U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Stall and Spin Awareness Training Date: 1/6/16 AC No: 61-67C Initiated by: AFS-810 Change: 2
1. PURPOSE. This advisory circular (AC) explains the stall and spin awareness training required under Title 14 of the Code of Federal Regulations (14 CFR) part 61 and offers guidance to flight instructors who provide it. This AC also informs pilots of the airworthiness standards for the type certification of normal, utility, and acrobatic category airplanes prescribed in 14 CFR part 23, § 23.221, concerning spin maneuvers, and it emphasizes the importance of observing restrictions that prohibit the intentional spins of certain airplanes.
2. PRINCIPAL CHANGES. This change to the AC incorporates new language into subparagraphs 301a and 301b to clarify the current rule allowances for certificated flight instructor (CFI) training. This change also removes a reference to 14 CFR part 61, § 61.167, that is not applicable, and removes subparagraph 301c.
PAGE CONTROL CHART Remove Pages Dated Insert Pages Dated Page iii Page 14 9/25/00 9/25/00 Page iii Page 14 1/6/16 1/6/16 ORIGINAL SIGNED by /s/ John S. Duncan Director, Flight Standards Service
U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Stall and Spin Awareness Training Date: 9/25/00 AC No: 61-67C Initiated by: AFS-810 Change:
1. PURPOSE. This advisory circular (AC) explains the stall and spin awareness training required under Title 14 of the Code of Federal Regulations (14 CFR) part 61 and offers guidance to flight instructors who provide it. This AC also informs pilots of the airworthiness standards for the type certification of normal, utility, and acrobatic category airplanes prescribed in 14 CFR part 23, § 23.221, concerning spin maneuvers, and it emphasizes the importance of observing restrictions that prohibit the intentional spins of certain airplanes.
2. RELATED READING MATERIAL (current editions).
a. Report No. FAA-RD-77-26, General Aviation Pilot Stall Awareness Training Study. This document may be purchased from the National Technical Information Service (NTIS), U.S.
Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22161. To order by telephone call: (800) 553-6847. The NTIS identification number is ADA041310.
b. The following documents are available on the Internet at http://www.faa.gov/.
(1) AC 61-65, Certification: Pilots and Flight and Ground Instructors.
(2) FAA-H-8083-1, Aircraft Weight and Balance Handbook.
(3) FAA-H-8083-3, Airplane Flying Handbook.
(4) FAA-H-8083-9, Aviation Instructor’s Handbook.
(5) FAA-S-8081-3, Recreational Pilot - Practical Test Standards for Airplane and Rotorcraft.
(6) FAA-S-8081-6, Flight Instructor - Practical Test Standards for Airplane (Single-Engine/Multiengine).
(7) FAA-S-8081-8, Flight Instructor - Practical Test Standards for Glider.
(8) FAA-S-8081-12, Commercial Pilot - Practical Test Standards for Airplane.
(9) FAA-S-8081-14, Private Pilot - Practical Test Standards for Airplane.
(10) FAA-S-8081-22, Private Pilot - Practical Test Standards for Glider.
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(11) FAA-S-8081-23, Commercial Pilot - Practical Test Standards for Glider.
(12) FAA-S-8081-29, Sport Pilot - Practical Test Standards for Airplane, Gyroplane, Glider, Flight Instructor.
(13) FAA-S-8081-31, Sport Pilot - Practical Standards for Weight Shift Control, Powered Parachute, Flight Instructor.
3. BACKGROUND. In January 1980, the Federal Aviation Administration (FAA) announced its policy of incorporating the use of certain distractions during the performance of flight test maneuvers. This policy came about as a result of Report No. FAA-RD-77-26, General Aviation Pilot Stall Awareness Study, which revealed that stall/spin related accidents accounted for approximately one-quarter of all fatal general aviation accidents. National Transportation Safety Board (NTSB) statistics indicate that most stall/spin accidents result when a pilot is distracted momentarily from the primary task of flying the aircraft. Changes to part 61, completed in 1991, included increased stall and spin awareness training for recreational, private, and commercial Pilot Certificate applicants. The training is intended to emphasize recognition of situations that could lead to an inadvertent stall and/or spin by using realistic distractions such as those suggested in Report No. FAA-RD-77-26 and incorporated into the performance of flight test maneuvers. Although the training is intended to emphasize stall and spin awareness and recovery techniques for all pilots, only flight instructor-airplane and flight instructor-glider candidates are required to demonstrate instructional proficiency in spin entry, spins, and spin recovery techniques as a requirement for certification. Part 61 was extensively updated in 1997. Sections of part 23 (Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Category Airplanes) that apply to spin requirements and placards have changed. This AC incorporates those changes.
