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-   -   Not understanding AoA indicators... (https://www.airlinepilotforums.com/safety/84956-not-understanding-aoa-indicators.html)

Yoda2 11-15-2014 02:17 PM

Yes James, could you elaborate. In the meantime... I think lots of pilots confuse AOA with deck angle. They don't realize how small the AOA range is in comparison. Further, many students don't understand high speed stalls, or are never exposed to them.

JamesNoBrakes 11-15-2014 03:31 PM


Originally Posted by Adlerdriver (Post 1764512)
James, can you clarify the comparison you're making here? It's probably me - I'm having a hard time putting everything together - the AOA discussion in a descending turn vs level flight, ending up in trees at the end of the runway (approach end/departure end?) and the video.

A descending turn, which is usually done at low power (that's a good indicator right there), is usually at a fairly low AOA if done a any kind of normal speed.

A level turn, which requires higher power, may be done when a pilot is already fairly low on the downwind and base, so he's "saving" for final, but they often start to slow up, put in flaps, etc. This can create an excessively high AOA situation coupled with a turn. The stall warning may help, but this usually comes on pretty fast and some advance notice would be nice.

Then there was the issue of takeoff, when the airplane isn't climbing, but it is in the air and covering ground, there may not be a great appreciation as to where the AOA really is. The pilot may think they have some protection because they are moving fairly fast over the ground, but the AOA is so high and the induced drag so high that it's not going to end well. Maybe with this indication earlier one would fly it to a safe-spot earlier, avoiding trees later.

I think what I'm getting at is that we tend to not appreciate where the AOA is. Plenty of these attitudes are "normal" for flight, I've seen plenty of airplanes in almost level flight "attitude", yet their AOA is nearly off the scale (in terms of right about to stall). That's probably one of the bigger issues with that takeoff video, the plane "appeared" to be in a normal attitude, so the guy probably thought the AOA was "normal". It wasn't.

Yoda2 11-15-2014 03:53 PM

JNB, I get what you're saying for the most part; though if they are in the realms you speak of or are not flying the typical/standard profiles, they better know how to fly an airplane if venturing into those zones. Generally speaking, I don't think, a measurable portion... of newer pilots are satisfactorily familiar with those areas or really knowing their envelope, Etc. I could be wrong but it seemed the FAA started emphasizing LOC not long after the proliferation of TAA... If an instructor has roughly X amount of time to train a primary student and the TAA takes somewhat longer than a traditional 6 Pack, something has got to give. I think where it is giving is in the basic flying skills department. I think the FAA should increase the Min for Private Pilot by 10 Hrs. I know guys that have ferried jet airliners on some real raw data, less than a typical ferry kit. They got where they were going, because someone took the time to teach them to fly... If you want, probably, the best and most accurate summation of the state of basic flying skills; talk to the folks who specialize in tail wheel or seaplane ratings...

JetJocF14 11-15-2014 06:23 PM

[QUOTE=rickair7777;1763166]Adding AoA indication to GA aircraft would be an unnecessary cost, and would further be pointless unless pilots are trained to use

Unlike say a fighter, there are no normal phases of flight in which the AoA data would be interesting for GA aircraft...comply with the AFM speeds and attitudes and you'll never get near the AoA limit except maybe in the flare.

Those are two of the stupidest sentences I've ever read. You really have no idea how AOA works or what it is trying to tell you. To you it's just a gauge with some pretty colors attached to it. Like USMC says, " I'd take a AOA gauge in every airplane that I've ever flown. In fact I plan on installing one in my personal Comanche at my next annual.

cardiomd 11-15-2014 07:59 PM


Originally Posted by JamesNoBrakes (Post 1764491)
I've investigated several accidents where the pilots just didn't realize the AOA they were at. I think there are many accidents where this is the case. I don't think many pilots realize the radical difference in AOA between making a descending power (mostly) off turn descending to base and final vs. doing the same thing at the same airspeed and maintaining level flight. More than one accident I've investigated involved "some flight" but running into trees at the end of the runway. Here is a classic one: LiveLeak.com - (Must Watch!!) Plane crash video from inside cockpit

I think the perception is that due to the forward movement, the AOA must be "ok", but if you were to look at it, it'd be "screaming" the whole time.

Yes, cockpit clutter is an issue, not to mention really using the outside horizon as a pitch reference (rather than just saying "look outside, which can be equally useless as looking inside), but GA accident rates are in the spotlight these days. There's resistance to do anything at any level, whether it's increasing training hours, increasing standards, etc., but this will hopefully have a positive effect, and based many accidents that I've seen, it's likely.

