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). Refer to figure 12. Refer to paragraph 23.61b(2) for further guidance.
(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. Refer to figure 12.
(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:
Table 5 - AFM Acceleration Height Given Takeoff surface pressure altitude (Hp) = 2,000 feet Airport standard temperature absolute (TS ) = 11 oC+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), 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 fi nding 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 ef fect, 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 proce dures necessary to achieve this performance.
h. Section 23.57(e)(2) - Takeoff Path Segment Conditions.
(l) Explanation. Section 23.57(e)(2) requi res 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 (l); or
(ii) The actual performance variation during the segment.
i. 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 equipmen t (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 non-standard 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.
7. § 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 figures 6 and 7 and discussed in paragraph b(l)(a) or (b), whichever yields the higher value. The distances indicated below are measured horizontally from the main landing gears at initial brake release to that same point on the airplane when the lowest part of the departing airplane is 35 feet above the surface of the runway 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. Refer to figure 6.
~ t t L/ _________ / } t I:
11/16/2011 AC 23-8C Figure 6 Takeoff Distance Critical Engine Failure Recognized at V1 Start V1 VLOF Takeoff Distance 35'
(ii) 115 percent of the distance measured to 35 feet with all engines operating.
Refer to figure 7.
Figure 7 - Takeoff Distance - All Engines Operating Start VLOF All Engine Distance 35' Takeoff Distance = 1.15 * All Engine Distance to 35'
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 6 and 7, and discussed in paragraph b(1)(i)(a) and (b), whichever yields the higher value. 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.
I:
I:
(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. Refer to figure 8.
Figure 8 - Takeoff Run - Critical Engine Failure Recognized at V1 Start V1 VLOF Mid-point Clearway Ground Roll Takeoff Run Takeoff Distance 35'
(b) 115 percent of the distance from start of roll to the mid-point between liftoff and the point at which the airplane attains a height of 35 feet above the takeoff surface, with all engines operating. Refer to figure 9.
Figure 9 - Takeoff Run - All Engines Operating Clearway
1.15 * Distance to Mid-point Takeoff Run = Required Runway Takeoff Distance = 1.15 * All Engine Distance to 35' Mid-point Start VLOF 35' Takeoff Path
(ii) There may be situations in which the one-engine-inoperative condition (paragraph b(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 b(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. Refer to figure 10.
~/~ r---~~ ~~/ - ~~~~~-- J Figure 10 - Clearway Profiles Clearway 35' Takeoff Path Clearway Plane
1.25% Maximum
8. § 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). Refer to figure 11.
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 fourengine airplanes. Refer to figure 12.
(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.
/ / / / / ?-- -- 11/16/2011 AC 23-8C Figure 11 - Takeoff Segments and Nomenclature GROUND ROLL 1st 2nd ACCELERATION FINAL
DOWN RETRACTION RETRACTED
TAKEOFF RETRACTING ENROUTE POSITION
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
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 FT HEIGHT > 1500 FT HEIGHT > 400 FT
HEIGHTS ARE
REFERENCED TO
RUNWAY ELEVATION AT
END OF TAKEOFF DISTANCE SEE NOTE SEE NOTE V2 SEGMENT*
LANDING GEAR FLAPS POWER
AIRSPEED
ENGINES
PROPELLER / FAN UP TO 400 FT 400 FT OR GREATER 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 12- Net Takeoff Flight Path 35' 35' Net Flight Path Level from Takeoff Surface >400' Obstacle Clearance
9. § 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 (refer to § 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 47
- 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 three minutes or 3,000 feet minimum while holding airspeed substantially constant. Climbs should be conducted 90 degrees to the wind and, alternately, on reciprocal headings to minimize the effects of windshear. Since the rate at whic h the altitude changes is the primary consideration of the test, particular care should be taken to observe the precise altimeter indication at precise time intervals. Time intervals of not more than 30 seconds are recommended for altimeter readings.
Airspeed, ambient temperatures, r.p.m., and other engine power parameters also should be recorded, permissibly at longer intervals. Rates-of-climb/sink observed for test conditions should be greater than +100 feet-per-minute. Rates of climb near zero tend to be unreliable. A running plot of altitude-versus-time provides an effective means of monitoring acceptability of test data as the run progresses, and a running plot of the observed rate of climb obtained for each airspeed enables similar monitoring of the sawtooth program. This procedure is recommended because it affords opportunity for promptly observing and economically rectifying questionable test results.