4. COMMENTS INVITED. Comments regarding this publication should be directed to:
Federal Aviation Administration General Aviation and Commercial Division, AFS-800 800 Independence Ave., S.W.
Washington, DC 20591 Every comment will not necessarily generate a direct acknowledgment to the commenter.
Comments received will be considered in the development of upcoming AC revisions or other related technical material.
5. INTERNET. AC 61-67C, Stall and Spin Awareness Training, can be accessed on the Internet at http://rgl.faa.gov/.
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CONTENTS Paragraph Page
CHAPTER 1. GROUND TRAINING: STALL AND SPIN AWARENESS1
100. Stall/Spin Effects and Definitions1
101. Distractions3
102. Wing Contamination Effects on Stall Warning, Stall Speed, and Poststall Recovery3
103. Stall Recognition4
104. Types of Stalls4
105. Stall Recovery4
106. Secondary Stalls5
107. Spins5
108. Weight and Balance5
109. Primary Cause5
110. Types of Spins6
111. Spin Recovery6
112. Spiral Mode Recovery7
113. thru 199. Reserved7
CHAPTER 2. FLIGHT TRAINING: STALLS9
200. Stall Training9
201. thru 299. Reserved11
CHAPTER 3. FLIGHT TRAINING: SPINS13
300. Spin Training13
301. Spin Training and Parachutes14
302. thru 399. Reserved14
CHAPTER 4. AIRWORTHINESS STANDARDS15
400. Operating Limitations15
401. Placards16
402. Pilot Awareness16
403. thru 499. Reserved16
Par 100 Page 1 CHAPTER 1. GROUND TRAINING: STALL AND SPIN AWARENESS
100. STALL/SPIN EFFECTS AND DEFINITIONS. A stall occurs when the smooth airflow over the airplane’s wing is disrupted, and the lift degenerates rapidly. This is caused when the wing exceeds its critical angle of attack (AOA). This can occur at any airspeed, in any attitude, with any power setting. If recovery from a stall is not achieved in a timely and appropriate manner by reducing the AOA, a secondary stall and/or a spin may result. All spins are preceded by a stall on at least part of the wing. The angle of the relative wind is determined primarily by the aircraft's airspeed and attitude. Factors such as aircraft weight, center of gravity (CG), configuration, and the amount of acceleration used in a turn are also considered. The speed at which the critical angle of the relative wind is exceeded is the stall speed. Stall speeds are listed in the Airplane Flight Manual (AFM) or the pilot’s operating handbook (POH) and pertain to certain conditions or aircraft configurations, e.g., landing configuration. Other specific operational speeds are calculated based upon the aircraft's stall speed in the landing configuration. Airspeed values specified in the AFM or POH may vary under different circumstances. Factors such as weight, CG, altitude, temperature, turbulence, and the presence of snow, ice, or frost on the wings will affect an aircraft’s stall speed. To thoroughly understand the stall/spin phenomenon, some basic factors affecting aircraft aerodynamics and flight should be reviewed with particular emphasis on their relation to stall speeds. Much of the information in this AC is also applicable to gliders. The following terms are defined as they relate to stalls/spins.
a. Angle of Attack (AOA). AOA is the angle at which the chord line of the wing meets the relative wind. The chord line is a straight line drawn through the profile of the wing connecting the extremities of the leading edge and trailing edge. The AOA must be small enough to allow attached airflow over and under the airfoil to produce lift. AOA is an element of lift.
