Table 6 - WAT Chart Regulation
23.67(a)(1 )
23.67(a)(2) 23.67(b)(1) 23.67(b)(2) 23.67(c)(1)
23.67(c)(2 )
23.67(d)(1) 23.67(d)(2) 23.67(d)(3) 23.67(d)(4) Category Normal, Utility, and Aerobatic Normal, Utility, and Aerobatic Turbojets > 6,000 lbs and Commuter Engine Type and Airplane Weight Recip 6,000 lbs or less Recips > 6,000 lbs and Turboprops Turbojets 6,000 lbs or less VSO (kts) >61 61 Power On Operative Engine MCP MCP MTOP MCP MTOP MCP MTOP MTOP MCP MTOP Configuration Flap and gear retracted Flap and gear retracted Take-off flap, gear retracted Flap and gear retracted Take-off flap, gear retracted Flap and gear retracted Take-off flap, gear extended Take-off flap, gear retracted Flap and gear retracted Approach flap1, gear retracted Propeller Position on Inop Engine Minimum drag Minimum drag Minimum drag Minimum drag Position it automatically and rapidly assumes Position it automatically and rapidly assumes Minimum drag Minimum drag Attitude Wings level Climb Speed 1.2VS1 1.2VS1 Equal to that achieved at 50ft demon strating
23.53 1.2VS1 Equal to that achieved at 50ft demon strating
23.53 1.2VS1 V2 V2 1.2VS1 As in procedures but 1.5VS1 Altitude (ft) 5,000 5,000 400 1,500 400 1,500 Take-off surface 400 1,500 400 Required Climb Gradient (%) 1.50 No minimum but must determine steady climb/ descent gradient 1.00 0.75 1.20 0.75 Measurably positive2 2.003 1.204 2.105 Notes:
1 Approach position(s) in which VS1 does not exceed 110 percent of the VS1 for the related all-engines-operating landing positions.
2 Measured positively for two-engine airplanes, 0.3 percent for three-engine airplanes, or 0.5 percent for four-engine airplanes.
3 2.0 percent for two-engine airplanes, 2.3 percent for three-engine airplanes, 2.6 percent for four-engine airplanes.
4 1.2 percent for two-engine airplanes, 1.5 percent for three-engine airplanes, 1.7 percent for four-engine airplanes.
5 2.1 percent for two-engine airplanes, 2.4 percent for three-engine airplanes, 2.7 percent for four-engine airplanes.
6 MCP is maximum continuous power 54
b. Procedure.
(1) Critical Engine. To accomplish these objectives, it is necessary that sawtooth climbs be conducted with the critical engine inoperative and with the prescribed configuration and power condition. The "critical-inoperative-engi ne" for performance considerations is that engine which, when inoperative, results in the lowest rate of climb. The critical engine should be determined by conducting a set of sawtooth climbs, one engine at a time.
(2) Test Technique. One-engine-inoperative climb tests should be conducted at airspeeds and at altitudes as outlined for all-engine climbs under § 23.65. The test technique and other considerations noted under § 23.65 also apply. In climb tests with one engine inoperative, however, trim drag can be a significant factor and one-engine-inoperative climb tests should be conducted on a steady heading with the wings laterally level or, at the option of the applicant, with not more than a five-degree bank into the good engine in an effort to achieve zero sideslip.
A yaw string or yaw vane is needed to detect zero sideslip. The AFM should describe the method used and the approximate ball position required to achieve the AFM performance.
c. Jet Aircraft > 6,000 pounds and Commuter Category Airplanes.
(1) Climb Gradient. The required climb gradient s are specified in § 23.67(d).
(2) Climb Performance Methods. Climb performance should be determined in the configurations necessary to construct the net takeoff flight path and to show compliance with the approach climb requirements of § 23.67(d). Some net takeoff flight path conditions will require wings level climb data. Refer to paragraph 23.57g(1). If full rudder with wings level cannot maintain constant heading, small bank angles into the operating engine(s), with full rudder, should be used to maintain a constant heading. For all other conditions, climb performance may be determined with up to a five-degree bank into the good engine. Two methods for establishing the critical one-engine-inoperative climb performance follow:
(i) Method No. 1. Reciprocal heading clim bs are conducted at several thrust-to-weight conditions from which the performance for the AFM is extracted.
(ii) Method No. 2. Drag polars and engine-out yaw drag data are obtained for expansion into AFM climb performance. Refer to appendix 2. Reciprocal heading check climbs are conducted to verify the predicted climb performance.
(3) Landing Gear Position. The climb performance test s with landing gear extended in accordance with § 23.67(d) should be conducted with the landing gear and gear doors extended in the most unfavorable in-transit drag position. It has been acceptable to consider that the critical configuration is associated with the largest frontal area. For the landing gear, it usually exists with no weight on the landing gear. For gear doors, it is usually with all the gear doors open. If it is evident that a more critic al transitional configuration exists, such as directional rotation of the gear, testing should be conducted in that configuration. In all cases where the critical configuration occurs during a transition phase that cannot be maintained except 55
by special or extraordinary procedures, it is permissible to apply corrections based on other test data or acceptable analysis.
