Bruce Landsburg at the AOPA Air Safety Foundation writes in "Spinning In" on Feb 2003: "The FAA's Small Aircraft Directorate...looked at more than 1,700 stall/spin accidents dating back to 1973 and concluded that 93 percent of those airplanes were at or below pattern altitude — too low for spin recovery...." A good many pilots might say... "they got too slow". But, I'm not so sure that's correct. Consider, please (and remember: I AM NOT A CFI)...

Is it “Too Slow”? ... or... Could it be “Too Fast”?
I have a personal theory that we are flying TOO FAST in the traffic pattern. I believe that what is killing pilots ... and most of these are very experienced pilots ... is NOT that they are getting too slow.

Instead, it may be that they are very aware of the G-Force vs. Angle-Of-Bank curve, and so they pad the book speeds [5kts for gusts, two more for one’s wife, two more for the kids, six for circles, ten for Telluride, etc.] to the point that they are much too fast when they initiate the downwind to final series of turns.

Now that may be fine if we widen out the pattern to fly a wider ground track, but in the case where (by habit, perhaps?) we keep a close-in distance from the runway, we set up a possible overshoot, especially during the turn to Final. Any extra speed results in a much wider-than-normal radius of the turn.

Then ... an unhealthy human tendency to “get there” by banking a "just a bit more" and pulling up-elevator for the runway results in overly steep banks and an accelerated stall at low level. An unloaded stall may well be recoverable, even at low level ... but a G-loaded stall won't be.

What do you think? Does this theory make any sense to you?
Please email your thoughts on this.

But suppose the pilot were more precisely aware of how close s/he was to an incipient stall? An Alpha display can tell us exactly how much margin we have. Then, having that assurance and comfort level, we can FLY SAFELY SLOWER and the turn radius decreases significantly.

Two displays can help us with that: the Mechanical AoA display is very simple and entirely mute. While it is true that one must be looking at it for it to have any benefit, it's a great teaching device; it helps us "see the air". The Enhanced Legacy AoA Display is aerodymanically similar, yet much more capable; and it talks to us much as the Pilot Not Flying might, even if we are looking out the window. Nice.

SETTING UP the MECHANICAL DISPLAY. I suggest that you calibrate it so that the Greek letter Alpha (at the Red/Yellow transition) is set at a small margin only very slightly above stall (~1.2Vso to ~1.3Vs.). THAT Optimum Angle of Attack (OAA) gives you a repeatable known margin, a repeatable known buffer, and at THAT Alpha point...you will not stall.

Needle high? Push it down.
Needle low? Pull it up.
(except when inverted, of course)

So that means your very Short Final segment will be flown in the red zone above OAA, with a smaller stall margin. That's surely exactly the way you "fly short" now. Could you shift the probe, later on ... as you get to know the device? (Perhaps even set very close to stall, for a very specific purpose, such as in very tight bush pilot Ops?). Of course. But whatever target you choose, be sure to placard the setting, so the next pilot will know what Alpha it's calibrated to.

SETTING UP the ENHANCED LEGACY DISPLAY ("Enhanced" means it includes an Aural Early Warning by "Slow Sarah" and the "Deedle-Deedle" tones) . This is a more sophisticated device, designed for early stall warning as well as precision flying. I think of it as a real-time Vref calculator. The reference ... Vref ... is the green donut. The display is arranged fairly intuitively - a bifurcated donut in the middle ("ON SPEED; at Vref"), an amber chevron on the bottom ("You're OK, just a bit faster than Vref") and a red chevron on the top ("Danger Zone"). [Here, the display is in Self-Test; in flight, we only see one or two segments.]

The Legacy AOA can help us when we are not even looking at it. It can alert our distracted brains with an aural "Getting Slow" and if that alert should occurs at 30% or 35% above stall, that's close enough. Later, when deep into the near-stall, we'll hear a lady's voice "Too Slow"..."Too Slow"..."Too Slow"

We suggest that you calibrate it so that the Green Donut is set at a good safe margin above stall (~1.2Vso to ~1.3Vs.). THAT Optimum Angle of Attack (OAA) gives you a repeatable known margin, a repeatable known buffer, and at THAT Alpha point...you will not stall. It also makes the green donut into a really good Vref target for manevering.

In my King Air, I set my electronic "AoA Cruise" calibration point to the top end of the Flap Arc. This Alpha point keeps the display dark in high speed cruise (140-210+KIAS ... when I don't need it) and it also compresses the range of each Legacy AoA light segment, making the device more precise, and easier to fly. In my ~270KTAS King Air, the Legacy ambers only comes alive at the top of my full flap range, which gives me a green donut at a range of 108KIAS to 100KIAS, wings-level. There is no magic in that choice, nor is it "right" or "wrong"; it's simply my preference.

How to FLY The AoA? For me, I just think of...and use...the AoA dislay as a real-time Vref calculator. Especially in a banked turn, or during a max-effort landing, I'll glance at the AoA display, quickly noting my Airspeed fast/slow vs. the Vref Optimum Alpha. I'll perhaps also set in a correcting pitch input so as to re-center the needle/donut on the target OAA, and then go back to and use the primary instrument, the ASI (while staying at that bank angle) to retain the "sure thing", the assurance, that the buffer is available. So: the ASI is always the primary instrument; the AoA is the Vref calculator. Does that logic appeal to you?

