Learning to Aviate with Rich Stowell
Technology can offer powerful tools to enhance aviation safety and efficiency. It’s best used to complement deep knowledge and well-developed skills, not as a substitute for them. It also must be proven effective.
On December 26, 2024, the FAA issued a Special Airworthiness Information Bulletin encouraging the use of angle of attack alerting systems. The Bulletin “provides information to help general aviation aircraft owners and operators.”[2] It then cites the fatal accident of Colgan Air Flight 3407, a transport category aircraft with two professional pilots in the cockpit. The captain responded inappropriately to stick shaker activation, “which led to an aerodynamic stall from which the airplane did not recover.”[3]
The Bulletin claims that “[r]esearch has shown AOA indicators assist pilots with stall margin awareness, stall prevention, and recovery from unusual attitudes or upset.”[4] The Bulletin attributes three sources to this statement.
The first is a 1977 study of stall avoidance in general aviation (GA) airplanes (the Ellis study). The second is the flight test manual for the U.S. Navy test pilot school. The third is a 1972 study by the U.S. Air Force on AOA training. It involved twelve Air Force flight instructors flying a T-38 with a Bendix AOA system.
The Bulletin talks about several airline accidents and refers to military source material. But how applicable is that to GA, where the pilots, airplanes, and operations are significantly different?
Airline pilots have attained the highest level of certification recognized by the FAA. Military pilots weed out all but the best of the best. In contrast, GA is accessible to almost anyone. We are a diverse group three-quarters of a million pilots strong.
Airline and military operations are highly standardized. Typical GA is less structured. A large gap in knowledge and teaching skills exists among our instructors. Unfortunately, teaching to the test is the norm as well.
Regular training is an integral part of the job for airline and military pilots. We’re only required to do an hour each of ground and flight refresher training once every two years.
Of course, some things translate across these sectors. Manual flying skills, for example. Cockpit resource management concepts from the airlines adapted to GA are another example. But does the successful use of AOA systems in the airline and military context apply to GA? We fly mostly during the daytime in visual conditions. Our focus should be outside the cockpit 90 percent of the time.[8]
Is the FAA showing us the whole picture about AOA alerting systems for GA? Let’s have a closer look.
The Bulletin says AOA indicators “assist pilots with…recovery from unusual attitude or upset.”[9] It also says, “AOA indicators could aid pilots in diagnosing problems with a pitot tube…or static port.”[10] These claims come from a 2014 review of research by NASA on the effectiveness of AOA indicators. Here’s the full context:
“The most beneficial use of an AoA display may be as an aid in upset prevention/recovery situations and the detection of pitot or static system failures. However, definitive works quantifying these benefits were not found [emphasis added].”[11]
The Ellis study explored several types of stall warning: stall horn, stick shaker, and three styles of AOA indicator. Test subjects preferred the tactile stick shaker stall warning. Further, “when used in conjunction with a horn or shaker, [AOA indicators] provide a very useful indication of whether the situation was progressing into or away from the stall [emphasis added].”[12]
Other studies have reported mixed results using AOA indicators in GA airplanes.
“[T]he private pilot course predominately involves ‘contact flight techniques’, i.e., perception of the attitude of an airplane by visual reference to the horizon…. A significant difference in performance among private pilots attributed to the angle of attack indicator or any other instrument, therefore, would be unusual.”[13]
The recommendation: “No further consideration be given to using an angle of attack indicator in addition to airspeed for the purpose of improving flight training at the private pilot level.”[14]
“Some of the expected advantages of [AOA], such as visual indication of stall margin…were realized; however, certain aerodynamic characteristics of the airplane…were found to limit and tended to negate some of the expected advantages. As a result, this use of angle of attack did not show a significant improvement in performance and flight safety.”[15]
The study concluded that “angle-of-attack information is a usable parameter, but not necessarily a superior one.”[16]
Purdue University, Ohio State University, and the Florida Institute of Technology partnered with the FAA on an AOA study.[17] The purpose: “determine if the use of an angle of attack (AOA) display can provide a pilot with additional information necessary to increase the stability of an approach.”[18]
“For instances in which the approach for landing was conducted under traditionally normal circumstances…the use of the AOA system did not significantly impact the stability of the approach….
