Safe and reliable also means that it is extremely improbable that the system can mislead the flight crew or will allow gross asymmetric power settings, for example, forward thrust on one engine versus reverse thrust on the other. In achieving this level of reliability, the system should not increase crew workload or require excessive crew attention during a very dynamic time period. Also, the approved performance data should be such that the average pilot can duplicate this performance by following the AFM procedures.
22. SECTION 23.57 TAKE-OFF PATH.
a. Section 23.57(a).
(1) Explanation.
(i) The takeoff path requirements of § 23.57 and the reductions required by § 23.61 are established so that the AFM performance can be used in making the necessary decisions relative to takeoff weights when obstacles are present. Net takeoff flight path data should be presented in the AFM as required by § 23.1587(d)(6).
(ii) The required performance is provided in the AFM by either pictorial paths at various power-to-weight 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 23.57(a) requires that the takeoff path extend to the higher of where the airplane is 1500 feet above the takeoff surface or to the altitude at which the transition to en route configuration is complete and a speed is reached at which compliance with § 23.67(c)(3) is shown.
(ii) Section 23.66 requires the airplane not to be banked before reaching a height of 50 feet as shown by the net takeoff flight path data.
(iii) The AFM should contain information required to show compliance with the climb requirements of § 23.57 and § 23.67(c)(3). This should include information related to the transition from the takeoff configuration and speed to the en route configuration and speed. The effects of changes from takeoff power to maximum continuous power should also be included.
(iv) Generally, the AFM shows takeoff paths at low power to weight that include acceleration segments between 400 and 1500 feet and end at 1500 feet. At high power to weight, these takeoff paths extend considerably higher than 1500 feet above the takeoff surface. On some airplanes, either the takeoff speed schedules or the flap configuration, or both, do not require acceleration below 1500 feet, even at limiting performance gradients.
b. Section 23.57(a)(1) - Takeoff Path Power Conditions.
(1) Explanation. The takeoff path should represent the actual expected performance at all points. If the path is constructed by the segmental method, in accordance with § 23.57(d)(2) and § 23.57(d)(4), it should be conservative and should be supported by at 32
least one demonstrated fly-out to the completed en route configuration. This is necessary to ensure all required crew actions do not adversely impact the required gradients.
(2) Procedures.
(i) To substantiate that the predicted takeoff path is representative of actual performance, the power used in its construction must comply with § 23.45. This requires, in part, that the power for any particular flight condition be that for the particular ambient atmospheric conditions that are assumed to exist along the path. The standard lapse rate for ambient temperature is specified in Appendix 7 of this AC under "Standard Atmosphere" and should be used for power determination associated with each pressure altitude during the climb.
(ii) Section 23.57(c)(4) requires that the power up to 400 feet above the takeoff surface represents the power available along the path resulting from the power lever setting established during the initial ground roll in accordance with AFM procedures. This resulting power should represent the normal expected variations throughout the acceleration and climb to 400 feet and should not exceed the limits for takeoff power at any point.
(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 power lapse resulting from a fixed power lever. An analysis may be used to account for various engine bleeds, for example, ice protection, air conditioning, and so forth. In some airplanes, the power growth characteristics are such that less than full rated power is required to be used for AFM takeoff power limitations and performance.
(iv) Engine power lapse with speed and altitude during the takeoff and climb, at fixed power lever settings, may be affected by takeoff pressure altitude.
(v) Most turboprop engines are sensitive to increasing airspeed during the takeoff roll.
The applicant's procedure should be evaluated and, if acceptable, the procedure should be reflected in the AFM. The AFM takeoff field length and takeoff power setting charts are based on the approved procedure. Approved procedures should be ones that can be accomplished in service by pilots of normal skill. For example, if a power adjustment is to be made after brake release, the power should be adjustable without undue attention.
Only one adjustment is allowed.
(vi) A typical "non-rolling" takeoff procedure is as follows:
(A) After stopping on the runway, adjust all engines to a static takeoff power setting (selected by the applicant).
(B) Release brakes.
(C) Upon reaching 50 to 60 knots, adjust power levers to maintain torque and temperatures within limits. Only one adjustment is allowed.
(vii) A typical "rolling takeoff" procedure is as follows:
(A) Release brakes.
(B) Adjust power levers to takeoff power in a smooth motion.
(C) As speed increases, make a small adjustment as necessary to preclude exceeding torque or temperature limits.
c. Section 23.57(a)(2) - Engine Failure.