Change in AOA will affect the amount of lift that is produced. An excessive AOA will disrupt the flow of air over the airfoil. If the AOA is not reduced, a section of the airfoil will reach its critical AOA, lose lift, and stall. Exceeding the critical AOA for a particular airfoil section will always result in a stall of that section.
b. Airspeed. Airspeed is controlled primarily by the elevator or longitudinal control position for a given configuration and power. Conversely, airspeed is controlled by power at a given configuration and AOA. If an airplane’s speed is too slow, the AOA required for level flight will be so large that the air can no longer follow the upper curvature of the wing. The result is a separation of airflow from the wing, loss of lift, a large increase in drag, and eventually a stall if the AOA is not reduced. The stall is the result of excessive AOA—not insufficient airspeed. For example, at a 60° banked turn in level coordinated flight, the load factor is 2 G’s and the stall speed increases 40 percent over the straight and level stall speed. A stall can occur at any airspeed, in any attitude, at any power setting.
c. Configuration. Flaps, landing gear, and other configuring devices can affect an airplane’s stall speed. Extension of flaps and/or landing gear in flight will increase drag. Flap extension will generally increase the lifting ability of the wings, thus reducing the airplane’s stall speed. The effect of flaps on an airplane’s stall speed can be seen by markings on the airplane’s airspeed indicator, where the lower airspeed limit of the white arc (power-off stall speed with
Page 2 Par 100 gear and flaps in the landing configuration) is less than the lower airspeed limit of the green arc (power-off stall speed in the clean configuration).
d. VSO. VSO is the stall speed or the minimum steady flight speed in the landing configuration.
e. VS1. VS1 is the stall speed or the minimum steady flight speed obtained in a specified configuration.
f. VA. VA is the design maneuvering speed. Do not use full or abrupt control movements at or above this speed. It is possible to exceed the airplane structural limits at or above VA. Rapid and large alternating control inputs, especially in combination with large changes in pitch, roll, or yaw (e.g., large side slip angles) may result in structural failures at any speed, even below VA.
g. Load Factor. Load factor is the ratio of the lifting force produced by the wings to the actual weight of the airplane and its contents. Load factors are usually expressed in terms of “G.”
The aircraft’s stall speed increases in proportion to the square root of the load factor. For example, an airplane that has a normal unaccelerated stall speed of 45 knots can be stalled at 90 knots when subjected to a load factor of 4 G’s. The possibility of inadvertently stalling the airplane by increasing the load factor (i.e., by putting the airplane in a steep turn or spiral) is much greater than in normal cruise flight. When an airplane stalls at a higher indicated air speed due to excessive maneuvering loads, it is called an accelerated maneuver stall. A stall entered from straight and level flight or from an unaccelerated straight climb will not produce additional load factors. In a constant rate turn, increased load factors will cause an airplane's stall speed to increase as the angle of bank increases. Excessively steep banks should be avoided because the airplane will stall at a much higher speed. If the aircraft exceeds maneuvering speed, structural damage to the aircraft may result before it stalls. If the nose falls during a steep turn, the pilot might attempt to raise it to the level flight attitude without shallowing the bank. This situation tightens the turn and can lead to a diving spiral. A feeling of weightlessness will result if a stall recovery is performed by abruptly pushing the elevator control forward, which will reduce the up load on the wings. Recoveries from stalls and spins involve a tradeoff between loss of altitude (and an increase in airspeed) and an increase in load factor in the pullup. However, recovery from the dive following spin recovery generally causes higher airspeeds and consequently higher load factors than stall recoveries due to the much lower position of the nose. Significant load factor increases are sometimes induced during pullup after recovery from a stall or spin. It should be noted that structural damage can result from the high load factors that could be imposed on the aircraft by intentional stalls practiced above the airplane’s design maneuvering speed. Large, aggressive control reversals can also lead to loads that can exceed the structural design limits, even at speeds below the airplane’s design maneuvering speed.
