motion may then be observed while restraining the control stick at the trim position (controls-fixed short period) or with the control stick free (controls-free short period).
(iii) Sequence of Control Inputs. Pulses may also be performed by first applying airplane nose-down longitudinal control.
(4) Conditions and Configurations. Short period dynamic longitudinal stability should be checked under all the conditions and configurations where static longitudinal stability is checked; therefore, the test pilot may find it convenient to test for both on the same flights. It is not intended nor required that every point along a stick force curve be checked for dynamic stability; however, a sufficient number of points should be checked in each configuration to ensure compliance at all operational speeds.
c. Procedures - Longitudinal Long Period (phugoid ) Dynamic Stability.
(1) General. The test for the phugoid mode is accomplished as follows:
(i) Cause the airplane to depart a significant amount from trim speed (about +10 percent should be sufficient) with an elevator input; and
(ii) Allow the ensuing oscillations in speed, rate of climb and descent, altitude, and pitch attitude to proceed without attempting to constrain any of the variables as long as airspeed, load factor, or other limitations are not exceeded.
(2) The Pulse Input. An appropriate control input for the phugoid test is a relatively slow elevator pulse to cause the airplane to increase or decrease speed from the trim point. Once the speed deviation is attained, the control is moved back to the original position and released.
(3) Conditions and Configurations. Long period dynamic stability should be checked under all of the conditions and configurations for which longitudinal static stability is checked. As in the short period case, it is not intended that every point along a stick force curve be checked for phugoid damping; however, enough conditions should be checked to determine acceptable characteristics at all operational speeds.
(4) Data. The phugoid motion proceeds slowly enough that it is reasonable to record minimum and maximum airspeed excursions as a function of time and enable construction of an envelope from which time to half-double amplitude may be determined.
d. Explanation - Lateral/Directional Dynamic Stability. Characteristic lateral-directional motions normally involve three modes:
(1) A highly-damped convergence, called the roll mode, through which the pilot controls roll rate and, hence, bank angle;
(2) A slow-acting mode, called the spiral, that may be stable but is often neutrally stable or even mildly divergent in roll and yaw; and
(3) An oscillatory mode, called the Dutch roll, that involves combined rolling and yawing motions and that may be excited by either rudder or aileron inputs or by gust encounters.
In addition, short period yawing oscillations due to rudder floating may sometimes be observed.
The roll mode will almost always be satisfactory as judged by the ability to precisely control bank angle and counter gust upsets unless the response is slowed by high roll inertia or inadequate roll 80
control power. Section 23.181(b) requires that the Dutch roll mode be investigated and determined to damp to 1/10 amplitude within 7 cycles. Also, any short period yawing oscillation associated with rudder motions must be heavily damped.
e. Procedures - Lateral/Directional. Two of the methods that may be used are described below:
(1) Rudder Pulsing. The rudder pulsing technique excites the Dutch roll motion nicely while suppressing the spiral mode if performed correctly. In addition, this technique can be used to develop a large amplitude oscillation that aids in data gathering and analysis, particularly if the Dutch roll is heavily damped. It is performed as follows:
(i) Flight Condition. Stabilize and trim carefully in the desired configuration at the desired flight condition.
(ii) Control Inputs. Smoothly apply alternating left and right rudder inputs in order to excite and reinforce the Dutch roll motion. Restrain the lateral cockpit control at the trim condition or merely release it. Continue the cyclic rudder pulsing until the desired magnitude of oscillatory motion is attained, then smoothly return the rudder pedals to the trim position and release them (controls free) or restrain them (controls fixed) in the trim position.
(iii) Input Frequency. The frequency with which the cyclic rudder inputs are applied depends on the frequency and response characteristics of the airplane. The test pilot should adjust the frequency of rudder pulsing to the particular airplane. The maximum Dutch roll response will be generated when the rudder pulsing is in phase with the airplane motion and the frequency of the rudder pulses is approximately the same as the natural (undamped) frequency of the Dutch roll.
(iv) Spiral Motion. The test pilot should attempt to terminate the rudder pulsing so that the airplane oscillates about a wings-level condition. This should effectively suppress the spiral motion.