(4) Cooling Air. If means, such as variable in take doors, are provided to control powerplant cooling air supply during takeoff, climb, and en route flight, they should be set in a position that will maintain the temperature of major powerplant components, engine fluids, and so forth, within the established limits. The effect of these procedures should be included in the climb performance of the airplane. These provisions apply for all ambient temperatures up to the highest operational temperature limit for which approval is desired.
(5) Power. Refer to paragraph 23.57b.
12. § 23.71 Glide (Single-Engine Airplanes).
a. Explanation.
(1) Gliding Performance. Section 23.71 requires the optimum gliding performance to be scheduled, with the landing gear and wing flaps in the most favorable position and the propeller in the minimum drag position.
(2) Background. The primary purpose of this inform ation is to provide the pilot with the airplane gliding performance. Such data will be used as an approximate guide to the gliding range that can be achieved, but they will not be used to the same degree of accuracy or commercial significance as many other aspects of performance information. Hence, some reasonable approximation in its derivation is acceptable.
b. Means of compliance.
(1) Engine-inoperative Tests. Clearly the simplest way of obtaining accurate data is to perform actual engine-inoperative glides. These tests should be carried out over an airfield, thereby permitting a safe landing to be made if the engine does not restart at the end of the test.
(i) Fixed-Pitch Propeller. Most likely, the propeller will be windmilling after the fuel is shut off. If this is the case and the pr opeller does not stop after slowing to the best glide speed, then the gliding performance should be based on a windmilling propeller. Stalling the airplane to stop the propeller from windmilling is not an acceptable method of determining performance because the procedure could cause the average pilot to divert attention away from the primary flight task of gliding to a safe landing.
(ii) Constant-speed/Variable-pitch Propeller Airplanes. For these propellers, the applicant may assume that the means to change propeller pitch is still operational and, therefore, the propeller should be set at the minimum drag configuration. For most installations, this will be coarse pitch or feather.
(iii) Turbojet airplanes. Reserved.
(2) Sawtooth Glides. A method of determining glide performance is sawtooth glides.
These glides can be flown using the same basic procedures in § 23.65 of this AC minus the power considerations. For simplific ation, the test need only be flown at an intermediate altitude and gross weight generating one speed for the pilot to use. The best lift over drag speed is frequently higher than the best rate of climb speed; therefore, the airspeed range to flight test may be bracketed around a speed 10 to 15 percent higher than the best rate of climb speed.
(3) Performance Data. A chart or table should be constructed for the AFM that presents the literal (over-the-ground) gliding distances for the altitude range expected in service, at the best demonstrated glide speed. As a minimum, a statement of nautical miles (NM) per 1,000 feet loss of altitude at the demonstrated configuration and speed at MTOW, standard day, no wind, should be given.
13. § 23.75 Landing.
a. Explanation.
(1) Purpose. The purpose of this requirement is to evaluate the landing characteristics and to determine the landing distance. The landing distance is the horizontal distance from a point along the flight path 50 feet above the landing surface to the point where the airplane has come to a complete stop, or to a speed of three knots for seaplanes or amphibians on water.
(2) Companion Requirements. Sections 23.143(a)(6), 23.153, 23.231, and 23.233 are companion requirements and, normally, tests to determine compliance would be accomplished at the same time. Additionally, the requirements of § 23.473 should be considered.
(3) Approach and Landing. The steady approach, the pilot skill, the conditions, the vertical accelerations, and the airplane actions in § 23.75(a), (b), and (c) are concerned primarily with not requiring particularly skillful or abrupt maneuvers after passing the 50-foot point. It has generally been considered that some power may be used during a steady gliding approach to maintain at least 1.3 VS1 control sink rate on final approach. For those airplanes using power during approach, power may be decreased after passing the 50-foot point and there should be no abrupt maneuvers using the longitudinal control. For those airplanes approaching with power off, the longitudinal control may be used as necessary to maintain a safe speed for flare. In both cases, there should be no change in configuration and power should not be increased. The landing distance and the procedure specified in the AFM are then based on the power used for the demonstration. The power used and the technique used to achieve the landing distances should be clearly stated in the AFM. This applie s to portions of the approach prior to and after the 50-foot height.
(4) Adverse Landing Conditions. The airplane should be satisfactorily controllable when landing under the most unfavorable conditions to be encountered in service, including crosswinds, wet runway surfaces, and with one engine inoperative. Demonstration of landing with an adverse crosswind of at least 0.2 VSO is addressed in § 23.233. Op erations on wet (but not contaminated) runway surfaces have been simulated by disconnecting the nosewheel steering on large part 23 airplanes. The effect of wei ght on the landing distance due to its influence on controllability of reverse thrust should be considered. The criticality of the adverse landing conditions should guide the level of complexity applicants use in determining controllability.
Existing flight test practices have proven adequate for propeller driven part 23 airplanes, but they may not be adequate for small jets. Additional guidance may be found in AC 25-7B. Part 23 jets typically have higher landing speeds and little drag to help slow the airplane. Landing 57
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