To: The Airman Certification Standards Working Group
The following remarks pertain to requirements in the Private Pilot-Airplane Airman Certification Standards (ACS) regarding maneuvering during slow flight, specifically: PA.VII.A.S2 and PA.VII.A.S3.(1)
For some context, I have been a full time flight instructor since 1987. I am a nine-time Master Instructor, the 2014 National FAA Safety Team Representative of the Year, and the 2006 National Flight Instructor of the Year. I am a recognized subject matter expert on loss of control in general aviation with the following experience:
* 10,000 hours of total flight time
* 9,000 hours of flight instruction given
* 25,000 landings
* 34,000 spins in 235 general aviation aircraft
* 500 single-engine aircraft N-numbers in my logbook
* 380 aviation talks presented
* More than 75 aviation articles and three aviation textbooks published
At issue is wording in the ACS that requires applicants to demonstrate the following levels of skill while maneuvering during slow flight:
“Establish and maintain an airspeed, approximately 5-10 knots above the 1G stall speed, at which the airplane is capable of maintaining controlled flight without activating a stall warning.”
“Accomplish coordinated straight-and-level flight, turns, climbs, and descents with landing gear and flap configurations specified by the evaluator without activating a stall warning.”(2)
ACS Wording Versus Airworthiness Standards
Given FAA airworthiness standards concerning stall warning systems, the simultaneous requirements of “5–10 knots above the 1G stall speed” and “without activating a stall warning” are incompatible. Airworthiness standards in effect in 1993, for example, required the following:
“stall warning must begin at a speed exceeding the stalling speed by a margin of not less than 5 knots, but not more than the greater of 10 knots or 15 percent of the stalling speed…”(3)
Airworthiness standards since 1996, on the other hand, have required stall warning activation to begin “at a speed exceeding the stalling speed by a margin of not less than 5 knots…”(4) This standard does not specify an upper speed limit for activation of stall warning systems. As a result, while stall warning could be activated—indeed, should be activated per airworthiness standards—no less than 5 knots before the reference stall speed, it could activate with a significantly greater margin to the stall speed.
The ACS requirement to fly without activating stall warning clearly conflicts with the simultaneous requirement to establish and maintain an airspeed 5–10 knots above the reference stall speed. Moreover, design parameters that determine when artificial stall warning activates are beyond the control of the applicant—so much so that an applicant may be forced to transition out of slow flight to prevent stall warning from activating, defeating the purpose of this task altogether.
The incompatibility between the ACS wording and airworthiness standards notwithstanding, the FAA has offered the following justifications:
“The guidance has always intended for there not [emphasis added] to be a stall warning—and that is consistent with slow flight guidance published in AC 120-111.”(5)
“Advocating maneuvering the airplane just below the critical angle of attack with the stall warning activated is neither desirable nor intended.”(6)
These assertions are demonstrably false. For at least several decades now, FAA guidance has been unambiguous about its intent to have stall warning activated while maneuvering during slow flight. For example, in the FAA’s General Aviation Pilot Stall Awareness Training Study conducted in 1975–76 (the FAA Study):
“the student slowed the aircraft to the speed at which the visual or aural stall warning indicator was continually activated [emphasis added]…. Turns were also made at 30° angle of bank with the stall warning indicator continually activated [emphasis added].”(7)
The objective during the FAA Study was for student-participants “to maintain desired heading and altitude at an airspeed and angle of attack which activated the stall warning device [emphasis added], but which did not cause the aircraft to stall.”(8) Two noteworthy results from this study:
“The most effective additional training was slow flight with realistic distractions, which exposed the subjects to situations where they are likely to experience inadvertent stalls.”(9)
“The extra stall and slow flight training was effective in preventing unintentional spins [emphasis added]”(10)
Training in slow flight with stall warning activated coupled with realistic distractions was effective in preventing unintentional spins. Read that again: Slow flight with stall warning activated coupled with realistic distractions was effective in preventing unintentional spins.