(v) Data. Obtaining quantitative information on Dutch roll characteristics from cockpit instruments and visual observations requires patience, particularly if the motion is heavily damped. If instrumentation is available to record sideslip angle versus time, the dynamic characteristics of the maneuver can readily be determined. The turn needle of the needle-ball instrument can also be used to observe 1/10 amplitude damping and the damping period.
(2) Steady Sideslip. The steady sideslip release can also be used to excite the Dutch roll;
however, the difficulty in quickly returning the controls to trim and the influence of the spiral mode often precludes the gathering of good quantitative results. Full rudder or a large amplitude sideslip may cause high loads on the airplane. The rudder pulsing technique usually produces better Dutch roll data. The steady sideslip release technique is performed as follows:
(i) Flight Condition. Stabilize and trim carefully in the desired configuration at the desired flight condition.
(ii) Control Input. Establish a steady heading sideslip of a sufficient magnitude to obtain sufficient Dutch roll motion for analysis. Utilize maximum allowable sideslip, using rudder as required. Stabilize the sideslip carefully. Quickly, but smoothly, return all cockpit controls to trim and release them (controls-free Dutch roll) or restrain them at the trim position (controls-fixed Dutch roll). Both methods should be utilized.
f. Stability Augmentation Systems (SAS). If the airplane is equipped with SAS, the airplane's characteristics should be evaluated throughout the approved operating envelope following failures that affect the damping of the applicable mode. Following a SAS failure, if unsatisfactory damping is confined to an avoidable flight area or configuration and is controllable to return the airplane to a satisfactory operational condition for continued safe flight, the lack of appreciable positive damping may be acceptable. Control of the airplane, including recovery, should be satisfactory using applicable control inputs. Following a critical failure, the degree of damping required should depend on the effect the oscillation will have on pilot tasks, considering environmental conditions. The capability to handle this condition should be demonstrated and evaluated. If a satisfactory reduced operational envelope is developed, appropriate procedures, performance, and limitations should be placed in the AFM. If a critical failure results in an unsafe condition, a redundant SAS may be required.
g. Data Acquisition and Reduction. Data acquisition for this test should support a conclusion that any short period oscillation is heavily damped and any Dutch roll is damped to 1/10 amplitude in 7 cycles.
h. Maximum Allowable Speed. Should be taken to mean VFE, VLE, VNE, and VFC/MFC, as appropriate.
76.-85. RESERVED.
Section 7. STALLS
86. SECTION 23.201 WINGS LEVEL STALL.
a. Explanation.
(1) Stall. Section 23.201(c) defines when the airplane can be considered stalled for airplane certification purposes. When one of three conditions occurs, whichever occurs first, the airplane is stalled. The conditions are as follows:
(i) Uncontrollable downward pitching motion;
(ii) Downward pitching motion that results from the activation of a device (for example, stick pusher); or
(iii) The control reaches the stop.
The term "uncontrollable downward pitching motion" is the point at which the pitching motion can no longer be arrested by application of nose-up elevator and not necessarily the first indication of nose-down pitch. Figure 17-1 shows a graphic representation of stall speed time histories for various configurations.
(2) Related Sections. The stalled condition is a flight condition that comes within the scope of §§ 23.49, 23.141, 23.143(b), 23.171, and 23.173(a). Section 23.143(b) requires that it be possible to effect a "smooth transition" from a flying condition up to the stalled flight condition and return without requiring an exceptional degree of skill, alertness, or strength.
Any need for anticipated or rapid control inputs exceeding that associated with average piloting skill is considered unacceptable.
(3) Recovery. The flight tests include a determination that the airplane can be stalled, and flight control recovered, with normal use of the controls. Section 23.201(a) requires that it must be possible to produce and correct roll by unreversed use of the roll control and to produce and correct yaw by unreversed use of the directional control. The power used to regain level flight may not be applied until flying control is regained. This is considered to mean not before a speed of 1.2 VS1 is attained in the recovery dive.
(4) Power.
(i) Power off. The propeller condition for the "power-off" tests prescribed by § 23.201(e)(4) should be the same as the "throttles closed" condition prescribed for the stalling speed tests of § 23.49, that is, propellers in the takeoff position, engine idling with throttles closed. The alternative of using sufficient power to produce zero propeller thrust does not apply to stall characteristics demonstrations.
