AC 25-7D CHG 1 Figure 4-18. Net Takeoff Flight Path
4.7 Climb: General—§ 25.117.
4.7.1 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 CG for each configuration.
The effects of changes in the airplane’s true airspeed during a climb at the recommended constant indicated (or calibrated) climb speed should be taken into account when showing compliance with these climb requirements.
4.7.2 Procedures.
None.
4.8 Landing Climb: All-Engines-Operating—§ 25.119.
4.8.1 Explanation.
Section 25.119(a) states that the engines are to be set at the power or thrust that is available 8 seconds after starting to move the power or thrust controls from the minimum flight idle position to the go-around power or thrust setting. Use the procedures given below for the determination of this maximum power or thrust for showing compliance with the climb requirements of § 25.119.
4.8.2 Procedures.
4.8.2.1 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 4-66
AC 25-7D CHG 1 controllers is typically negligible (but any such claim should be adequately substantiated).
4.8.2.2 At the most adverse test altitude, not to exceed the maximum field elevation for which certification is sought plus 1,500 feet, and with the most adverse bleed configuration expected in normal operations, stabilize the airplane in level flight with symmetrical power or thrust 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 RPM, as defined below, for the test engine(s) while maintaining level flight or the minimum rate of descent obtainable with the power or thrust of the remaining engine(s) not greater than maximum continuous thrust (MCT). Engine flight idle RPM 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 RPM versus time.
4.8.2.3 For the critical air bleed and power extraction configuration, stabilize the airplane in level flight with symmetric power or thrust 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 RPM stabilization time determined in paragraph 4.8.2.2 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.
4.8.2.4 The power or thrust that is available 8 seconds after starting to move the power or thrust controls from the minimum flight idle position, in accordance with paragraph 4.8.2.3 above, is 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 D of this AC) for each of the bleed and power extraction combinations tested in accordance with paragraph 4.8.2.3 above. Unless AFM performance data are presented for each specific bleed and power extraction level, the AFM performance data should be based on the power or thrust obtained with the most critical power extraction level.
4.8.2.5 For airplanes equipped with autothrottles that will be used for approach and go-around, the effect of using the autothrottle to set go-around power 4-67
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or thrust should be determined. One way to do this would be to complete the test procedure given in paragraph 4.8.2.3, except that the airplane should be stabilized on -3° approach path, nominal power extraction, at the weight that gives the lowest power or thrust for that condition. The autothrottle should then be used to increase the power or thrust to the go-around power or thrust setting. The power or thrust used to show compliance with § 25.119(a) should be the lesser of:
4.8.2.5.1 The power or thrust that is available 8 seconds after selection of go-around power or thrust using the autothrottle; or
4.8.2.5.2 The power or thrust determined under paragraph 4.8.2.4 of this AC.
4.9 Climb: One-Engine-Inoperative—§ 25.121.
4.9.1 Explanation.
Section 25.121 contains one-engine-inoperative climb gradient capability requirements for the first, second, and final takeoff segments as well as for approach.
4.9.2 Procedures.
4.9.2.1 Two methods for establishing one-engine-inoperative climb performance follow:
4.9.2.1.1 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. Control forces should be trimmed out as much as possible, except for the takeoff climbs with gear extended where the takeoff trim settings are to be retained to represent an operationally realistic drag level. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
4.9.2.1.2 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.
4.9.2.2 If full rudder with wings level cannot maintain constant heading, small bank angles of up to 2° to 3° 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 4-68
AC 25-7D CHG 1 the lights extended for § 25.121(a) Takeoff; landing gear extended, § 25.121(b) Takeoff; landing gear retracted, and § 25.121(d) Approach.
4.9.2.3 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 a stable fully extended position. However, 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. Since the takeoff path will be determined either from continuous takeoffs or checked by continuous takeoffs if constructed by the segmental method (Refer to § 25.111(d)), any non-conservatism arising from the gear doors “closed” climb data will be evident and should be corrected for. 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. While during an actual takeoff the airplane may accelerate from VLOF towards V2, the climb gradient for showing compliance with § 25.121(a) is based on the VLOF speed as specified in the rule.
4.9.2.4 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. (See § 25.1043.)
4.9.2.5 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 power or thrust lapse rates above the point where retraction of the landing gear is begun.
4.9.2.6 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 go-around.
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 4-69
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approach configuration does not exceed 110 percent of VREF/1.23. 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.
4.9.2.7 Section 25.121(d) permits the use of a climb speed established in connection with normal landing procedures, but not more than 1.4 VSR.
