AC 25-7D CHG 1
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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AC 25-7D CHG 1
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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AC 25-7D CHG 1
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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AC 25-7D CHG 1
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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AC 25-7D CHG 1
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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AC 25-7D CHG 1
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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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
AC 25-7D CHG 1
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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