If grandpa can't even figure out how to lean an engine for altitude takeoff, taking off a full 3,000 feet DA above performance limit at max gross weight, and not aborting after the multiple opportunities he had, he's sure as hell not going to learn how to interpret an AOA gauge.

Adlerdriver 11-15-2014 08:45 PM

I disagree with you're assessment that a level turn poses a higher potential threat than a descending turn. I think an AOA gauge would help a pilot in both scenarios, but IMO, more so to the descending turn pilot, especially if he accidentally strays into the high AOA regime.

Originally Posted by JamesNoBrakes (Post 1764538)
A descending turn, which is usually done at low power (that's a good indicator right there), is usually at a fairly low AOA if done a any kind of normal speed.

What is the low power a good indicator of?

From my perspective, the final turn (i.e. a descending turn with power back) is notoriously dangerous because pilots fail to appreciate the lack of energy available in their aircraft. I’ll go out on the limb and suggest that more pilots have lost control of their aircraft in the final turn than on a level turn from downwind to base. Ask that pilot in the descending turn to level off or tighten his turn to prevent an overshoot and the AOA gauge will water his eyes. His relatively low AOA 3 seconds ago is going to shoot into the danger area far quicker without proper power and flying technique than his buddy in the level turn back up at pattern altitude.


Originally Posted by JamesNoBrakes (Post 1764538)
A level turn, which requires higher power, may be done when a pilot is already fairly low on the downwind and base, so he's "saving" for final, but they often start to slow up, put in flaps, etc. This can create an excessively high AOA situation coupled with a turn. The stall warning may help, but this usually comes on pretty fast and some advance notice would be nice.

I don’t get the “saving for final” term. Also, is he lower than he would be in the turn to final? Certainly, excessive AOA and a turn are not a good combination. However, adding a descent to those two is worse, IMO. Personally, if I had to choose between encountering a stall in a level turn versus a descending turn, I’ll take level every time. If you’re turning level at high AOA and you stall at pattern altitude, you have altitude to recover. If your AOA spikes in a descending turn, you don’t, plus you already have a significant sink rate you have to counter as well.



Originally Posted by JamesNoBrakes (Post 1764538)
Then there was the issue of takeoff, when the airplane isn't climbing, but it is in the air and covering ground, there may not be a great appreciation as to where the AOA really is. The pilot may think they have some protection because they are moving fairly fast over the ground, but the AOA is so high and the induced drag so high that it's not going to end well. Maybe with this indication earlier one would fly it to a safe-spot earlier, avoiding trees later.

I think what I'm getting at is that we tend to not appreciate where the AOA is. Plenty of these attitudes are "normal" for flight, I've seen plenty of airplanes in almost level flight "attitude", yet their AOA is nearly off the scale (in terms of right about to stall). That's probably one of the bigger issues with that takeoff video, the plane "appeared" to be in a normal attitude, so the guy probably thought the AOA was "normal". It wasn't.

Are you saying there are scenarios in a GA aircraft that could result in an “almost level flight attitude” with AOA “nearly off the scales” and the pilot would be unaware were it not for an AOA gauge? I don’t have a huge amount of experience with those aircraft, so perhaps you can give me some of the scenarios you are referring to.

That takeoff was a classic density altitude accident. I think his problem was more of energy deficiency than simply high AOA (at least at first). I could be off base here, so correct me if I’m wrong. I assume he attained the normal takeoff/climb IAS when he got airborne. Because of the density altitude, his TAS was higher to produce the same IAS. With little to no excess thrust for his climb, in order to maintain that IAS and the usual AOA at such an extreme density altitude, he had to hold a lower pitch attitude and he was unable to climb. So, when they were muddling along in semi-level flight after takeoff, wouldn’t the AOA gauge (if he had one) have been indicating something close to normal? Assuming he was holding the IAS he wanted (even if that required a descent), wouldn’t he see the roughly the same AOA he saw every other flight at that IAS?

I think, what would have shown him he was in trouble would have been ANY attempt to turn, climb or just increase back pressure on the yoke when his airspeed began to decrease. Now he would have seen that AOA gauge spike into the danger zone faster and further than with those same inputs at lower density altitude – giving him a true understanding of how low on energy he really was. So, to your point, there were definitely times during that flight an AOA gauge would have clued him about how close to the edge he really was. I’m just not sure he would have had an AOA indication that was “not normal” for the entire flight.

cardiomd 11-16-2014 03:37 AM

Uh, wow.

JNB was simply saying you trade a good deal of potential to kinetic energy when descending. I'm sure you remember doing power-off approaches in the pattern and being surprised how much altitude you have to trade during the turn.