The results of this landmark study have driven FAA stall/spin training policy ever since, starting with the introduction of realistic distractions in 1980, followed by the shift from “stall avoidance training” to “stall and spin awareness training” in 1991.(11,12)
Derived from the FAA study, the series of Advisory Circulars (ACs) entitled, Stall and Spin Awareness Training has offered “guidance to flight instructors who provide that training.”(13) The following wording appears in AC 61-67B published in May 1991 through AC 61-67C (Change 2) published in January 2016. All of these ACs recommend the following in Chapter 2, “Stall Avoidance Practice at Slow Airspeeds”:
“(1) Assign a heading and an altitude. Have the student reduce power and slow to an airspeed just above the stall speed…”
“(2) Have the student maintain heading and altitude with the stall warning device activated [emphasis added].”(14,15)
FAA guidance for at least a quarter century has been crystal clear, and for good reason: Training in slow flight with stall warning activated, coupled with realistic distractions, is effective in preventing unintentional spins. “Maneuvering an airplane just below the critical angle of attack with the stall warning activated” not only has been intended, but also is desirable if preventing unintentional spins remains a safety priority with FAA.
Regarding the reference to AC 120-111, slow flight is described therein as “flight just above the stall speed.”(16) This specialized flight training element is intended to expose pilots to “how to maneuver the airplane…without stalling.”(17) The status of the stall warning system during slow flight is not mentioned in this AC. However, the AC does list “manually controlled slow flight” under the heading “Extended Envelope Training.”(18) Revising the long-understood meaning of slow flight as a condition “with the stall warning system activated” now to one “without activation” is incongruous with, and a move away from, the whole concept of “Extended Envelope Training” mandated by CFR §121.423.
In reality, the treatment of slow flight in AC 120-111 is consistent with recommendations made by the International Civil Aviation Organization (ICAO). ICAO describes this specialized training element as follows:
“Slow flight exposes the trainee to flight right above the stall speed of the aeroplane and to manoeuvring [sic] the aeroplane at this speed without stalling. The purpose is to reinforce the basic stall characteristics learned in academics and allow the pilot to obtain handling experience and motion sensations when operating the aeroplane at slow speeds during the entire approach-to-stall regime in various aeroplane attitudes, configurations and bank angles.”(19)
The “approach-to-stall regime” referenced by ICAO is defined as “Flight conditions bordered by stall warning and aerodynamic stall.”(20) Activation of the stall warning system during slow flight is an obvious and integral part of ICAO’s Upset Prevention and Recovery Training (UPRT) framework—the very same framework that informed AC 120-111.(21)
The assertion that no activation of stall warning is somehow “consistent with guidance on slow flight published in AC 120-111” is unsubstantiated at best, disingenuous at worst.
The August 2016 issue of DPE Tips offers further justification for the ACS wording: “The FAA does not advocate disregarding a stall warning while maneuvering an airplane.”(22)
It does not follow that having a student learn to maneuver in slow flight with stall warning activated advocates “intentional disregard” for stall warning. I am not aware of any studies that show a correlation between exposure to stall warning and increased inoculation to it. Recall the FAA Study found that training in slow flight with stall warning activated coupled with realistic distractions was effective in preventing unintentional spins.
Consistent with longstanding FAA guidance on stall and spin awareness training, pilots should be taught to integrate sight, sound, and feel while maneuvering in slow flight. They should also be taught to acknowledge stall warning and understand its ramifications. The ability to fly the airplane precisely while stall warning is activated can be a confidence building exercise as well as a way to incorporate angle of attack (AOA) and G-load awareness in real time. While many permutations are possible, following is an example of dialogue that might occur between an instructor (CFI) and student (STU) while practicing slow flight with stall warning activated:
CFI: Do you hear the stall warning?
CFI: From now on, I want you at least to verbally acknowledge it every time you hear it.
CFI: We are hearing stall warning in this particular configuration, but when else might we hear it?
STU: At any speed, in any attitude, at any power setting.
CFI: Is mechanical stall warning 100 percent reliable?
CFI: What other indications of reduced margin to the stall might we expect?
STU: Reduced control effectiveness and more pronounced engine effects.
CFI: What conditions could cause you to miss hearing the stall warning?
STU: High workload in the traffic pattern, distractions, stress, lack of proficiency.
