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).
19. Landing - § 25.125.
a. Explanation.
(1) The landing distance is the horizontal distance from the point at which the main gear of the airplane is 50 ft. above the landing surface (treated as a horizontal plane through the touchdown point) to the point at which the airplane is brought to a stop. (For water landings, a speed of approximately 3 knots is considered “stopped.”) In this AC, the distance is treated in two parts: the airborne distance from 50 ft. 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.
(2) The minimum value of VREF is specified in § 25.125(b)(2). It is intended to provide an adequate margin above the stall speed to allow for likely speed variations during an approach in light turbulence. 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).
(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).
b. Procedures for Determination of the Airborne Distance. Three acceptable means of compliance are described in paragraphs (1), (2), and (3) below. These differ from the “traditional” method in which steep approaches and high touchdown sink rates were permitted.
Such a demonstration of maximum performance is no longer considered acceptable. However, the distances obtained using that method resulted in a satisfactory operational safety record. The methods given here allow credit for the amount of testing an applicant is prepared to conduct, such that if the method described in paragraph 19b(3) (the most complex) is chosen, distances typical of those from the “traditional” method should be obtained, but without incurring the associated risks during testing.
NOTE: If it is determined that the constraints on approach angle and touchdown rate-of-sink described in paragraphs (2) and (3), below, are not appropriate due to novel or unusual features of future transport category airplane design, new criteria may be established. Such a change would be acceptable only if it is determined that an equivalent level of safety to existing performance standards and operational procedures is maintained.
(1) Experience shows an upper bound to the part 25 zero-wind airborne distances achieved in past certifications and, similarly, a minimum speed loss. These are approximated by the following:
Air Distance (feet) = 1.55 (V REF-80)1.35+800 where VREF is in knots TAS
74 Touchdown Speed = V REF-3 knots
An applicant may choose to use these relationships to establish landing distance in lieu of measuring airborne distance and speed loss. If an applicant chooses to use these relationships, the applicant should show by test or analysis that they do not result in air distances or touchdown speeds that are nonconservative.
(2) If an applicant chooses to measure airborne distance or time, at least six tests covering the landing weight range are required for each airplane configuration for which certification is desired. These tests should meet the following criteria:
(a) A stabilized approach, targeting a glideslope of -3 degrees and an indicated airspeed of VREF, should be maintained for a sufficient time prior to reaching a height of 50 feet above the landing surface to simulate a continuous approach at this speed. During this time, there should be no appreciable change in the power setting, pitch attitude, or rate of descent. The average glideslope of all landings used to show compliance should not be steeper than -3 degrees.
(b) Below 50 feet, there should be no nose depression by use of the longitudinal control and no change in configuration, except for reduction in power.
(c) The target rate of descent at touchdown should not exceed 6 feet per second.
Target values cannot be achieved precisely; however, the average touchdown rate of descent should not exceed 6 feet per second.
(3) If the applicant conducts enough tests to allow a parametric analysis (or equivalent method) that establishes, with sufficient confidence, the relationship between airborne distance (or time) as a function of the rates of descent at 50 feet and touchdown, the 14 CFR part 25 airborne distances may be based on an approach angle of -3.5 degrees, and a touchdown sink rate of 8 feet per second (see paragraph 19h for a sample of this analysis method).
(a) The air distance or air time established by this method should not be less than 90 percent of the lowest demonstrated value obtained using the target values for approach angle and touchdown sink rate specified in paragraph (b), below. Test data with approach angles steeper than -3.5 degrees, or touchdown sink rates greater than 8 feet per second, should not be used to satisfy this requirement.
(b) In order to determine the parametric relationships, it is recommended that test targets should span approach angles from -2.5 degrees to –3.5 degrees, and sink rates at touchdown from 2-6 ft. per second. Target speed for all tests should be VREF.
(c) Below 50 feet, there should be no nose depression by use of the longitudinal control and no change in configuration that requires action by the pilot, except for reduction in power.