(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.
Flight Condition Spins from Wing Level Attitude Spin Number Flaps Up Flaps Appch. (As Approp.)
Test with Normal Spin Controls Left Spin 1 thru 6 1 2 3 4 5 6 X X 7 8 9 10 11 12 13 14 15 16 17 18 Test with Abnormal Spin Controls Left Spin Aileron Against 7 thru 12 (Repeat 7 through 12 from a right spin) Left Spin Aileron with 13 thru 18 Flaps Landing Gear Up Gear Down Cowl Flaps Closed Cowl Flaps As Required Power Off Power On Forward C.G.
Aft C.G.
Lateral C.G.
X X X X X X X X X X X X X X X X X X X X XX X X X X XX XX XX Repeat 1 through 6 from a right spin.
Repeat 1 through 6 fromleft and right turning flight.
X X XXX X X
XX X XX X X
XX XX X X X
X X X XX X X
X X X XX X X
X XXX X X X
X X XX X X X
X X X X X X X
X X X X X X X
X X XX X X X
X XX XX XX
X X X X X X X Repeat 13 through 18 from a right spin.
Repeat 7 through 18 from left and right turning flight.
SPIN EVALUATION CONFIGURATION X XX X X XX X
FIGURE 100-1 - SPIN EVALUATION CONFIGURATION MATRIX
101.-105. RESERVED.
Section 9. GROUND AND WATER HANDLING CHARACTERISTICS
106. SECTION 23.231 LONGITUDINAL STABILITY AND CONTROL.
a. Explanation.
(1) For landplanes, §§ 23.231(a) and 23.233 are companion requirements to § 23.75.
(2) For floatplanes, §§ 23.231(b) and 23.233 are companion requirements to § 23.75.
(3) The requirements for both landplanes and floatplanes apply to amphibians.
b. Procedures.
(1) Landplanes should be operated from all types of runways applicable to the type of airplane. Taxi, takeoff, and landing operations should be evaluated for acceptable characteristics. This should include idle power landings as well as landings and takeoffs with procedures used in §§ 23.75 and 23.51.
(2) Floatplanes should be operated under as many different water conditions as practical up to the maximum wave height appropriate to the type of airplane. Taxi (both displacement and step), takeoff, and landing operations should be evaluated for acceptable characteristics.
This includes idle power landings as well as landings and takeoffs with procedures used under §§ 23.75 and 23.51.
(3) Amphibians should be evaluated in accordance with both items (1) and (2) above.
c. Procedures - Multiengine Airplanes. Evaluate all of the considerations contained in paragraph 106b plus the effects of one engine loss during water operations.
d. Airplane Flight Manual (AFM). The AFM should include appropriate limitations plus demonstrated wind and sea state conditions.
107. SECTION 23.233 DIRECTIONAL STABILITY AND CONTROL.
a. Explanation.
(1) Crosswind. This regulation establishes the minimum value of crosswind that must be demonstrated. Since the minimum required value may be far less than the actual capability of the airplane, higher values may be tested at the option of the applicant. The highest 90- degree crosswind component tested satisfactorily should be put in the AFM as performance information. If a demonstrated crosswind is found limiting, it has to be introduced in Section 2 of the AFM.
(2) Ground Loops. Section 23.233(a) does not preclude an airplane from having a tendency to ground loop in crosswinds, providing the pilot can control the tendency using engine power, brakes, and aerodynamic controls. The operating procedures should be placed in the AFM in accordance with § 23.1585(a).
(3) Controllability. Section 23.233(b) is not related to the crosswind requirement of § 23.233(a). The demonstration of compliance with this requirement is accomplished into the wind. The test pilot is searching for any unusual controllability problems during landing and 93
must use judgment as to what constitutes "satisfactorily controllable" since, at some point in the landing rollout, the aerodynamic controls may become ineffective.
(4) Taxi Controllability. Section 23.233(c) requires the airplane to have adequate directional controllability for taxi operations on land for landplanes, on water for floatplanes, and on land and water for amphibians.
b. Procedures.
(1) Crosswind.
(a) The airplane should be operated throughout its approved loading envelope at gradually increasing values of crosswind component until a crosswind equivalent to 0.2 VSO is reached. All approved takeoff and landing configurations should be evaluated.
Higher crosswind values may be evaluated at the discretion of the test pilot for AFM inclusion.
(b) For floatplanes, the use of water rudders or the use of airplane attitude on the water to control weathervaning should be described in the AFM.
(2) Controllability.
(a) A landplane should demonstrate satisfactory controllability during power-off (idle power) landings through landing rollout. This may be conducted into the existing wind and should be evaluated at all key loading envelope points.
