In December 2024 the FAA released a Special Airworthiness Information Bulletin (SAIB) recommending the use of angle of attack (AOA) in all GA aircraft. The bulletin has caused a bit of a stir, as does the topic of AOA whenever it’s brought up in non-military circles. Some commentators have gone so far as call the use of AOA to assist with aircraft handling “virtue signaling.” Most of the pushback comes from folks who have neither participated in military aviation or have extensive experience flying with and teaching the use of AOA for approach and landing, power management and maneuvering.
To be clear, AOA isn’t a silver bullet for all that ails GA, but it is a system adopted by fixed wing military aviation that successfully reduced the number of loss of control (LOC) mishaps under circumstances similar to those we face in GA. Some recent published data contains an interesting analysis that concludes adoption of AOA by GA simply won’t be much of a factor in reducing mishap risk. If we drill down a bit, we can see some negatives with the approach taken since AOA specifically addresses LOC mishaps that are the result of an unintentional stall, although the overall conclusion that GA will benefit from better training is sound. The other bellwether argument can be summarized as “we are not them,” i.e., GA is fundamentally different from other aviation communities—the airlines and the military. Pilots that draw this conclusion have a great deal of GA experience and are highly credentialled, well-meaning, smart people, but lack experience in military aviation and/or the airlines.
My background includes GA instruction (about 3000 hours or so, all in airplanes without AOA), the airlines (about 8000 of mostly the same hour where AOA is cleverly disguised as the “foot” on the airspeed tape) and fixed-wing military aviation (about 3500 hours in fighter aircraft where AOA is a primary reference for approach and landing as well as maneuvering flight). During my time in the military, I was fortunate to be a “replacement training unit” instructor (where we checked new pilots out in their assigned airplane), an instructor at the fighter weapons school, and a test pilot. Throughout my career, I’ve maintained my CFI/II/ME and have always participated in GA. I still actively instruct in GA and scare myself regularly in my RV-4. I’ve had a great career and have dipped my toes in each of the big aviation ponds. Part of my “give back” program was forming an all-volunteer, non-profit group dedicated to applying military AOA lessons learned to reduce loss of control risk in GA. We were fortunate to be selected as the first-place winner in the 2018 EAA Founder’s Innovation Prize in 2018 and overall grand champion in 2021 for our work. Having lived on all sides of the great divide, I feel reasonably qualified to comment on the difference between flying in each of the various communities as well as recognizing when an airplane is an airplane, aircraft handling is aircraft handling and when lessons learned in one community are directly applicable to another.
“2 out of 3 doctors smoke camels.” There are statistics, damn statistics and lies. About the only useful skill an undergrad learns while majoring in history is quantitative analysis, to be able to sort out that simple matrix. There are many reasons pilots die in airplanes. Loss of control is only one of them, but it does result in the most fatalities of any mishap cause. It’s been this way since the current NTSB database was started in 1962. Another point to ponder is that LOC is an equal opportunity killer—ATP’s die with the same frequency as student pilots. “Flying by the seat of your pants” is a common fallacy. Paul Dye recently wrote an excellent short essay on that topic, and the shear amount of vitriol in the comments its publication generated is indicative of how strong this myth persists. I’m a relatively well trained and experienced pilot, and I depend on technology. I’m sure flying a Sopwith Camel is an interesting flying experience (and I’m a big Snoopy fan), but I prefer my RV-4 with modern avionics and am glad my combat experience was in a modern 4th generation fighter. While I don’t discount the training value of visual flying in a simple airplane with a good instructor, I don’t want to see accident rates revert to what they were in 1948 when such airplanes were common.
Part of our charter at FlyONSPEED.org is to conduct AOA flight research. We are currently designing an experiment to conduct in simulators to determine the efficacy of AOA in various GA scenarios. It’s based on prior work conducted in the UK. Although a bit technical in nature, the results of the UK study are published here, and I encourage you to take a look here. If nothing else, read the abstract and conclusions. As has been pointed out by other commentors, more research is required, and this is an effort to do so.
While designing this experiment, a mishap analysis was conducted using the searchable NTSB database encompassing 2008 thru the present. The tables below are the result and speak for themselves. Some interesting takeaways are that most mishaps occur during the takeoff and initial climb phase rather than during approach and landing, and most mishaps occur during day, VMC conditions with less than ten knots of wind—conditions most of us would consider 100-dollar hamburger weather.