(ii) Power on. For the power-on tests, an extreme nose up attitude is normally considered to be a pitch attitude of more than 30 degrees.
(5) Configurations. Stall characteristics should be evaluated as follows:
(i) At maximum to minimum weights at aft c.g., aft light loadings may be the most critical in airplanes with high thrust-to-weight ratios;
(ii) With the elevator up stop set to the maximum allowable deflection;
(iii) With maximum allowable lateral imbalance; and
(iv) At or near maximum approved altitude.
Also, airplanes with de-rated engines should be evaluated up to the critical altitude of the engine and at maximum altitude for which the airplane is to be certified. An airplane may be approved if it has stick pusher operation in one configuration, such as power on, and has acceptable stall characteristics for the remaining configurations.
b. Procedures.
(1) Emergency Egress. It is the responsibility of the applicant to provide adequate provision for crew restraint, emergency egress, and use of parachutes (reference § 21.35(d)).
(2) Buildup. Generally, the stalls at more rearward, c.g. positions are more critical than at the forward c.g. position. For this reason, the stall characteristics at forward c.g. should be investigated first. Altitude should be low enough to ensure capability of setting 75 percent power, but high enough to accomplish a safe recovery. The 75 percent power requirement means 75 percent of the rated power adjusted to the temperature and altitude test conditions.
Reciprocating engine tests conducted on a hot day, for example, would require higher manifold pressures to be set so that when chart brake horsepower is adjusted for temperature the result is 75 percent power.
(3) Pilot Determinations. During the entry and recovery, the test pilot should determine the following:
(i) That the stick force curve remains positive up to the stall (that is, a pull force is required) (reference § 23.171) when the trim speed is higher than the stall speed.
(ii) That it is possible to produce and correct roll and yaw by unreversed use of the rolling and directional control.
(iii) The amount of roll or yaw encountered during the recovery.
(4) Speed Reduction Rate. Section 23.201(b) requires the rate of speed reduction for entry not exceed one knot per second.
c. Data Acquisition and Reduction.
(1) Instruments. The applicant should provide a recently calibrated sensitive altimeter, airspeed indicator, accelerometer, outside air temperature gauge, and appropriate propulsion instruments; such as a torque meter or manifold pressure gauge and tachometer, a means to depict roll, pitch, and yaw angles; and force gauges when necessary.
(2) Data Recording. Automatic data recording is desirable, but not required, for recording time histories of instrumented parameters and such events as stall warning, altitude loss, and stall break. The analysis should show the relationship of pitch, roll, and yaw with respect to various control surface deflections. (See figure 17-1, stall speed determination.)
d. Stick Pusher.
(1) Background. Stick pushers have been installed in some airplanes that would not meet the requirements of § 23.201. This was accomplished under the provisions of § 21.21b(1). In some airplanes, operation of the stick pusher was not critical to safe flight and, in others, stick pusher performance was essential to safe flight. In the latter case, the stick pusher typically functions as a stall barrier to prevent an airplane from entering flight regimes where a nonrecoverable stall could occur.
(2) Stall Prevention. There are two basic situations where a stick pusher would be necessary to show compliance with regulations. These are the following:
(i) Airplane Recoverable. The stall characteristics are investigated and, during these tests, the airplane does not meet regulatory requirements but an inadvertent aerodynamic stall would not be catastrophic or require exceptional piloting skill to recover. For example, during certain conditions of c.g., weight, or power, the airplane exceeds the l5 degree roll limit because of excessive angle-of-attack or other conditions. The pusher is installed and designed to function at some angle-of-attack where the 15 degrees of roll will not be exceeded. If this pusher system fails to function, the airplane is still recoverable from the stalled flight condition. For this system, the occurrence of a failure should be evaluated for an unsafe condition.
(ii) Airplane Not Recoverable. When the airplane is not capable of recovering from stalls or the applicant chooses not to investigate the consequences of stalling demonstrations with the pusher system rendered inoperative, then if the stick pusher fails to perform its intended function, an unsafe condition would exist.
