AC 25-7D CHG 1
25.109(e) are met. In addition, the procedures associated with the use of reverse thrust, which § 25.101(f) requires the applicant to provide, must meet the requirements of § 25.101(h). The following criteria provide acceptable means of demonstrating compliance with these requirements:
4.3.7.10.1 Procedures for using reverse thrust during a rejected takeoff should be developed and demonstrated. These procedures should include all of the pilot actions necessary to obtain the recommended level of reverse thrust, maintain directional control and safe engine operating characteristics, and return the reverser(s), as applicable, to either the idle or the stowed position. These procedures need not be the same as those recommended for use during a landing stop, but should not result in additional hazards
(e.g., cause a flameout or any adverse engine operating characteristics), nor should they significantly increase flightcrew workload or training needs.
4.3.7.10.2 It should be demonstrated that using reverse thrust during a rejected takeoff complies with the engine operating characteristics requirements of § 25.939. The reverse thrust procedures may specify a speed at which the reverse thrust is to be reduced to idle in order to maintain safe engine operating characteristics.
4.3.7.10.3 The time sequence for the actions necessary to obtain the recommended level of reverse thrust should be demonstrated by flight test. The time sequence used to determine the accelerate-stop distances should reflect the most critical case relative to the time needed to deploy the thrust reversers.
For example, on some airplanes the outboard thrust reversers are locked out if an outboard engine fails. This safety feature prevents the pilot from applying asymmetric reverse thrust on the outboard engines, but it may also delay the pilot’s selection of reverse thrust on the operable reversers.
In addition, if the selection of reverse thrust is the fourth or subsequent pilot action to stop the airplane (e.g., after manual brake application, thrust/power reduction, and spoiler deployment), a one-second delay should be added to the demonstrated time to select reverse thrust. (See figure 4-1 of this AC.)
4.3.7.10.4 The response times of the affected airplane systems to pilot inputs should be taken into account. For example, delays in system operation, such as thrust reverser interlocks that prevent the pilot from applying reverse thrust until the reverser is deployed, should be taken into account. The effects of transient response characteristics, such as reverse thrust engine spin-up, should also be included.
4.3.7.10.5 To enable a pilot of average skill to consistently obtain the recommended level of reverse thrust under typical in-service conditions, a lever position that incorporates tactile feedback (e.g., a detent or stop) should be 4-49
AC 25-7D CHG 1 provided. If tactile feedback is not provided, a conservative level of reverse thrust should be assumed.
4.3.7.10.6 The applicant should demonstrate that exceptional skill is not required to maintain directional control on a wet runway with a ten-knot crosswind from the most adverse direction. For demonstration purposes, a wet runway may be simulated by using a nose wheel free to caster on a dry runway. Symmetric braking should be used during the demonstration, and both all-engines-operating and critical-engine-inoperative reverse thrust should be considered. The brakes and thrust reversers may not be modulated to maintain directional control. The reverse thrust procedures may specify a speed at which the reverse thrust is reduced to idle in order to maintain directional controllability.
4.3.7.10.7 Compliance with the requirements of §§ 25.901(b)(2), 25.901(c),
25.1309(b), and 25.1309(c) will be accepted as providing compliance with the “safe and reliable” requirements of §§ 25.101(h)(2) and 25.109(e)(1).
4.3.7.10.8 The number of thrust reversers used to determine the wet runway accelerate-stop distance data provided in the AFM should reflect the number of engines assumed to be operating during the rejected takeoff, along with any applicable system design features. The all-enginesoperating accelerate-stop distances should be based on all thrust reversers operating. The one-engine-inoperative accelerate-stop distances should be based on failure of the critical engine. For example, if the outboard thrust reversers are locked out when an outboard engine fails, the one-engine-inoperative accelerate stop distances can only include reverse thrust from the inboard engine thrust reversers.
4.3.7.10.9 For the engine failure case, it should be assumed that the thrust reverser does not deploy (i.e., no reverse thrust or drag credit for deployed thrust reverser buckets on the failed engine).
4.3.7.10.10 For approval of dispatch with one or more inoperative thrust reverser(s), the associated performance information should be provided either in the AFM or the master minimum equipment list (MMEL).
