The Desanctification of AoA


Because I lack the common decency to avoid saying I told you so, this is an I-told-you-so blog. Well, sort of, because what I thought or maybe predicted would happen didn’t happen. At least not in the way I might have imagined.

About five years ago, there appeared on the market a handful of angle-of-attack indicator products. I’m not sure why the timing unfolded as it did, but I think it might have been a confluence of several events. One, the technology became cheaper and easier to deliver to market, including displays, envelope protection was becoming a thing, the FAA relaxed the approval process and we were starting to talk about stalls as a persistent accident cause. Wait, what the hell am I saying? When have we not talked about stalls as a persistent accident cause? Wilbur and Orville even had a name for the spin that follows: well drilling.

Thanks in part to marketing fluff, in part to appreciative press reviews and yes, a dose of unfounded expectations, AoA suddenly became the galloping knight that would banish stall accidents or at least reduce them. If the promo didn’t say that in so many words, it encouraged the belief. It was just a good thing to have, many seemed to agree. Not me.

At the time—and still—I think the only way AoA indicators will make a dent in GA stall accidents is if the technology is thoroughly integrated into a persistent, industry-wide ab initio training doctrine. And even then, it risks being just another hey-look-at-me light among many that seem to be multiplying on the typical glass panel.

I could never understand why people reasoned that a pilot too clueless to sense impending stall in the usual ways—control feel, aural cues, airspeed, flight attitude—would somehow miraculously have the cognizance to interpret yet another beseeching indicator vying for his task-saturated attention. I wouldn’t be surprised if the very pilots most in need of this technological crutch are the very ones least capable of reacting to it.

Turning my attention to the Boeing 737 MAX—you knew I would—a similar sort of hubris may have been at work. AoA data has been available in airliners for decades and Boeing has as much experience with it as anyone. So much so that it apparently felt confident enough to use a single AoA vane to drive the MCAS autotrim system that was, inexplicably, capable of applying full nose-down stabilizer trim in certain circumstances that proved not that rare. Boeing has since seen the flaw in that approach and has defanged MCAS’s aggressive trim and plumbed what’s left of it into both AoA vanes. If the lesson sticks, designers will tap the brakes next time they think single-sensor input is a good enough in a world driven by 10-9 expectations.

As Boeing’s travails were unfolding, Cirrus had its own night in the barrel with the AoA system on the VisionJet. Again, faulty data from the vane could inappropriately trigger the airplane’s stall-protection system. Although not as aggressive as Boeing’s system, Cirrus was worried enough to ground all the VisionJets until the vanes could be replaced or repaired. Cirrus says the airplanes are just getting back into the air now. But they still rely on that single vane, a somewhat delicate slice of metal exposed to the errant elbow of the fueler or curious bystanders.

The Luddites among us will—not without reason, perhaps—decry these developments as yet another example of how automation is displacing the basic understanding of how to fly an airplane. I wouldn’t go quite that far because I think envelope protection is fundamentally a sound idea. The technology is there and it works. Why not apply it and use it?

But then we get a little too clever by half, as the Brits might say. The expectations of what this tech might achieve are overinflated as evidenced by Boeing’s conviction that the pilots didn’t even need to know about it and the GA expectation that sure, an AoA indicator on the panel might tamp this stall thing down. In Boeing’s case, the company apparently thought that even though the typical 60th percentile pilot needed a little stabilizer nudge to make the airplane feel right, he or she would nonetheless have no problem at all sorting out a single-side stick shaker with the electric trim running intermittently amok and stick forces escalating to the Charles Atlas range.

I have no objection to AoA in light aircraft, but I have no great expectations for its impact, either. In flying these systems from time to time, I have found just one killer app for AoA: Flying max-performance short-field approaches and landings. You can just notch the airplane right into the perfect angle and ignore gyrations in airspeed. When you get the knack of it, the performance uptick is quite impressive. If I were going to install one, that would be the reason.

Otherwise, on some days and maybe even for good, I would like to declare a moratorium on industry hand wringing over stall accidents and further things we might do to prevent them. If you can levitate the damn airplane off the runway, you can surely figure out stalls and how to avoid them without a 10-hour block of classroom instruction. Go out in the airplane and do it. You don’t need an instructor. Just go fly the stall series and see what it looks, sounds and feels like. Fly departure stalls and turning stalls and accellerated stalls. If that proves boring, you’re probably stall proof. You could stick an AoA on the airplane just for the entertainment value.


  1. We installed an AoA sensor in my club’s Dakota a couple years ago in an attempt to get members feeling more comfortable landing the plane (which can be a bit nose-heavy), more than to prevent the stall-spin accidents we were not having. It appears to be finally having a positive effect in getting members more comfortable with the aircraft. The only downside we have seen is that you need a calm day to properly calibrate the sensor, so ours currently reads a bit on the conservative side (meaning, landings are a bit faster than necessary). Even so, I think it’s a good aid to show pilots that it’s okay to fly final a bit slower than they’re used to, and that they can get the same results without an instructor on board to tell them if they’re getting a little slow because the display is fairly intuitive to interpret. I was never under the impression that these devices would dramatically lower the stall-spin accident, but as a tool for visually showing what relationship angle-of-attack, load factor, and airspeed have on each other, it can be valuable if used properly.

  2. To me, angle of attack is a very valuable tool, so long as you use it as intended. I’m speaking of small airplane AOA, not commercial aircraft (different animal). As with most tools, one should understand what it will do, and what it won’t. It’s kind of like the perception that tower controlled airports are safer than uncontrolled fields. AOA won’t take over the plane and rescue you from poor flying technique. How many YouTube videos have you seen where a pilot lands gear up while the gear up alarm wails in his ears? Warning devices only warn if you listen.

