67 Figure 13-6. Clearway Profiles
(4) The profile shows no fixed obstacle projecting above the clearway plane.
However, in accordance with the definition of clearway in part 1, the airport authorities must have control of this area to ensure that no flight will be initiated using a clearway unless it is determined that no movable obstacles will exist within the clearway when the airplane flies over.
14. Takeoff Flight Path - § 25.115.
a. Takeoff Flight Path - § 25.115(a).
(1) Explanation . The takeoff flight path begins at the end of the takeoff distance and at a height of 35 ft. above the takeoff surface, and ends when the airplane’s actual height is the higher of 1,500 ft. above the takeoff surface or at an altitude at which the configuration and speed have been achieved where the requirements of § 25.121(c) can be met. (See paragraph 12 of this AC (§ 25.111) for additional discussion.) Section 25.115(a) states that the takeoff “shall be considered to begin 35 feet above the takeoff surface,” recognizing that in the case of a wet runway the airplane will only be at a height of 15 feet. For takeoffs from wet runways, the actual airplane height will be 20 feet lower than the takeoff flight path determined under § 25.115.
Therefore, the airplane will be 20 feet closer vertically to obstacles after taking off from a wet runway compared to taking off from a dry runway.
(2) Procedures.
Figure 14-1. Takeoff Segments & Nomenclature
TAKEOFF FLICHT PATH *ACTUAL HICHT --- ≥ 1500 FEET 1500 FEET PATH 2/ * OF I ENG INOPTAKFOFF OR- TAKEOFF DISTANCE LONGER 1.15 ALL ENG TAKEOFF) PATH 1 ACTUAL HEIGHT ≥ 400 FEET
ACTUAL HEIGHTS ARE VEr VLOF GEAR RETRACTION COMPLETE REFERENCED TO RUNWAY ELEVATION AT END OF TAKEOFF 35,FI DISTANCE SEGMENT* GROUND ROLL IST 2ND ACCELERATION. FINAL
LANDING GEAR DOWN PRETRACTION RETRACTED
ENROUTE
FLAPS TAKEOFF RETRACTING (SEE NOTE) POSITION THRUST/POWER TAKEOFF ABOVE 400 FT THRUST CAN BE REDUCED IF THE REQUIREMENTS (SEE NOTE) OF 25, 11UCH3) CAN BEET WITH LESS THAN TAKEOFE THRUN → CONTINUOUS MAXIMUM
AIRSPEED ACCELERATING ACCELERATING WFTO
ENGINES ALL OPERATING ONE INOPERATIVE
PROPELLER TAKEOFF ONE AUTOFEATHERED OR WINDMILLING ONE FEATHERED UP TO 400 FEET 400 FEET OR GREATER NOTE: The final takeoff segment will usually begin with the airplane in the en route configuration and with maximum continuous thrust, but it is not required that these conditions exist until the end of the takeoff path when compliance with § 25.121(c) is shown. The time limit on takeoff thrust cannot be exceeded.
* Segments as defined by § 25.121.
b. Net Takeoff Flight Path - § 25.115(b) and (c).
(1) Explanation.
(a) The net takeoff flight path is the actual flight path diminished by a gradient of
0.8 percent for two-engine airplanes, 0.9 percent for three-engine airplanes, and 1.0 percent for four-engine airplanes.
(b) For the level flight acceleration segment, these prescribed gradient reductions may be applied as an equivalent reduction in acceleration in lieu of reduction in net flight path.
(See paragraph 12 (ref. § 25.111) of this AC for additional discussion.)
(c) SR-422B, and § 121.189(d), require that no airplane may take off at a weight in excess of that shown in the AFM to correspond with a net takeoff flight path that clears all 68
69 obstacles either by at least a height of 35 ft. vertically, or by at least 200 ft. horizontally within the airport boundaries, and by at least 300 ft. horizontally after passing beyond the boundaries.
(d) With turns in the net takeoff flight path, obstacle clearance determination requires consideration of both radius of turn and climb gradient decrement. Radius of turn, for use in obstacle lateral separation, is not airplane dependent and is readily calculated from speed and bank angle. Climb gradient decrements, however, are airplane dependent. Climb gradient decrements for bank angles up to at least 15 degrees should be contained in the AFM.