4.3.7.10.11 The effective stopping force provided by reverse thrust in each, or at the option of the applicant, the most critical takeoff configuration, should be demonstrated by flight test. (One method of determining the reverse thrust stopping force would be to compare unbraked runs with and without the use of thrust reversers.) Regardless of the method used to demonstrate the effective stopping force provided by reverse thrust, flight test demonstrations should be conducted using all of the stopping means on which the AFM wet runway accelerate-stop distances are based in order to substantiate the accelerate-stop distances and ensure that no adverse 4-50
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combination effects are overlooked. These demonstrations may be conducted on a dry runway.
4.3.7.10.12 For turbopropeller powered airplanes, the criteria of paragraphs 4.3.7.10.1 through 4.3.7.10.11 above remain generally applicable. Additionally, the propeller of the inoperative engine should be in the position it would normally assume when an engine fails and the power lever is closed.
Reverse thrust may be selected on the remaining engine(s). Unless this selection is achieved by a single action to retard the power lever(s) from the takeoff setting without encountering a stop or lockout, it should be regarded as an additional pilot action for the purposes of assessing delay times. If this action is the fourth or subsequent pilot action to stop the airplane, a one-second delay should be added to the demonstrated time to select reverse thrust.
4.4 Takeoff Path—§ 25.111.
4.4.1 Section 25.111(a).
4.4.1.1 Explanation.
The takeoff path requirements of § 25.111, and the reductions to that path required by § 25.115, are established so that performance data can be provided in the AFM for use in assessing vertical clearance of obstacles under the takeoff flight path.
4.4.1.2 Procedures.
The height references in § 25.111 should be interpreted as geometric heights. Section 25.111(a) requires the actual takeoff path (from which the net takeoff flight path is derived) to extend to the higher of where the airplane is 1,500 feet above the takeoff surface or to the altitude at which the transition to en route configuration is complete and the final takeoff speed (VFTO) is reached.
4.4.2 Section 25.111(a)(1)—Takeoff Path Power/Thrust Conditions.
4.4.2.1 Explanation.
In accordance with § 25.111(d), the takeoff path must be established either from continuous demonstrated takeoffs or by synthesis from segments. If determined from segments, it must be shown by continuous demonstrated takeoff to be conservative, in accordance with § 25.111(d)(4).
4.4.2.2 Procedures.
4.4.2.2.1 To be assured that the predicted takeoff path is representative of actual performance, construct the path using the power or thrust required by § 4-51
AC 25-7D CHG 1
25.101(c). This requires, in part, that the power or thrust be based on the particular ambient atmospheric conditions that are assumed to exist along the path. The standard lapse rate for ambient temperature as specified in the 1962 U.S. Standard Atmosphere part 1 should be used for power or thrust determination associated with each pressure altitude during the climb.
4.4.2.2.2 In accordance with § 25.111(c)(4), the power or thrust up to 400 feet above the takeoff surface must represent the power or thrust available along the path resulting from the power lever setting established during the initial ground roll in accordance with AFM procedures. This resulting power or thrust may be less than that available from the rated inflight setting schedule.
4.4.2.2.3 A sufficient number of takeoffs, to at least the altitude above the takeoff surface scheduled for V2 climb, should be made to establish the power or thrust lapse for a fixed power or thrust lever setting. An analysis may be used to account for various engine bleeds (e.g., ice protection, air conditioning, etc.) and for electrical, pneumatic, and mechanical power extraction. In some airplanes, the power or thrust growth characteristics are such that less than full rated power or thrust is used for AFM takeoff power/thrust limitations and performance. This is to preclude engine limitations from being exceeded during the takeoff climbs to 400 feet above the takeoff surface.
4.4.2.2.4 Engine power or thrust lapse with speed and altitude during the takeoff and climb, at fixed power or thrust lever settings), can be affected by takeoff pressure altitude.
4.4.2.2.5 Most turbine engines are sensitive to crosswind or tailwind conditions, when setting takeoff power under static conditions, and may stall or surge.
To preclude this problem, it is acceptable to establish a rolling takeoff power or thrust setting procedure, provided the AFM takeoff field length and the takeoff power or thrust setting charts are based on this procedure.
Demonstrations and analyses have been accepted in the past showing a negligible difference in distance between static and rolling takeoffs. A typical test procedure is as follows:
1. After stopping on the runway, set an intermediate power or thrust on all engines (power setting selected by applicant).
2. Release brakes and advance power or thrust levers.
3. Set target power or thrust setting as rapidly as possible prior to reaching 60 to 80 knots.
4. No adverse engine operating characteristics should exist after completion of the power setting through the climb to 1,500 feet 4-52
AC 25-7D CHG 1
above the airport and attainment of the en route configuration.
