accidents dominate the non-fatal accidents for small jets. This is a critical phase of flight for small jets and adequate attention should be given to adverse landing conditions such as wet runways.
(5) Landing Gear Loads. Sink rate at touchdow n during landing distance determination should be considered and should not exceed the design landing gear loads established by § 23.473(d).
(6) Landing Distance Credit for Disking Drag and Reverse Thrust. Most turboprop installations embody provisions for reduction of propeller blade pitch from the "flight" regime to a "ground" regime to produce either a significant level of disking drag or reverse thrust or both, following touchdown on landing. For purposes of this discussion, disking drag is defined as not less than zero thrust at zero airspeed. Section 23.75(f) permits means other than wheel brakes to be used in determining landing distance, when the conditions specified in § 23.75(f) are met.
Such disking drag or reverse thrust may be acceptable in showing compliance with § 23.75(f) provided the means is safe and reliable.
(i) Reliable. Compliance with the "reliable" provision of the rule may be accomplished by an evaluation of the pitch changing/reversing system in accordance with § 23.1309. The methods of AC 23.1309-1 should be used in the evaluation even though type-certificated engine or propeller systems may not have been subjected to the AC 23.1309-1 analysis during certification. Additionally, Society of Automotive Engineers (SAE) document ARP-926A, "Fault/Failure Analysis Procedure," will assist in conducting reliability and hazard assessments.
(a) For commuter category airplanes, § 23.1309 requires the system to be designed to safeguard against hazards to the airplane in the event the system or any component thereof malfunctions or fails. An acceptable means for showing compliance with the requirement would be to conduct a FMEA of the system. An acceptable analysis would show that the effects of any system or component malfunction or failure would not result in a hazard to the airplane and that the propeller reversing system is reliable. SAE document, ARP-926A, contains acceptable criteria for conducting such an analysis.
(b) Safe and reliable should also mean that it is extremely improbable that the system can mislead the flight crew or will allow asymmetric power settings, that is, forward thrust on one engine versus reverse thrust on the other. In achieving this level of reliability, the system should not increase crew workload or require excessive crew attention during a very dynamic time in the landing phase. Also, the approved performance data should be such that the average pilot can duplicate this performance by following the AFM procedures.
(ii) Safe. Compliance with the "safe" provisions of § 23.75(f)(1) will require an evaluation of the complete system, including operational aspects, to ensure no unsafe feature exists.
(iii) Disking Drag for Multiengine Installations with Flight Idle and Ground Idle.
Symmetrical power/thrust may be used, with power levers at flight-idle position during air run, and at ground-idle position after touchdown. Procedures for consistently achieving ground idle should be established to ensure that the operational pilot gets the power lever back to ground idle, thus providing consistent results in service. Two of the designs that have been found acceptable for ground-idle positioning are a dedicated throttle gate or tactile positioning of the throttle. In effecting thrust changes followi ng touchdown, allowance should be made for any time delays that reasonably may be expected in service, or which may be necessary to assure that the airplane is firmly on the surface. Refer to b(2) for commuter category time delays.
Associated procedures should be included in the AFM. If the disking drag or some other 58
powerplant-related device has a significant effect on the landing distance, the effect of an inoperative engine should be determined and published in the AFM performance section.
(iv) Disking Drag for Single-Engine Installations with Flight Idle and Ground Idle. Landing distances should be determined with the power levers at flight-idle position during air run, and at ground-idle position after touchdown. Procedures for consistently achieving ground idle should be established. Two of the designs that have been found acceptable for ground-idle positioning are a dedicated throttle gate or tactile positioning of the throttle. In effecting thrust changes following touchdown, allowance should be made for any time delays that reasonably may be expected in service, or which may be necessary to assure that the airplane is firmly on the surface. Associated procedures should be included in the AFM.
(v) Reverse Thrust for Multiengine Airplanes. In the approval of reverse thrust for turboprop and turbojet airplanes, due consideration should be given for thrust settings allowed, the number of operating engines, and control of the aircraft with one engine inoperative.
If the landing distance depends on the operation of any engine and the landing distance would be noticeably increased (2 percent has been found acceptable) when a landing is made with that engine inoperative, then the landing distance should be determined with that engine inoperative.