(1) Explanation. Propeller thrust/drag characteristics should represent conditions that occur when the engine is actually failed. The power time history used for data reduction and expansion should be substantiated by test results.
(2) Procedures. Sufficient tests should be conducted utilizing actual fuel cuts to establish the propeller thrust decay history.
d. Section 23.57(c)(1) - Takeoff Path Slope.
(1) Explanation. For showing compliance with the positive slope required by § 23.57(c)(1), the establishment of a horizontal segment, as part of the takeoff flight path, is considered to be acceptable, in accordance with § 23.61(c). See figure 24-2. See paragraph 24b(2) for further discussion.
(2) Procedures.
(i) The level acceleration segment in the AFM net takeoff profile should begin at the horizontal distance along the takeoff flight path where the net climb segment reaches the AFM specified acceleration height. See figure 24-2.
(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 temperature so that the geometric height required for obstacle clearance is assured. For example:
Given:
• Takeoff surface pressure altitude (Hp) = 2,000 feet
• Airport standard temperature absolute (TS ) = 11oC+273.2 = 284.2°k
• Airport ambient temperature absolute (TAM) = -20°C+273.2 = 253.2°k
• Geometric height required (∆h) = 1,500 feet above takeoff surface
Find:
• Pressure altitude increment (∆Hp) above the takeoff surface ∆Hp = ∆h(TS/TAM) = 1500 feet (284.2°k/253.2°k) ∆Hp = 1684 feet
e. Section 23.57(c)(2) - Takeoff Path Speed.
(l) Explanation.
(i) It is intended that the airplane be flown at a constant indicated airspeed to at least 400 feet above the takeoff surface. This speed should meet the constraints on V2 of § 23.51(c)(4).
(ii) The specific wording of § 23.57(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.
(2) Procedures. None.
f. Section 23.57(c)(4) - Configuration Changes.
(l) Explanation.
(i) The intent of this requirement is to permit only routine crew actions to establish the engine-inoperative takeoff path. The power levers may only be adjusted early during the takeoff roll, as discussed under § 23.57(a)(1) (paragraph 22b(2)(b)), and then left fixed until at least 400 feet above the takeoff surface.
(ii) Simulation studies and accident investigations have shown that when heavy workload occurs in the cockpit, as with an engine loss 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, because 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 based on a feathered propeller up to 400 feet above the takeoff surface, automatic propeller feathering devices may be approved if adequate system reliability is shown in accordance with § 23.1309. Other automatic systems such as one which minimizes drag of the inoperative propeller by sensing negative torque may also be approved. Drag reduction for a manually feathered propeller is permitted for flight path calculations only after reaching 400 feet above the takeoff surface.
(ii) For flap retraction above 400 feet, a speed of not less than the lesser of 1.1 VMC or
1.2 VS1 should be maintained.
g. Section 23.57(d) - Takeoff Path Construction.
(1) Explanation. To take advantage of ground effect, AFM takeoff paths utilize a continuous takeoff path from VLOF to 35 feet, covering the range of power-to-weight ratios. From that point, free air performance, in accordance with § 23.57(e), is added segmentally. This methodology may yield an AFM flight path that is steeper with the gear down than up. The airplane should not be banked before reaching a height of 50 feet as shown by the net takeoff flight path. This requires determination of climb data in the wings level condition.
(2) Procedures. The AFM should include the procedures necessary to achieve this performance.
h. Section 23.57(e)(2) - Takeoff Path Segment Conditions.
(l) Explanation. Section 23.57(e)(2) requires that the weight of the airplane, the configuration, and the power 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 be based on that available at the most critical point in time during the segment, not that the individual variables (weight, approximate power setting, and so forth) should each be picked at its 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 22h(l); or
(ii) The actual performance variation during the segment.
i. Section 23.57(d)(4) - Segmented Takeoff Path Check.
(1) Explanation. None.
(2) Procedures. The takeoff path should be checked by continuous demonstrated takeoffs.
A sufficient number of these, using the AFM established takeoff procedures and speeds, and covering the range of power-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 power and test speeds.
j. Turboprop Reduced Power Takeoffs.
(1) Reduced takeoff power is a power less than approved takeoff power for which power setting and airplane performance is established by corrections to the approved power setting and performance. When operating with reduced takeoff power, the power setting that establishes power for takeoff is not considered a limitation.
(2) It is acceptable to establish and use a takeoff power setting that is less than the approved takeoff power provided the following:
(i) The establishment of the reduced power takeoff data is handled through the type certification process and contained in the AFM.