Tests should be conducted to determine if any engine operating problems exist for takeoffs conducted throughout the altitude range for which takeoff operations are to be scheduled in the AFM.
4.4.2.2.6 If the applicant wishes to use a different procedure, it should be evaluated and, if found acceptable, the procedure should be reflected in the AFM.
4.4.3 Section 25.111(a)(2)—Engine Failure.
4.4.3.1 Explanation.
4.4.3.1.1 Since the regulations cannot dictate what type of engine failures may actually occur, it could be assumed that the engine failure required by the regulation occurs catastrophically. Such a failure would cause the power or thrust to drop immediately, with the associated performance going from all-engines-operating to one-engine-inoperative at the point of engine failure.
4.4.3.1.2 This conservative rationale notwithstanding, there is a basis for assuming that the failed engine power or thrust will not decay immediately. Unlike reciprocating engines, the locking-up of a jet engine fan without causing the engine to separate from the airplane is highly unlikely. Separation of the engine or fan, or fan disintegration, would remove weight and/or the ram drag included in the engine inoperative performance, providing compensation for the immediate thrust loss.
4.4.3.1.3 With these considerations, it may be acceptable to use the transient power or thrust as the failed engine spools down at VEF. The power or thrust time history used for data reduction and expansion should be substantiated by test results.
4.4.3.1.4 In the case of propeller-driven airplanes, consideration should also be given to the position of the failed engine’s propeller during the engine failure. These airplanes typically incorporate an automatic system to drive the propeller to a low drag position when an engine fails. The loss of power in this case will be much more sudden than the turbojet engine spooldown described above.
4.4.3.2 Procedures.
4.4.3.2.1 For turbojet powered airplanes, if transient thrust credit is used during engine failure in determining the one-engine-inoperative AFM takeoff performance, sufficient tests should be conducted using actual fuel cuts to establish the thrust decay as contrasted to idle engine cuts. For derivative programs not involving a new or modified engine type (i.e., a modification 4-53
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that would affect thrust decay characteristics), fuel cuts are unnecessary if thrust decay characteristics have been adequately substantiated.
4.4.3.2.2 For propeller driven airplanes, the use of fuel cuts can be more important in order to ensure that the takeoff speeds and distances are obtained with the critical engine’s propeller attaining the position it would during a sudden engine failure. The number of tests that should be conducted using fuel cuts, if any, depends on the correlation obtained with the idle cut data and substantiation that the data analysis methodology adequately models the effects of a sudden engine failure.
4.4.4 Section 25.111(a)(3)—Airplane Acceleration.
4.4.4.1 Explanation.
None.
4.4.4.2 Procedures.
None.
4.4.5 Section 25.111(b)—Airplane Rotation and Gear Retraction.
4.4.5.1 Explanation.
The rotation speed, VR, is intended to be the speed at which the pilot initiates action to raise the nose wheel(s) off the ground during the acceleration to V2. Consequently, the takeoff path, determined in accordance with § 25.111(a) and (b), should assume that pilot action to raise the nose wheel(s) off the ground will not be initiated until the speed VR has been reached.
4.4.5.2 Procedures.
The time between liftoff and initiation of gear retraction during takeoff distance demonstrations should not be less than that necessary to establish an indicated positive rate of climb plus one second. For the purposes of flight manual expansion, the average demonstrated time delay between liftoff and initiation of gear retraction may be assumed; however, this value should not be less than 3 seconds.
4.4.6 Section 25.111(c)(1)—Takeoff Path Slope.
4.4.6.1 Explanation.
4.4.6.1.1 Establishing a horizontal segment as part of the takeoff flight path is considered to be acceptable, per § 25.115(c), for showing compliance with the positive slope required by § 25.111(c)(1).
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4.4.6.1.2 The net takeoff flight path is the flight path used to determine compliance with the airplane obstacle clearance requirements of the applicable operating rules. Section 25.115(b) states the required climb gradient reduction to be applied throughout the flight path for the determination of the net flight path, including the level flight acceleration segment. Rather than decreasing the level flight path by the amount required by § 25.115(b), § 25.115(c) allows the airplane to maintain a level net flight path during acceleration, but with a reduction in acceleration equal to the gradient decrement required by § 25.115(b). By this method, the altitude reduction is exchanged for increased distance to accelerate in the level flight portion of the net takeoff path.