However, if the use of compensating means (such as reverse thrust on the operating engine) will result in a landing distance not more than that with each engine operating, then the landing distance does not need to be determined with that engine inoperative. This assumes that there are no other changes in configuration, for example, flap setting associated with one engine inoperative, that will cause an increase in landing distance. In effecting thrust changes following touchdown, allowance should be made for any time delays that reasonably may be expected in service, or which may be necessary to assure that the airplane is firmly on the surface. Refer to b(2) for commuter category time delays. Associated procedures should be included in the AFM.
(vi) Reverse Thrust for Single-Engine Airplanes. In effecting thrust changes following touchdown, allowance should be made for any time delays that reasonably may be expected in service, or which may be necessary to assure that the airplane is firmly on the surface. Associated procedures should be included in the AFM.
(7) Balked Landing Transition. For the power conditions selected for the landing demonstration (except one engine inoperative), and other steady state conditions of speed and rate of sink that are established during the landing approach, it should be possible, at the 50-foot point, to make a satisfactory transition to the balked landing climb requirement of § 23.77 using average piloting skill without encountering any unsafe conditions.
(8) Expansion of Landing Data for a Range of Airport Elevations. When the basic landing tests are accomplished between sea level and approximately 3,000 feet, the maximum allowable extrapolation limits are 6,000 feet above and 3,000 feet below the test field elevation.
If you desire to extrapolate beyond these limits, one of two procedures may be employed. These procedures are given in paragraph 23.53b(7).
b. Procedures.
(1) Technique. The landing approach should be stabilized on target speed, power, and the airplane in the landing configuration prior to reaching the 50-foot height to assure stabilized conditions when the airplane passes through the reference height. The engine fuel control should be adjusted to the maximum flight-idle fuel flow permitted on airplanes in service unless it is shown that the range of adjustment has no effect on landing distance. A smooth flare should be made to the touchdown point. The landing roll should be as straight as possible and the airplane brought to a complete stop (or three knots for seaplanes) for each landing test.
Normal pilot reaction times should be used for power reduction, brake application, and use of other drag/deceleration devices. Refer to b(2) for commuter category time delays. These reaction times should be established by a deliberate application of appropriate controls as would be used by a normal pilot in service. They should not represent the minimum times associated with the reactions of a highly trained test pilot.
(2) Commuter Category Time Delays.
(i) The time delays shown in figure 16 should be used.
(ii) For approved automatic deceleration devices (for example, autospoilers, etc.)
for which performance credit is sought for AFM data expansion, established times determined during certification testing may be used without the application of the one-second minimum time delay required in the appropriate segment above.
(3) Applicant's Procedures. The procedures to be followed should be those recommended by the applicant.
Figure 16 - Landing Time Delays TOUCH DOWN PILOT
ACTUATION
OF FIRST
DECELERATION DEVICE PILOT
ACTUATION
OF SECOND
DECELERATION
DEVICE STOP 1 2 Transition from touchdown Full braking to full braking configuartion configuration to stop - This segment represents the flight test measured average time from touchdown to pilot actuation of the first deceleration device. For AFM data expansion, use one second or the test time, whichever is longer.
- This segment represents the flight test measured average test time from pilot actuation of the first deceleration device to pilot actuation of the second deceleration device. For AFM data expansion, refer to item above.
Segment is repeated until pilot actuation of all deceleration devices has been completed and the airplane is in the full braking configuration.
(4) Number of Landings. At least six landings should be conducted on the same wheels, tires, and brakes to establish the proper functioning required by § 21.35(b).
(5) Winds. Wind velocity and direction should be measured adjacent to the runway during the time interval of each test run. Refer to paragraph 23.21a(5) of this AC for wind velocity and direction tolerances.
(6) Weight. Landing tests should be conduc ted at maximum landing weight.
(7) Approach Angles Greater than Three Degrees. If the applicant chooses an approach angle greater than three degrees, landing distances that result from utilizing a threedegree approach angle should be determined and published in the AFM to enable operators to comply with related operational rules.
c. Data Acquisition.
(1) The data to be recorded for landing distance tests are:
(i) Vertical and horizontal path of the airplane relative to the runway. Two methods that have been used are 1) runway observers and 2) time histories, though runway observers are typically used for small, simple airplanes. Sink rate at touchdown and descent gradients may be computed from time histories.
(ii) Pressure altitude.
(iii) Ambient air temperature.
(iv) Airplane weight (fuel used or time since engine start).
(v) Engine power or thrust data.
(vi) Cowl flap position.