Section 25.101(g) requires that the procedures for the execution of missed approaches associated with the conditions prescribed in § 25.121(d) be established. Consequently, the speeds and flap configuration used to show compliance with the minimum climb gradient requirements of § 25.121(d) need to be consistent with the speeds and flap configurations specified for go-around in the AFM operating procedures. To demonstrate the acceptability of recommended procedures, the applicant should conduct go-around demonstrations to include a weight, altitude, temperature (WAT)-limited or simulated WAT-limited thrust condition. In accordance with § 25.101(h), the established procedures must:
Be able to be consistently executed in service by crews of average skill, Use methods or devices that are safe and reliable, and Include allowance for any time delays in the execution of the procedures that may reasonably be expected in service.
4.9.2.8 FAA policy, as explained in policy PS-ANM100-1995-00058, Go-Around Power/Thrust Settings on Transport Category Airplanes, dated August 15, 1995, states that there should only be one power/thrust setting procedure used to show compliance with both §§ 25.119 and 25.121(d).
4.9.2.8.1 This policy is based on crew workload issues as discussed in the preamble for the ATTCS final rule (amendment 25-62):
4.9.2.8.2 That preamble states, “. . . current regulations preclude a higher thrust for approach climb (§ 25.121(d)) than for landing climb (§ 25.119). The workload required for the flightcrew to monitor and select from multiple inflight thrust settings in the event of an engine failure during a critical point in the approach, landing, or go-around operation is excessive.”
4.9.2.8.3 If the approach climb power/thrust setting is higher than the landing climb power/thrust setting, a throttle push would be required to obtain the AFM performance in the event of an engine failure after an all-engines-operating go-around has been initiated. The FAA considers the 4-70
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need to manually reset the engine power/thrust setting in a high workload environment to be unacceptable.
4.9.2.8.4 Systems that automatically reset power/thrust to a higher value after an engine failure (for example, ATTCS used for go-arounds) have been found acceptable as long as there is a single go-around power/thrust setting procedure for the one-engine-inoperative (approach climb) and all-engines-operating (landing climb) conditions.
4.10 En Route Flight Paths—§ 25.123.
4.10.1 Explanation.
This guidance is intended for showing compliance with the requirements of § 25.123.
4.10.2 Procedures.
4.10.2.1 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.
4.10.2.2 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.
4.10.2.3 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).
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4.11 Landing—§ 25.125.
4.11.1 Explanation.
4.11.1.1 The landing distance is the horizontal distance from the point at which the main gear of the airplane is 50 feet above the landing surface (treated as a horizontal plane through the touchdown point) to the position of the nose gear when the airplane is brought to a stop. (For water landings, a speed of approximately 3 knots is considered “stopped.”) The beginning of the landing distance is referenced to the main gear because it is the lowest point of the airplane when the airplane is 50 feet above the landing surface. The end of the landing distance is referenced to the nose gear because it is the most forward part of the airplane in contact with the landing surface, and it should not extend beyond the certified landing distance. In this AC, the landing distance is divided into two parts: the airborne distance from 50 feet 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.
4.11.1.2 The minimum allowable value of VREF is specified in § 25.125(a)(2)(i) and
(ii). It is intended to provide an adequate margin above the stall speed to allow for likely speed variations during an approach in light turbulence and to provide adequate maneuvering capability. 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).
Further, if procedures recommend the use of approach speeds that are higher than VREF for reasons other than wind, flight tests should be conducted to determine whether the recommended VREF speeds are readily achievable at the landing threshold. If VREF is not readily achievable, then the AFM landing distances must include the effect of the excess speed at the landing threshold.
4.11.1.3 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).
4.11.2 Procedures for Determination of the Airborne Distance.
Three acceptable means of compliance are described in paragraphs 4.11.2.1, 4.11.2.2 and 4.11.2.3 on the following pages.
Note: If it is determined that the constraints on approach angle and touchdown rate-of-sink described in paragraphs 4.11.2.2 and 4.11.2.3 below are not appropriate due to novel or unusual features of the airplane’s design, new criteria may be 4-72
AC 25-7D CHG 1 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.
4.11.2.1 Experience shows an upper bound to the part 25 zero-wind airborne distances achieved in past certifications and, similarly, a minimum speed loss.
4.11.2.1.1 These are approximated by the following:
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.
4.11.2.2 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:
4.11.2.2.1 A stabilized approach, targeting a glideslope of -3° 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 or thrust setting, pitch attitude, or rate of descent. The average glideslope of all landings used to show compliance should not be steeper than -3°.
4.11.2.2.2 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 or thrust.
4.11.2.2.3 The target rate of descent at touchdown should not exceed 6 feet per second. Although target values may not be precisely achieved, the average touchdown rate of descent should not exceed 6 feet per second.
4.11.2.3 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 part 25 airborne distances may be based on an approach angle of -3.5°, and a touchdown sink rate of 8 feet per second. (See paragraph 4.11.8 for an example of this analysis method.)