(2) Procedures.
Figure 14-2. Net Takeoff Flight Path
15. Climb: General - § 25.117.
a. Explanation . This section states the climb requirements of §§ 25.119 and 25.121 must be complied with at each weight, altitude, and ambient temperature within the operational limits established for the airplane and with the most unfavorable center of gravity for each configuration.
b. Procedures. None.
16. Landing Climb: All-Engines-Operating - § 25.119.
a. Explanation. Section 25.119(a) states that the engines are to be set at the power or thrust that is available 8 seconds after initiating movement of the power or thrust controls from the minimum flight idle position to the go-around power or thrust setting. The procedures given below are for the determination of this maximum thrust for showing compliance with the climb requirements of § 25.119.
b. Procedures.
(1) The engines should be trimmed to the low side of the idle trim band, if applicable, as defined in the airplane maintenance manual. The effect of any variation in the idle fuel flow schedule for engines with electronic fuel controllers is typically negligible (but any such claim should be adequately substantiated).
(2) At the most adverse test altitude, not to exceed the maximum field elevation for which certification is sought plus 1,500 ft., and with the most adverse bleed configuration expected in normal operations, 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. Retard the throttle(s) of the test engine(s) to flight idle and determine the time needed to reach a stabilized
r.p.m., as defined below, for the test engine(s) while maintaining level flight or the minimum rate of descent obtainable with the thrust of the remaining engine(s) not greater than maximum continuous thrust (MCT). Engine flight idle r.p.m. is considered to be stabilized when the initial rapid deceleration of all rotors is completed. This has usually been 8-20 seconds. This can be determined in the cockpit as the point where rapid movement of the tachometer ceases. For some airplanes it may be desirable to determine the deceleration time from plots of r.p.m. versus time.
(3) For the critical air bleed configuration, stabilize the airplane in level flight with symmetric power on all engines, landing gear down, flaps in the landing position, at a speed of VREF, simulating the estimated minimum climb-limited landing weights at an altitude sufficiently above the selected test altitude so that time to descend to the test altitude with the throttles closed equals the appropriate engine r.p.m. stabilization time determined in paragraph (2) above.
Retard the throttles to the flight idle position and descend at VREF to approximately the test altitude. When the appropriate time has elapsed, rapidly advance the power or thrust controls to the go-around power or thrust setting. The power or thrust controls may first be advanced to the forward stop and then retarded to the go-around power or thrust setting. At the applicant’s option, additional less critical bleed configurations may be tested.
(4) The thrust that is available 8 seconds after the initiation of movement of the power or thrust controls from the minimum flight idle position, in accordance with paragraph (3) above, will be the maximum permitted for showing compliance with the landing climb requirements of § 25.119(a), and Section 4T.119(a) of SR-422B (see Appendix 4) for each of the bleed combinations tested in accordance with paragraph (3) above. If AFM performance is presented such that there is no accountability for various bleed conditions, the thrust obtained with the most critical airbleed should be used for landing climb performance for all operations. The effects of anti-ice bleed should be accounted for.
17. Climb: One-Engine-Inoperative - § 25.121.
a. Explanation. None.
b. Procedures.
(1) Two methods for establishing one-engine-inoperative climb performance follow:
(a) Reciprocal heading climbs are conducted at several thrust-to-weight conditions from which the performance for the AFM is extracted. These climbs are flown with the wings nominally level. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
(b) Drag polars and one-engine-inoperative yaw drag data are obtained for expansion into AFM climb performance. These data are obtained with the wings nominally level. Reciprocal heading check climbs are conducted to verify the predicted climb performance.
These check climbs may be flown with the wings maintained in a near level attitude. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
(2) 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 constant heading.
Unless the landing lights automatically retract with engine failure, testing should be conducted with the lights extended for § 25.121(a) Takeoff; landing gear extended, § 25.121(b) Takeoff;
landing gear retracted, and § 25.121(d) Approach.