(ii) The reduced takeoff power setting:
(A) Does not result in loss of systems or functions that are normally operative for takeoff, such as engine failure warning, configuration warning, autofeather, automatic throttles, rudder boost, automatic ignition, or any other safety related system dependent upon a minimum takeoff power setting.
(B) Is based on an approved engine takeoff power rating for which airplane performance data is approved.
(C) Does not introduce difficulties in airplane controllability or engine response/operation in the event that approved takeoff power is applied at any point in the takeoff path.
(D) Is at least 75 percent of the approved takeoff power.
(E) Is predicated on a careful analysis of propeller efficiency variation in all applicable conditions.
(iii) Relevant speeds used for reduced power takeoffs are not less than those that will show compliance with the required controllability margins with the approved takeoff power.
(iv) The AFM states, as a limitation, that reduced takeoff power settings may not be used as follows:
(A) When the antiskid system (if installed) is inoperative;
(B) On runways contaminated with standing water, snow, slush or ice;
(C) On wet runways unless suitable performance accountability is made to the increased acceleration and stopping distances on these surfaces; or
(D) Where items affecting performance cause a significant increase in crew workload. Examples are inoperative equipment (for example, inoperative engine gauges, reversers or engine systems resulting in the need for additional performance corrections) or non-standard operations (that is, any situation requiring a nonstandard takeoff technique).
(v) Procedures for reliably determining and applying the reduced takeoff power value are simple, and the pilot is provided with information to obtain both the reduced power and approved takeoff power for each ambient condition.
(vi) The AFM provides adequate information to conduct a power check, using the approved takeoff power and, if necessary, establish a time interval.
(vii) Procedures are given for the use of reduced power.
(viii) Application of reduced power in service is always at the discretion of the pilot.
23. SECTION 23.59 TAKEOFF DISTANCE AND TAKEOFF RUN.
a. Takeoff Distance - Section 23.59(a).
(1) Explanation. The takeoff distance is either of the two distances depicted in figure 23-1 and 23-2 and discussed in paragraph 23a(l)(a) or (b), whichever is greater. 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 37
above the surface of the runway and accomplished in accordance with the procedures developed for § 23.57.
(i) The distance measured to 35 feet with a critical engine failure recognized at V1. See figure 23-1.
Takeoff Distance Start V 1 V LOF 35'
FIGURE 23-1 TAKEOFF DISTANCE Critical Engine Failure Recognized at V1
(ii) One hundred fifteen percent (115%) of the distance measured to 35 feet with all engines operating. See figure 23-2.
All Engine Distance Start V LOF 35' Takeoff Distance = 1.15 * All Engine Distance to 35'
FIGURE 23-2 - TAKEOFF DISTANCE All Engines Operating
b. Takeoff Run - Section 23.59(b).
(1) Explanation.
(i) Takeoff run is a term used for the runway length when the takeoff distance includes a clearway and the takeoff run is either of the two distances depicted in figure 23-1 and 23- 2, and discussed in paragraph 23b(1)(i)(A) or (B), whichever is greater. A clearway is where the accelerate-go distance does not remain entirely over the runway.. These distances are measured as described in § 23.59(a). When using a clearway to determine the takeoff run, no more than one-half of the air distance from VLOF to the 35 foot point may be flown over the clearway.
(A) The distance from start of 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 a critical engine failure recognized at V1. See figure 23-3.
Clearway Ground Roll Takeoff Run Takeoff Distance Mid-pointStart V1 VLOF 35'
FIGURE 23-3 - TAKEOFF RUN Critical Engine Failure Recognized at V1
(B) One hundred fifteen percent (115%) of the distance from start of roll to the midpoint between liftoff and the point at which the airplane attains a height of 35 feet above the takeoff surface, with all engines operating. See figure 23-4.
Clearway
1.15 * Distance to Mid-point Takeoff Run = Required Runway Takeoff Distance = 1.15 * All Engine Distance to 35' Mid-pointStart VLOF 35' Takeoff Path
FIGURE 23-4 - TAKEOFF RUN All Engines Operating
(ii) There may be situations in which the one-engine-inoperative condition (paragraph 23b(1)(i)(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 23b(1)(i)(B)) would dictate the other; therefore, both conditions should be considered.
(iii) For the purpose of establishing takeoff distances and takeoff runs, the clearway plane is defined in Part 1. The clearway is considered to be part of the takeoff surface, and a height of 35 feet may be measured from that surface. See figure 23-5.