“During instances in which a simulated engine-out approach was conducted, it was anticipated that the AOA system could be used as a tool for approach stability…. However, it was determined that participants for two universities did not have differences in the stability of the approach in a simulated engine-failure situation….
“This result was not anticipated, but the highly structured programs within the collegiate environment and the level of proficiency present in practicing emergency and abnormal situations might be a contributing factor because the participants…might have relied on their previous experience to conduct as stable an approach as possible.”[19]
Experience and proficiency with the engine-out scenario were as effective as relying on AOA for the stabilized approach.
On one hand, “[t]he qualitative feedback…from the participants and the statistical results…indicate there is merit in the promotion of the use of AOA displays.”[20]
On the other hand, “there is insufficient information to draw conclusions as to exactly who would benefit most from the usage of AOA devices and the exact circumstances under which this mitigation strategy would be the most effective. Additional research is required to identify those characteristics.”[21]
The call for more research has been a common theme in AOA studies. Moreover, “most of the literature concerning the benefits…is conjecture based on the information available from an AoA display and how it may be used.”[22] Yet the consensus among advocates for AOA seems to be that the issue is settled.
Safety advocate Ed Wischmeyer looked at recent NTSB accident reports involving the takeoff/initial climb, approach, and landing phases of flight:[24]
. Of the 342 accidents that were neither fatal nor involved stalls, AOA was unlikely to have helped in 96 percent of the cases. AOA might have helped in four percent of the accidents.
. Of the 99 accidents involving stalls (fatal and non-fatal), AOA was unlikely to have helped
in 83 percent of the cases. AOA might have helped in 16 percent of the cases.
. Of the 76 fatal accidents that did not involve a stall, AOA likely would not have helped in 99
percent of the cases. It might have helped in one percent of the cases.
Combined, AOA was unlikely to have helped in 94 percent of the 517 accidents. AOA might have helped in six percent of the cases.
Parsing the NTSB data was a difficult task. Wischmeyer cautions that his estimates are “very rough.” Even so, the ratio between AOA “likely would not have helped” and “might have helped” is 16-to-1.
Data is supposed to drive initiatives to improve GA safety. Yet it seems like confirmation bias or other factors could be driving the support for angle of attack indicators in every GA airplane.
The mixed results from studies and accident reports suggest broader issues:
. How to balance using technology and maintaining foundational flying skills; and,
. How best to improve aviation safety and education.
We like our technology. Tech is cool. Tech is tangible. We can show it off, with every detail of it discussed ad nauseam. We love to trick out our rides with the latest gadgets and accessories. Those who tinker with their cars do it. We do it with our airplanes. Even Olympic athletes boost performance with technology.
Training is different. Training is personal. Training is hard. We only see and feel the effects of training, not the training itself. And the skills we acquire are perishable, needing constant practice.
We are continually reminded that manual flying skills are “the foundation upon which other technical skills are built.”[25] Yet we don’t address the poor quality of flight training going on in general aviation. Worse, our industry sometimes removes training elements that have been shown to be effective in preventing things like unintentional spins!
In 2016 for example, the FAA deleted the longstanding requirement for slow flight with the stall warning activated from the private pilot ACS.[26] That change was a step backward in the fight to reduce inflight loss of control.[27]
Read Rich Stowell's Remarks on the 2016 ACS change
Using technology as a tool to supplement knowledge and skills is one thing. Using it as a crutch to mask deficiencies in knowledge and skill can create a false sense of security, feeding hazardous attitudes like invulnerability.
Should you invest your flying dollars in ongoing training, more technology, or both? You’ve got to weigh the cost against the potential benefits. I recommend prioritizing as follows:
1. Invest in yourself first. Keep learning. Seek only high educational value training. And
practice, practice, practice.
2. Invest in more technology only in support of priority number one.
If you’re considering installing a supplemental AOA indicator system in your airplane, do your homework. Know what the studies have found. Be honest about the reason you’re adding it to your airplane. And be aware of the system’s limitations, including issues with installation and calibration.
