What NTSB Reports Say About Impossible Turns and Angle of Attack (Part I)

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Editor’s Note: Air Facts is pleased to present a two-part series by Dr. Ed Wischmeyer on visual angle of attack indicators and executing a 180 degree, low-level turn back to the airport following an engine failure (the impossible turn). The first installment focuses on data and methodology while the second installment focuses on analysis and additional questions raised.

What NTSB Reports Say About Impossible Turns and Angle of Attack—Part 1: Data, Methodology, and Next Steps

The objective of this research is to invite and challenge the greater general aviation safety community to expand their focus to all aspects of general aviation safety, and not to be content with seemingly cool approaches to very limited scope problems. This broad scope approach is ultimately needed to help keep our friends, created in the image of God, alive.

emergency return

The current emphasis in general aviation (GA) safety is on visual angle of attack (AOA) indicators and impossible turns (return to the airport following engine failure). The many analyses and videos on these topics have been done in what can best be described as laboratory conditions, carefully selected optimum conditions of pilot, airplane, and environment.

In contrast, this study sought to examine AOA in the context of all accidents. This approach gives perspective on all factors, including those that might otherwise be ignored or unrecognized. This, in turn, helps address the question of whether the current emphasis on AOA indicators and impossible turns is justified.

Instead of concentrating on standard accident causations and progression, this study concentrated on these major questions:

Was AOA a major factor in the accident, either in the causality or progression?
- Would a visual AOA indicator have helped?
Was this a power loss after takeoff, whether or not the pilot chose to fly an impossible turn? Details?
Did the data suggest anything new?

Any good safety study ultimately addresses the question of how to most effectively allocate safety resources including training, regulations, publications, videos, and other areas. That question is addressed in the second article of this series.

The current emphasis in general aviation (GA) safety is on visual angle of attack (AOA) indicators.

NTSB Reports Studied

The NTSB reports studied were all of the single engine events from 2021-2022 operating under FAR Part 91. These were flights not for hire, but included flight instruction.

NTSB data was accessed with the CAROL database. The Excel download of the data had 44 columns describing the aircraft, pilot, event statistics, and the NTSB report itself.

Some of that report data was processed data as opposed to raw data. For example, broad phase of flight and probable cause (being somebody else’s opinions) were not analyzed directly and were accessed only as memory and sorting aids. Similarly, the summary cause classifications and findings were not even read.

Fields of particular interest were the Highest Injury Level, i.e., fatal or not, and links to the event narrative and the event docket which includes supporting documents, diagrams, interviews and sometimes videos.

A derived parameter for each event was whether the word “stall” was present in the event summary.

As would be expected, the NTSB data were not completely consistent and error-free:

The completeness of the NTSB reports varied;
Several reports stated that stall speed depends on bank angle, ignoring the real factor, the G-load of the turn;
The term “stall/spin” was sometimes used as a default causal factor;
Go arounds were sometimes classified as landing events, but other times as takeoff events.

Additional Parameters Generated

Five more parameters were generated to help facilitate the analysis. Again, because of the wide range of accident circumstances and variations in the NTSB reports, these parameters were not and could not be completely precise. However, given that the primary objective of this study was to examine AOA, not to perform a traditional causality study, such variations were tolerable.

The first parameter was the quick summary, used as event descriptors rather than for generating statistics. There were 45 different entries in this category, some overlapping, but the most numerous of these was No Stall/Spin. Others included Failed Impossible Turn, Impossible Turn OK/Crash, IMC LOC, Overloaded, Stall, Stall/Spin, Water in Gas, and Windshear.