“Virtue signaling.” AOA is the difference between the relative wind and an aircraft reference line. It’s a direct indication of how hard the wing is working. If we display that information to the pilot, it won’t help mitigate other mishap causes other than unintentional stall and isn’t a substitute for sound judgment. It is, however, the single simplest, most inexpensive technical solution with the potential to mitigate stall-induced loss of control accidents; and improve basic aircraft handling skills and energy management. While mentioning AOA at the bar always elicits an opinion, informed or not; I’ve never noted push back against other modern flight instrumentation, GPS, moving map displays, inexpensive auto pilots with vertical navigation, etc. Those technologies have readily flowed into GA, and the adoption of moving map displays has resulted in a measurable decrease in controlled flight into terrain (CFIT) mishaps. This is what scientists call a “natural experiment.” As AOA becomes more prevalent, a similar natural experiment is occurring. I suspect in about 5-10 years, discussing the application of AOA will be as commonplace as talking about programming a GNS, using an electronic flight bag, gusty crosswind landing technique and whether to three-point an airplane with conventional gear.
“They are not us.” As experienced military, airline and GA pilot, I can firmly state we are all aviators, regardless of the type of airplane we fly. All fixed wing airplanes fly using the same physics. In many regards, flying an F-15 is easier than flying a C172. Going around in a heavy 172 at moderate density altitude with a thrust to weight ratio of only .16 to 1 in gusty crosswinds is more of a handful than putting two F-100 engines into afterburner. Like all powered fixed wing airplanes, the C172 and F-15 control energy (a combination of altitude and airspeed) with power and angle of attack. It does take more training to produce an F-15 pilot than a C172 pilot, but surprisingly not that much more with the same basic flying (not combat) qualifications. If the C172 pilot is in an immersion training program, the pace of training is similar. While it’s true there is some attrition in military pilot training, pilot candidates are selected to succeed in training. Actual attrition is low—usually about 5% per class. Having been a flight instructor at an FBO, I don’t recall having 95% of the folks that started learning to fly complete training successfully; and would hazard a guess that actual training attrition is higher overall in GA training than the military when we compare the number of people that start training with the number of people that successfully complete their private check ride. The simple fact is flying isn’t for everybody; and student pilots figure that out as they go along, regardless of the training pipeline that they are in, be it Part 61, 141, undergraduate pilot training in the military, etc.
Military adoption of AOA started with the Navy. Landing an airplane on an aircraft carrier is the most challenging landing scenario in aviation. Landing an F-8 or F-4 aboard an Essex Class deck originally engineered for F4F/F6F class piston engine airplanes was a challenge. Because AOA for approach remains constant regardless of conditions, the Navy developed a control technique of managing AOA with pitch to maintain an “on speed” condition and using throttle to manage glide slope, improving consistency of “coming aboard,” especially under challenging conditions--imagine a pitching deck in the weather at night. On speed is the angle of attack associated with VREF at 1 G, adjusted for current gross weight. It’s a small band of AOA that equates to an airspeed range of about +/- 2 ½ knots of desired approach condition. Like airspeed, AOA can be a relatively “noisy” signal, and it’s simply not practical to fly an exact AOA. The way the military applies AOA for approach and landing is shown in Figure 1, which depicts the visual AOA display (known as an “indexer”) used in the F-18. Note that the Hornet pilot thinks of AOA as airspeed as shown in the figure. We are simply “fast” or “slow” relative to where we want to be (on speed). This makes perfect sense, because when an airplane is in a stable, trimmed condition, AOA controls airspeed [1]
The US Air Force wasn’t as quick to adopt AOA as the USN; but by the mid 60’s had a problem with loss of control and landing mishap rates in the century series airplanes and the trainer used to prepare pilots to fly them, the T-38. Learning from Navy experience, the Air Force equipped the T-38 and its primary fighter at the time, the F-4, with AOA systems that worked just like the system shown in Figure 1. This proved to be remarkably successful at reducing mishap rates in both airplanes. The USAF went one step further and took a page from the Royal Navy playbook and added an “AOA tone” to the F-4 that had a simple audio pattern that worked just like the indexer, without a requirement to look at it. A young engineer fresh out of college named Bert Rutan was instrumental in the effort to reduce F-4 LOC mishap rates. That work is summed up in the phrase “unload for control,” meaning reduce AOA to maintain positive aircraft control.