For example, markings and placards must state, “Not for use as a primary instrument for flight [emphasis added].”[28] The system “is to be used only as supplemental information…[and] may not be used as a substitution for the certified aircraft stall warning system.”[29]
If your airplane already has AOA, get with a knowledgeable instructor and dig into the details about the system. Review its limitations and check its calibration. Identify the specific operations where you might want to use it. Also, be clear about what AOA can and can’t do for you.
Whatever you do, do your own research. Make sure you’ve developed good flying skills and keep them sharp. If you have AOA, treat it as another tool in your toolbox, not as a replacement for all your other tools. And don’t use it as a crutch.
Download the Special Airworthiness Bulletin Regarding Several AOA Studies
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---References---
[1] Tim Stobierski, “The Advantages of Data-Driven Decision-Making,” Harvard Business Review Online, August 26, 2019, updated February 19, 2021, accessed January 14, 2025 at https://online.hbs.edu/blog/post/data-driven-decision-making.
[2] FAA, “Stall Warning System, Angle of Attack Alerting Systems,” Special Airworthiness Bulletin 2024-7, December 26, 2024, 1.
[3] Ibid.
[4] Ibid., 2.
[5] Naval Air Warfare Center Aircraft Division, “U.S. Naval Test Pilot School Flight Test Manual: Fixed Wing Stability and Control Theory and Flight Test Techniques,” USNTPS-FTM-No. 103, Revised January 1997, Background.
[6] Max L. Odle, “ATC Angle of Attack Training,” IFC-TR-72-3, July 1972, 31.
[7] Ibid, 32.
[8] FAA, “Airplane Flying Handbook,” FAA-H-8083-3C, 2021, 3-5.
[9] FAA, Special Airworthiness Bulletin, 2.
[10] Ibid.
[11] Lisa R. Le Vie, “Review of Research on Angle-of-Attack Indicator Effectiveness,” NASA/TM–2014-218514, August 2014, 34.
[12] David R. Ellis, “A Study of Lightplane Stall Avoidance and Suppression,” Report No. FAA-RD-77-25, February 1977, 31.
[13] Frank G. Forrest, “Angle of Attack Presentation in Pilot Training,” Report No. DS-69-6, March 1969, 20.
[14] Ibid., 21.
[15] Shu W. Gee, Harold G. Gaidsick, and Einar K. Enevoldson, “Flight Evaluation of Angle of Attack as a Control Parameter in General-Aviation Aircraft,” NASA TN D-6210, March 1971, Abstract.
[16] Ibid., 1.
[17] PEGASAS: FAA’s Partnership to Enhance General Aviation Safety, Accessibility and Sustainability.
[18] Brian Dillman, Shawn Pruchnicki, Dennis Wilt, et al., “Angle of Attack Equipment in General Aviation Operations,” DOT/FAA/TC-18/28, Final Report November 2018, x.
[19] Ibid, xi.
[20] Ibid., xii.
[21] Ibid.
[22] Le Vie, NASA/TM–2014-218514, 35.
[23] GAJSC is the General Aviation Joint Safety (formerly Steering) Committee. It “works to improve general aviation (GA) safety through data-driven risk reduction efforts focused on education, training, and enabling new equipment in GA aircraft.” See https://www.gajsc.org.
[24] Ed Wischmeyer, see “What NTSB Reports Say About Impossible Turns and Angle of Attack (Part I),” Air Facts Journal, September 9, 2024, accessed January 16, 2025 at https://airfactsjournal.com/2024/09/what-ntsb-reports-say-about-impossible-turns-and-aoa/, and “What NTSB Reports Say About Impossible Turns and Angle of Attack (Part II),” Air Facts Journal, September 13, 2024, accessed January 16, 2025 at https://airfactsjournal.com/2024/09/what-ntsb-reports-say-about-impossible-turns-and-angle-of-attack-part-ii/.
[25] FAA, “Flightpath Management,” Advisory Circular 120-123, November 21, 2022, 3-1.
[26] ACS: Airman Certification Standards.
[27] The FAA recently reintroduced flight at minimum controllable airspeed, but only for flight instructor applicants.
[28] FAA Memorandum, “Approval of Non-Required Angle of Attack (AoA) Indicator Systems,” AIR100-14-110-PM01, February 5, 2014, 3.
[29] Ibid.
>> This post was written by a human <<
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