The other quick look parameters are:

Instigating Event	Where event started	Result	Stall warning
Aircraft performance	Approach	CFIT	Irrelevant to accident
Bird strike	Climb	Crash	Might have helped
Carb Ice	Cruise	Forced landing	Not an accident
CFIT	FASF (see below)	LOC	Sounded
Density altitude	Final approach	Midair collision	Unknown
Fuel mismanagement	Go around	Normal landing	Would not have helped
Gust	Impossible turn	Spin
IMC	Runway
Mechanical problem	Traffic pattern
Midair collision
Note-worthy
Other
Pilot miscontrol
Reckless
Unknown
Unsuitable surface

A Surprise in the Data: Failure to Achieve Sustained Flight

As hoped for, there was a surprise in the NTSB data. That phenomenon is best named Failure to Achieve Sustained Flight (FASF). An incomplete summary description of FASF is whether the airplane made it out of ground effect.

FASF events included running off the side of the runway, failed takeoff abort, mechanical problems, fuel problems, gusts/tailwind/shear, hit obstacle, unable to climb, carb ice (especially in older planes), unlicensed pilots, rudder pedal jammed after total knee replacement surgery, student pilot/dual instruction, bird or deer strikes, first flights in that airplane, and pretty much anything you can think of. Some FASF events made it past the airport property before a ground collision or forced landing. And some made it as high as 100 feet but were still consistent with the spirit of FASF.

But from an angle of attack perspective, the unifying factor in all of these was that angle of attack was not a factor either because the wing never generated lift, or, if the plane became airborne, the flight situation was so precarious that the pilot’s attention would have been 100% outside the airplane, looking to keep it in the air without running into something. In all cases, stress made the pilot cognitively unavailable to watch any flight instruments, even if they could have provided any useful information.

Another consequence of the FASF concept is that, in any accident analysis, FASF or not, it’s worth considering whether stress made the pilot cognitively unavailable to watch any flight instruments. This is in line with well-known stress phenomena, such as aural cues being dropped.

Comparing AOA Videos to the Real World and Real World Pilots

It is no surprise that videos purporting to show the advantage of AOA indicators are shot under ideal conditions. Such videos may contain these elements:

Calm air, no gusts
Stable flight paths, constant g load
Power on approaches
Optimum calm air glides
No forced landing glides as in a glide to a point in the windshield
No birds or planes to avoid
No aural distractions, radio or cockpit communications
Skilled, safety conscious pilot
Technically sophisticated pilot
Rational, unstressed pilot, cognitively available for all cues
High situational awareness
Non-emergency flight
Relaxed flight, no time pressure

In contrast, there are conditions in which visual AOA guidance is unlikely to add value:

When the pilot is so task saturated that she has is unable to read any flight instruments
When the pilot is cognitively unavailable due to distractions, startle, or surprise
When the law of primacy kicks in and the pilot reverts to airspeed
When the pilot simply does not understand AOA. A credible source emailed me that, “A long-time PPC (EAA Pilot Proficiency Center) sim instructor observed that the visual AOA was not as intuitive for a number of the pilots as he thought it would be.”
In maneuvering flight such as turns in the pattern. (I once flew downwind, base, and final at a constant AOA. To get the extra lift required for the turns, I had to dive to get extra airspeed so that the plane could turn at that same AOA. That produced a strange traffic pattern with roller coasters at the corners.)
When the precision of flying with AOA is insignificantly greater than indicated airspeed, as described in NASA TN D-6210
When turbulence makes the AOA indication unreadable as readings bounce all over the scale
Landings other than at best glide, e.g. spot in windshield techniques as is required in some forced landings
In ground effect: stall AOA is different, eyes are outside. This is more theoretical than practical for visual AOA, but can affect some proposals such as a general aviation stick shaker.
Aircraft where installation is unlikely such as ultralights, Ercoupes, Taylorcraft, J-3 Cubs, and low hull value aircraft
Where the pilot perceives no need for AOA, the panel is already full, and AOA training is required but not be readily available
When the pilot’s learning style does not adapt to abstractions or complexity
When the pilot has such a good feel for the airplane that visual AOA adds little to the pilot’s innate sense of what the airplane is doing

But beyond these points, the general pilot population includes the unreachables and unteachables (as somebody put it). In my own flying career, I’ve seen plenty of small airport pilots unconcerned with safety messages, to put it mildly. One more gadget in the cockpit cannot remedy deficits in skill, judgement, and attitude.