(b) Although power-off landings are not expressly required for floatplanes under § 23.233(b), it is recommended they be evaluated.
(3) Taxi Controllability.
(a) A landplane should have sufficient directional control available through the use of nose/tail wheel steering, differential braking (if provided), differential power (multiengine airplanes), and aerodynamic control inputs to allow taxiing at its "maximum demonstrated crosswind" value.
(b) A floatplane should have sufficient directional control available through the use of water rudders, airplane attitude (displacement or plow), taxi technique (displacement or step), differential power (multiengine floatplanes) and aerodynamic control inputs to allow taxiing at its "maximum demonstrated crosswind" value. This is not intended to suggest that all of the above must be evaluated at 0.2 VSO, but accepted techniques using one or more of the above must allow controllable taxiing.
(c) Amphibians should exhibit suitable directional controllability on both land and water in accordance with the preceding two paragraphs. In addition, amphibians should have suitable directional controllability to taxi from the water to a land facility and vice-versa unless prohibited by the operating limitations.
c. Data Acquisition and Reduction. The determination of compliance is primarily a qualitative one. However, wind readings (velocity and direction) should be taken and compared to the wind component chart (Appendix 7) to determine that the minimum 90-degree crosswind component has been tested.
108. SECTION 23.235 OPERATION ON UNPAVED SURFACES.
a. Explanation. This requirement says the airplane landing gear shock absorbing mechanism must function as intended throughout the expected operating envelope of the airplane.
b. Procedures. During the development and certification flight testing, the airplane should be operated on a variety of runways including those considered to be the worst (in terms of roughness) appropriate to the type of airplane. There should be no evidence of damage to the airplane during these operations.
109. SECTION 23.237 OPERATION ON WATER.
Allowable water surface conditions should be established during the certification flight testing, depending on the type of aircraft, to ensure safe operation and attainment of the published takeoff and landing performance.
110. SECTION 23.239 SPRAY CHARACTERISTICS.
a. Explanation. This rule is intended to ensure that any spray produced during water operation neither excessively interferes with the pilot's visibility nor damages, beyond "normal wear-and-tear," the airplane itself.
b. Procedures.
(1) Taxi, takeoff, and landing operations should be conducted throughout the approved loading envelope. Spray patterns should be specifically noted with respect to visibility and their contact areas on the airplane. These areas should be monitored to assure compliance with the rule.
(2) Airplanes with reversing propellers should be demonstrated to comply at the highest reverse power expected to be applicable to the airplane operation.
111.-119. RESERVED.
Section 10. MISCELLANEOUS FLIGHT REQUIREMENTS
120. SECTION 23.251 VIBRATION AND BUFFETING.
a. Explanation.
(1) Flutter. The test required under this section should not be confused with flutter tests, which are required under § 23.629. No attempt is made to excite flutter, but this does not guarantee against encountering it. Therefore, the test should be carefully planned and conducted.
(2) Test Speeds. Prior to the test, the pilot should coordinate with the airframe engineer to determine that the flutter requirements of § 23.629 have been satisfied and to determine the most critical weight and c.g. for the test. The flight test engineer and pilot should obtain from the airframe engineer the dive equivalent airspeed and Mach number to which the test should be conducted. In the absence of a well-calibrated Mach meter, knowing the Mach number and equivalent airspeed, a schedule of pressure altitude and indicated airspeed should be developed for the test.
(3) Airspeed Determination. Another major consideration is calibrated airspeed determination during the test. In this regard, a calibrated, sensitive airspeed indicator should be installed to provide accurate readability. Careful study of the airplane's airspeed position error/correction curve is required with respect to the characteristics of the slope at the highspeed end and how the airspeed calibration was conducted. This is necessary to determine the adequacy of the airspeed position error curve for extrapolating to VD/MD. Refer to Appendix 7, figure 5, for compressibility corrections. An expanded Mach number calibratedairspeed graph may be found in the Air Force "Flight Test Engineering Handbook" (see Appendix 2, paragraph f(2) of this AC).
(4) Springs. If the airplane incorporates spring devices in any of the control systems, the test should be conducted with the spring devices connected and disconnected. Alternately, if satisfactory spring reliability is shown in accordance with § 23.687, tests with springs disconnected are not required. Also see paragraph 45 of this AC.
(5) Mach Limits. For those airplanes that are observing Mach limits, the tests should be repeated at MD speed. Careful selection of the test altitude for both MD and VD tests will help cut down on the number of repeat runs necessary to determine compliance. Attempting to combine the tests at the knee of the airspeed/Mach curve should be approached cautiously since it can result in overshooting the desired speed.
b. Procedures.