(3) System Tolerances. Stick pusher system(s) tolerances should be evaluated and accounted for during certification flight tests. The applicant normally specifies the system tolerances in terms of plus or minus so many knots. The system(s) should be set to the minus (lowest stall speed) side of the tolerance when investigating stall characteristics and minimum longitudinal trim capability. The system(s) should be set to the plus (highest stall speed) side of the tolerance for stall speed determination and for determining performance stall speed multiples.
Alternately, a nominal stick pusher stall speed may be used when it is determined that stick 84
pusher tolerances result in no more than 3 knots or 5 percent variation in stall speed, whichever is greater.
(4) Airspeed Margins. The airspeed margin between unsatisfactory stall characteristics and the minimum stick pusher actuation speed, for identical flight conditions, should be evaluated. The following information is provided as a guide. For airplanes with unsatisfactory, hazardous or unrecoverable aerodynamic stall characteristics, the minimum speed margin between aerodynamic stall and minimum stick pusher systems actuation speed should not be less than 5 knots. For other airplanes with known and less hazardous aerodynamic stall characteristics, the speed margin may be reduced to not less than 2 knots.
(5) Preflight Check. If a reliability credit is to be given for a preflight check, the following should be evaluated:
(i) The check includes the functioning of the complete system, including the incidence sensors, so all faults would be detected.
(ii) The check is easily conducted, and requires little pilot time or effort.
(iii) A note in the limitations section of the AFM requires the check to be accomplished prior to flight.
(iv) The AFM identifies the criticality of the system and the need to accomplish the preflight check.
(6) Inadvertent Operation. Inadvertent stick pusher operation should be extremely improbable or investigated and shown not to be hazardous and to be recoverable.
87. SECTION 23.203 TURNING FLIGHT AND ACCELERATED TURNING STALLS.
a. Explanation.
(1) Explanations 86.a.(2) and (4) for wings level stalls also apply to turning flight and accelerated turning stalls.
(2) The only differences between the investigation required for turning flight and accelerated turning stalls are in the speed reduction rate and the accepted roll off bank angles.
b. Procedures.
(1) Procedure 86.b.(1) for wings level stalls applies to turning flight and accelerated turning stalls.
(2) During the maneuver, the test pilot should determine the following:
(i) That the stick force remains positive up to the stall;
(ii) That the altitude lost is not, in the test pilot's opinion, excessive;
(iii) There is no undue pitch up;
(iv) That there are no uncontrollable spinning tendencies; that is, while the airplane may have a tendency to spin, a spin entry is readily preventable;
(v) That the test pilot can complete the recovery with normal use of the controls and average piloting skill;
(vi) Roll does not exceed the value specified in the requirements; and
(vii) For accelerated turning stalls, maximum speed or limit load factors were not exceeded.
(3) Section 23.203(a) requires the rate of speed reduction for a turning flight stall not exceed one knot per second; for an accelerated turning stall, 3 to 5 knots per second with steadily increasing normal acceleration.
c. Data Acquisition. Same as for wings level stalls.
88. SECTION 23.205 RESERVED
89. SECTION 23.207 STALL WARNING.
a. Explanation.
(1) Purpose. The purpose of this requirement is to ensure an effective warning in sufficient time to allow a pilot to recover from an approach to a stall without reaching the stall.
(2) Types of Warning. The effective warning may be from either aerodynamic disturbances or from a reliable artificial stall-warning device such as a horn or a stick shaker. The aerodynamic warning is usually manifested by a buffet, which vibrates or shakes the airplane.
The type of warning should be the same for all configurations.
(3) Artificial Stall Warning. Stall warning devices may be used in cases where there is inadequate aerodynamic warning. The warning signal from the devices should be clear and distinctive and not require the pilot's attention to be directed inside the airplane. A stall warning light by itself is not acceptable. If a stick shaker is installed, the warning should be unmistakable even if flying hands off.
b. Procedures. The stall warning tests should be conducted in conjunction with the stall tests required by §§ 23.201 and 23.203.
90.-99 RESERVED.
Section 8. SPINNING
100. SECTION 23.221 SPINNING.
a. Explanation.
(1) Spin. A spin is a sustained autorotation at angles-of-attack above stall. The rotary motions of the spin may have oscillations in pitch, roll, and yaw superimposed upon them.