The parametric analysis method with these approach angle and touchdown 4-73
AC 25-7D CHG 1 sink rate values should only be used for landing distances for which the operational safety margins required by § 121.195(b) or (c), § 135.385(b),
(c), or (f), or equivalent will be applied.
4.11.2.3.1 At a given weight, 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 4.11.2.3.2 below. Test data with approach angles steeper than -3.5°, or touchdown sink rates greater than 8 feet per second, should not be used to satisfy this requirement.
4.11.2.3.2 In order to determine the parametric relationships, it is recommended that test targets span approach angles from -2.5° to –3.5°, and sink rates at touchdown from 2 to 6 feet per second. Target speed for all tests should be VREF.
4.11.2.3.3 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 or thrust.
4.11.2.3.4 If an acceptable method of analysis is developed by the applicant, a sufficient number of tests should be conducted in each aerodynamic configuration for which certification is desired to establish a satisfactory confidence level for the resulting air distance. 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.
4.11.2.3.5 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 power or 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 a sufficient number of tests to establish a satisfactory confidence level and be justified by a comparison of tested and calculated landing airborne distances.
4.11.2.3.6 For a derivative airplane with an aerodynamic configuration that has been 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, regardless of whether the previous certification was conducted by this method or not. If a new 4-74
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aerodynamic configuration is proposed, the guidance described in paragraph 4.11.2.3.4 above, should be used.
4.11.2.3.7 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 4.11.2.3.
4.11.2.4 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.
4.11.2.4.1 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 or thrust should not be increased to facilitate the flare.
4.11.2.4.2 All power/thrust levers should be in their minimum flight idle position prior to touchdown.
4.11.2.4.3 The normal flare technique should be used, resulting in a touchdown speed approximately 5 knots less than the touchdown speed used to establish the landing distance. The rate of descent at touchdown should not be greater than 6 feet per second.
4.11.2.4.4 This demonstration should be performed over a range of weights (typically at maximum landing weight and near minimum landing weight), or at the most critical weight and CG combination as established by analysis or other acceptable means.
4.11.2.4.5 These VREF-5 knots landing demonstrations should not require the use of high control forces or full control deflections.
4.11.3 Procedures for Determination of the Transition and Stopping Distances.
4.11.3.1 The transition distance extends from the initial touchdown point to the point where all approved deceleration devices are operating. The stopping distance extends from the end of transition to the point where the airplane is stopped. The two phases may be combined at the applicant’s option.
4.11.3.2 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.
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4.11.3.3 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 brakes may be in any wear state as long as an acceptable means is used to determine the landing distances with fully worn brakes for presentation in the AFM. 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. An automatic braking system can be armed before touchdown.
4.11.3.4 Describe the airplane operating procedures appropriate for determination of landing distance in the performance section of the AFM.
4.11.3.5 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.
4.11.3.5.1 If, with the normal operational ground idle setting procedure, 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 gives not more than a slight negative thrust at zero airspeed. A slight negative thrust is that which will not cause the airplane, at light weight and without brakes being applied, to roll on a level surface. If the normal operational ground idle setting produces greater 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.
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4.11.3.5.2 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. Differential braking may be used to maintain directional control. This testing should be conducted at the critical weight/CG position and landing speed. The propeller/engine rigging should be at the most adverse allowable tolerance. If the resulting distance does not exceed the all-engines-operating landing distance by more than two percent (2 percent), it is not “noticeably increased” and no further testing is required to take performance credit for all-engines-operating ground idle drag in the certified landing distances.
4.11.3.5.3 If the distances determined in paragraph 4.11.3.5.2 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 ground idle 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 the ground idle setting. The airplane configuration for this test should be the same as that used for the all-engines-operating landing distance determination, except that the propeller reverse thrust position is used. 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. Procedures for using propeller reverse thrust during the landing must be developed and demonstrated. The procedures associated with the use of propeller reverse thrust, required by § 25.101(f), must meet the requirements of § 25.101(h). The criteria outlined below may be applied to derive the levels of propeller reverse thrust consistent with recommended landing procedures and provide an acceptable means of demonstrating compliance with these requirements. This testing should be conducted at the critical weight/CG position and landing speed. The propeller/engine rigging should be at the most adverse allowable tolerance. If the “compensating means” do not allow performance credit for the all-engines-operating ground idle drag, a minimum of three weights that cover the expected range of operational landing weights and speeds should be tested.
4.11.3.5.4 In accordance with § 25.101(f), procedures for using propeller reverse thrust during landing must be developed and demonstrated. These procedures should include all of the pilot actions necessary to obtain the recommended level of propeller reverse thrust, maintain directional control, ensure safe engine operating characteristics and cancel propeller reverse thrust.
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