What’s interesting about military and some civilian AOA systems, is that they provide directive information, not descriptive information like most flight instrumentation. Notice that the chevrons on the standard display in Figure 1 show the pilot what to do with the stick to establish on speed. An AOA system works like a flight director and tells the pilot what to do with pitch and power, without requiring the pilot to interpret a trend and take corrective action. It's like flying with a flight instructor all the time. The F-4 tone does the same thing without the requirement to look at anything. That doesn’t mean AOA is a “crutch” any more than using a moving map display or enclosing the cockpit is a “crutch” to make up for a lack of airmanship. It is simply a more ergonomic way to convey the key information the pilot needs to fly the wing. It’s not even new technology. The first system was patented by Orville in 1913, and you could buy one from the Wright Airplane Company. Interestingly, if you adjust the price for inflation, it cost about 2000 dollars.
Like all of aviation, military aviation has benefited from technological advances. The T-38 and older century series fighters were hard to land and had simple hydraulic flight controls operated manually by the pilot. In contrast, modern airplanes have fully-automatic flight controls and are easy to land, including the T-7, the airplane that will replace the T-38 after 65 years of service. The USN’s “Magic Carpet” system re-maps flight control logic in landing configuration to make coming aboard easier, and all modern fighters are easier to land on 10,000 feet of non-moving pavement and more forgiving in the traffic pattern than their mid-60’s forebearers. The F-35 allows the pilot to synch the auto-throttles to control AOA on approach. This is progress, and similar progress will occur in GA; but now we are at the same crossroads the military was at a half century ago: our GA airplanes have manual flight controls and we have a problem with LOC mishap rates.
What I’ve learned as an instructor, someone who must take a check ride every 9 months and is still learning after 45 years of flying, is that from a student perspective, attitude is everything. Students that show up well prepared and eager to learn do well. Not all students with the right attitude will make it successfully through training, they will fall into the 5% or more who won’t successfully earn their wings. But with the right attitude, students can overcome a myriad of problems, even air sickness. Flying is a completely alien activity for our land-bound species, it’s a leaned skill. It’s perfectly natural to be apprehensive at times whether you are strapped into a fighter plane, an Airbus or a C172. We all learn at our own pace. Military, immersion flying training and airline syllabi can be inherently unforgiving; but in GA, if the student or pilot has the potential to learn, I’ll take the time to work with them. We have much more flexibility to tailor training to the student in GA than we have in the military and airlines.
One thing that’s different is that in fixed-wing primary training in the military, we introduce AOA on the first flight; and trainers are equipped with standardized displays like the one in Figure 1. Many GA airplanes don’t have AOA installed yet, and when they do, there isn’t yet a standard display. Furthermore, civilian systems require field calibration. Automatic calibration and accuracy have already been overcome with proper engineering and modern “compute” capability. As the GA community gains experience, it will coalesce around standards like those used by the military. At a minimum, all AOA systems (when properly calibrated) provide progressive stall warning, and the best provide precise performance cues to the pilot. One other thing that is different in fixed wing military aviation is that all military aviators are taught spins and spin recovery. The FAA eliminated the requirement for spin training in 1949, citing a high number of training accidents. In 1993, an extensive survey-based study was conducted comparing US military and civilian knowledge of spins. The survey spanned military pilots and instructors, civilian pilots, flight instructors and designated pilot examiners. All fixed wing military aviators receive spin training in an airplane. The study showed military student and instructor pilots demonstrated good working knowledge of spins but civilian pilots, even instructors and examiners, demonstrated poor to average knowledge with flight instructors who aspired to be airline pilots performing more poorly than their peers [2]. Besides adoption of AOA, another military lesson learned is to provide spin training to all pilots.
Conclusion. The fatality ratio due to unintentional loss of control has remained consistent at 40-50% annually since the NTSB began maintaining accident databases in 1962, with a slight reduction in the number of accidents after 2008 that is likely the result of a change in way accident events are coded and named in the database [3]. Widespread adoption AOA and teaching pilots how to use it as a technical aid has the potential to reduce LOC mishaps caused by an unintentional stall. It worked in the military under similar circumstances to those we face today (and always have) in GA. It won’t fix poor judgment or a lack of airmanship, and it won’t address shortfalls in airman certification standards, but it shouldn’t be perceived as a “crutch” any more than brakes, pavement and moving the small wheel to the front are “crutch.” We do not want to revert to late 40’s mishap rates and we can do better than 1963. Accurate, ergonomic AOA information presented to the pilot is another arrow in the quiver, just as a GPS moving map display is.
Notes
[1] Rogers, David F., “Angle of Attack Controls Airspeed,” 2013.
[2] Viellette, P.R., “Reexamination of Stall and Spin Prevention Training,” Transportation Research Record 1379, 1993.
[3] Fala, Nicoletta, “An Analysis of Fixed-Wing Stall-Type Accidents in the United States," Aerospace, 9, 2022.