(3) The climb performance tests with landing gear extended, in accordance with § 25.121(a), may be conducted with the landing gear and gear doors in the position they finally achieve after “gear down” selection. The critical configuration for the landing gear extended climb is considered to be that which presents the largest frontal area to the local airflow. This would normally be with no weight on the landing gear (full strut extension and trucks tilted) and all gear doors open. However, since the takeoff path will be determined by measurement of continuous takeoffs, or checked by continuous takeoffs if constructed by the segmental method (Ref. § 25.111(d)), any non-conservatism arising from the gear doors “closed” climb data will be evident. Also, some measure of conservatism is added to the landing gear extended climb performance by the requirement of § 25.111(d)(3) for the takeoff path data to be based on the airplane’s performance without ground effect.
(4) If means, such as variable intake 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, etc., 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. (Reference: § 25.1043)
(5) The latter parts of §§ 25.121(a)(1) and (b)(1), which state “...unless there is a more critical power operating condition existing later along the flight path...” are intended to cover those cases similar to where a wet engine depletes its water and reverts to dry engine operation.
This is not intended to cover normal altitude thrust lapse rates above the point where the landing gear is fully retracted. (Reference: Preamble to SR-422A)
(6) Section 25.121(d) requires that the reference stall speed for the approach configuration not exceed 110 percent of the reference stall speed for the related landing configuration. This stall speed ratio requirement is to ensure that an adequate margin above the stall speed in the selected approach configuration is maintained during flap retraction in a goaround. An alternative means of providing an adequate operating speed margin during flap retraction in a go-around would be to increase VREF for the landing configuration to provide an equivalent operating speed margin. That is, VREF could be increased such that the reference stall speed for the approach configuration does not exceed 110 percent of 23.1REFV . An equivalent level of safety finding should be used to document the use of this alternative versus direct compliance with § 25.121(d). To maintain equivalent safety, the increase in VREF should not be excessive (for example, greater than 5 knots) to minimize the effect on safety of longer landing distances, higher brake energy demands, and reduced margins between VREF and VFE.
18. En Route Flight Paths - § 25.123.
a. Explanation. This guidance is intended for showing compliance with the requirements of § 25.123 and application to the operating requirements of §§ 121.191 and 121.193, which specify the clearances over terrain and obstructions required of the net en route flight paths subsequent to the failure of one or two engines.
b. Procedures.
(1) Sufficient en route climb performance data should be presented in the AFM to permit the determination of the net climb gradient and the net flight path in accordance with § 25.123(b) and (c) for all gross weights, altitudes, and ambient temperatures within the operating limits of the airplane. This en route climb performance data should be presented for altitudes up to the all-engines-operating ceiling to permit the calculation of drift-down data in the event of an en route engine failure.
(2) Fuel Consumption Accountability. The effect of the variation of the airplane’s weight along the flight path due to the progressive consumption of fuel may be taken into account using fuel flow rates obtained from airplane manufacturers’ test data. If measured fuel flow data is unavailable, a conservative fuel flow rate not greater than 80 percent of the engine specification flow rate at maximum continuous thrust (MCT) may be used.
(3) The procedures and flight conditions upon which the en route flight path data are based should be provided to the flightcrew. Credit for fuel dumping, if available and included in the flightcrew procedures, may be used to achieve the performance capability presented in the AFM. A conservative analysis should be used in taking into account the ambient conditions of temperature and wind existing along the flight path. All performance should be based on the net flight path and with MCT on the operating engine(s).
19. Landing - § 25.125.
a. Explanation.
(1) The landing distance is the horizontal distance from the point at which the main gear of the airplane is 50 ft. above the landing surface (treated as a horizontal plane through the touchdown point) to the point at which the airplane is brought to a stop. (For water landings, a speed of approximately 3 knots is considered “stopped.”) In this AC, the distance is treated in two parts: the airborne distance from 50 ft. to touchdown, and the ground distance from touchdown to stop. The latter may be further subdivided into a transition phase and a full braking phase if the applicant prefers this method of analysis.