4.4.6.2 Procedures.
The level acceleration segment in the AFM net takeoff profile should begin at the horizontal distance along the takeoff flight path where the actual airplane height, without the gradient reductions of § 25.115(b), reaches the AFM specified acceleration height.
4.4.7 Section 25.111(c)(2)—Takeoff Path Speed.
4.4.7.1 Explanation.
4.4.7.1.1 It is intended that the airplane be flown at a constant indicated airspeed to at least 400 feet above the takeoff surface. This speed must meet the constraints on V2 of § 25.107(b) and (c).
4.4.7.1.2 The specific wording of § 25.111(c)(2) should not be construed to imply that above 400 feet the airspeed may be reduced below V2, but instead that acceleration may be commenced.
4.4.7.2 Procedures.
4.4.7.2.1 For those airplanes that take advantage of reduced stall speeds at low pressure altitude, the scheduling of V2 should not be factored against the stall speed obtained at the takeoff surface pressure altitude. Such a procedure would result in a reduced stall speed margin during the climb, which would be contrary to the intent of § 25.107(b).
4.4.7.2.2 For those airplanes mentioned in paragraph 4.4.7.1 above, the V2 should be constrained, in addition to the requirements of § 25.107(b) and (c), by the stall speed 1,500 feet above the takeoff surface. Weight reduction along the takeoff path, due to fuel burn, may be considered in the calculation of the stall speed ratios, provided it is well established.
However, many applicants have measured stall speeds at 10,000 to 15,000 feet, which provides a conservative stall margin at lower takeoff field pressure altitudes.
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4.4.8 Section 25.111(c)(3)—Required Gradient.
4.4.8.1 Explanation.
None.
4.4.8.2 Procedures.
None.
4.4.9 Section 25.111(c)(4)—Configuration Changes.
4.4.9.1 Explanation.
4.4.9.1.1 The intent of this requirement is to permit only those crew actions that are conducted routinely to be used in establishing the one-engine-inoperative takeoff path. The power/thrust levers may only be adjusted early during the takeoff roll and then left fixed until at least 400 feet above the takeoff surface.
4.4.9.1.2 Simulation studies and accident investigations have shown that when high workload occurs in the cockpit, as with an engine failure during takeoff, the crew might not advance the power/thrust on the operative engines, even if the crew knows the operative engines have been set at reduced power/thrust and a power/thrust increase is needed for terrain avoidance.
This same finding applies to manually feathering a propeller. The landing gear may be retracted, however, as this is accomplished routinely once a positive rate of climb is observed. Also, automatic propeller feathering is specifically allowed by the rule. Guidance related to performance credit for automatic propeller feathering is provided in paragraph 4.4.9.2 below.
4.4.9.1.3 Although performance credit for pilot action to increase power/thrust below 400 feet above the takeoff surface is not permitted, performance credit is allowed for an automatic power advance. ATTCS are addressed in § 25.904, and the related performance requirements are described in appendix I to part 25.
4.4.9.2 Procedures.
4.4.9.2.1 Propeller pitch setting generally has a significant effect on minimum control speeds and airplane drag. The magnitude of these effects is such that continued safe flight may not be possible should a combined failure of an engine and its automatic propeller feathering system occur at a takeoff speed based on operation of that system. When this is the case, § 25.1309(b)(1) requires the probability of this combined failure to be extremely improbable (on the order of 10-9 per flight hour).
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4.4.9.2.2 In determining the combined engine and automatic propeller drag reduction system failure rate of paragraph 4.4.9.2.1 above, the engine failure rate should be substantiated. Notwithstanding the in-service engine failure rate, the failure of the automatic propeller drag reduction system should be shown not to exceed 10-4 per flight hour.
4.4.9.2.3 The automatic propeller feathering system should be designed so that it will automatically be disabled on the operating engine(s) following its activation on the failed engine. The probability of an unwanted operation of the automatic propeller drag reduction system on an operating engine, following its operation on the failed engine, should be shown to be extremely improbable (on the order of 10-9 per flight hour).
4.4.9.2.4 If performance credit is given for operation of the automatic propeller feathering system in determining the takeoff distances, the propeller of the failed engine must also be assumed to be in the reduced drag position in determining the accelerate-stop distances.
4.4.9.2.5 The limitations section of the AFM should require the flightcrew to perform a functional check of the automatic propeller feathering system.
The frequency with which flightcrew functional checks and ground maintenance checks must be performed should be considered in the evaluation of the system reliability.
4.4.9.2.6 Clear annunciations should be provided to the flightcrew to indicate the following when:
The automatic propeller drag reduction system is “ARMED”; and A malfunction exists in the automatic propeller feathering system.