(vii) Wing flap position.
(vii) Runway slope.
(ix) Direction of landing run.
(x) Wind direction and velocity at a height of six feet adjacent to the runway near the touchdown point.
(xi) Landing procedures noted for inclusion in the AFM.
(2) Means of acquiring the required data are listed below:
(i) Time history data is obtained by use of a takeoff and landing camera, electronic equipment such as differential GPS, or a phototheodolite having a known surveyed location. If landing gear loads are a concern, sink rate at touchdown may be computed, or alternately, vertical load factor may be measured by an accelerometer at the c.g.
(ii) Pressure altitude may be obtained with a calibrated sensitive altimeter.
(iii) Ambient air temperature should be obtained with a calibrated temperature sensor.
(iv) The airplane weight may be computed from a known weight at start of test minus the fuel used to the time of test.
(v) Engine power or thrust data may be determined using calibrated airplane powerplant instruments to provide the basic parameters required.
(vi) Cowl flap position may be obtained from a calibrated indicator or a measured position.
(vii) Wing flap position may be obtained from a calibrated indicator or a measured position.
(viii) Slope of the runway can be obtained from the official runway survey or other suitable data obtained using accepted survey practices.
(ix) Direction of the landing run will be the direction of the runway used or an accurate compass indication.
(x) The wind direction and velocity should be obtained with an accurate compass and a calibrated anemometer. Wind data obtained from airport control towers should not be used.
14. § 23.77 Balked Landing Climb.
a. Explanation (Normal, Utility, and Acrobatic Category). Reciprocating engine airplanes with a MTOW of 6,000 pounds (2730 kg) or less.
(1) Purpose. The configuration that is specified for this climb requirement ordinarily is used in the final stages of an approach for landing. The objective of requiring the prescribed climb capability is to ensure that the descent may readily be arrested, and that the airplane will be able to "go around" for another attempt at landing, in the event conditions beyond control of the pilot make such action advisable or necessary.
(2) Flap Retraction. As an alternative to having the flaps in the landing position, compliance with the balked landing climb requirement may be demonstrated with flaps in the retracted position, provided the flaps are capable of being retracted in two seconds or less. Also, provided the airplane's flight characteristics during flap retraction satisfy the constraints imposed by the regulation; that is, flaps must be retracted with safety, without loss of altitude, without sudden change in angle-of-attack, and without need for exceptional piloting skill. Evaluation should include satisfactory demonstration of ability to promptly arrest the descent by application of takeoff power in conjunction with rapid retraction of the flaps during final approach to landing.
(3) Flaps That Will Not Fully Retract in Two Seconds. If the flaps will not fully retract in two seconds, the climb available with the flap position at the end of two seconds may be used and the position noted in the AFM. Other considerations should include flight characteristics, ease of operation and reliability. If the flap is not mechanical, the flap mechanism should be reliable in order to receive credit for a partially retracted flap.
b. Procedures. Climb performance tests are conducted to establish compliance with the prescribed climb requirement and for inclusion in the AFM. The procedures outlined under § 23.65 are equally applicable to the balked landing climb, except that the cooling and other 63
considerations that recommend exploration of a speed range by conducting sawtooth climbs do not apply to the balked landing climb. In lieu of sawtooth climbs, the balked landing climb performance may be established as the average of not less than three continuous run pairs at the climb speed selected by the applicant.
c. Explanation (Normal, Utility and Acrobatic Aircraft with MTOW greater than 6,000 pounds (2730 kg) and Turbine Engine Aircraft and Commuter Category Aircraft).
Sections 23.77(b)(1) and 23.77(c)(1) state that the engines are to be set at the power or thrust that is available eight seconds after initiation of movement of the power controls from minimum flight idle to the takeoff position. The procedures given are for the determination of this maximum power for showing compliance with the climb requirements of § 23.77.
d. Procedures. (Aircraft with a MTOW greater than 6,000 pounds and turbine-engine aircraft.)
(1) Engine Trim. Trim engines to the minimum idle speed/power to be defined in the airplane maintenance manual.
(2) Engine Power Tests. Engine power tests should be conducted at the most adverse landing elevation and temperature condition, or the range of landing altitude and temperature conditions if the most adverse cannot be readily determined.