(2) The minimum value of VREF is specified in § 25.125(b)(2). It is intended to provide an adequate margin above the stall speed to allow for likely speed variations during an approach in light turbulence. If the landing demonstrations show that a higher speed is needed for acceptable airplane handling characteristics, the landing distance data presented in the AFM must be based upon the higher reference landing speed per § 25.125(b)(2).
(3) The engines should be set to the high side of the flight idle trim band, if applicable, for the landing flight tests. The effect of any variation in the idle fuel flow schedule for engines with electronic fuel controllers is typically negligible (but any such claim should be adequately substantiated).
b. Procedures for Determination of the Airborne Distance. Three acceptable means of compliance are described in paragraphs (1), (2), and (3) below. These differ from the “traditional” method in which steep approaches and high touchdown sink rates were permitted.
Such a demonstration of maximum performance is no longer considered acceptable. However, the distances obtained using that method resulted in a satisfactory operational safety record. The methods given here allow credit for the amount of testing an applicant is prepared to conduct, such that if the method described in paragraph 19b(3) (the most complex) is chosen, distances typical of those from the “traditional” method should be obtained, but without incurring the associated risks during testing.
NOTE: If it is determined that the constraints on approach angle and touchdown rate-of-sink described in paragraphs (2) and (3), below, are not appropriate due to novel or unusual features of future transport category airplane design, new criteria may be established. Such a change would be acceptable only if it is determined that an equivalent level of safety to existing performance standards and operational procedures is maintained.
(1) Experience shows an upper bound to the part 25 zero-wind airborne distances achieved in past certifications and, similarly, a minimum speed loss. These are approximated by the following:
Air Distance (feet) = 1.55 (V REF-80)1.35+800 where VREF is in knots TAS
74 Touchdown Speed = V REF-3 knots
An applicant may choose to use these relationships to establish landing distance in lieu of measuring airborne distance and speed loss. If an applicant chooses to use these relationships, the applicant should show by test or analysis that they do not result in air distances or touchdown speeds that are nonconservative.
(2) If an applicant chooses to measure airborne distance or time, at least six tests covering the landing weight range are required for each airplane configuration for which certification is desired. These tests should meet the following criteria:
(a) A stabilized approach, targeting a glideslope of -3 degrees and an indicated airspeed of VREF, should be maintained for a sufficient time prior to reaching a height of 50 feet above the landing surface to simulate a continuous approach at this speed. During this time, there should be no appreciable change in the power setting, pitch attitude, or rate of descent. The average glideslope of all landings used to show compliance should not be steeper than -3 degrees.
(b) Below 50 feet, there should be no nose depression by use of the longitudinal control and no change in configuration, except for reduction in power.
(c) The target rate of descent at touchdown should not exceed 6 feet per second.
Target values cannot be achieved precisely; however, the average touchdown rate of descent should not exceed 6 feet per second.
(3) If the applicant conducts enough tests to allow a parametric analysis (or equivalent method) that establishes, with sufficient confidence, the relationship between airborne distance (or time) as a function of the rates of descent at 50 feet and touchdown, the 14 CFR part 25 airborne distances may be based on an approach angle of -3.5 degrees, and a touchdown sink rate of 8 feet per second (see paragraph 19h for a sample of this analysis method).
(a) The air distance or air time established by this method should not be less than 90 percent of the lowest demonstrated value obtained using the target values for approach angle and touchdown sink rate specified in paragraph (b), below. Test data with approach angles steeper than -3.5 degrees, or touchdown sink rates greater than 8 feet per second, should not be used to satisfy this requirement.
(b) In order to determine the parametric relationships, it is recommended that test targets should span approach angles from -2.5 degrees to –3.5 degrees, and sink rates at touchdown from 2-6 ft. per second. Target speed for all tests should be VREF.
(c) Below 50 feet, there should be no nose depression by use of the longitudinal control and no change in configuration that requires action by the pilot, except for reduction in power.