    As you said, AOA is great for short field work. However, if you will use it, it makes all approaches better by getting the pilot’s attention off chasing airspeed. It can also improve cruise performance and optimize max performance climbs. But, you still have to learn its capabilities and incorporate them into your flying skill set. It’s A tool, not THE tool. Good article, well timed.

  3. AoA is just one more step to removing the pilot from the cockpit (Autonomous Aircraft). The more information you feed an autopilot system the more capable it will become.

    Next year at this time, because of these 737 Max accidents FAA approved software fix, we’ll see much more talk about eliminating the Flap Operator (FO) in the right seat. That’s my prediction anyway.

  4. We installed an AOA called a “Lift Reserve Indicator” in our missionary C182. It’s purpose was exactly what the name implied…at any given airspeed, weight, bank angle, and G load, you knew how close you were to a stall far more precisely than indicated airspeed, sound, feel, buffet, etc. The instructions said to completely cover the airspeed indicator during calibration as one’s normal tendency to visually cross check an airspeed readout with the current feel of the airplane would prevent you from ever get to the very ragged edge of the performance envelope. Since we had wing extensions, modified leading edge cuff, bigger engine, and a host of other standard mods for the mission modified 182’s, without covering it up, indeed, that was the case. When we did cover it up, and literally depended on sight picture, sound, feel, and slowly but deliberately reaching for the very edge of the performance envelope, once established and calibrated, this was not only a handy gizmo, but a bacon saver.

    As Paul pointed out, it’s usefulness in a STOL contest or when trying to stick your Super Carbon Over-The-Top VG’d, winglet, Turbocharged, GAMI equipped, Monte Barrett, massaged TIO-540 with Top Prop, Unicorn Cub onto a 50ft long gravel bar with a 10 knot tailwind, doing this on purpose with scads of previous practice is a neat gizmo to physically confirm all the tactile information.

    However, when leaving a mission strip, with a cabin full of babies, sick and/or injured, moaning/screaming people, with a sweaty, over-worked pilot at the controls, on a hot day with some serious obstacle negotiations required for a ‘normal’ departure, this Lift Reserve Indicator/AOA allowed you to safely fly the airplane fully to it’s limits. We did not encourage pushing every flight to it’s absolute limits promoting some sort of religious aerial cowboy image. But in the course of flying in third world countries, it made the difference between hoping your pre-flight calculations and decisions were right vs knowing at a glance what was left of the flight envelope.

    Properly used, precisely calibrated, and properly trained in its usage an AOA is an amazing device for improved situational awareness, not just for competition, but when you are tired, in cockpit overload, or meeting an emergency and knowing at a glance just what is left in the airplane can be a lifesaver.

    Otherwise it is just another set of colored LED lights added to one’s latest gee whiz panel.

    • I admire your viewpoint from the perspective of a seasoned pilot, wit in comparing real life experiences to add-ons proven in large aircraft from commercial to military but of little importance to small engine aircraft steered by experience with more distractions than anyone could ever imagine assuming their ‘superior’ skills at so called multitasking while driving their car, texting, talking, gps navigating and tuning in a favorite radio station. Perhaps I have a myopic view since helicopters can’t use an AoA device………….

  5. I flew a fighter in the 70s that introduced me to using AOA as a primary envelope reference. Since the F111 had no felt stall warning ( other than horns, stick shaker, stick pusher, etc)and no recovery one kept a close eye on the AOA. My first civilian flight instructor in the early 60s taught me that you can stall an airplane at any airspeed but not at “0” G. He had a 4 digit CFI number so I figured he was smart and lucky. I learned early to unload the airplane and fly the airplane. So far so good.

  6. MCAS was designed to avoid excessive pitch up due to the new design. A 737 is not going to stall on level flight. Why was MCAS activation never limited by the attitude indicator? That would be pretty easy to program and you have redundancy from two different instruments.

    • Can’t stall a 737 in level flight?
      In level flight at flight idle at a safe altitude, slow to stall speed plus 20 kts.
      Pitch the nose down 30 degrees.
      Let the airspeed build to a scary value.
      Quickly but smoothly pitch the nose up to zero degrees pitch.
      Have a nice day!

  7. “A 737 is not going to stall on level flight.”

    No? I can stall my PA-28 in a level flight attitude. Just descend power-off and then pull back aggressively enough and I’ll get to a level flight attitude at the stall break. That just goes back to basic aerodynamics in that you can stall a wing in any flight attitude and airspeed.

    By the way, what happened to comment bylines? It looked like the first couple responses had one, but now none of them do.

  8. Paul. I love your wit an writing style!

    As for the pilots you mentioned there is an old saying “you can’t make something idiot proof”

    I fly with AOA all the time and no longer rely on indicated airspeed, especially during landing.

  9. Paul..
    The comments above, while polite and almost reverential, show your presentation is clever as always but not really well grounded. You use all manner of references that are somehow related to AOA but ultimately use a negative to try to prove a positive about the importance of training and practice. The Boeing Max737 and Cirrus history and talk about the Luddites do not really speak to the subject at hand. Logical fallacies abound.

    If the military uses AOA successfully for decades and real world GA users benefit, AS CLEARLY REFLECTED IN THE COMMENTS ABOVE, how can it be that those “Fluffy” AOA devices only have one “killer” application that actually creates a safer environment. The intended pun was not funny.

    Good to see emphasis on training and practice but the presentation would better serve by use of direct positive information that reflects actual pilot experience. Want proof?? Just read the above comments from your readers.

    “”Properly used, precisely calibrated, and properly trained in its usage an AOA is an amazing device for improved situational awareness, not just for competition, but when you are tired, in cockpit overload, or meeting an emergency and knowing at a glance just what is left in the airplane can be a lifesaver.”” That is NOT FLUFF.