The fully developed spin is attained when the trajectory has become vertical and the spin characteristics are approximately repeatable from turn to turn. Some airplanes can autorotate for several turns, repeating the body motions at some interval, and never stabilize. Most airplanes will not attain a fully developed spin in one turn.
(2) Category Spins. Section 23.221 addresses three situations:
(i) Normal category spins.
(ii) Utility category spins.
(iii) Acrobatic category spins.
(3) Reserved.
(4) Utility Category Airplanes. Utility category is used for airplanes intended for limited acrobatic operations in accordance with § 23.3. Spins (if approved for the particular type of airplane) are considered to be a limited acrobatic operation. This type of airplane may be approved in accordance with § 23.221(a), normal category, or with § 23.221(c), acrobatic category.
b. Discussion and Procedures Applicable to Both Normal and Acrobatic Category Spins.
(1) Weight and C.G. Envelope. See paragraph 7.a. of this AC for discussion of weight and
c.g. envelope exploration.
(2) Moments of Inertia. Moments of inertia should also be considered when evaluating the
c.g. envelope. Most general aviation airplanes have low inertias combined with high aerodynamic damping and relatively similar moments of inertia along the wing and fuselage axis. However, designs of modifications, such as wingtip fuel tanks, can change the spin recovery time and possibly the recovery method. Applicants are encouraged to consider these effects and approach flight testing at extreme mass distributions with caution.
(3) Control Deflections. Control surface deflections should be set to the critical side of the allowable tolerances for the selected critical configurations. For example, a possible spin flight test program could be to perform the spin matrix with the controls set at the nominal deflection values. Analysis of the data will show the critical conditions for entry and recovery. Once the critical conditions are defined and agreed upon by the Certification Authority, these critical tests are repeated with the control deflections set to the most critical tolerances. If satisfactory, these tests must be repeated with the antispin system removed.
(4) Emergency Egress. It is the responsibility of the applicant to provide adequate provision for crew restraint, emergency egress, and use of parachutes (reference § 21.35(d)).
(5) Spin Recovery Parachutes.
(i) Spin recovery parachutes should be installed on all airplanes requiring spin testing for certification.
(ii) The anti-spin system installation should be carefully evaluated to determine its structural integrity, reliability, susceptibility to inadvertent or unwanted deployment or jettison, and adequate or redundant jettison capability. NASA recommendations should be referred to when evaluating the design of the chute deployment and jettison systems.
The chute type, diameter, porosity, riser length, and lanyard length should be determined in accordance with NASA recommended practices to maximize the probability the chute will be effective in spin recovery. Chute sizes, and particularly riser and lanyard lengths, depend strongly on such aircraft variables as wing design, fuselage shape, tail arm, and mass properties. The sizes and lengths shown in the referenced NASA reports are for 87
particular aircraft that were tested in the NASA Langley Spin Tunnel and will not necessarily be the correct size to recover other aircraft, even if the aircraft layout is similar. Appropriate NASA recommendations can be found in the following publications:
(A) NASA Technical Paper 1076, "Spin-Tunnel Investigation of the Spinning Characteristics of Typical Single-Engine General Aviation Airplane Designs," dated November 1977.
(B) NASA Technical Note D-6866, "Summary of Design Considerations for Airplane Spin-Recovery Parachute Systems."
(C) NASA Conference Paper, CP-2127, l4th Aerospace Mechanisms Symposium, May 1980, entitled, "A Spin-Recovery System for Light General Aviation Airplanes."
The NASA documents are available from:
National Technical Information Service (NTIS) 5285 Port Royal Road Springfield, Virginia 22161
(iii) Final certification of the spin characteristics should be conducted with the external spin chute removed unless it is determined that spin chute installation has no significant effect on spin characteristics.
(6) Build-Up. When any doubt exists regarding the recovery characteristics of the test airplane, a build-up technique should be employed consisting of spin entries and recoveries at various stages as the maneuver develops. Excessive aerodynamic control wheel back pressure indicates a possibility of unsatisfactory spin characteristics. Any control force lightening or reversal is an indication of possible deep stall entry. See subparagraph c(7) for definition of excessive back pressure. A yaw rate instrument is valuable in detecting progress toward a fully developed spin condition or an uncontrollable maneuver. Unusual application of power or controls has sometimes been found to induce uncontrollable spins. Leading with elevator in recovery and cutting power as the airplane rolls into a spin have been known to induce uncontrollable spins.