This is why the "impossible turn" is difficult for people to judge and people tend to attempt it when not advised.

Agree that high DA crash sequence started way before power was applied. An AOA gauge won't fix stupid.

BoilerUP 11-16-2014 04:03 AM

While I certainly understand considering the value proposition of retrofitting older aircraft....AoA can and should be as much of a "game changa" in GA as avionics-driven safety advances like synthetic vision, or even terrain & traffic awareness devices.

Do you "need" any of them in a piston-driven aircraft? Nope.

Do they provide tangible operational benefits in a variety of situations? Yes.

Do you need training in order to fully take advantage of them? Absolutely!

Timbo 11-16-2014 04:52 AM

Here's one for you guys with light airplanes:

Advanced Flight Systems

About the only place I found the AOA useful was in the final turn in the T38, and in a Scout I was flying for the Sheriff's Dept. where I had to do a lot of low speed steep turns, so the Sheriff in back could take pictures of the grow houses we were circling over.

The airplane had one of those little vanes on the strut called a "Bacon Saver" which was nothing more than a 2" wedge on a card with some red paint in the 'no go' zone.

Because it was mounted on the left strut, it was right in line with my sight as I turned final. I found I looked at that more than the airspeed indicator in the pattern, and certainly while doing the steep turns taking pictures.

But like someone said above, you can't fix stupid. Putting an AOA vane on all airplanes won't stop idiots from killing themselves in airplanes, especially light airplanes, if they try hard enough, they will always find a way!

I tried to find a link for the Bacon Saver, but can't, maybe they are out of business? It was a really low tech, cheap AOA with no electronics required, just bolt it on the strut, but it wouldn't have a place to mount on a low wing airplane, you need the wing strut to mount it on.

JamesNoBrakes 11-16-2014 08:55 AM


Originally Posted by Adlerdriver (Post 1764649)
I disagree with you're assessment that a level turn poses a higher potential threat than a descending turn. I think an AOA gauge would help a pilot in both scenarios, but IMO, more so to the descending turn pilot, especially if he accidentally strays into the high AOA regime.


Here's what happens a lot around here:

People often scout out a landing spot just a few hundred feet above the ground, often with terrain considerations besides trees and brush. Then they start turning to "line up", but because they are already at such a low altitude, they don't descend, but they do start slowing up. This has resulted in more than one landing accident around here, but I think it's equally applicable to guys flying SR22s that get slow making these same turns, often not realizing they have to either get the nose down to speed back up or get rid of the excessive bank and coordination issues, but again, many of those have "spiraled" right in. In the 1st scenario, it's somewhat of a conscious decision to "stay high" and stray into the higher AOA region, but I wonder if those pilots really understand where their AOA is and how much higher it is than a normal descent. In the 2nd scenario, probably not quite as concious, as they get distracted by something like looking for traffic, configuration changes, etc, and don't notice the other warning signs, keeping the nose high while possibly staying fixated on the runway (ever see how a runway is like a magnet for a pilot's head on base? I've witnessed plenty of attitude deviations just due to this)

The other scenario is climbing out, letting the nose get too high, not noticing the decay in airspeed, and a similar result.


From my perspective, the final turn (i.e. a descending turn with power back) is notoriously dangerous because pilots fail to appreciate the lack of energy available in their aircraft. I’ll go out on the limb and suggest that more pilots have lost control of their aircraft in the final turn than on a level turn from downwind to base. Ask that pilot in the descending turn to level off or tighten his turn to prevent an overshoot and the AOA gauge will water his eyes. His relatively low AOA 3 seconds ago is going to shoot into the danger area far quicker without proper power and flying technique than his buddy in the level turn back up at pattern altitude.
Well, in years of watching pilots, the ones pulling back to tighten turns and not realizing they are pulling the nose up while their eyes are fixated on "the numbers" are the ones that scare me. If they are throwing in the bank while descending, because they are actually looking at where they are going, vs. where they want to go, I'm far less concerned.


I don’t get the “saving for final” term. Also, is he lower than he would be in the turn to final?
See above, also, plenty of situations in the pattern where you don't descend on base, either due to distraction, being extended, other traffic, etc.


Certainly, excessive AOA and a turn are not a good combination. However, adding a descent to those two is worse, IMO.
Going to have to disagree here, pushing the nose down when you reduce the thing that is propelling you forward (power) is usually a good thing. Don't do this, and you'll stray into an ever-increasing AOA situation. Lots of people get "ground scared" and want to save their approach, so the closer they get to the ground, the more they pull up, but I'd rather scream a few hundred feet off the ground at high speed than at 40kts straight down in a spin.