(d) If an acceptable method of analysis is developed by an applicant to statistically establish a satisfactory confidence level for the resulting parametric relationships, then 12 tests, in each aerodynamic configuration for which certification is desired, should be sufficient. More tests should be conducted if the distribution of the data does not give sufficient confidence in the parametric correlation. Past experience has shown that a total of 40 landings would establish a satisfactory confidence level without further analysis. Autolands may be included in the analysis but should not comprise more than half of the data points. If it is apparent that configuration is not a significant variable, all data may be included in a single parametric analysis.
(e) If an applicant proposes any other method as being equivalent to a parametric analysis, that method should be based on a developed mathematical model that employs performance-related variables such as thrust, attitude, angle-of-attack, and load factor to adequately reproduce the flight test trajectory and airspeed variation from the 50 foot point to touchdown. Such a mathematical model should be validated by not less than 12 tests in each aerodynamic configuration for which certification is desired, and be justified by a comparison of tested and calculated landing airborne distances.
(f) For the same aerodynamic configuration as previously certificated -- if new tests are necessary to substantiate performance to a weight higher than that permitted by the extrapolation limits of § 25.21(d), two landings per configuration should be conducted for each 5 percent increase in landing weight (but no more than a total of six landings should be needed).
These may be merged with previous certification tests for parametric analysis, whether the previous certification was conducted by this method or not. If a new aerodynamic configuration is proposed, the 12 tests per configuration described in paragraph (d), above, should be conducted.
(g) In calculating the AFM landing distances, the speed loss from 50 feet to touchdown, as a percentage of VREF, may be determined using the conditions described in paragraph 19b(3).
(4) Whichever method is chosen to establish airborne distances, satisfactory flight characteristics should be demonstrated in the flare maneuver when a final approach speed of VREF-5 knots is maintained down to 50 feet.
(a) Below 50 feet, the application of longitudinal control to initiate flare should occur at the same altitude as for a normal “on-speed” landing; no nose depression should be made and power should not be increased to facilitate the flare.
(b) All power levers should be in their minimum flight idle position prior to touchdown.
(c) The normal flare technique should be used such that the touchdown speed should be at least 5 knots less than the touchdown speed used to establish the landing distance and the rate of descent at touchdown should not be greater than 6 feet per second.
(d) This demonstration is performed at both maximum landing weight and near minimum landing weight.
(e) These V REF-5 knots landing demonstrations should not require the use of high control forces or full control deflections.
c. Procedures for Determination of the Transition and Stopping Distances .
(1) The transition distance extends from the initial touchdown point to the point where all approved deceleration devices are operative. The stopping distance extends from the end of transition to the point where the airplane is stopped. The two phases may be combined if the applicant prefers this method of analysis.
(2) If sufficient data are not available , there should be a minimum of six landings in the primary landing configuration. Experience has shown that if sufficient data are available for the airplane model to account for variation of braking performance with weight, lift, drag, ground speed, torque limit, etc., at least two test runs are necessary for each configuration when correlation for multiple configurations is being shown.
(3) A series of at least six measured landing tests covering the landing weight range should be conducted on the same set of wheels, tires, and brakes in order to substantiate that excessive wear of wheel brakes and tires is not produced in accordance with the provisions of § 25.125(c)(2). The landing tests should be conducted with the normal operating brake pressures for which the applicant desires approval. The main gear tire pressure should be set to not less than the maximum pressure desired for certification corresponding to the specific test weight.
Longitudinal control and brake application procedures should be such that they can be consistently applied in a manner that permits the airplane to be de-rotated at a controlled rate to preclude an excessive nose gear touchdown rate and so that the requirements of § 25.125(b)(4) and (5) are met. Nose gear touchdown rates in the certification landing tests should not be greater than eight feet per second. Certification practice has not allowed manually applied brakes before all main gear wheels are firmly on the ground.
(4) Describe the airplane operating procedures appropriate for determination of landing distance in the performance section of the AFM.
(5) Propeller pitch position used in determining the normal all-engines-operating landing stopping distance should be established using the criteria of § 25.125(g) for those airplanes that may derive some deceleration benefit from operating engines. Section 25.125(g) states that if the landing distance determined using a “device” that depends on the operation of any engine would be “noticeably increased” when a landing is made with that engine inoperative, the landing distance must be determined with that engine inoperative, unless a “compensating means” will result in one-engine-inoperative landing distances not greater than those with all engines operating. Acceptable interpretations of the terms “device,” “noticeably increased,” and “compensating means” are described below.
