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

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 (below), focuses on analysis and remaining questions.

What NTSB Reports Say About Impossible Turns and Angle of Attack—Part 2: Analysis, Questions Raised, and Next Steps

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 ideal conditions of pilot, airplane, and environment.

In contrast, this study sought to evaluate 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 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 event an impossible turn or could it have been? 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 this installment.

Part 1 of this series focused on data and methodology.       

First Rhetorical Question:  How have successful turns been accomplished without AOA indicators?

Because successful impossible turns are not accidents and not reportable to the NTSB, none showed up in the NTSB data. However, the very embarrassing rhetorical question is, how did all those past impossible turns succeed when none of those aircraft had a visual AOA indicator? Given the rarity of visual AOA indicators in recent years, it’s a safe bet that visual AOA indicators would not have been installed in any, or hardly any, of those airplanes.

Impossible Turn (Attempts) Overview

In the NTSB data, a number of themes recur:

• Many takeoff/go-around/climb accidents were failure to achieve sustained flight (FASF). None of these achieved enough altitude to have permitted a successful impossible turn, but there were pilots who tried, anyway.
• Not all turnbacks started from straight out departures. Most of the simulated impossible turn videos are based on straight out departures because, I suspect, the math is more easily simplified and solved. NTSB ERA22LA169 describes a funny engine noise that prompted an earlier than planned turn to crosswind for an anticipated return to the airport. That return did not make it to the airport.
• Many 180° turns were completed after engine failure, but that did not guarantee success. Rather, after burning altitude in the 180° turn, pilots had less altitude and less time to find a suitable landing site, often with tragic results.

Completing the 180° Turn May Not Be Enough

NTSB ERA22FA261, pictured below, documents a successful 180° turn but with no suitable landing site after the turn. The result was fatal.

Well-Prepared for an Impossible Turn

NTSB CEN23LA068 is the story of a night, IMC impossible turn. The engine problem was unaddressed carburetor ice. The instructor was able to complete the turn, but the airplane overshot the runway. The instructor’s preparation for an engine failure is exemplary.

The pilot flying wrote, “After completing the turn back to the field we saw the airport environment and we were located over the runway but more than halfway down runway 17. From my point of view it was evident that we did not have enough room to safely land on Runway 17. We continued our descent for a couple of seconds and then he began a turn again to the left towards the taxiway. During this turn, the plane stalled at a couple of feet over the ground and the left wing struck the ground followed by the nose.”

The instructor wrote, “As far as my proficiency with the existing weather conditions, I was comfortable, current, and proficient. I had practiced the same turn many times before as well as studied the surroundings of the airport on google maps. If the runway could not be made my plan was to put the aircraft down in the field west of the airport close to the VOR. All airports I frequent I have a plan for encase [sic] of a [sic] emergency landing. Weeks prior to the incident I had flown many approaches in IMC in which IMC was maintained at and beyond the FAF.”

Second Rhetorical Question:  If the pilot wasn’t watching the airspeed, would AOA have been looked at?

NTSB ERA22LA393 shows an airplane slow on approach that flared high. When power was added, there were brief pitch oscillations before the plane departed the left side of the runway, as if P-factor and lack of right rudder input were present. In the docket of that report is an airport surveillance video that shows that event.

The airspeed indicator would have provided all necessary information to avoid this incident. There were also all the tactile, visual, and aural cues that would have allowed a proficient pilot to land even without the airspeed indicator. So if all those cues were ignored, is there any reason to believe that an angle of attack indicator would have been observed?

Some would argue that a glareshield-mounted indicator would have been more visible, but a full discussion of that topic would include a discussion of human factors, including cognitive capture. In simplest terms, cognitive capture means that when a person is strongly focused on something, other visual items can be ignored, no matter how close to what was being observed, or how conspicuous the other item was.

Some argue for aural AOA guidance, but it is well known in human factors circles that aural cues can be the first to be dropped under stressful situations.

In my own experience, I was once flying the downwind leg in my Cessna 175 at an airport known for gusts. I had an extra 10 MPH cushion when all of a sudden, the bottom fell out. I maintained attitude and added additional power, keeping the airplane under control. Only when the event was over did the stall warning horn come on. Or was it that I only heard the stall warning horn when I was no longer focused solely on aircraft control and on the sight picture?

Third Rhetorical Question: Can AOA help raw pilot psychology?

Many NTSB reports indicated that the pilot was trying much too hard, attempting low altitude maneuvers that are hard to justify. Such attempts also occurred when sustained flight was not achieved.

NTSB WPR22FA235 is an exemple of a very sharp turn at low altitude. An airport surveillance video camera snippet of the accident is below. Again, this video is in the docket.

The scenario was that the pilot was returning due to weather. Although the traffic pattern was otherwise normal, the base leg was to the end of the runway, with no provision for final approach. The turn to final started at roughly 50 feet when the plane was already over the runway, or nearly.

The lesson from the NTSB reports is that stressed pilots can operate in ways contrary to training, and there are numerous psychological terms that may apply.

It is unlikely that an additional cockpit instrument, such as AOA, will provide any additional safety benefit in such stressed pilot situations.

Stressed pilots can operate in ways contrary to training.