h. Center of Gravity (CG). The CG location has a direct effect on the effective lift and AOA of the wing, the amount and direction of force on the tail, and the degree of stabilizer deflection needed to supply the proper tail force for equilibrium. The CG position, therefore, has a significant effect on stability and stall/spin recovery. As the CG is moved aft, the amount of elevator deflection needed to stall the airplane at a given load factor will be reduced. An increased AOA will be achieved with less elevator control force. This could make the entry into inadvertent stalls easier, and during the subsequent recovery, it would be easier to generate
Par 100 Page 3 higher load factors due to the reduced elevator control forces. In an airplane with an extremely aft CG, very light back elevator control forces may lead to inadvertent stall entries and if a spin is entered, the balance of forces on the airplane may result in a flat spin. Recovery from a flat spin is often impossible. A forward CG location will often cause the stalling AOA to be reached at a higher airspeed. Increased back elevator control force is generally required with a forward CG location.
i. Weight. Although the distribution of weight has the most direct effect on stability, increased gross weight can also have an effect on an aircraft's flight characteristics, regardless of the CG position. As the weight of the airplane is increased, the stall speed increases. The increased weight requires a higher AOA to produce additional lift to support the weight.
j. Altitude and Temperature. Altitude has little or no effect on an airplane’s indicated stall speed. Thinner air at higher altitudes will result in decreased aircraft performance and a higher true airspeed for a given indicated airspeed. Higher than standard temperatures will also contribute to increased true airspeed for a given indicated airspeed. However, the higher true airspeed has no effect on indicated approach or stall speeds. The manufacturer’s recommended indicated airspeeds should therefore be maintained during the landing approach, regardless of the elevation or the density altitude at the airport of landing.
k. Snow, Ice, or Frost on the Wings. Even a small accumulation of snow, ice, or frost on an aircraft’s surface can cause an increase in that aircraft’s stall speed. Such accumulation changes the shape of the wing, disrupting the smooth flow of air over the surface and, consequently, increasing drag and decreasing lift. Flight should not be attempted when snow, ice, or frost have accumulated on the aircraft surfaces.
l. Turbulence. Turbulence can cause an aircraft to stall at a significantly higher airspeed than in stable conditions. A vertical gust or wind shear can cause a sudden change in the relative wind, and result in an abrupt increase in AOA. Although a gust may not be maintained long enough for a stall to develop, the aircraft may stall while the pilot is attempting to control the flightpath, particularly during an approach in gusty conditions. When flying in moderate to severe turbulence or strong crosswinds, a higher than normal approach speed should be maintained. In cruise flight in moderate or severe turbulence, an airspeed well above the indicated stall speed and below maneuvering speed should be used. Maneuvering speed is lower at a lower weight.
101. DISTRACTIONS. Stalls resulting from improper airspeed management are most likely to occur when the pilot is distracted by one or more other tasks, such as locating a checklist or attempting a restart after an engine failure; flying a traffic pattern on a windy day; reading a chart or making fuel and/or distance calculations; or attempting to retrieve items from the floor, back seat, or glove compartment. Pilots at all skill levels should be aware of the increased risk of entering into an inadvertent stall or spin while performing tasks that are secondary to controlling the aircraft.
102. WING CONTAMINATION EFFECTS ON STALL WARNING, STALL SPEED, AND POSTSTALL RECOVERY. Stall speeds and stall characteristics are usually determined with uncontaminated airfoils. For airplanes that are certified for flight in icing conditions, ice
Page 4 Par 102 shapes may have also been considered for their effects on aircraft. However, not all possible icing conditions and configurations can be tested. Icing is the primary concern, but any contamination or alteration of the leading edge caused by factors such as mud, insect residue, or ice can significantly alter the aerodynamic characteristics of the wing, but it is icing that is of primary concern.
a. In some icing conditions there are adverse changes to the stall speed, stall characteristics, performance, and handling characteristics of the airplane. These adverse changes are potentially hazardous for several reasons. First, aerodynamic stall may occur with little or none of the usual cues in advance. These cues include airframe or control surface buffet, reduced control effectiveness, and activation of the stall warning horn, stick shaker, and stick pusher.