(7) Entry. Spins should be entered in the same manner as the stalls in §§ 23.201 and 23.203 with trim at 1.5 VS1 or as close as practical. As the airplane stalls, with ailerons neutral, apply full-up elevator and full rudder in the direction of spin desired. Refer to paragraphs l00c and l00d for further discussion of spin entries.
(8) Recovery. Recoveries should consist of throttle reduced to idle, ailerons neutralized, full opposite rudder, followed by forward elevator control as required to get the wing out of stall and recover to level flight. For acrobatic category spins, the manufacturer may establish additional recovery procedures, provided they show compliance for those procedures with this section.
(9) Trimmable Stabilizer. For airplanes that trim with the horizontal stabilizer, the critical positions should be investigated.
(10) Altitude. The effect of altitude should be investigated.
(11) Initial Investigation. In all cases, the initial spin investigation should be accomplished at as high an altitude above the ground as reasonably possible and a predetermined, pre-briefed "hard" altitude established to be used as the emergency egress altitude. In other words, if the airplane cannot be recovered by that altitude, all occupants should exit the airplane without hesitation. The altitude selected should take into account the opening characteristics of the parachutes, the difficulty of egress, the estimated number of turns to get out and the altitude loss per turn, the distance required to clear the airplane before deploying the parachutes, and so forth.
(12) Power. The use of power for spin entry for both normal and abnormal control use is recommended in order to determine the effects of power on spin characteristics and spin recovery procedures. For power on normal category spins, the throttle can be reduced to idle after one turn.
c. Discussion and Procedures Applicable to Normal Category Spins.
(1) Objective. The basic objective of normal category spin testing is to assure that the airplane will not become uncontrollable within one turn (or 3 seconds, whichever takes longer) if a spin should be encountered inadvertently and that recovery can be effected without exceeding the airplane design limitations. Type certification testing requires recovery capability from a one-turn spin while operating limitations prohibit intentional spins. This one-turn "margin of safety" is designed to provide adequate controllability when recovery from a stall is delayed. Section 23.221(a) does not require investigation of the controllability in a true spinning condition for a normal category airplane. Essentially, the test is a check of the controllability in a delayed recovery from a stall.
(2) Recovery from Spins with Normal Control Usage During Entry and Recovery. Normal category airplanes must recover from a spin in no more than one turn after the initiation of the first control action for recovery. For example, if you are spinning left with ailerons neutral, recover by reducing power to idle, if not already at idle, apply full right rudder followed by forward elevator. Start the count (heading, ground reference, and so forth) for recovery with the application of the first action, which may be the reduction of power. See subparagraph c(5) for use of flaps. Intentional, inadvertent, normal, up to 60 degrees bank, and accelerated stalls should be considered.
(3) Recovery from Spins Following Abnormal Control Usage. Abnormal control usage should be evaluated during the spin to ensure that uncontrollable spins do not occur. The intent of these tests is to induce all of the types of control usage, whether they are right or wrong, that might be used during the operation of the airplane. The parameters that need to be investigated depend on the design of the airplane as well as on the results of the Normal Spin Tests. These checks include, as a minimum, the following: the effect of ailerons with and against the spin, the effect of elevator applied before the rudder at recovery, the effect of slow elevator release, the effect of entry attitude, the effect of power on at the entry, and the effect of power left on during the spin. Ailerons with and against the spin should be applied at entry and during spins. Elevator and rudder against the spin should be applied during the spin. Spinning should continue for up to 3 seconds, or for one full turn, while the effects of abnormal aerodynamic control inputs are observed. Apply normal recovery controls as outlined in subparagraph c(2). Up to two turns for recovery is considered acceptable.
(4) Spin Matrix. The effects of gear, flaps, power, accelerated entry and control abuse should be investigated. A suggested matrix for spin investigation is given in Figure 100-1. It is the responsibility of the applicant to explore all critical areas. It may be possible to eliminate the need to conduct some of the additional conditions once the airplane responses are known.
