12. TAKEOFF PATH - § 25.111 .
a. Section 25.111(a).
(1) Explanation.
(i) The takeoff path requirements of § 25.111, and the reductions to that path required by §
25.115, are established so that the AFM performance can be used in making necessary decisions relative to takeoff weights when obstacles are present. Such considerations are required by § 121.189 when operations are conducted in accordance with 14 CFR part 121.
(ii) The required performance is provided in AFMs by either pictorial paths at various thrust-toweight (T/W) conditions, with corrections for wind, or by a series of charts for each segment, along with a procedure for connecting these segments into a continuous path.
(2) Procedures .
(i) Section 25.111(a) requires that the actual takeoff path (from which the AFM net takeoff flight path is derived) extend to the higher of where the airplane is 1,500 ft. above the takeoff surface or to the altitude at which the transition to en route configuration is complete and a speed is reached where compliance with the final segment requirements of § 25.121(c) can be met. Section 25.115(b) allows termination of the AFM “net” flight path below 1,500 ft. in some cases.
(ii) The AFM should contain information required to show compliance with the climb requirements of §§ 25.111 and 25.121(c). This should include information related to the transition from the takeoff configuration and speed to the final segment configuration and speed. The effects of changes from takeoff thrust to maximum continuous thrust should also be included.
(iii) Generally, the AFM shows low T/W takeoff paths ending at 1500 ft. above the takeoff surface, with acceleration segments between 400 and 1,500 ft., and high T/W takeoff paths extending considerably higher than 1,500 ft. above the takeoff surface. On some airplanes, the takeoff speed schedules, or certain flap configurations, do not require acceleration below 1,500 ft., even at limiting performance gradients. Although §
25.111(a) permits the takeoff path to be terminated as low as 1,500 feet above the takeoff surface, it is recommended that the flight path data, or associated AFM methodology, be presented so that the flight path can be determined to 3,000 ft. above the takeoff surface. This will permit obstacle clearance analysis for distant obstacles of considerable elevation that may be encountered in operations from mountain airports.
(iv) The § 25.115(b) net takeoff flight path, required by § 25.1587(b) to be included in the AFM, need not extend to the altitude specified in § 25.111(a). It may be terminated at a height, generally called “NET HEIGHT,” that is directly related to the actual airplane height specified in § 25.111(a). The “NET HEIGHT” is calculated using the actual airplane takeoff climb performance, to the point where the altitude requirements of § 25.111(a) are met, reduced by the climb gradient decrements specified in § 25.115(b).
b. Section 25.111(a)(1)- Takeoff Path Thrust Conditions .
(1) Explanation. The takeoff path established from continuous demonstrated takeoffs must at all points represent the actual expected performance, or be conservative, per §§ 25.111(d)(2) and 25.111(d)(4), if the path is constructed by the segmental method.
(2) Procedures .
(i) To be assured that the predicted takeoff path is representative of actual performa nce, the thrust used in its construction must comply with § 25.101(c). This requires, in part, that the thrust be based on the particular ambient atmospheric conditions that are assumed to exist along the path. The standard lapse rate for ambient temperature is specified in Part 1 of the FAR under “Standard Atmosphere,” and should be used for thrust determination associated with each pressure altitude during the climb.
(ii) In accordance with § 25.111(c)(4), the thrust up to 400 ft. above the takeoff surface must represent the thrust available along the path resulting from the power lever setting established during the initial ground roll in accordance with AFM procedures. This resulting thrust may be less than that available from the rated inflight setting schedule.
(iii) A sufficient number of takeoffs, to at least the altitude above the takeoff surface scheduled for V2 climb, should be made to establish the fixed power lever thrust lapse. An analysis may be used to account for various engine bleeds (e.g. ice protection, air conditioning, etc.). In some airplanes, the thrust growth characteristics are such that less than full rated thrust must be used for AFM takeoff power limitations and performance. This is to preclude engine limitations from being exceeded during the takeoff climbs to 400 ft. above the takeoff surface.
(iv) Engine thrust lapse with speed and altitude during the takeoff and climb, at fixed power lever settings, can be affected by takeoff pressure altitude.