But, if I change the bank? I'd just re-check the AoA, and re-set my mental ASI target ... AirSPEED is the certificated primary indicator; AoA is only advisory. That's important.

Simple enough. Cross-check AoA with Airspeed as the primary reference. Works for me. But if there is a better way to fly Alpha, I'd sure like to learn about it.

An Example: Here's a slightly different take on using an AoA, even a very simple device, as a reference for certain speeds, such as Best Glide and Best Endurance

David F. Rogers is a PhD, ATP and Professor of Aerospace Engineering (Emeritus) at the US Naval Academy in Annapolis, MD. Dave has been greatly helpful to us and our Alpha project. In late Dec 2011, on the Beech Owners' List, he was explaining that... "...there are three angles of attack that are independent of density altitude and weight. Those angles are: 1. Stall 2. Best glide 3. Minimum power required (minimum sink / maximum endurance) "Fly the Airspeed for best glide and you will be at the best glide angle of attack. "The Airspeed for minimum power required/minimum sink (L/Dmax) is 76% of best glide speed. Fly that Airspeed and you will be at the angle of attack for minimum power required." Old Bob Siegfried (Bonanza owner, retired UAL 747 Captain) then asked: "... how do I know when I am at the proper speed?  It seems to me that if we had a good Angle of Attack instrument [in our light aircraft], the rest would be easy. Marc interjects, from Canada: "Doc Dave was agreeing with you, Bob. He [was assuming that we already have an AoA installed and he] suggested that we ... fly the proper 'speed for the weight' airspeed for Best Glide and then record that AOA point; then do the same for Best Endurance. Once you have [found] the corresponding AOA, you would thereafter not need to know the weight and could just fly the AOA [target]." ... and Dave Rogers replied: "Exactly. This works because the angle of attack is independent of density altitude and weight. Do it once accurately, mark the [Glide, Endurance] angle of attack on the gauge and you are done. "So ... If you have an angle of attack gauge ... " 1. Look up the value in the POH for best glide speed. It will be given as an indicated or calibrated airspeed in the emergency section. "2. Then get in the airplane and climb to some convenient altitude. Configure as the POH suggests, then establish best glide speed - use the value in the POH. I suggest using idle power in a glide. "3. Mark the angle of attack gauge at whatever indication is displayed. "4. That is the angle of attack for best glide at any weight and any altitude. "5. That is all. You are done. "If you want the angle of attack for L/Dmax (maximum endurance / minimum power required) then calculate that value as 0.76 times (best glide speed) and repeat Steps 2 & 3 above. That is the angle of attack for maximum endurance / minimum power required at any weight and any altitude." For much more on this, please see a technical reference in which, according to Bernard (Bud) Carson, another engineer at the USNA, the maximum duration speed is calculated as V-L/Dmax (best glide speed) divided by 1.316. So: 1/1.316 is 0.76 or 76%V-L/Dmax. He also defines a faster Optimum Cruising Speed ("Carson's Speed") in terms of the maximum speed per gallon as being V-L/Dmax times 1.316. Walter from Germany suggests: "... assuming a Fuel Flow instrument is connected to a GPS and shows NM/Gal, and also assuming a no- wind day...then play with the power to achieve a maximized NM/Gal. That will be equivalent to a Max L/D for that given weight. Then read the AoA indication; it then becomes a valid L/Dmax AoA point for all weights.". Bingo! It avoids the math, but it works! John Collins concludes: "...if best glide speed is 105 Kts, then max. range speed is 105 Kts, and maximum duration speed is 105Kts X .76 = 80 Kts, and optimum fuel flow/knot speed (Carson's Speed) is 138 Kts..."

NEVER FORGET that a AOA Display will NOT improve any aircraft's performance, NOT EVEN A LITTLE BIT! An AOA WILL PROVIDE much greater comfort and security by letting an aviator KNOW FOR SURE what stall margin remains available...and with that knowledge, it becomes a lot safer (or: more secure, comforting, less risky...) to approach the limits of the aircraft's performance envelope. An AOA can make a good pilot better and enable her to fly more precisely, but AOA data won't reduce the POH-specified landing roll by a single foot, nor increase the range by a mile, nor increase the rate of climb by 1 FPM, etc. ....

Disclaimer: The information provided in this website and AoA/Aircraft portion is provided free of charge. All information provided on this web site is provided 'AS IS'. No guarantee is provided for the accuracy of the information or the application of the information provided herein. I accept no responsibility or liability with regards to the accuracy or currency of the information provided. By using, reading or accessing this web site, you agree to be the user of the information provided. The user accepts full responsibility for all information provided. Although I try to keep the information on this site as accurate as possible, there is no guarantee that the reference materials or the material on this site is correct. This information is provided entirely in the spirit of helpful cooperation.

Incidentally, here's a summary of regulatory guidance clearly indicating that installation of an independent secondary advisory AOA like the "Legacy" is a "minor alteration" on the vast majority of light general aviation aircraft.

Newly-published magazine articles, Spring & Summer 2011

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