(i) In the critical air bleed configuration, if applicable, stabilize the airplane in level flight with symmetrical power on all engines, landing gear down, flaps in the landing position, at a speed of VREF at an altitude sufficiently above the selected test altitude so that time for descent to the test altitude with all throttles closed will result in minimum flight-idle power at test altitude.
(ii) Retard throttles to flight idle and descend at VREF, as defined in § 23.73, to approximately the test altitude. When power has stabilized, advance throttle(s) in less than one second to obtain takeoff power.
(iii) The power that is available eight seconds after the initiation of movement of the power controls from the minimum flight idle position is the maximum permitted for showing compliance with the landing climb of § 23.77 for each of the bleed combinations tested.
(iv) If AFM performance is presented so there is no accountability for various bleed conditions, the power obtained with the most critical air bleed should be used for landing climb performance for all operations, including the effects of anti-ice bleed.
e. Data Acquisition and Reduction. The information presented under § 23.65 of the regulation applies to the balked landing climb.
Section 3. Flight Characteristics of 14 CFR § 23.141
1. § 23.141 General
a. Explanation.
(1) Minimum Flight Characteristics. The purpose of these requirements is to specify minimum flight characteristics that are considered essential to safety for any airplane. This section deals primarily with controllability and maneuverability. A flight characteristic is an attribute, a quality, or a feature of the fundamental nature of the airplane that is assumed to exist because the airplane behaves in flight in a certain consistent manner when the controls are placed in certain positions or are manipulated in a certain manner. In some cases, measurements of forces, control surface positions, or acceleration in pitch, roll, and yaw may be made to support a decision but, normally, it will be a pass/fail judgement by the Civil Aviation Authority’s/FAA test pilot.
(2) Exceptional Skills. The phrase "exceptional piloting skill, alertness, or strength," is used repeatedly throughout the regulations and requires highly qualitative judgments on the part of the test pilot. The judgments should be based on the pilot's estimate of the skill and experience of the pilots who normally fly the type of airplane under consideration (that is, private pilot, commercial pilot, or airline transport pilot skill levels). Exceptional alertness or strength requires additional judgment factors when the control forces are deemed marginal or when a condition exists that requires rapid recognition and reaction to be coped with successfully.
b. Procedures. None.
Section 4. Controllability and Maneuverability
1. § 23.143 General.
a. Explanation.
(1) Temporary Control Forces. Temporary application, as specified in the table in § 23.143(c)(1), may be defined as the period of time necessary to perform the necessary pilot motions to relieve the forces, such as trimming or reducing power. The values in the table under § 23.143 of part 23 are maximums. There may be circumstances where a lower force is required for safety. If it is found that a lower force is nece ssary for safety, then that lower force should be established under § 21.21(b)(2).
(2) Prolonged Control Forces. Prolonged application would be for some condition that could not be trimmed out, such as a forward c.g. landing. The time of application would be for the final approach only if the airplane could be flown in trim to that point. Section 23.689 includes discussion concerning a failed cable. .
(3) Controllability. Controllability is the ability of the pilot, through a proper manipulation of the controls, to establish and maintain or alter the attitude of the airplane with respect to its flight path. It is intended in the design of the airplane that it be possible to "control" the attitude about each of the three axes, the longitudinal, the lateral, and the vertical axes. Angular displacements about the longitudi nal axis are called "roll." Those about the lateral axis are called "pitch" and those about the directional axis are called "yaw."
Controllability should be defined as "satisfactory" or "unsatisfactory." Unsatisfactory controllability would exist if the test pilot finds the controllability to be so inadequate that a 65
dangerous condition might easily occur and is unacceptable as a showing of compliance with the regulations.
(4) Maneuverability. Maneuverability is the ability of the pilot, through a proper manipulation of the controls, to alter the direction of the flight path of the airplane. In order to accomplish this, the airplane should be controllable, since a change about one of the axes is necessary to change a direction of flight. Any change in the direction of flight involves an acceleration normal to the flight path. Maneuverability is so closely related to controllability as to be inseparable in any real motion of the airplane. It is also similarly largely qualitative in its nature and should be treated in the same manner as has been suggested for controllability above.
(5) Spring Devices. If a spring device is insta lled in the control system, § 23.687 requires that the airplane not have any unsafe flight characteristics without the use of the spring device, unless the reliability of the device can be established by tests simulating service conditions. The airplane does not have to meet the handling, stability, and control requirements with a failed spring device; however, the airplane has to demonstrate that it is easily controllable by the pilot to continue flight to a safe landing with the failed spring(s).