(v) 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 thrust setting procedure, provided the AFM takeoff field length and the takeoff 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:
(A) After stopping on the runway, set an intermediate power on all engines (power setting selected by applicant).
(B) Release brakes and advance power levers.
(C) Set target power setting as rapidly as possible prior to reach ing 60 to 80 knots.
(D) No adverse engine operating characteristics should exist after completion of the power setting through the climb to 1,500 ft. 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.
(vi) 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.
c. Section 25.111(a)(2) - Engine Failure .
(1) Explanation.
(i) 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 thrust to drop immediately, with the associated performance going from all-engines-operating to one-engineinoperative at the point of engine failure.
(ii) This con servative rationale notwithstanding, there is a basis for assuming that the failed engine 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.
(iii) With these considerations, it may b e acceptable to use the transient thrust as the failed engine spools down at VEF. The thrust time-history used for data reduction and expansion should be substantiated by test results.
(iv) In the case of propeller-driven airplanes, consideration shou ld 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 thrust in this case will be much more sudden than the turbojet engine spooldown described above.
(2) Procedures .
(i) For turbojet powered airplanes , if transient thrust credit is used during engine failure in determining the accelerate-go AFM 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 that would affect thrust decay characteristics), fuel cuts are unnecessary if thrust decay characteristics have been adequately substantiated.
(ii) 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.
d. Section 25.111(a)(3) - Airplane Acceleration .
(1) Explanation. None.
(2) Procedures . None.
e. Section 25.111(b) - Airplane Rotation and Gear Retraction .
(1) Explanation. The rotation speed, V R, is intended to be the speed at which the pilot initiates action to raise the nose gear off the ground during the acceleration to V 2. Consequently, the takeoff path, determined in accordance with §§ 25.111(a) and (b), should assume that pilot action to raise the nose gear off the ground will not be initiated until the speed V R has been reached.
(2) Procedures . The time between liftoff and initiation of gear retraction should not be less than that necessary to establish an indicated positive rate of climb plus one second.
f. Section 25.111(c)(1) - Takeoff Path Slope .
(1) Explanation.
(i) The establishment of 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).
(ii) The net takeoff flight path is the flight path used to determine the airplane obstacle clearance for turbine powered airplanes (§ 121.189(d)(2)). 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 applicant exchanges altitude reduction for increased distance to accelerate in level flight in determination of the level flight portion of the net takeoff path.
(2) Procedures .
(i) The level acceleration segment in the AFM net takeoff profile should begin at the same horizontal distance along the takeoff flight path that the climb segment, without the gradient reductions of § 25.115(b), reaches the AFM specified acceleration height.
(ii) The AFM acceleration height should be presented in terms of pressure altitude increment above the takeoff surface. This information should allow the establishment of the pressure altitude “increment” (∆hp) for off-standard ambient temperatures so that the geometric height required for obstacle clearance is assured.
For example:
Given:
o Takeoff surface press ure altitude (hp) = 2,000 ft.
o Airport std. temp. abs. (T S) = 11oC+273.2o = 284.2oK o Airport ambient temp. abs. (T AM) = -20oC+273.2o = 253.2oK o Geometric height required ( ∆h) = 1,700 ft. above the takeoff surface Find:
o Pressure a ltitude increment (∆hp) above the takeoff surface ∆hp = ∆h(TS/TAM) = 1,700 ft. (284.2oK/253.2oK) ∆hp = 1,908 ft.
g. Section 25.111(c)(2) - Takeoff Path Speed .
(1) Explanation.
(i) It is intended that the airplane be flown at a constant i ndicated airspeed to at least 400 ft. above the takeoff surface. This speed must meet the constraints on V 2 of §§ 25.107(b) and (c).
(ii) The specific wording of § 25.111(c)(2) should not be construed to imply that above 400 ft. the airspeed may be reduced below V 2 , but instead that acceleration may be commenced.
(2) Procedures .
(i) 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).
(ii) For those airplanes mentioned in paragraph (i), above, the V 2 should be constrained, in addition to the requirements of §§ 25.107(b) and (c), by the stall speed 1,500 ft. 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 ft., which provides stall margin conservatism at lower takeoff field pressure altitudes.
h. Section 25.111(c)(3) - Required Gradient .