4.4.10 Section 25.111(d)—Takeoff Path Construction.
4.4.10.1 Explanation.
This regulation should not be construed to mean that the takeoff path must be constructed entirely from a continuous demonstration or entirely from segments. To take advantage of ground effect, typical AFM takeoff paths use a continuous takeoff path from VLOF to the gear up point, covering the range of thrust-to-weight ratios. From that point free air performance, in accordance with § 25.111(d)(2), is added segmentally. This methodology may yield an AFM flight path that is steeper with the gear down than up.
4.4.10.2 Procedures.
The AFM should include the procedures necessary to achieve this performance.
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4.4.11 Section 25.111(d)(1)—Takeoff Path Segment Definition.
4.4.11.1 Explanation.
None.
4.4.11.2 Procedures.
None.
4.4.12 Section 25.111(d)(2)—Takeoff Path Segment Conditions.
4.4.12.1 Explanation.
Section 25.111(d)(2) states: “The weight of the airplane, the configuration, and the power or thrust must be constant throughout each segment and must correspond to the most critical condition prevailing in the segment.”
The intent is that, for simplified analysis, the performance is based on that value available at the most critical point in time during the segment, not that the individual variables (weight, approximate power or thrust setting, etc.) are each picked at their most critical value and then combined to produce the performance for the segment.
4.4.12.2 Procedures.
The performance during the takeoff path segments should be obtained using one of the following methods:
4.4.12.2.1 The critical level of performance as explained in paragraph 4.4.12.1 above;
4.4.12.2.2 The average performance during the segment; or
4.4.12.2.3 The actual performance variation during the segment.
4.4.13 Section 25.111(d)(3)—Segmented Takeoff Path Ground Effect.
4.4.13.1 Explanation.
This requirement does not intend the entire flight path to necessarily be based upon out-of-ground-effect performance simply because the continuous takeoff demonstrations have been broken into sections for data reduction expediency. For example, if the engine inoperative acceleration from VEF to VR is separated into a power or thrust decay portion and a windmilling drag portion, the climb from 35 feet to gear up does not necessarily need to be based upon out-of-ground-effect performance.
(Also, see the explanation of § 25.111(d) in paragraph 4.4.10.1 of this AC.)
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4.4.13.2 Procedures.
None.
4.4.14 Section 25.111(d)(4)—Segmented Takeoff Path Check.
4.4.14.1 Explanation.
None.
4.4.14.2 Procedures.
If the construction of the takeoff path from brake release to out-of-groundeffect contains any portions that have been segmented (e.g., airplane acceleration segments with all-engines-operating and one-engine-inoperative), the path should be checked by continuous demonstrated takeoffs. A sufficient number of these, employing the AFM established takeoff procedures and speeds and covering the range of thrust-to-weight ratios, should be made to ensure the validity of the segmented takeoff path. The continuous takeoff data should be compared to takeoff data calculated by AFM data procedures but using test engine thrusts and test speeds.
4.4.15 Section 25.111(e)—Flight Path with Standby Power Rocket Engines.
[Reserved]
4.5 Takeoff Distance and Takeoff Run—§ 25.113.
4.5.1 Takeoff Distance on a Dry Runway—§ 25.113(a).
4.5.1.1 The takeoff distance on a dry runway is the longer of the two distances described in paragraphs 4.5.1.1.1 and 4.5.1.1.2 below. The distances indicated below are measured horizontally from the main landing gears at initial brake release to that same point on the airplane when the lowest part of the departing airplane is 35 feet above the surface of the runway.
4.5.1.1.1 The distance measured to 35 feet with a critical engine failure occurring at VEF as shown in figure 4-11 below.
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AC 25-7D CHG 1 Figure 4-11. Takeoff Distance on a Dry Runway: Critical Engine Fails at VEF
4.5.1.1.2 One hundred fifteen percent of the distance measured to the 35 feet height above the takeoff surface with all-engines-operating as shown in figure 4-12 below. In establishing the all-engines-operating takeoff distance, § 25.113(a)(2) requires the distance to be “...determined by a procedure consistent with § 25.111” (Takeoff Path). The interpretation of this statement is that the all-engines-operating takeoff distance 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.
Figure 4-12. Takeoff Distance: All-Engines-Operating
4.5.1.2 In accordance with § 25.101(f), the takeoff distance must be based on the procedures established for operation in service.
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