A Second Example of Possible Pilot Psychology

NTSB ERA21LA287 describes intermittent power interruptions on takeoff and immediately afterwards. The pilot wrote, “so I decided that I was getting to have altitude and airspeed sufficient to make a full circuit and land back on the departure runway.” This decision may have been made from subconscious psychological pressure in addition to the hope of sufficient engine power.

As for psychological pressure, I experienced something similar myself when, years ago, just as I was passing the departure end of the runway, part of the exhaust system of my RV-4 came adrift. Since the plane could still climb, I chose to fly a full pattern. I also informed another airplane in the pattern that I had an engine problem and that I was going to cut him off in the pattern. He cooperated and went around.

This event, and others in the data, illustrate the pilots will make all kinds of decisions, apparently trying to save the airplane. More instrumentation will, again, not change human nature.

Pilots will make all kinds of decisions, apparently trying to save the airplane.

Visual AOA Indicators Do Not Meet Guidance Needs for All Aircraft

1. Wrong question: What information does an AOA display system provide?
2. Better question: What action should the pilot perform differently, or what decisions should the pilot make differently, because of this AOA information?
3. Does an AOA system enforce a hidden agenda, such as always fly at 1.3 V_s0, or some other speed?
4. Does this hidden AOA agenda reflect somebody’s belief that this AOA speed is a silver bullet that is all that is needed for safety? And that the flexibility and utility achieved at other speeds are implicitly not worthy of consideration? (After all, human nature looks for the easy way out…)

Here are three responses to Question 3:

• AOA does not provide guidance required for takeoff in my own RV-9A. That engine ran hot when I bought the plane. We did all the baffling and cooling air tricks, finally switching carburetors to one that ran richer, giving additional cooling in the Georgia summer. But because of the need for cooling air, and because a Vy climb has an impossibly steep deck angle, and because there are buzzards in the Savannah airport traffic pattern, I routinely climb at Vy + 30. I have to settle for “only” 1,000 feet per minute climb. AOA (which is installed and calibrated in the airplane) does not provide guidance for my three requirements, but airspeed does.
• In my old flying club, two checkouts in the Cessna 210 were required because of different handling qualities with gross weight. One checkout was at normal weight and c.g. and one at full gross weight and aft c.g. But despite the wide weight range, the POH showed only one short field approach speed. This one approach speed at varying weights would require varying AOA, so there were aircraft considerations other than just AOA.
• One year, the Cessna 150 pilot’s handbook (before POHs were required), showed an increase in the short field landing speed by 6 MPH or so. But as there were no airframe changes, the increased speed was to provide more safety margin for practicing student pilots. A fixed AOA reference would not have flexibility to provide this safety margin.

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 impossible turns are not in the data.

Given these limitations, here are very rough (very rough) estimates:

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:
  • 83 unlikely to help, 16 visual AOA might have helped (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 AOA 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.

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 AOA indicators, despite their popularity.

Those who attend flight instructor conferences and talk to pilot examiners 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 to address.

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 pilots 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.

A previously published Air Facts article, Angle of Attack for Dummies, is an exmple of how a technical subject can be dimplified for lower levels of pilot experience.

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.

Addendum

On Wednesday afternoon at AirVenture 2024, I observed two other CFIs attempting AOA-aided impossible turns in Redbird simulators programmed to fly like Cessna 172s. Instrumentation was round gauges on the electronic displays.

The simulators had a glareshield mounted AOA, similar to the Garmin GI 260 AOA indicator.

The simulators had a glareshield mounted AOA, similar to the Garmin GI 260 AOA indicator. It was briefed that the simulator gave a two second lag in the indicator. The Garmin AOA indicator in my airplane does not have any perceptible lag, however.

As I recall, the pilots flew warmup exercises using the AOA, and that gave a speed between Vx and Vy. According to the airspeed indicator, the pilots were flying well below normal Cessna 172 speeds.

Then each pilot attempted at least two impossible turns. None succeeded or even came close.

Factors I observed were:

• Limited over the nose visibility in the simulator, making it hard to establish the recommended 8° nose down attitude for the turn.
• Excessive focus on the AOA indicator, especially when establishing the turn. This AOA indicator is a performance indicator, not a guidance indicator. The two second lag in the system made it even harder to use, analogous to chasing the airspeed indicator, or comparing a turn and slip (with lag) compared to a turn coordinator (where roll rate is used to reduce lag).
• Difficulty in seeing the runway where the return was desired.

Also included in the preflight briefing was a discussion of the TLAR app for calculating all the parameters of an impossible turn, including stop/go takeoff calculations. for several general aviation airplanes. My impression was that in the real world, few if any pilots would go through the steps to program the app, and that the voice callouts of the app could be distracting in a busy environment.

Based on this admittedly limited information, my impression was that a successful impossible turn in this simulator would only succeed with very precise piloting and optimum conditions.

A credible source emailed me that, “A long-time PPC sim instructor observed that the visual AOA was not as intuitive for a number of the pilots as he thought it would be.”

Official results from the sim sessions are not public at this time.

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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.

Latest posts by Ed Wischmeyer (see all)

• What NTSB Reports Say About Impossible Turns and Angle of Attack (Part II) - September 13, 2024
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