(2) Procedures .
(a) To permit the takeoff to be conducted using less than rated power, automatic power advance devices have been approved. These devices are addressed in § 25.904, and the related performance requirements are described in Appendix I to 14 CFR part 25.
(b) To permit the takeoff to be based on a feathered propeller up to 400 ft. above the takeoff surface, automatic propeller feathering devices have been approved. Guidance related to performance credit for automatic propeller feathering devices, below 400 feet above the takeoff surface, is presented in paragraph 239 of this AC.
(c) Drag reduction for a manually feathered propeller is permitted for flight path calculations only after reaching 400 ft. above the takeoff surface.
j. Section 25.111(d) - Takeoff Path Construction.
(1) Explanation. This regulation should not be construed to mean that the takeoff path be constructed entirely from a continuous demonstration or entirely from segments. To take advantage of ground effect, typical AFM takeoff paths utilize 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.
(2) Procedures. The AFM should include the procedures necessary to achieve this performance.
k. Section 25.111(d)(1) - Takeoff Path Segment Definition.
(1) Explanation. None.
(2) Procedures. None.
l. Section 25.111(d)(2) - Takeoff Path Segment Conditions .
(1) Explanation. The subject paragraph states “The weight of the airplane, the configuration, and the power or thrust setting 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 thrust setting, etc.) are each picked at their most critical value and then combined to produce the performance for the segment.
(2) Procedures. The performance during the takeoff path segments should be obtained using one of the following methods:
(a) The critical level of performance as explained in paragraph (1);
(b) The average performance during the segment; or
(c) The actual performance variation during the segment.
m. Section 25.111(d)(3) - Segmented Takeoff Path Ground Effect .
(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 thrust decay portion and a windmilling drag portion, the climb from 35 ft. 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 12j(1) of this AC.)
(2) Procedures . None
n. Section 25.111(d)(4) - Segmented Takeoff Path Check.
(1) Explanation . None.
(2) Procedures . If the construction of the takeoff path from brake release to out-ofground-effect 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.
o. Section 25.111(e) - Flight Path with Standby Power Rocket Engines . [Reserved]
13. Takeoff Distance and Takeoff Run - § 25.113.
a. Takeoff Distance on a Dry Runway - § 25.113(a).
(1) The takeoff distance on a dry runway is the greater of the two distances depicted in
(a) or (b) 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 ft. above the surface of the runway.
(a) The distance measured to 35 ft. with a critical engine failure occurring at V EF as shown in figure 13-1.
Figure 13-1. Takeoff Distance on a Dry Runway
Critical Engine Fails at VEF
(b) One hundred fifteen (115) percent of the distance measured to the 35 ft. height above the takeoff surface with all-engines-operating as shown in figure 13-2. 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:
1 Be based on the airplane reaching a speed of V 2 before it is 35 feet above the takeoff surface; and
2 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 13-2. Takeoff Distance
(All-Engines-Operating)
(2) The takeoff procedure adopted should be reflected in the takeoff distance.
b. Takeoff Distance on a Wet Runway - § 25.113(b) .
(1) The takeoff distance on a wet runway is the greater of the takeoff distance on a dry runway (using the dry runway V1 speed), determined in accordance with paragraphs 13a(1)(a) and (b) of this AC, or the distance on a wet runway using a reduced screen height (and the wet runway V1 speed) as described in paragraph (2), below.
(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 ft. above the takeoff surface. The airplane must attain a height of 15 ft. above the takeoff surface before reaching the end of the runway in a manner that will allow V2 to be achieved before reaching a height of 35 ft. above the takeoff surface in accordance with § 25.113(b)(2) and as shown in figure 13-3.
65 Figure 13-3. Takeoff Distance On a Wet Runway
Critical Engine Fails at VEF
c. Takeoff Run - § 25.113(c).
(1) Takeoff run is a term used for the runway length when the takeoff distance includes a clearway (i.e., where the accelerate-go distance does not remain entirely over the runway), and the takeoff run is either of the two distances depicted in (a) or (b) below, whichever is greater.
These distances are measured as described in § 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.
(a) 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 ft. above the takeoff surface, with a critical engine failure occurring at VEF, as shown in figure 13-4. 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 r u n w a y ) .