Drs. Neelakshi Majumdar and Karen Marais extensively documented the demographics and experience of pilots who experienced loss of control accidents (see https://arc.aiaa.org/doi/10.2514/1.D0432). Their Figure 3 tends to support to my supposition that real world loss of control pilots are substantially less accomplished than those who promote visual AOA guidance.

It’s also interesting that the technique of flying a visual AOA approach never seems to be explained beyond, “It’s simple. I can teach you in five minutes.” Contrast this purported simplicity to the never-ending discussions of pitch/power for airspeed/altitude.

Two Obvious Questions

So if the pilot is in an accident situation and is so stressed, too cognitively unavailable to watch the airspeed indicator, how likely is it that the same pilot can watch AOA?

That question, in turn, raises a more fundamental question: Is the safety community’s continued focus on AOA the best way to reduce overall accident rates? Or does that focus on AOA just distract the safety community from more fruitful safety efforts?

Is the safety community’s continued focus on AOA the best way to reduce overall accident rates?

Is Optimum Glide Always the Objective?

Visual AOA is touted as the way to get “optimum” glide, but there are a number of interesting facets to this discussion.

Glider pilots know that best glide speed for distance covered over the ground varies with wind: faster into the wind, slower downwind. AOA indicators do not permit this compensation. And in the very high-tech world of competition sailplanes, they are not equipped with AOA indicators.

Glider pilots know that best glide speed for distance covered over the ground varies with wind.

An interesting question is how much performance benefit a perfectly calibrated AOA indicator would give over an airspeed indicator. NASA TN D-6210, “Flight evaluation of angle of attack as a control parameter in general-aviation aircraft” indicated that the advantage was not operationally significant. Given all the elements of human factors, sensor noise, and filtering lag, I suspect that modern AOA systems would give the same result. That study would make an interesting thesis topic, however.

Tedious numerical interpolation is not required when adjusting airspeed for weight, contrary to the claims of some AOA advocates. Airspeed variations with weight in light general aviation aircraft are only a handful of knots, so it’s easy to fly the published slow speed when light, the faster speed when heavy, and something in the middle when the aircraft weight is something in the middle. No math required. What computational errors there might be would not be more significant than the piloting skills or other errors.

The standard glide estimation technique, as would be used in a forced landing, turned up again when landing at my home field on the way back from Oshkosh. On downwind, ATC had me at 3,000 feet going over the departure end of the crossing runway. Turning final, I was still way, way high. Even with full flaps, the issue at first seemed in doubt but glide estimation, taught to student pilots, was used.

I could see that the spot on the ground in the windshield that was not moving was short of the runway. This meant that I could land normally on the runway, not overshoot, and did not need to be concerned with the airliners on the crossing runway. “Optimum” glide was not the issue here, and a visual AOA indicator would have had no value. This descent used the same technique that (would have) had value in many of the NTSB accidents involving engine failure after takeoff.

Approximate Statistics

As noted in the many caveats above, precise statistics are not attainable from this data set and are not the goal, anyway. And recall that successful power loss outcomes are not in the data.

Given these limitations, here are very rough—very rough—estimates, realizing that if airspeed already provided sufficient information but was ignored, a visual AOA indicator was unlikely to help.