CFI: I dropped my pencil, please pick it up for me.
STU: Not now, I’m busy aviating!
CFI: What does stall warning mean?
STU: We are operating at high angle of attack, close to the critical angle.
CFI: With regard to your control inputs, what else does stall warning mean?
STU: Do not pull the elevator control any farther aft.
CFI: Are we in a stall?
STU: No, it’s just stall warning.
CFI: What will happen if you apply additional back elevator pressure now?
STU: We’ll stall the airplane.
CFI: What could happen if we encountered a vertical gust right now?
STU: We could stall the airplane.
CFI: What will happen if we increase the G-load by trying to execute a steep turn now?
STU: We’ll probably stall the airplane.
CFI: What should you do if we encounter the stall?
STU: Push the elevator forward.
CFI: What should you do if the engine were to quit now?
STU: Push the elevator forward.
CFI: What should you do to increase our margin of safety to the stall?
STU: Push the elevator forward.
CFI: What should you do to silence stall warning?
STU: Push the elevator forward.
CFI: What should you do to lower the angle of attack?
STU: Push the elevator forward.
CFI: Outside of this training exercise, what will you do if you inadvertently trigger stall warning?
STU: Push the elevator forward.
CFI: If you’re not sure what to do when stall warning activates, what should you do?
STU: Push the elevator forward.
CFI: Do you see a trend in the answers to the above questions?
STU: Yes, push on the elevator, don’t pull.
Despite the ACS wording and attempts to justify it, the FAA “still expects a pilot to know and understand the aerodynamics behind how the airplane performs from the time the stall warning is activated to reaching a full stall.”(23) Based on this, it seems not only logical to continue to train and test this critical task as it was done in the FAA Study and as recommended in FAA guidance on stall and spin awareness training. It is also imperative for safety since doing this has been shown to be effective in preventing unintentional spins.
As worded, ACS PA.VII.A.S2 and PA.VII.A.S3:
* Retreat from an established training paradigm shown to be “effective in preventing unintentional spins” and, in combination with realistic distractions, the “most effective” training for situations where pilots “are likely to experience inadvertent stalls.”(24,25)
* Diminish the importance of gaining valuable experience and confidence with degradation in flight control responsiveness and more pronounced engine effects, as well as the importance of proper coordination in slow flight near the critical angle of attack.
* Contradict longstanding FAA policy and guidance on stall and spin awareness training, as well as recent ICAO recommendations on upset prevention and recovery training.
* Will impede efforts to reduce fatal loss of control accidents in general aviation.
Rather than moving away from a training and testing strategy proven effective in preventing unintentional spins, as well as from the current trend toward incorporating UPRT into all levels of pilot training, I strongly urge FAA to:
- Realign wording in the ACS and Airplane Flying Handbook (FAA-H-8083-3) with longstanding FAA guidance and more recent ICAO recommendations on training and testing within the approach-to-stall regime.
- Abandon plans to revise other FAA publications to reflect current ACS wording, and rescind Safety Alert for Operators 16010.
- Redouble its efforts to emphasize and encourage stall/spin awareness training according to longstanding guidance.
- Ensure that ground and flight instructors are indeed well-versed in stall/spin dynamics in theory and in practice, as well as in the available training guidance.
- Promote AOA and G-load awareness per recommendations from the SAFE Symposium Curricula Breakout Group.(26)
The current ACS wording on slow flight is a step backwards, discourages incorporation of UPRT concepts and extended envelope training, and has the potential to reduce safety.
Rich Stowell, MCFI-A
(1) FAA, Private Pilot–Airplane, Airman Certification Standards (FAA-S-ACS-6, Change 1), June 2016, 54.
(2) FAA, Private Pilot–Airplane, Airman Certification Standards, 54.
(3) FAA, Part 23–Airworthiness Standards (specifically §23.207), January 1, 1993, 164.
(4) FAA, Part 23–Airworthiness Standards (specifically §23.207), accessed August 19, 2016, available http://www.faa.gov/regulations_policies/faa_regulations/
(5) Email from 9-AVS-ACS-Focus-Team@faa.gov to Howard Wolvington, 10 June 2016.