(a) If the propeller produces drag at any speed during the stopping phase of the normal all-engines-operating landing distance, the maximum drag from this “device” for which performance credit may be taken is that which results from a propeller pitch position that renders zero thrust at zero airspeed. If the normal operational ground idle setting produces negative thrust at zero airspeed, the all-engines-operating stopping distances should be determined using a special flight test power lever stop to limit the propeller blade angle.
(b) Distances should be measured for landings made with the propeller feathered on one engine, and ground idle selected after touchdown on the operating engines. The airplane configuration for this test, including the ground idle power lever position, should be the same as that used for the all-engines-operating landing distance determination. The nose wheel should be free to caster, as in VMCG tests, to simulate wet runway surface conditions. Differential braking may be used to maintain directional control. This testing should be conducted at a minimum of three weights that cover the expected range of operational landing weights. If the resulting distances do not exceed the all-engines-operating landing distances by more than two percent (2%), they are not “noticeably increased” and no further testing is required to take performance credit for all-engines-operating disking drag in AFM landing distances.
(c) If the distances determined in paragraph (b), above, are more than two percent greater than the all-engines-operating landing distances, there should be a “compensating means” in order to take performance credit for the all-engines-operating disking drag. Reverse propeller thrust on the operating engines is considered a “compensating means” if the resulting landing distances, with one propeller feathered, are demonstrated to be not longer than those determined for all-engines-operating with disking drag. The airplane configuration for this test should be the same as that used for the all-engines-operating landing distance determination. The nose wheel should be free to caster, as in VMCG tests, to simulate wet runway surface conditions.
Differential braking may be used to maintain directional control. Reverse thrust should not be selected until one second after nose wheel touchdown. This testing should be conducted at a minimum of three weights that cover the expected range of operational landing weights.
d. Instrumentation and Data . Instrumentation should include a means to record the airplane’s glide path relative to the ground, and the ground roll against time, in a manner that permits determining the horizontal and vertical distance time-histories. The appropriate data to permit analysis of these time-histories should also be recorded.
e. Landing on Unpaved Runways . Guidance material for evaluation of landing on unpaved runways is contained in Chapter 8 of this AC.
f. Automatic Braking Systems. Guidance material relative to evaluation of auto-brake systems is provided in paragraph 55c(6) of this AC.
g. Airplane Flight Manual Landing Distances .
(l) As a minimum, the AFM must include data for standard temperature and zero runway gradient showing the variation of landing distance with weight (up to maximum takeoff weight), altitude, and wind as required by §§ 25.1587(b) and 25.125(a). If the airplane is
78 intended for operation under part 121, the distances presented should include the operational field length factors for both dry and wet runways required by § 121.195.
(2) In accordance with § 25.101(i), AFM landing distances must be determined.
with all the airplane wheel brake assemblies at the fully worn limit of their allowable wear range.
The brakes may be in any wear state during the flight tests used to determine the landing distances, as long as a suitable combination of airplane and dynamometer tests is used to determine the landing distances corresponding to fully worn brakes. Alternatively, the relationship between brake wear and stopping performance established during accelerate-stop testing may be used if it encompasses the brake wear conditions and energies achieved during the airplane flight tests used to establish the landing distances.
(3) In deriving the scheduled distances, the time delays shown below should be assumed.
Figure 19-1. Landing Time Delays
(a) This segment represents the flight test measured average time from touchdown to pilot activation of the first deceleration device. For AFM data expansion, use the longer of 1 second or the test time.
(b) This segment represents the flight test measured average test time from pilot activation of the first deceleration device to pilot activation of the second deceleration device. For AFM data expansion, use the longer of 1 second or the test time.
(c) Step is repeated until pilot activation of all deceleration devices has been completed and the airplane is in the full braking configuration.
(4) For approved automatic deceleration devices (e.g., autobrakes or auto-spoilers, etc.) for which performance credit is sought for AFM data expansion, established times