(6) Powered Trim Without Manual Backup. Most of the part 23 airplanes built since the 1990s use some type of powered trim and have eliminated the manual trim wheel that was traditionally available to the pilot. This configuration makes the failure of the trim system more critical than in the past because pilots cannot change the trim position after the failure. If the failure of the trim system occurs during a slower flight regime such as climb, the control forces to return and land should be reasonable. If, on the other hand, the failure occurs during highspeed cruise in a fast airplane, the control forces when slowing down to land may exceed the prolonged (and maybe even the temporary) force limits in § 23.143. Applicants should account for this possibility and consider mitigation strategies to include in the AFM on how to handle this failure condition.
b. Procedures.
(1) Landing. Using the AFM recommended approach/landing speeds and power settings, determine that airplane controllability is satisfactory with the wing flaps extended and retracted. These tests should be accomplished at the critical weight/c.g. combination within the allowable landing range. For turboprop airplanes, the engine fuel control should be adjusted to the minimum flight-idle fuel flow permitted on airplanes in service unless it is shown that the range of adjustment permitted on airplanes in service has no measurable effect on flight-idle sink rate.
(2) Other Flight Conditions. Controllability and mane uverability procedures for other flight conditions, such as takeoff and VMC, are covered in their respective sections.
(3) Lateral imbalance. Lateral imbalance flight evaluations should be conducted on all airplanes configured such that lateral trim and controllability may be affected. The following configurations should be considered and evaluated as appropriate:
(i) Takeoff - All engine, one-engine-inoperative (multiengine airplanes), VMC, and crosswind operations.
(ii) Enroute - All engine, one-engine-inoperative (multiengine airplanes), and autopilot coupled operations.
(iii) Approach and Landing - All engine, one-engine-inoperative (multiengine airplanes), VMC (where applicable), crosswind, and autopilot coupled operations.
(a) As a result of flight tests, appropriate lateral imbalance limitations and procedures should be developed. Different valu es of fuel imbalance for the various flight configurations may be required. Imbalance limits, if any, should be included in the AFM.
c. Data Acquisition and Reduction. A qualitative determination by the test pilot will usually suffice unless the control force limits are considered marginal. In this case, force gauges are used to measure the forces on each affected control while flying through the required maneuvers.
2. § 23.145 Longitudinal Control.
a. Explanation.
(1) Elevator Power. This regulation requires a seri es of maneuvers to demonstrate the longitudinal controllability during pushovers from low speed, flap extension and retraction, and during speed and power variations. The prime determinations to be made by the test pilot are whether or not there is sufficient elevator power to allow pitching the nose downward from a minimum speed condition and to assure that the required maneuvers can be performed without the resulting temporary forces becoming excessive.
(2) Speeds Below Trim Speeds. The phrase, "speeds below the trim speed," as used in § 23.145(a), means speeds down to VS1.
(3) Wing Flaps. If gated or detented flap pos itions are provided, refer to the requirements in § 23.697(c). (An acceptable gate or detent is one that allows the pilot to readily determine the flap position without seriously detracting from other piloting duties under any flight condition, day or night.)
(4) Loss of Primary Control Systems. Section 23.145(e) is intended to cover a condition where a pilot has sustained some failure in the primary longitudinal control system of the airplane (for some multiengine airplanes, also loss of the directional control system) and is required to land using the power and trim system without the primary control. It is not intended that this test be demonstrated to an actual landing; however, a demonstration may be performed using manipulation of trim and power to a landing, if desired. Section 23.145(e) is the flight test to demonstrate compliance with the requirement that specifies a failure of the primary control system.
(5) Analysis of System. An analysis of the control system should be completed before conducting the loss of primary control system test. On some airplanes, the required single longitudinal control system failure could result in loss of both the downspring and the primary longitudinal control system. If this failure occurred on an airplane utilizing an extremely large 67
downspring, the loss of the downspring may result in a nose-up pitching moment at aft c.g. that could not be adequately countered by the basic pitch trim system.
b. Procedures. The wording of the regulation sufficiently describes the maneuvers required to show compliance. The selection of altitudes, weights, and c.g. positions to be flight tested by the FAA will depend on a study of the applicant's flight test report. Normally, the following combinations are checked during the certification tests:
(1) Altitude. Select a nominal altitude considering power available. Longitudinal control would not be expected to change much with typical part 23 altitude capabilities, so repeating tests near maximum altitude should only be needed when controllability is marginal and/or the airplane has high altitude capability like some of the part 23 jets.