Next, because insufficient power or thrust to increase speed while holding constant altitude to reduce the AOA. Finally, poststall recovery of a contaminated airplane may be complicated by gross changes in control effectiveness, airplane response characteristics, and abnormal control forces. As a result of these factors, large losses in altitude can occur during recovery.
b. Accordingly, in these conditions, a prompt control input to decrease pitch attitude to recover lateral control, with aggressive power application ensures the most rapid recovery with minimum altitude loss. The AOA must be reduced immediately as the wing, or part of the wing is already stalled and no margin remains to allow holding altitude/attitude as power is applied.
The pilot should note the AOA (or airspeed) at upset and not approach that AOA (airspeed) during the recovery or another upset may occur. This AOA may be well below the normal stall AOA (below shaker AOA) and the airspeed may be well above normal stall airspeed. Stall speed increases as high as 50 knots have been observed in post upset data review.
c. Further complications involve use of the autopilot. The autopilot may apply control inputs that will mask detection of some of these tactile cues by the pilot or attempt to control the airplane in the stall. Sudden autopilot self-disconnect with control surfaces trimmed into extreme positions or with controls trimmed into uncoordinated flight will complicate poststall recovery and may lead to a spin or spiral.
103. STALL RECOGNITION. There are several ways to recognize that a stall is impending before it actually occurs. When one or more of these indicators is noted, initiation of a recovery should be instinctive (unless a full stall is being practiced intentionally from an altitude that allows recovery at least 1,500 feet above ground level (AGL) for single-engine airplanes and 3,000 feet AGL for multiengine airplanes). One indication of a stall is a mushy feeling in the flight controls and less control effect as the aircraft's speed is reduced. This reduction in control effectiveness is attributed in part to reduced airflow over the flight control surfaces. In fixed pitch propeller airplanes, a loss of revolutions per minute (rpm) may be evident when approaching a stall in power-on conditions. For both airplanes and gliders, a reduction in the sound of air flowing along the fuselage is usually evident. Just before the stall occurs, buffeting, uncontrollable pitching, or vibrations may begin. Many aircraft are equipped with stall warning devices that will alert the pilot 4 to 8 knots prior to the onset of a stall. Finally, kinesthesia (the sensing of changes in direction or speed of motion), when properly learned and developed, will warn the pilot of a decrease in speed or the beginning of a mushing of the aircraft. These preliminary indications serve as a warning to the pilot to increase airspeed by adding power, lowering the nose, and/or decreasing the angle of bank.
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104. TYPES OF STALLS. Stalls can be practiced both with and without power. Stalls should be practiced to familiarize the student with the aircraft’s particular stall characteristics without putting the aircraft into a potentially dangerous condition. In multiengine airplanes, single-engine stalls must be avoided. Descriptions of some different types of stalls follows:
a. Power-off stalls (also known as approach-to-landing stalls) are practiced to simulate normal approach-to-landing conditions and configuration. Many stall/spin accidents have occurred in these power-off situations, such as crossed control turns from base leg to final approach (resulting in a skidding or slipping turn); attempting to recover from a high sink rate on final approach by using only an increased pitch attitude; and improper airspeed control on final approach or in other segments of the traffic pattern.
b. Power-on stalls (also known as departure stalls) are practiced to simulate takeoff and climbout conditions and configuration. Many stall/spin accidents have occurred during these phases of flight, particularly during go-arounds. A causal factor in such accidents has been the pilot’s failure to maintain positive control due to a nose-high trim setting or premature flap retraction, and during short field takeoffs has also been a causal accident factor.
c. Accelerated stalls can occur at higher-than-normal airspeeds due to abrupt and/or excessive control applications. These stalls may occur in steep turns, pullups, or other abrupt changes in flightpath. Accelerated stalls usually are more severe than unaccelerated stalls and are often unexpected because they occur at higher-than-normal airspeeds.