(1) Configuration. In the clean configuration at the gross weight, most critical c.g. (probably most aft) and the altitude selected for the start of the test, the airplane should be trimmed in level flight at maximum continuous power. Speed is gained in a dive in gradual increments until VD/MD is attained. The airplane should be trimmed, if possible, throughout the maneuver. Remain at the maximum speed only long enough to determine the absence of excessive buffet, vibration, or controllability problems.
(2) Flaps extended. With flaps extended and the airplane trimmed in level flight at a speed below VFE, stabilize at VFE in a shallow dive and make the same determinations as listed in
(1) above.
121. SECTION 23.253 HIGH SPEED CHARACTERISTICS.
a. Explanation.
(1) Related Sections. The design dive speeds are established under the provisions of § 23.335, with the airspeed limits established under the provisions of § 23.1505. There is distinction made in both regulatory sections for airplanes that accelerate quickly when upset.
The high-speed characteristics, in any case, should be evaluated by flight demonstration.
Section 23.1303(a)(5) gives the requirements for a speed-warning device.
(2) Dynamic Pressure and Mach. In general, the same maneuvers should be accomplished in both the dynamic pressure (q) and Mach (M) critical ranges. All maneuvers in either range should be accomplished at thrust and trim points appropriate for the specific range being evaluated. Some maneuvers in the Mach range may be more critical for some airplanes due to drag rise characteristics.
(3) Flight Crew Duties. The airplane's handling characteristics in the high-speed range should be investigated in terms of anticipated action on the part of the flight crew during 96
normal and emergency conditions. Consideration should be given to their duties, which not only involve piloting the airplane but also the operational and navigational duties having to do with traffic control and record keeping necessary to the progress of safe flight.
(4) Upset Axes. The upset criteria of § 23.335(b)(4)(i) is predicated on an upset in pitch while operational evaluation of upsets expected to occur in service should cover pitch, roll, yaw, and critical combinations of multi-axis upsets.
(5) Factors. The following factors are involved in the flight test investigation of high-speed characteristics:
(i) Effectiveness of longitudinal control at VMO/MMO and up to the demonstrated VD/MD speed;
(ii) Effect of any reasonably probable mis-trim on upset and recovery;
(iii) Dynamic and static stability;
(iv) The speed increase that may result from likely mass movement that occurs when trimmed at any cruise speed to VMO/MMO;
(v) Trim changes resulting from compressibility effects. Evaluation should cover Mach tuck, control reversal, or other phenomena associated with high speed;
(vi) Characteristics exhibited during recovery from inadvertent speed increase;
(vii) Upsets due to turbulence (vertical, horizontal, and combination gusts);
(viii) Effective and unmistakable aural speed warning at VMO plus 6 knots, or MMO plus
0.0lM;
(ix) Speed control during application of devices (power, speed brakes, high-speed spoilers, and so forth); and
(x) Characteristics and controllability during and after failure or malfunction of any stability augmentation system.
(6) Type of Warning. Operational experience has revealed that an important and effective deterrent to inadvertent overspeeding is an aural warning device, which is distinctively different from aural warning used for other purposes. Aerodynamic buffeting is influenced by, and is similar to, the effects of turbulence at high speed and is not normally considered to be suitable as an overspeed warning.
(7) Speed Margins. Once it is established whether the airplane limits will be VNE or VMO, appropriate speed margins and markings may be evaluated. The factors outlined in § 23.335 have been considered in establishing minimum speed margins during past type certification programs for the appropriate speeds. The factors to be considered are the following:
(i) Increment allowance for gusts (0.02M);
(ii) Increment allowance for penetration of jet stream or cold front (0.0l5M);
(iii) Increment allowance for production differences of airspeed systems (0.005M), unless larger tolerances or errors are found to exist;
(iv) Increment allowance for production tolerances of overspeed warning errors (0.0lM), unless larger tolerances or errors are found to exist;
(v) Increment allowance M, due to speed overshoot from MMO, established by upset during flight tests in accordance with § 23.253, should be added to the values for production differences and equipment tolerances. The minimum acceptable combined value should not be less than that required by § 23.335(b)(4) between MMO and MD. The value of MMO should not be greater than the lowest value obtained from each of the following equations and from § 23.1505:
MMO = MD - ∆M - .005M - .01M
or MMO = MD - the Mach increment required by § 23.335(b)(4)
(vi) Altitudes where q is limiting, the allowances of items (a) and (b) are applicable, and the Mach increment is converted to the units used for the limits;
(vii) At altitudes where q is limiting, the increment allowance for production differences of airspeed systems and production tolerances of overspeed warning errors are 3 and 6 knots, respectively, unless larger differences or errors are found to exist; and
(viii) Increment allowance ∆V, due to speed overshoot from VMO established by upset during flight tests in accordance with § 23.253, should be added to the values for production differences and equipment tolerances. The value of VMO should not be greater than the lowest obtained from the following:
VMO = VD - ∆ V - 3 knots (prod. diff.) - 6 knots (equip. tol.)
