AC 25-7D CHG 1
4.5.2 Takeoff Distance on a Wet Runway—§ 25.113(b).
4.5.2.1 The takeoff distance on a wet runway is the longer of the takeoff distance on a dry runway (using the dry runway V1 speed), determined in accordance with paragraphs 4.5.1.1.1 and 4.5.1.1.2 of this AC, or the distance on a wet runway using a reduced height at the end of the takeoff distance (and the wet runway V1 speed) as described in paragraph 4.5.2.2 below.
4.5.2.2 The takeoff distance on a wet runway is determined as the horizontal distance the main landing gear travels from brake release to the point where the lowest part of the airplane is 15 feet above the takeoff surface.
The airplane must attain a height of 15 feet above the takeoff surface in a manner that will allow V2 to be achieved before reaching a height of 35 feet above the takeoff surface in accordance with § 25.113(b)(2) and as shown in figure 4-13 below.
Figure 4-13. Takeoff Distance on a Wet Runway: Critical Engine Fails at VEF
4.5.3 Takeoff Run—§ 25.113(c).
4.5.3.1 The concept of takeoff run was introduced by SR-422A to allow credit for a portion of the airborne part of the takeoff distance to be flown over a clearway. (See paragraph 4.5.3.3 of this AC for a definition of clearway.)
The takeoff run is the portion of the takeoff distance that must take place on or over the runway in accordance with the applicable operating rules. If there is no clearway, the takeoff run is equal to the takeoff distance. If there is a clearway, the takeoff run is the longer described in paragraph 4.5.3.1.1 or 4.5.3.1.2 below. These distances are measured as described in paragraph 4.5.1.1 for § 25.113(a). When using a clearway to determine the takeoff run, no more than one half of the air distance from VLOF to V35 may be flown over the clearway.
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AC 25-7D CHG 1
4.5.3.1.1 The takeoff run is the distance from the start of the takeoff roll to the midpoint between liftoff and the point at which the airplane attains a height of 35 feet above the takeoff surface, with a critical engine failure occurring at VEF, as shown in figure 4-14 below. For takeoff on a wet runway, the takeoff run is equal to the takeoff distance (i.e., there is no clearway credit allowed on a wet runway).
Figure 4-14. Takeoff Run: Critical Engine Fails at VEF
4.5.3.1.2 One hundred fifteen percent of the distance from the start of the takeoff roll to the mid-point between liftoff and the point at which the airplane attains a height of 35 feet above the takeoff surface, with all engines operating, as shown in figure 4-15 of this AC. In establishing the all-engines-operating takeoff run, § 25.113(c)(2) requires the distance to be “...determined by a procedure consistent with § 25.111” (Takeoff Path).
The interpretation of that statement is that the all-engines-operating takeoff run should:
Be based on the airplane reaching a speed of V2 before it is 35 feet above the takeoff surface; and Be consistent with the achievement of a smooth transition to the steady initial climb speed at a height of 400 feet above the takeoff surface.
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AC 25-7D CHG 1 Figure 4-15. Takeoff Run: All-Engines-Operating
4.5.3.2 There may be situations where the takeoff run may be longer for the one-engine-inoperative condition (paragraph 4.5.3.1.1 of this AC) while the takeoff distance is longer for the all-engines-operating condition (paragraph 4.5.3.1.2 of this AC), or vice versa. Therefore, both conditions should always be considered.
4.5.3.3 Clearway is defined in 14 CFR part 1 as a plane extending from the end of the runway with an upward slope not exceeding 1.25 percent, above which no object nor any terrain protrudes. For the purpose of establishing takeoff distances and the length of takeoff runs, the clearway is considered to be part of the takeoff surface extending with the same slope as the runway, and the 35 feet height should be measured from that surface. (See figure 4-16 of this AC.)
Figure 4-16. Clearway Profiles 4-63
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4.6 Takeoff Flight Path—§ 25.115.
4.6.1 Takeoff Flight Path—§ 25.115(a).
4.6.1.1 Explanation.
The takeoff flight path begins at the end of the takeoff distance and at a height of 35 feet above the takeoff surface. The takeoff flight path ends when the airplane’s actual height is the higher of 1,500 feet above the takeoff surface or at an altitude at which the en route configuration and final takeoff speed have been achieved. (See paragraph 4.4 of this AC 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’s actual height will only be 15 feet.
This wording allows the same takeoff flight path determined under § 25.115 for a dry runway takeoff to also be used for a wet runway takeoff. For takeoffs from wet runways, the actual airplane height will be 20 feet lower than the takeoff flight path determined under § 25.115 for takeoff from a dry runway. 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.
4.6.1.2 Procedures.
See figure 4-17 of this AC.
4.6.1.2.1 In figure 4-17, the final takeoff segment will usually begin with the airplane in the en route configuration and with maximum continuous power or 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 power or thrust cannot be exceeded.
4.6.1.2.2 In figure 4-17, path 1 depicts a flight path based on a minimum 400-foot level-off for acceleration and flap retraction following the second segment climb portion of the flight path. Path 2 depicts the upper limit of the takeoff flight path following an extended second segment. Depending on obstacle clearance needs, the second segment may be extended to a height of more than 1500 feet above the takeoff surface.
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AC 25-7D CHG 1 Figure 4-17. Takeoff Segments and Nomenclature
4.6.2 Net Takeoff Flight Path—§ 25.115(b) and (c).
4.6.2.1 Explanation.
4.6.2.1.1 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.
4.6.2.1.2 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 4.4.6 of this AC for additional discussion.)
4.6.2.2 Procedures.
See figure 4-18 below.
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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
AC 25-7D CHG 1
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
AC 25-7D CHG 1
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
AC 25-7D CHG 1
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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AC 25-7D CHG 1
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