(1) Explanation. None.
(2) Procedures . None.
i. Section 25.111(c)(4) - Configuration Changes .
(1) Explanation.
(i) 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 levers may only be adjusted early during the takeoff roll, as discussed in paragraph 12b(2), and then left fixed until at least 400 ft. above the takeoff surface.
(ii) Simulation studies and accident investigations h ave shown that when heavy workload occurs in the cockpit, as with an engine failure during takeoff, the crew might not advance the operative engines to avoid the ground, even if the crew knows the operative engines have been set at reduced power. 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. This also establishes the delay time to be used for data expansion purposes.
(2) Procedures .
(i) 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 Part 25 of the FAR.
(ii) 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 241 of this AC.
(iii) 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 V LOF to the gear up point, covering the range of thrust-toweight 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 must be 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.) should each be 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:
(i) The critical level of performance as explained in paragraph (1);
(ii) The average performance during the segment; or
(iii) 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 V EF 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 explanation under § 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-of-ground-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 (i) or (ii) 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.
(i) 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 V EF *
(ii) 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:
(A) Be based on the airplane reaching a speed of V 2 before it is 35 feet above the takeoff surface; and (B) 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.
(2) The takeoff procedure adopted should be re flected 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 V 1 speed), determined in accordance with paragraphs 13a(1)(i) and (ii) of this AC, or the distance on a wet runway using a reduced screen height (and the wet runway V 1 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 as shown in Figure 13-
3.
FIGURE 13-3. TAKEOFF DISTANCE ON A WET RUNWAY Critical Engine Fails at V EF
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 (i) or (ii) 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.
(i) The distan ce 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 V EF, 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 runway *
* FIGURE 13-4. TAKEOFF RUN Critical Engine Fails at V EF *
(ii) One hundred fifteen (115) percent of 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 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:
(A) Be based on the airplane reaching a speed of V 2 before it is 35 feet above the takeoff surface; and (B) 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.
(2) There may be situations in which the one-engine-inoperative condition (paragraph 13c(1)(i)) 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)(ii)) 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.
(4) The profile shows no fixed obstacle projecting above the clearway plane. However, the airport authorities must have control of the movable obstacles in this area to ensure that no flight will be initiated using a clearway unless it is determined with certainty 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 at a height of 35 feet, 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 FLIGHI PATH
• ACTUAL HITCHT ≥ 1500 FEET 1500 FEET PATH 2 TAKEOFF DISTANCE (LONGER ACTUAL HEIGHI ≥ 400 FEET + OF 1 ENG INOP TAKEOFF OR —
1.15 ALL ENG TAKEOFF) PATH I
ACTUAL HEICHTS ARE VEr VLOF GEAR RETRACTION COMPLETE RUNWAY ELEVATION REFERENCED TO AT END OF TAKEOFF
DISTANCE SECMENT* LANDING GEAR GROUND ROLL DOWN RETRACHON IST 2ND →4 ACCELFRATION RETRACTED FINAL
ENROUTE
FLAPS TAKEOFF RETRACTING (SEE NOTE) POSITION POWER TAKEOFF "ABOVE 400 FTTARUST CAN BE REDUCED THE REQUIREMENTS OF 25. 111(CY) CAN BE MET WITH LESS THAN TAKEOFF THRUST SEE NOTE CONTINUOUS MAXIUM AIRSPEED ACCELERATING ACCELERATING, 21.25 V;
ENGINES ALL OPERATINC ONE INOPERATTVE
PROPELLER TAKEOFF ONE AUTOFRATHERED OR WINDMILANG ONE FEATHERED UP TO 400 FEET 400 FEET OR CREATER 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.
(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.
(ii) 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.)
(iii) 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 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.
(iv) 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 .
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. When approval of an airplane for operation in known icing conditions is requested, compliance with the approach climb requirements of § 25.121(d), and landing climb requirements of § 25.119, should be demonstrated with residual ice accretions on unprotected areas of the airframe.
For further guidance on this subject see paragraph 231, “Performance Requirements for Flight in Icing Conditions,” in Chapter 8 of this AC.
b. Procedures . None.