(2) Weight. Maximum gross weight for all tests, except where otherwise described in paragraph (3) below.
(3) C.G. For conventional configurations, § 23.1 45(a), most aft c.g. and most aft c.g.
approved for any weight; § 23.145 paragraphs (b) 1 through (b) 6, most forward and most aft
c.g.; § 23.145(c), most forward c.g.; § 23.145(d), most forward c.g. and most forward c.g.
approved for any weight; and § 23.145(e), both the forward and aft c.g. locations. Section 23.145(e) is sometimes more difficult to achieve at the aft c.g. than the forward limit, particularly if the airplane exhibits neutral to divergent phugoid tendencies.
(4) Power or Configuration. Pitching moments resulting from power or configuration changes should be evaluated under all conditions necessary to determine the most critical demonstration configuration.
c. Data Acquisition. No special instrumentation is required. The exception to this would be the l0-pound force in § 23.145(d), which should be measured with a force gauge. All longitudinal forces should be measured if the forces are considered marginal or excessive.
3. § 23.147 Directional and Lateral Control.
a. Explanation.
(1) Yawed Flight. Section 23.147(a) is intended as an investigation for dangerous characteristics during sideslip, which may result from blocked airflow over the vertical stabilizer and rudder. Rudder lock and possible loss of directional control are exam ples of the kinds of characteristics the test is aimed at uncovering. Section 23.177 also addresses rudder lock.
Compliance may be demonstrated if the rudder stop is reached prior to achieving either l5 degrees of heading change or the l50-pound force limit, providing there are no dangerous characteristics. The control stop serves more effectively than the l50-pound force to limit the pilot's ability to induce a yaw beyond that demonstrated as acceptable.
(2) Controllability following sudden engine failure. Section 23.147(b) requires a demonstration of controllability following sudden engine failure during en route climb.
b. Procedures.
(1) Yawed Flight. The airplane configurations to be tested according to § 23.147(a) are:
(i) One engine inoperative and its propeller in the minimum drag position.
(ii) The remaining engines at not more than maximum continuous power.
(iii) The rearmost allowable c.g.
(iv) The landing gear: both retracted and extended
(v) The flaps retracted.
(vi) Most critical weight.
(vii) Airplane trimmed in the test condition, if possible.
(2) Controllability Following Sudden Engine Failure. In complying with the testing required by § 23.147(b), from an initial condition of straight flight with wings level, zero sideslip and in trim, simulate a sudden and complete failure of the critical engine. To allow for an appropriate delay, no action should be taken to recover the airplane for two seconds following the first indication of engine failure. The recovery action should not involve movement of the engine, propeller or trimming controls. At no time should the bank angle exceed 45 degrees or excessive yaw be developed. The evaluation of da ngerous attitudes and characteristics should be based on each particular airplane characteristic and the flight test pilot's evaluation.
(i) The method used to simulate engine failure should be:
(a) For a reciprocating engine, closure of the mixture control; or
(b) For a turbine engine, termination of the fuel supply by the means which results in the fastest loss of engine power or thrust. Engine shut-off procedures would normally be sufficient.
c. Loss of Primary Control Systems. (Also, refer to AC 23-17.)
(1) Explanation. Section 23.147(c) is intended to cover a condition where a pilot has sustained some failure in the primary lateral control system of the airplane. If a single failure in the primary lateral control system could also cause the loss of additional control, then the loss of the additional controls must be considered. It must be shown that, with the loss of the primary lateral control, the airplane is safely controllable in all configurations and could be landed without exceeding the operational and structural limitations of the airplane. The rule calls out any engine configuration, speed, or altitude. This rule is interpreted to mean safely controllable such that the pilot can transition into a smaller, limited flight and configuration envelope, if necessary, for continued safe flight and landing. It is not intended that this test be demonstrated to an actual landing; however, a demonstration may be performed using manipulations of either lateral trim or sideslip, or both, generated by the rudder and differential power if available to a landing. Section 23.147(c) is the flight test to de monstrate compliance with the requirement that specifies a failure in the primary lateral control system. This failure implies a disconnection on the primary control system such that the ailerons are free to float and the lateral trim (if installed) is operational.