(5) Flaps. Section 23.221(a) specifies that, for the flaps extended condition, the flaps may be retracted during the recovery. Flap retraction should not be initiated until after airplane rotation has ceased.
(6) Aerodynamic Back Pressure. Excessive aerodynamic back pressure is cause for noncompliance. Excessive aerodynamic back pressure is a judgment item and is defined as excessive force required to pitch the airplane down in recovery. Back pressure should not be more than normal elevator control forces and should not interfere with prompt and normal recovery.
d. Discussion and Procedures Applicable to Acrobatic Category Spins.
(1) Objective. The basic objective of acrobatic category spin testing is to ensure that the airplane will not become uncontrollable when a spin is intentionally entered and the following:
(i) The controls are used abnormally (as well as normally) either during the entry or during the spin, or both;
(ii) The airplane will recover in not more than 1 1/2 turns after completing application of normal or manufacturer-prescribed recovery controls; and
(iii) No airplane limitations are exceeded, including positive maneuvering load factor and limit speeds.
(2) Pilot Training. It is assumed that the pilot of the acrobatic category airplane that spins for six turns is doing so intentionally. If spinning is intentional, the pilot should have had proper instruction and proficiency to effect a proper recovery. The pilot should be expected to follow the published procedure to recover from this planned maneuver.
(3) Abnormal Control Usage. The discussion of "abnormal" use of controls in paragraph l00c(3) also applies to acrobatic category spins. Abnormal control usage should be evaluated at several points throughout the spin to ensure that uncontrollable spins do not occur. These checks include, as a minimum, the following: the effect of ailerons with and against the spin, the effect of elevator applied before the rudder at recovery, the effect of slow elevator release, the effect of entry attitude, the effect of power on at the entry, and the effect of power left on during the spin. Spinning should continue for up to six full turns while the effects of abnormal aerodynamic control inputs are observed. The effect of leaving power on in the spin need only be examined by itself up to one full turn. Following abused control usage, reversion to normal pro-spin controls for up to two turns is acceptable, prior to the normal recovery control inputs, which must result in recovery in not more than two turns. In addition, going directly from the control abuse condition to the normal recovery control condition should not render the spin unrecoverable. For example, after evaluating the effect of relaxing the back stick input during the spin, it would be reasonable to expect the pilot to apply normal recovery use of rudder and elevator without first returning to full back stick.
(4) Flaps. If an acrobatic category airplane is placarded against intentional flaps down spins, then only normal category procedures need be used for the flaps down configurations.
(5) Spin Matrix. The effects of gear, flaps, power, accelerated entry, and normal and abnormal control use should be investigated. A suggested matrix for spin investigation is given in figure 100-1. It is the responsibility of the applicant to explore all critical areas. It is necessary to expand the matrix to cover six-turn spins. The normal procedure is to continue 90
the same process and add one additional turn each time. It may be possible to eliminate the need to conduct some of the additional conditions once the airplane responses are known.
(6) Spiral Characteristics. The acrobatic spin requirement stipulates that, for the flap retracted six-turn spin, the spin may be discontinued after 3 seconds if spiral characteristics appear. This does not mean that the spin test program is discontinued. Each test point should stand alone and that spin be discontinued only after a spiral has developed. Limit speed should not be exceeded in the recovery. The airplane may be certificated as an acrobatic airplane whether or not it can spin a minimum of six turns.
(7) Recovery Placard. Section 23.1583(e)(4) requires that acrobatic airplanes have a placard listing the use of controls required to recover from spinning maneuvers. Utility category airplanes approved for spins should also have such a placard. Recovery control inputs should be conventional. If special sequences are employed, then they should not be so unique to create a recovery problem.
(8) Complex Instrumentation. When complex instrumentation is installed, such as wing tip booms or a heavy telemetry system, the instrumentation may affect the recovery characteristics. Critical spin tests should be repeated with the instrumentation removed.
e. Data Acquisition. The test airplane should be equipped with a calibrated airspeed indicator, accelerometer, and altimeter. Precise control of weight and balance and control deflections is essential.
f. Optional Equipment. In those cases where an airplane is to be certified with and without optional equipment such as deicing boots, asymmetric radar pods, outer wing fuel tanks, or winglets, sufficient tests should be conducted to ensure compliance in both configurations.