105. STALL RECOVERY. The key factor in recovering from a stall is regaining positive control of the aircraft by reducing the AOA. At the first indication of a stall, the aircraft AOA must be decreased to allow the wings to regain lift. Every aircraft in upright flight may require a different amount of forward pressure or relaxation of elevator back pressure to regain lift. It should be noted that too much forward pressure can hinder recovery by imposing a negative load on the wing. The next step in recovering from a stall is to smoothly apply maximum allowable power (if applicable) to increase the airspeed and to minimize the loss of altitude. Certain high performance airplanes may require only an increase in thrust and relaxation of the back pressure on the yoke to effect recovery. As airspeed increases and the recovery is completed, power should be adjusted to return the airplane to the desired flight condition. Straight and level flight should be established with full coordinated use of the controls. The airspeed indicator or tachometer, if installed, should never be allowed to reach their high speed red lines at any time during a practice stall.
106. SECONDARY STALLS. If recovery from a stall is not made properly, a secondary stall or a spin may result. A secondary stall is caused by attempting to hasten the completion of a stall recovery before the aircraft has regained sufficient flying speed. When this stall occurs, appropriate forward pressure or the relaxation of back elevator pressure should again be performed just as in a normal stall recovery. When sufficient airspeed has been regained, the aircraft can then be returned to straight and level flight.
107. SPINS. A spin may be defined as an aggravated stall that results in what is termed “autorotation” wherein the airplane follows a downward corkscrew path. As the airplane rotates around a vertical axis, the rising wing is less stalled than the descending wing creating a rolling,
Page 6 Par 107 yawing, and pitching motion. The airplane is basically being forced downward by gravity, rolling, yawing, and pitching in a spiral path.
108. WEIGHT AND BALANCE. Minor weight or balance changes can affect an aircraft’s spin characteristics. For example, the addition of a suitcase in the aft baggage compartment will affect the weight and balance of the aircraft. An aircraft that may be difficult to spin intentionally in the utility category (restricted aft CG and reduced weight) could have less resistance to spin entry in the normal category (less restricted aft CG and increased weight) due to its ability to generate a higher AOA and increased load factor. Furthermore, an aircraft that is approved for spins in the utility category, but loaded in the normal category, may not be recoverable from a spin that is allowed to progress beyond one turn or 3-second spin, whichever is longer (refer to 14 CFR part 23, § 23.221(a)).
109. PRIMARY CAUSE. The primary cause of an inadvertent spin is exceeding the critical AOA while applying excessive or insufficient rudder and, to a lesser extent, aileron. Insufficient or excessive control inputs to correct for Power Factor (PF), or asymmetric propeller loading, could aggravate the precipitation of a spin. At a high AOA the downward moving blade, which is normally on the right side of the propeller arc, has a higher AOA and therefore higher thrust than the upward moving blade on the left. This results in a tendency for the airplane to yaw around the vertical axis to the left. If insufficient or excessive rudder correction is applied to counteract PF, uncoordinated flight may result. A classic situation where PF could play an important role in a stall/spin accident is during a go-around or short field takeoff where the airplane is at a high pitch attitude, high power setting, and low airspeed. In an uncoordinated maneuver, the pitot/static instruments, especially the altimeter and airspeed indicator, are unreliable due to the uneven distribution of air pressure over the fuselage. The pilot may not be aware that a critical AOA is approaching until the stall warning device activates. If a stall recovery is not promptly initiated, the airplane is more likely to enter an inadvertent spin. For example, stall/spin accidents have occurred during a turn from base to final because the pilot attempted to rudder the airplane around (skid) so as not to overshoot the runway nor use excessive bank angle in the traffic pattern. The spin that occurs from cross controlling an aircraft usually results in rotation in the direction of the rudder being applied, regardless of which wingtip is raised. In a skidding turn, where both aileron and rudder are applied in the same direction, rotation will be in the direction the controls are applied. However, in a slipping turn, where opposite aileron is held against the rudder, the resultant spin will usually occur in the direction opposite the aileron that is being applied.
110. TYPES OF SPINS.
a. An incipient spin is that portion of a spin from the time the airplane stalls and rotation starts, until the spin becomes fully developed. Incipient spins that are not allowed to develop into a steady state spin are commonly used as an introduction to spin training and recovery techniques.
b. A fully developed, steady state spin occurs when the aircraft angular rotation rate, airspeed, and vertical speed are stabilized from turn-to-turn in a flightpath that is close to vertical.