training.

It should also be noted (as its sometimes overlooked)

A Stall can occur at ANY airspeed

A stall by definition is when there

...is a reduction in the lift coefficient generated by a foil as angle of attack increases

You are correct that sometimes people pull back on the controls (nose up) when a stall occurs. This is why stick shakers and pushers exist. Its not very instinctive to push the stick and subsequently dive the airplane towards the only real obstacle, the ground. The problem, sometimes is recognizing that the aircraft is stalling (one of the issues in the Air France 447 crash) failure to do this can lead to the pilot making the wrong corrective action because they don't know what is really happening to the plane.

In the case of 3407 it seems the pilots first mistake was not maintaining proper approach speed. The second mistake was not applying full throttle during the recovery and pitching the aircraft up to much. This put the plane into the stall which they could not recover.

Although only touched on in the Wiki article, the pilots did report Ice (although de-ice was activated) it should be noted that ice build up on the wings alters the stall and flight characteristics of a plane. On a similar note, both wings often do not stall at the same time. The drop a single wing during a stall can also lead to counter control that causes issues.

$\endgroup$
  • 1
    $\begingroup$ I think you're on to something with the wing drop or other aerodynamic effects. Most pilots have no problem recovering from a straight and more or less level stall-horn warning. It's when you get weird behavior from your aircraft that instincts cross you up. Wing drop is a good example, trying to counter it with aileron will drop the ailerons on the stalled wing causing more drag and further pushing it into the stall and impending spin. Likewise, an unexpected nose-drop can cause the instinctive reaction to pull back. $\endgroup$ – falstro Jun 8 '15 at 20:09
  • $\begingroup$ Although I am not an official on the matter my reading of the accident leads me to feel that (although not the only factor) ice may have played a roll in what happened to 3407. $\endgroup$ – Dave Jun 8 '15 at 21:52
  • $\begingroup$ To clarify here, there are usually a multitude of factors contributing to stall problems in commercial aircraft. In non-commercial aircraft the airfoil could be at an extreme angle but you could have more than enough airspeed to compensate for the given airframe -- like a stunt pilot doing doing a loop. In training the instructor stalls by slowing down and pulling up the nose when you're plenty high enough to recover. But in a commercial craft, the pilot could have more than enough airspeed and a normal attitude but something else is compromising the airfoil (landing gear, ice). $\endgroup$ – Dave Kanter Jun 10 '15 at 17:38
5
$\begingroup$

Just to second Dave's answer, typically a pilot who pulls up in stall does not realize that they have stalled and are just blindly reacting to a loss in altitude. To answer your specific questions:

Do you have to teach yourself to overcome a reflex to use proper recovery technique? Not really. Most dangerous stall situations are confusing enough that there is no "reflex", it's just a question of whether the pilot is calm enough to use their training and knowledge. An untrained person will just freeze or manipulate the controls wildly, there is no "reflex". Most fatal stalls occur close to the ground where even the correct reaction will come too late or in low-visibility conditions in which the pilot cannot see the horizon. It is pretty rare for a pilot who can see the horizon and has plenty of altitude to stall all the way to the ground.

The main benefit of training is not to overcome a reflex, it is to learn to react quickly to the situation, so you spend less time figuring out what is going on and react faster. Every pilot knows to push the stick forwards in a stall; the question is how fast do they realize they are stalled, and how fast do they react once they realize that?

...do airline pilots practice stall recovery in a simulator? Yes.

$\endgroup$
5
$\begingroup$

How unfortunate it is called "stall training" because I have never taught any of my students how to stall an aircraft! I teach them to recognize the impending stall and how to fix it before the stall happens. I show them a full stall and teach them how to recover. It should be renamed "stall recovery training" I try to surprise train also, during slow flight I keep stating they can fly slower and slower, I keep pushing to get them to fly slower....suddenly the plane drops out of the sky in an unexpected stall and they usually freeze for a couple of seconds then they recover. Or during unusual attitude I will turn the controls over just as the plane stalls. Point is, I focus more on recognition and recovery, than the stall itself.

$\endgroup$
1
$\begingroup$

As a pilot of a recreational aircraft (very small aircraft) I have become accustom to the feel of the aircraft in a stall. When the aircraft stalls, it drops suddenly. This is the same feeling as being in a rollercoaster that has just gone over the top and begun to fall.
My instinctive reaction in this case is to push the nose down. As soon as I have recovered from the disorientation of the stall (or turbulence which can cause the aircraft to drop momentarily), I can make better decisions.
I am fairly sure (without any research) that a large aircraft would not have this characterisic, and as such, the pilots would not develop an instinct for this.

$\endgroup$
  • 2
    $\begingroup$ A large aircraft will have similar feel, because the wings will loose some lift in the same way. However in large aircraft stall is more risky, so nobody practices stalls in large aircraft for real and simulator can't reproduce the feel well, because inertial forces can't be faked and even full-motion simulator can only drop a couple of feet. $\endgroup$ – Jan Hudec Jun 10 '15 at 6:37
0
$\begingroup$

There is one other thing to consider regarding stall training, namely how applicants for pilot certificates (especially at the Commercial and ATP level) are evaluated on their checkrides, which feeds directly into how they are trained.

The FAA is currently in the process of revamping its certification process with the Airmen Certification Standards replacing the old Practical Test Standards for the "checkride" (i.e. oral examination and flight test) portion of the certification process. However, one of the major differences between the Private Pilot level and the higher levels of certification was that, at the Private Pilot level, the testing standards called for

"[recognizing] and [recovering] promptly after a fully developed stall occurs"

Contrast with the evalution criteria for this maneuver at the Commercial and higher levels, where the applicant is expected to

"[recognize] and [recover] promptly at the “onset” (buffeting) stall condition"

Now, if you've followed the second link, you will also see a note immediately below that states:

Evaluation criteria for a recovery from an approach to stall should not mandate a predetermined value for altitude loss and should not mandate maintaining altitude during recovery. Proper evaluation criteria should consider the multitude of external and internal variables which affect the recovery altitude.

That addition is relatively recent. I don't have a PTS from circa 2007/2008 (when I was going through my own SEL and MEL Commercial training) handy, but I do not remember that section being there. In fact, the way evaluation criteria had evolved "in practice", was that any altitude loss during the maneuver was grounds for failure of that portion of the test.

On the one hand, that led applicants to be extremely proactive and initiate recovery the instant they felt a buffeting or they heard the stall warning horn going off. On the other, it also led applicants to recover by advancing the throttle to full and unloading the wing only the absolute minimum amount needed to avert an immediate stall, preferring a prolonged low-energy state over the altitude loss that a greater degree of unloading would have brought, even though unloading the wing more would have allowed the aircraft to accelerate out of the low-speed regime quicker.

Training is habit-forming (that's the whole point, after all) and that particular habit is now recognized to be dangerous enough that the FAA has both addressed it in the PTS and issued guidance to DPEs on the matter.

The Captain and FO on the Colgan flight, however, did their initial and recurrent training under the older way of doing things and likely picked up some habits that got them through their checkrides but where woefully lacking in a real-world scenario where they fell behind the airplane and found themselves in an actual stall, rather than at the "outset" of one.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.