(2) Air Quality. In order to obtain accurate result s, it is essential that the sawtooth climbs be conducted in smooth air. In general, the effects of turbulence are more pronounced in test data obtained at lower rates of climb and, when testing for compliance with minimum climb requirements, even slight turbulence may produce errors in observed climbs of such magnitude as to render the data inconclusive with respect both to rate of climb and best climb speed. Less obvious, but equally unacceptable for climb testing, is the presence of an inverse gradient in the ambient temperature.
(3) Test Airspeeds. The airspeeds selected for th e sawtooth should bracket the best climb speed, which for preliminary purposes may be estimated as 140 percent of the power-off stalling speed. The lowest climb test speed should be as near the stalling speed as can be flown without evidence of buffeting or necessity for abnormally frequent or excessive control movements, which might penalize the climb performance. Although the example shown in figure 13 has 10-knot intervals, the interval between test speeds should be smaller at the lowspeed end of the range and should increase as the speed increases. Suggested intervals are five knots at the low end, varying to 15 knots at the high end. In addition, the maximum level flight speed and VS (or VMIN) at the approximate mid-range test altitude provide a useful aid in defining the curves in figure 14.
(4) Data Plotting. Sawtooth climb data is plotted on a graph using altitude and time as the basic parameters as shown in figure 13. After the sawtooth data has been plotted, draw in the mean altitude line. A tange nt line can now be drawn to each of the sawtooth climb curves at the mean altitude intersection. By determining the slope of the tangent lines, the observed rate of climb at the mean altitude for each sawtooth can be determined.
(5) Data Corrections. For the density altitude met hod of data reduction (refer to appendix 2), it is necessary to correct the data to standard atmospheric conditions, maximum weight, and chart brake horsepower before proceeding any further with the observed data. These corrections sometimes change the observed data a significant amount. The maximum level flight speed (VMAX) data points should also be corrected to assist in defining the curves in figure 14.
130 K CAS w 4800 Q ~ i= -' < w c:: ::, V, 4400 .,, w R:
Vinoi:c• 165 IC CAS 4000 V111in• 72 IC CAS
TIME MINUTES 11/16/2011 AC 23-8C
(6) Plotting of Corrected Data. After the observed data has been corrected to the desired standards, it can be plotted as shown in figure 14 with the rate of climb versus CAS at various density altitudes. It should be noted that the stall speed point s are not usually true stabilized zero rate-of-climb data points. However, the stall speed point s are useful in defining the asymptotic character of the left hand part of the curve.
Figure 13 - Observed Data
(7) Speed Schedule Data Points. From the curves of figure 14, it is now possible to determine the airplane's best rate of climb speed schedule, VY. This is done by drawing a straight line through the peaks (highest rate of climb point) of each of the previously drawn curves of rate-of-climb vs. CAS. Also, it is possible to obtain from this graph the best angle of climb speed schedule, VX. This is done by drawing tangent lines to the rate-of-climb vs. CAS curves from the graph origin and connecting each of the tangent intersect points with a straight line. It should be noted that the V X and VY speed lines intersect at "zero" rate of climb. This is because zero rate of climb occurs at the airplane's absolute ceiling and VX, VY, VMIN, and VMAX are all the same speed at this point. (Note: V MIN as used here is not related to the VMIN in stall testing.)
(8) Speed and Rate of Climb. Directly from information obtained from figure 14, it is possible to plot the climb performance of the airplane into a more usable form. By reading the rates of climb at the VY intersect points and plotting them against altitude, as shown in figure 15, it is possible to determine the rate of climb from sea level to the absolute ceiling.
(9) Cowl Flap and Mixture. For propeller equipped airc raft, cowl flaps should be in the position used for cooling tests. The mixtur e setting should be set to that used during the cooling test.
(10) Weight and C.G. For climb performance tests, th e airplane's test weight, load distribution and engine power should be recorded. Usually, forward c.g. is critical for climb performance.
c. Continuous Climb. For engine changes where the objective is to determine that new climb performance is equal to or better than the old climb performance and the all-engine climb performance is obviously in excess of the requirements of § 23.65, a continuous climb may be used to obtain the data. The rate of climb da ta at a convenient number of points should be reduced to standard day conditions.
d. Extrapolation of Climb Data. The climb data expansion required by § 23.1587 from sea level to 10,000 feet and from ISA to ISA + 30 C can be accomplished by the methods in Appendix 2. Normally, the same method used for data reduction should be used for data expansion. Use caution in extra polating beyond altitudes that have not been verified by flight tests.