or for VNO airplanes:
VNO = VD - ∆V - 3 knots (prod. diff.) - 6 knots (equip. tol.)
b. Procedures. Using the VMO/VNO, MMO, or the associated design or demonstrated dive speeds determined in accordance with §§ 23.251, 23.335, and 23.1505, the airplane should be shown to comply with the high speed characteristics of § 23.253 and that adequate speed margins exist.
The airplane characteristics should be investigated at any speed up to and including VNO, VMO/MMO or VD/MD, as required by § 23.253. The recovery procedures used should be those selected by the applicant, except that the normal acceleration during recovery should not exceed
l.5g (total).
(1) C.G. Shift. The airplane should be upset by the c.g shift corresponding to the forward movement of a representative number of passengers depending upon the airplane interior configuration. The airplane should be allowed to accelerate for 3 seconds after the overspeed indication or warning occurs before recovery is initiated. Note the maximum airspeed. Do not exceed VD /MD.
(2) Inadvertent Control Movement. Simulate an evasive control application when trimmed at VMO/MMO by applying sufficient forward force to the elevator control to produce 0.5g (total) for a period of 5 seconds, after which recovery should be effected at not more than l.5g (total). Care should be taken not to exceed VD /MD during the entry maneuver.
(3) Gust Upset.
(i) Lateral Upset. With the airplane trimmed at any likely cruise speed up to VMO/MMO in wings level flight, perform a lateral upset to the same angle as that for autopilot approval, or to a maximum bank angle appropriate to the airplane, whichever is critical.
Operationally, it has been determined that the maximum bank angle appropriate for the airplane should not be less than 45 degrees, need not be greater than 60 degrees, and should depend upon airplane stability and inertia characteristics. The lower and upper limits should be used for airplanes with low and high maneuverability, respectively.
Following this, with the controls free, the evaluation should be conducted for a minimum of 3 seconds after the calibrated value of VMO/MMO (not overspeed warning) or 10 seconds, whichever occurs first.
(ii) Longitudinal Upset. Perform a longitudinal upset as follows:
(A) Trim at VMO/MMO using power required for level flight but with not more than maximum continuous power. If the airplane will not reach VMO/MMO at maximum continuous power, push over to VMO/MMO and trim.
(B) If descending to achieve VMO/MMO, return to level flight without changing trim.
(C) Perform a longitudinal upset from normal cruise by displacing the attitude of the airplane in the range between 6-12 degrees, which has been determined from service experience to be an optimum range. The value of displacement should be appropriate to the airplane type and should depend upon airplane stability and inertia characteristics. The lower and upper limits should be used for airplanes with low and high maneuverability, respectively.
(D) The airplane should be permitted to accelerate until 3 seconds after the calibrated value of VMO/MMO (not overspeed warning).
(iii) Two-Axis Upset. Perform a two-axis upset consisting of a longitudinal upset combined with a lateral upset. Perform a longitudinal upset by displacing the attitude of the airplane as in the previous paragraph, and simultaneously perform lateral upset by rolling the airplane to the 15-25 degree bank angle range, which was determined to be operationally representative. The values of displacement should be appropriate to the airplane type and should depend upon airplane stability and inertia characteristics. The lower and upper limits should be used for airplanes with low and high maneuverability, respectively. The established attitude should be maintained until the overspeed warning occurs. The airplane should be permitted to accelerate until 3 seconds after the calibrated value of VMO/MMO (not overspeed warning).
(4) Leveling Off From Climb. Perform transition from climb to level flight without reducing power below the maximum value permitted for climb until the overspeed warning has occurred. Recovery should be accomplished by applying not more than l.5g (total).
(5) Descent From Mach to Airspeed Limit Altitude. A descent should be initiated at MMO and performed at the airspeed schedule defined in MMO until the overspeed warning occurs.
The airplane should be permitted to descend into the airspeed limit altitude where recovery should be accomplished after overspeed warning occurs by applying not more than l.5g (total). The maneuver should be completed without exceeding VD.