Personally, if I had to choose between encountering a stall in a level turn versus a descending turn, I’ll take level every time. If you’re turning level at high AOA and you stall at pattern altitude, you have altitude to recover. If your AOA spikes in a descending turn, you don’t, plus you already have a significant sink rate you have to counter as well.
Won't matter if it's coordinated, but the idea is to use the AOA indicator to alert you to where your AOA is going, like pilot that starts slowing up and making a turn to base without descending, oops, getting into the yellow, let me push the nose down. Again, having watched pilots fly GA approaches over and over, I have often seen them fixated on the runway numbers and not aware of where the nose really is, sounds easy to fix, but more widespread and ingrained than you'd think, it's one of those places we let our guard down too because we are so concerned about "the runway", but I digress. If your AOA spikes during a descending turn, you are way WAY out of the norm, like 70 degrees of bank and uncoordinated, while that happens, I'd put money on distraction and not descending/pitching up while the aircraft is supposed to be descending.

Are you saying there are scenarios in a GA aircraft that could result in an “almost level flight attitude” with AOA “nearly off the scales” and the pilot would be unaware were it not for an AOA gauge? I don’t have a huge amount of experience with those aircraft, so perhaps you can give me some of the scenarios you are referring to.
Overloaded aircraft flying in ground effect. It might seem like you are at a normal climb attitude where the aircraft should be climbing, even if you lower the nose to an almost level attitude, but the combination of going slow, plus the weight, etc, the AOA is way out there, even though most everything "seems" normal and the aircraft would "usually" pass through this 2nd phase climb just fine. Also simply when you get slow when confined by terrain, more than one guy up here has landed on a mountain or in trees miles from where they took off because they "ran out of energy", or more accurately, the terrain required more than they had. Again, when they get slow, they can get into a regime where they are not at an excessive pitch attitude, so not stalled or stalling, but where they are sinking and the AOA is way high due to the combination of slow speed, induced drag, etc. One way to think about this is that stalls are often taught power on and power off, in both situations you are usually starting from a fairly excess amount of energy, so you can often get the nose pretty high up there before it stalls. Now think about getting much slower, maybe you'll notice your pitch attitude being higher, but if you've been flying for a few minutes like that, possibly not, and you have mountains and terrain obscuring the horizon, so you really have no good indication when the mountains are towering above. Now you get slow, now you want to turn around and the terrain is rising, do you not lower the nose because you'll hit the trees? How do you know if you have any reserve AOA to do this or whether you MUST lower the nose to have any chance? AOA gauge could come in pretty handy here.

That takeoff was a classic density altitude accident. I think his problem was more of energy deficiency than simply high AOA (at least at first). I could be off base here, so correct me if I’m wrong. I assume he attained the normal takeoff/climb IAS when he got airborne. Because of the density altitude, his TAS was higher to produce the same IAS. With little to no excess thrust for his climb, in order to maintain that IAS and the usual AOA at such an extreme density altitude, he had to hold a lower pitch attitude and he was unable to climb. So, when they were muddling along in semi-level flight after takeoff, wouldn’t the AOA gauge (if he had one) have been indicating something close to normal? Assuming he was holding the IAS he wanted (even if that required a descent), wouldn’t he see the roughly the same AOA he saw every other flight at that IAS?[/FONT]
His AOA would never have gotten out of the red in that situation. The AOA gauge is not going to care about TAS, it's going to care about air pressure against it, you'll have to go faster at high density altitude to get the same "pressure" on the wing, but the AOA gauge won't care, it will already be compensated for.

Yes, lots of things went wrong there, is it easier for us to re-evaluate every pilot that's gotten a license? Or require FADEC on every airplane? Or require a manifest and weight and balance be transmitted for every GA flight? No, those things are not practical, so the regulators try to see where a practical improvement can be made in safety.


I think, what would have shown him he was in trouble would have been ANY attempt to turn, climb or just increase back pressure on the yoke when his airspeed began to decrease.
That airplane was never really "flying". It never really got out of the 2nd segment climb. The AOA would have been spiking the entire time, at the least between yellow and red. If the pilot had been unfortunately enough to yank back on the controls earlier, he would have stalled much earlier. Based on my flying and that aircraft's attitude and speed, it should have been apparent early on that the aircraft was way out of the normal AOA and not transitioning into normal flight (from essentially slow flight). That's nice to say in retrospect, but perhaps an AOA would have helped and alerted him as he was flying around in the red. I know, that's a big assumption, it totally may not have made any difference in this case, but these are closer to the "typical" cases that I am discussing.


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