Figure 13-4. Takeoff Run
Critical Engine Fails at VEF
(b) One hundred fifteen (115) 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 ft.
above the takeoff surface, with all engines operating, as shown in figure 13-5. 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:
1 Be based on the airplane reaching a speed of V 2 before it is 35 feet above the takeoff surface; and
2 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 13-5. Takeoff Run
(All-Engines-Operating)
(2) There may be situations in which the one-engine-inoperative condition (paragraph 13c(1)(a)) would dictate one of the distance criteria, takeoff run (required runway) or takeoff distance (required runway plus clearway), while the all-engines-operating condition (paragraph 13c(1)(b)) would dictate the other. Therefore, both conditions should always be considered.
(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 ft. height should be measured from that surface.
67 Figure 13-6. Clearway Profiles
(4) The profile shows no fixed obstacle projecting above the clearway plane.
However, in accordance with the definition of clearway in part 1, the airport authorities must have control of this area to ensure that no flight will be initiated using a clearway unless it is determined that no movable obstacles will exist within the clearway when the airplane flies over.
14. Takeoff Flight Path - § 25.115.
a. Takeoff Flight Path - § 25.115(a).
(1) Explanation . The takeoff flight path begins at the end of the takeoff distance and at a height of 35 ft. above the takeoff surface, and ends when the airplane’s actual height is the higher of 1,500 ft. above the takeoff surface or at an altitude at which the configuration and speed have been achieved where the requirements of § 25.121(c) can be met. (See paragraph 12 of this AC (§ 25.111) for additional discussion.) Section 25.115(a) states that the takeoff “shall be considered to begin 35 feet above the takeoff surface,” recognizing that in the case of a wet runway the airplane will only be at a height of 15 feet. For takeoffs from wet runways, the actual airplane height will be 20 feet lower than the takeoff flight path determined under § 25.115.
Therefore, the airplane will be 20 feet closer vertically to obstacles after taking off from a wet runway compared to taking off from a dry runway.
(2) Procedures.
Figure 14-1. Takeoff Segments & Nomenclature
TAKEOFF FLICHT PATH *ACTUAL HICHT --- ≥ 1500 FEET 1500 FEET PATH 2/ * OF I ENG INOPTAKFOFF OR- TAKEOFF DISTANCE LONGER 1.15 ALL ENG TAKEOFF) PATH 1 ACTUAL HEIGHT ≥ 400 FEET
ACTUAL HEIGHTS ARE VEr VLOF GEAR RETRACTION COMPLETE REFERENCED TO RUNWAY ELEVATION AT END OF TAKEOFF 35,FI DISTANCE SEGMENT* GROUND ROLL IST 2ND ACCELERATION. FINAL
LANDING GEAR DOWN PRETRACTION RETRACTED
ENROUTE
FLAPS TAKEOFF RETRACTING (SEE NOTE) POSITION THRUST/POWER TAKEOFF ABOVE 400 FT THRUST CAN BE REDUCED IF THE REQUIREMENTS (SEE NOTE) OF 25, 11UCH3) CAN BEET WITH LESS THAN TAKEOFE THRUN → CONTINUOUS MAXIMUM
AIRSPEED ACCELERATING ACCELERATING WFTO
ENGINES ALL OPERATING ONE INOPERATIVE
PROPELLER TAKEOFF ONE AUTOFEATHERED OR WINDMILLING ONE FEATHERED UP TO 400 FEET 400 FEET OR GREATER NOTE: The final takeoff segment will usually begin with the airplane in the en route configuration and with maximum continuous thrust, but it is not required that these conditions exist until the end of the takeoff path when compliance with § 25.121(c) is shown. The time limit on takeoff thrust cannot be exceeded.
* Segments as defined by § 25.121.
b. Net Takeoff Flight Path - § 25.115(b) and (c).
(1) Explanation.
(a) The net takeoff flight path is the actual flight path diminished by a gradient of
0.8 percent for two-engine airplanes, 0.9 percent for three-engine airplanes, and 1.0 percent for four-engine airplanes.
(b) For the level flight acceleration segment, these prescribed gradient reductions may be applied as an equivalent reduction in acceleration in lieu of reduction in net flight path.
(See paragraph 12 (ref. § 25.111) of this AC for additional discussion.)