For 175 events in the data that were fatal, where the NTSB report included the word “stall,” or both:

99 Stall Events, both fatal and non-fatal
- 16 visual AOA might have helped, 83 unlikely to help (16% might)
34 Fatal Stall Events
- 25 takeoff or initial climb; 5 visual AOA might have helped (20% might)
- 9 approach and landing; 1 visual AOA might have helped (11% might)
76 Fatal Events, NTSB says No Stall
- 1 might have helped, 75 visual AOA unlikely to help (1% might)

For 342 events that were neither fatal nor stall:

327 visual AOA unlikely to have helped (95%)
13 visual AOA might have helped (4%)
1 event where the pilot wrote that airspeed sufficed
1 event where the stall warning sounded—early flap retraction, quartering tailwind

The Most Important Question: Where Are Safety Resources Best Expended?

For the industry as a whole, would safety resources be better expended on visual angle of attack indicators or on addressing other issues, such as teaching fundamentals of airmanship, basic piloting skills, or forced landing practice?

There is an impressive surge of AOA rhetoric—“lifesaving,” “correct,” “optimum”—but such language can be misleading. “Correct” and “optimum” may fit the context of the speaker but not necessarily apply to the situations of the listener, who may be considering other flight operations, or having to deal with real world scenarios, as is discussed in Part 2.

While the decision on where to expend safety resources will vary from pilot to pilot, the NTSB reports of this study do not support visual AOA indicators for impossible turns as a silver bullet to address overall safety issues.

Next Steps

Technical solutions that do not acknowledge the realities of operational environments and ranges of pilot skills and motivations will not achieve the degree of change required. This is especially true of visual angle of attack indicators, despite their popularity.

Those who attend flight instructor conferences and talk to DPEs know that there is a crisis in the quality of new pilots and CFIs, including graduates of universities and commercial flight training companies. The long-term effects of poorly-trained pilots is sobering. Addressing this problem is a desperate and worthy challenge for the safety community.

There are similar problems with those who have not kept up with change, aging pilot populations, second owners of homebuilts and older airplanes, those content with minimum standards, and those who do not understand or respect the crafts and oral traditions of general aviation flying and aircraft upkeep. I have encountered many such over the years.

A big part of any solution will be adapting to the extremely wide variety of pilots, airplanes, and operations that comprise general aviation. That variety may require multiple initiatives.

I think that currently, the most improvable aspects of general aviation safety likely will include improving basic flying skills including rudder usage and stall and slow flight well beyond ACS standards. Pilot psychology and human factors also need to be taught. Those “soft” psychological areas are easily disdained by pilots unless carefully presented.

All training should be as affirming and student focused as possible. After all, the objective is not to make pilots be subject matter experts on technical details, but rather for pilots to understand the implications of those technical details and apply them in flight. Angle of Attack for Dummies in an example of how a technical subject can be simplified for low experience pilots.

Fundamentally, improving safety and upgrading the pilot population’s flying skills is a marketing problem, a motivational problem, a problem that will require the whole industry to address. Until the industry as a whole, including training, publications, social media, and presentations all address the problem with positive reinforcement of pilots, it will not be reasonable to expect improvement.

There are already courses and training that address pilot skills. These include Patty Wagstaff’s Upset Prevention and Recovery Training, Rich Stowell’s spin training, my own Expanded Envelope Exercises®, SAFE CFI-PRO™, and numerous books and articles. Back in 1971, the EAA published the “EAA Pilot Proficiency.” All these indicate direction but are not enough in and of themselves enough to resolve the larger issues.

Author
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Ed Wischmeyer

Ed Wischmeyer is an ATP and CFI-I whose computerized logbook tallies nearly 200 makes and models of aircraft flown. He has written hundreds of pilot reports, articles and columns, many for Kitplanes. He has owned four experimental RVs, an AirCam and a Cessna 175. His professional experience includes Apple Computer, SRI International, Honeywell, Boeing, and Gulfstream -all in research and advanced development. He also taught gradudate school courses in aviation safety for two years. He earned his Ph.D. from MIT.

What NTSB Reports Say About Impossible Turns and Angle of Attack (Part I)

What NTSB Reports Say About Impossible Turns and Angle of Attack—Part 1: Data, Methodology, and Next Steps

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