(6) FAA, Safety Alert for Pilots (SAFO 16010), August 30, 2016, 3.
(7) William C. Hoffman and Walter M. Hollister, General Aviation Pilot Stall Awareness Training Study (FAA-RD-77-26), September 1976, 24.
(8) Hoffman and Hollister, General Aviation Pilot Stall Awareness Training Study, 29.
(9) Hoffman and Hollister, General Aviation Pilot Stall Awareness Training Study, 57.
(10) Hoffman and Hollister, General Aviation Pilot Stall Awareness Training Study, 56.
(11) See Use of Distractions During Pilot Certification Flight Tests (AC 61-91), January 25, 1980.
(12) See Stall and Spin Awareness Training (AC 61-67B), May 17, 1991.
(13) FAA, Stall and Spin Awareness Training (AC 61-67B), May 17, 1991, 1.
(14) FAA, Stall and Spin Awareness Training, 10.
(15) FAA, Stall and Spin Awareness Training (AC 61-67C, Change 2), January 6, 2016, 9.
(16) FAA, Upset Prevention and Recovery Training (AC 120-111), April 14, 2015, Appendix 1, 9.
(17) FAA, Upset Prevention and Recovery Training, Appendix 1, 9.
(18) FAA, Upset Prevention and Recovery Training, Appendix 1, 2.
(19) ICAO, Manual on Aeroplane Upset Prevention and Recovery Training, 2014, 3-9.
(20) ICAO, Manual on Aeroplane Upset Prevention and Recovery Training, x.
(21) FAA, Upset Prevention and Recovery Training, 1.
(22) DPE Tips (Vol 1, Issue 3), August 2016, 1.
(23) DPE Tips, 2.
(24) Hoffman and Hollister, General Aviation Pilot Stall Awareness Training Study, 56.
(25) Hoffman and Hollister, General Aviation Pilot Stall Awareness Training Study, 57.
(26) Society of Aviation and Flight Educators, Pilot Training Reform Symposium: Preliminary Report (June 6, 2011), 29.
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5 thoughts on “Rich Stowell Slow Flight Viewpoint!”
Thank you Rich, for taking the time to write this well researched and logical rebuttal to the latest nonsense from our FAA. My letter merely included the fact that in every loss of control incrdent I experienced during 15 years as DPE, my sebeeauent research revealed that the applicant had been instructed incorrectly; to fly slow flight at a speed above the stall warning and/or recover from stalls AT the stall warning horn.
Thanks again for your excellent response.
“sebeeauent (?) research revealed that the app…”. What is sebeeauent?
It would be meaningful to investigate techniques and procedures recommended to Part 121 pilots when encountering windshear. United Air Lines developed these techniques during the 1980s. They include intentionally flying at the onset of the stick-shaker by intentionally seeking to have it activate. This technique involves increasing the angle of attack until the stick shaker begins then decreasing it slightly until it stops but increasing it again immediately when it stops etc. etc. etc. These recommendations were developed with the understanding that pilots had previously acquired a comfort and skill level in this flight regime.
The findings of the Buffalo accident produced all of the ATP changes based on the need for better training in the basics, the main one of which was recognizing and recovery from stalls. How does this change address that effort?
Given the various disparities and inconsistencies so clearly pointed out, I would just like to know the NAME(S) of the person or persons who came up with the final draft of this new FAA document. I am not opposed to it, but I just want to know what planet they are from, in addition to the REAL amount of hours they have in the light GA aircraft which we have been using for the past 50 years. We are not giving flight training in Convair 440’s. Yes.. loss of aircraft control usually begins at speeds well above stall (stall/spin avoidance training for this). But, recognizing which control inputs are needed to get the plane to do what you want it to do in a situation where the opertor senses a stall or spin is imminent…, well, that is what learning to fly is all about. We need to teach people how to control the plane just before they lose control of it. I’m not impressed with grease-job landings from a fast power-on approaches. Learn to fly planes first. And while we’re at it, I’m just about sick of the proliferation of acronyms. I’ve been instructing since 1970.