(c) SR-422B, and § 121.189(d), require that no airplane may take off at a weight in excess of that shown in the AFM to correspond with a net takeoff flight path that clears all 68
69 obstacles either by at least a height of 35 ft. vertically, or by at least 200 ft. horizontally within the airport boundaries, and by at least 300 ft. horizontally after passing beyond the boundaries.
(d) With turns in the net takeoff flight path, obstacle clearance determination requires consideration of both radius of turn and climb gradient decrement. Radius of turn, for use in obstacle lateral separation, is not airplane dependent and is readily calculated from speed and bank angle. Climb gradient decrements, however, are airplane dependent. Climb gradient decrements for bank angles up to at least 15 degrees should be contained in the AFM.
(2) Procedures.
Figure 14-2. Net Takeoff Flight Path
15. Climb: General - § 25.117.
a. Explanation . This section states the climb requirements of §§ 25.119 and 25.121 must be complied with at each weight, altitude, and ambient temperature within the operational limits established for the airplane and with the most unfavorable center of gravity for each configuration.
b. Procedures. None.
16. Landing Climb: All-Engines-Operating - § 25.119.
a. Explanation. Section 25.119(a) states that the engines are to be set at the power or thrust that is available 8 seconds after initiating movement of the power or thrust controls from the minimum flight idle position to the go-around power or thrust setting. The procedures given below are for the determination of this maximum thrust for showing compliance with the climb requirements of § 25.119.
b. Procedures.
(1) The engines should be trimmed to the low side of the idle trim band, if applicable, as defined in the airplane maintenance manual. The effect of any variation in the idle fuel flow schedule for engines with electronic fuel controllers is typically negligible (but any such claim should be adequately substantiated).
(2) At the most adverse test altitude, not to exceed the maximum field elevation for which certification is sought plus 1,500 ft., and with the most adverse bleed configuration expected in normal operations, stabilize the airplane in level flight with symmetrical power on all engines, landing gear down, flaps in the landing position, at a speed of VREF. Retard the throttle(s) of the test engine(s) to flight idle and determine the time needed to reach a stabilized
r.p.m., as defined below, for the test engine(s) while maintaining level flight or the minimum rate of descent obtainable with the thrust of the remaining engine(s) not greater than maximum continuous thrust (MCT). Engine flight idle r.p.m. is considered to be stabilized when the initial rapid deceleration of all rotors is completed. This has usually been 8-20 seconds. This can be determined in the cockpit as the point where rapid movement of the tachometer ceases. For some airplanes it may be desirable to determine the deceleration time from plots of r.p.m. versus time.
(3) For the critical air bleed configuration, stabilize the airplane in level flight with symmetric power on all engines, landing gear down, flaps in the landing position, at a speed of VREF, simulating the estimated minimum climb-limited landing weights at an altitude sufficiently above the selected test altitude so that time to descend to the test altitude with the throttles closed equals the appropriate engine r.p.m. stabilization time determined in paragraph (2) above.
Retard the throttles to the flight idle position and descend at VREF to approximately the test altitude. When the appropriate time has elapsed, rapidly advance the power or thrust controls to the go-around power or thrust setting. The power or thrust controls may first be advanced to the forward stop and then retarded to the go-around power or thrust setting. At the applicant’s option, additional less critical bleed configurations may be tested.
(4) The thrust that is available 8 seconds after the initiation of movement of the power or thrust controls from the minimum flight idle position, in accordance with paragraph (3) above, will be the maximum permitted for showing compliance with the landing climb requirements of § 25.119(a), and Section 4T.119(a) of SR-422B (see Appendix 4) for each of the bleed combinations tested in accordance with paragraph (3) above. If AFM performance is presented such that there is no accountability for various bleed conditions, the thrust obtained with the most critical airbleed should be used for landing climb performance for all operations. The effects of anti-ice bleed should be accounted for.
17. Climb: One-Engine-Inoperative - § 25.121.
a. Explanation. None.
b. Procedures.
(1) Two methods for establishing one-engine-inoperative climb performance follow:
(a) Reciprocal heading climbs are conducted at several thrust-to-weight conditions from which the performance for the AFM is extracted. These climbs are flown with the wings nominally level. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
(b) Drag polars and one-engine-inoperative yaw drag data are obtained for expansion into AFM climb performance. These data are obtained with the wings nominally level. Reciprocal heading check climbs are conducted to verify the predicted climb performance.