Clearway 35' Takeoff Path Clearway Plane
1.25% Maximum
FIGURE 23-5 - CLEARWAY PROFILES
24. SECTION 23.61 TAKEOFF FLIGHT PATH.
a. Takeoff Flight Path - Section 23.61(a). The takeoff flight path begins 35 feet above the takeoff surface at the end of the takeoff distance determined in accordance with § 23.59. The takeoff flight path ends when the airplane's height is the higher of 1,500 feet above the takeoff surface or at an altitude at which the configuration and speed have been achieved in accordance with § 23.67(c)(3). See figure 24-1.
b. Net Takeoff Flight Path. - Section 23.61(b) and (c).
(1) The net takeoff flight path is the actual 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. See figure 24-2.
(2) The net takeoff flight path is the flight path used to determine the airplane obstacle clearance. Section 23.61(b) states the required climb gradient reduction to be applied throughout the flight path to determine the net flight path, including the level flight acceleration segment. Rather than decrease the level flight path by the amount required by § 23.61(b), § 23.61(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 § 23.61(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.
SEGMENT*
LANDING GEAR FLAPS POWER
AIRSPEED
ENGINES GROUND ROLL 1st 2nd ACCELERATION FINAL
DOWN RETRACTION RETRACTED
TAKEOFF RETRACTING ENROUTE POSITION
PROPELLER
TAKEOFF ABOVE 400 FT THRUST CAN BE REDUCED IF THE REQUIREMENTS OF 23.57(c)(3) CAN
BE MET WITH LESS THAN TAKEOFF THRUST
MAXIMUM
CONTINUOUS
ACCELERATING ACCELERATING VENROUTE
ALL OPERATING ONE INOPERATIVE
TAKEOFF ONE AUTOFEATHERED OR WINDMILLING ONE FEATHERED UP TO 400 FT 400 FT OR GREATER
V EF V LOF 35 FT
TAKEOFF DISTANCE (LONGER OF 1 ENG INOP TAKEOFF OR 1.15 ALL ENG TAKEOFF) PATH 1 PATH 2
TAKEOFF FLIGHT PATH 1500 FTHEIGHT > 1500 FT HEIGHT > 400 FT
HEIGHTS ARE
REFERENCED TO
RUNWAY ELEVATION AT
END OF TAKEOFF DISTANCE SEE NOTE SEE NOTE V2
Note: The en route takeoff segment* usually begins 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 § 23.67(c)(3) is shown. The time limit on takeoff thrust cannot be exceeded.
* Segments as defined by § 23.67.
FIGURE 24-1 - TAKEOFF SEGMENTS AND NOMENCLATURE 42
35' 35' Net Flight Path Level from Takeoff Surface >400' Obstacle Clearance
FIGURE 24-2 - NET TAKEOFF FLIGHT PATH
25. SECTION 23.65 CLIMB: ALL ENGINES OPERATING.
a. Explanation.
(1) Objectives. The climb tests associated with this requirement are performed to establish the airplane's all-engine performance capability for altitudes between sea level and not less than 10,000 feet with wing flaps set to the takeoff position. This is necessary to enable comparison with the minimum climb performance required and for AFM presentation of climb performance data of 10,000 feet including the effect of altitude and temperature (see § 23.1587) and including the effect of weight for aircraft over 6,000 pounds maximum takeoff weight (MTOW) and turbine engine aircraft.
(2) Cooling Climbs. Applicants with single engine reciprocating powered airplanes may vary the climb speeds to meet the requirements of § 23.1047. If variations in climb speeds are required to meet the cooling tests, the applicant may wish to establish the variation of rate of climb with speed.
(3) Sawtooth Climbs. A common method of determining climb performance is sawtooth climbs. A series of climbs, known as sawtooth climbs, should be conducted at several constant indicated airspeeds using a constant power setting and a prescribed configuration. A minimum of three series of sawtooth climbs should be conducted. The mean altitudes through which the sawtooth climbs are conducted should be:
(i) As near sea level as practical; and
(ii) Close to the ceiling (where 100 feet/minute can be maintained) for sea level engines;
and
(iii) An intermediate altitude, taking into consideration the power characteristics of the engine.
b. Procedures - Sawtooth Climbs.
(1) Climb Technique. With the altimeter adjusted to a setting of 29.92 inches Hg (pressure altitude), the series of climbs should be initiated at a chosen altitude. Stabilize airspeed and power prior to recording data. The time at the beginning of each run should be recorded for weight-accounting purposes, and the stabilized climb should be continued for 3 minutes or 43