These check climbs may be flown with the wings maintained in a near level attitude. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
(2) If full rudder with wings level cannot maintain constant heading, small bank angles into the operating engine(s), with full rudder, should be used to maintain constant heading.
Unless the landing lights automatically retract with engine failure, testing should be conducted with the lights extended for § 25.121(a) Takeoff; landing gear extended, § 25.121(b) Takeoff;
landing gear retracted, and § 25.121(d) Approach.
(3) The climb performance tests with landing gear extended, in accordance with § 25.121(a), may be conducted with the landing gear and gear doors in the position they finally achieve after “gear down” selection. The critical configuration for the landing gear extended climb is considered to be that which presents the largest frontal area to the local airflow. This would normally be with no weight on the landing gear (full strut extension and trucks tilted) and all gear doors open. However, since the takeoff path will be determined by measurement of continuous takeoffs, or checked by continuous takeoffs if constructed by the segmental method (Ref. § 25.111(d)), any non-conservatism arising from the gear doors “closed” climb data will be evident. Also, some measure of conservatism is added to the landing gear extended climb performance by the requirement of § 25.111(d)(3) for the takeoff path data to be based on the airplane’s performance without ground effect.
(4) If means, such as variable intake doors, are provided to control powerplant cooling air supply during takeoff, climb, and en route flight, they should be set in a position that will maintain the temperature of major powerplant components, engine fluids, etc., within the established limits. The effect of these procedures should be included in the climb performance of the airplane. These provisions apply for all ambient temperatures up to the highest operational temperature limit for which approval is desired. (Reference: § 25.1043)
(5) The latter parts of §§ 25.121(a)(1) and (b)(1), which state “...unless there is a more critical power operating condition existing later along the flight path...” are intended to cover those cases similar to where a wet engine depletes its water and reverts to dry engine operation.
This is not intended to cover normal altitude thrust lapse rates above the point where the landing gear is fully retracted. (Reference: Preamble to SR-422A)
(6) Section 25.121(d) requires that the reference stall speed for the approach configuration not exceed 110 percent of the reference stall speed for the related landing configuration. This stall speed ratio requirement is to ensure that an adequate margin above the stall speed in the selected approach configuration is maintained during flap retraction in a goaround. An alternative means of providing an adequate operating speed margin during flap retraction in a go-around would be to increase VREF for the landing configuration to provide an equivalent operating speed margin. That is, VREF could be increased such that the reference stall speed for the approach configuration does not exceed 110 percent of 23.1REFV . An equivalent level of safety finding should be used to document the use of this alternative versus direct compliance with § 25.121(d). To maintain equivalent safety, the increase in VREF should not be excessive (for example, greater than 5 knots) to minimize the effect on safety of longer landing distances, higher brake energy demands, and reduced margins between VREF and VFE.
18. En Route Flight Paths - § 25.123.
a. Explanation. This guidance is intended for showing compliance with the requirements of § 25.123 and application to the operating requirements of §§ 121.191 and 121.193, which specify the clearances over terrain and obstructions required of the net en route flight paths subsequent to the failure of one or two engines.
b. Procedures.
(1) Sufficient en route climb performance data should be presented in the AFM to permit the determination of the net climb gradient and the net flight path in accordance with § 25.123(b) and (c) for all gross weights, altitudes, and ambient temperatures within the operating limits of the airplane. This en route climb performance data should be presented for altitudes up to the all-engines-operating ceiling to permit the calculation of drift-down data in the event of an en route engine failure.
(2) Fuel Consumption Accountability. The effect of the variation of the airplane’s weight along the flight path due to the progressive consumption of fuel may be taken into account using fuel flow rates obtained from airplane manufacturers’ test data. If measured fuel flow data is unavailable, a conservative fuel flow rate not greater than 80 percent of the engine specification flow rate at maximum continuous thrust (MCT) may be used.
(3) The procedures and flight conditions upon which the en route flight path data are based should be provided to the flightcrew. Credit for fuel dumping, if available and included in the flightcrew procedures, may be used to achieve the performance capability presented in the AFM. A conservative analysis should be used in taking into account the ambient conditions of temperature and wind existing along the flight path. All performance should be based on the net flight path and with MCT on the operating engine(s).