Overhead Beginning of test Allowable lateral deviation Extended runway Point M Point K Point C Point F Microphone location PNLTM – 10 dB Overhead test window End of test Flight path Allowable vertical deviation test target altitude PNLTM – 10 dB Figure 24. Takeoff flight path tolerances 401(i)(3) Takeoff test procedure AMC §A36.9.2.1(c) [ETM AMC A2 8.1.1.2]
(1) Target test conditions Target test conditions are established for each noise me asurement. These target conditions specify the flight procedure, aerodynamic configuration to be selected, airplane weight, engine thrust (power), airspeed and, at the closest point of approach to the noise measurement point, airplane height. Regarding choice of target airspeeds and variation in test weights, the possible combinations of these test elements may affect the airplane angle-ofattack or airplane height and, therefore, possibly the airplane noise generation or propagation geometry (see 402(a)(1)(ii)(A) for guidance on the choice of target airspeeds and variation in test weights).
(2) Flight test procedures Before the start of noise testing the FAA should approve flight path tolerances (see A36.9.2.1 of part 36). Except when takeoffs with thrust (power) reduction are being demonstrated, the engine thrust (power), airplane flight path and aerodynamic configuration should be kept constant between points C and F (see Figure 24) during each approved certification flight test.
(3) Invalid test data Noise measurements obtained when the airplane flies outside the approved flight path envelope between points C and F (see Figure 24) during a noise certification test are c onsidered invalid, and the noise measurement is to be repeated.
401(i)(4) Approach test configuration GM §A36.9.2.2/B36.7(c) [ETM GM A2 8.1.1.3]
(1) Approach tests Figure 25 depicts the reference approach flight test configuration for noise certification testing of airplanes. The approach angle (steady glide angle) for this condition is 3 0.5, and the target airplane height vertically above the noise measurement point is 394 ft (120 m). Maximum PNLT may occur before or after the approach noise Page 157
measurement point.
6 562 ft 10 dB-down period PNLTM –10 dB Touchdown Distance Point P Point N Point O Point J Point I Point H End of test Flight path Stabilized conditions PNLTM – 10 dB Point G Glide slope = 3° ± 0.5° Microphone Altitude Figure 25. Approach with full landing
(2) Flight path deviations Approved height and centerline deviations along the extended runway approach flight path (see Figure 26) define an approved flight path envelope within which the flight crew should fly between points G and I. In cases where the flight crew has a clear view of the airport runway during the approach, it is common for the crew to consistently fly within the approved flight path envelope. Therefore, the approved centerline and height deviations for approach conditions may be smaller than during takeoff conditions.
Allowable lateral deviation PNLTM – 10 dB PNLTM – 10 dB 10 dB-down period Microphone Point P Point N Point H Flight path Point I Point G Beginning of test Allowable altitude deviation Test target altitude = 394 ft End of test Point O Extended runway Figure 26. Approach flight path tolerances 401(i)(5) Approach test procedure AMC §B36.7(c) [ETM AMC A2 8.1.1.3]
(1) Target test conditions Target test conditions should be established for each noise measurement. These specify the selected aerodynamic configuration, system operation, airplane weight, flight procedure (such as complete landings or flight path intercepts) height, thrust (power) and airspeed during each noise measurement. The applicant is required to select the approved airworthiness configuration for the approach noise certification that produces the highest noise level (i.e., the most critical from the standpoint of noise). The airspeed requirement for subsonic jet airplanes is VREF + 10 kt (VREF +19 km/h)). This airspeed is kept constant, within 3.0 percent, throughout the 10 dB-down period (i.e., between points G and I in Figure 26). The airplane configuration (e.g., flap setting, air conditioning and/or APU system operation) is to remain constant during the noise measurement period. Airspeed variations are measured in terms of IAS as determined by the pilot’s airspeed indicator.
(2) Engine idle trim For engines where the idle trim may affect the inter-c ompressor bleed valve schedule during the approach condition, the engine in-flight idle trim should be adjusted to the highest engine speed setting permitted by the engine manufacturer and consistent with airworthiness requirements. The engine may also provide ground idle trim adjustment, but the trim that needs adjustment is that which is operable during flight. In-flight idle trim may be adjusted to improve engine acceleration characteristic s to satisfy airworthiness compliance. The higher idle trim will cause the highest engine speed, and hence idle thrust (power), which results in a greater airplane angleof-attack and will result in the loudest approach noise requi red for certification. The applicant is to make those adjustments necessary to satisfy the airworthiness regulations. This idle trim adjustment may affect the performance or evaluation of approach NPD testing.
(3) Internal compressor bleed adjustment The internal compressor bleed operation, sometimes referred to as the surge bleed valve (SBV) operation, should be adjusted within the engine manufacturer’s specification to represent reference conditions as closely as possible. Most Page 159
turbojet engines are equipped with internal compressor bleed systems. The internal compressor bleed operates to reduce the possibility of internal engine surges during rapid throttle movements. Some jet engines have overboard bleed systems that generate high noise levels. These systems normally operate above in-flight idle and do not present a problem unless the applicant chooses to prepare an NPD database and the thrust (power) settings higher than inflight idle. The applicant is responsible for substantiating that either the internal compressor bleed operation does not affect the reference EPNL values during noise certification reference conditions, or the data contains the effects of the internal compressor bleed operation.
(4) Invalid test data Noise measurements obtained when the aircraft flies outside the approved flight path envelope between points G and I are invalid, and the noise measurement must be repeated.
401(i)(6) Lateral noise measurement GM §B36.4(b) [ETM GM A2 8.1.1.1]
(1) Measured lateral noise levels Measured lateral noise levels may not be the same at symmetrical noise measurement points even when the data are adjusted for airplane position for flight directly over the extended runway centerline. This non-symmetrical nature of measured sideline noise is primarily attributable to the direction of engine or propeller rotation. Because of inlet shielding, jet-powered airplanes may exhibit 1 to 2 dB di fferences in lateral noise levels. Turbo-propeller-powered airplanes can exhibit differences in lateral noise levels in excess of 6 dB. Due to their inherent lateral noise asymmetry, B36.4(b) of part 36 specifies that, fo r propeller-driven airplane s, simultaneous measurements be made at each and every test noise measurement point at its symmetrical position on the opposite side of the flight track.
401(i)(7) Integrated procedure adjustment GM §A36.9.4 [GM A2 8.4]
(1) Integrated procedure adjustments Section A36.9.4 of part 36 provides details of an approved integrated adjustment method when the airplane is operated at stabilized flight path and thrust (power) conditions dur ing the noise measurement period. Measured and reference flight paths are illustrated in Figures A36-11 (a) and A36-11 (b) of part 36.
401(i)(8) Acoustic emission angles GM §A36.9.4.2 [GM A2 8.3.1.2]
(1) Acoustic e mission angles For the integrated method, each one-half-second noise data record will define a separate acoustic emission angle. This angle will then define the location of each data record along the reference flight path. The distance between consecutive data records along the reference flight path, divided by the reference path speed, provides the time interval between reference data records. The reference duration of each of these data records can be determined by obtaining the average of the two intervals between the adjacent data records. This may be different than 0.5 seconds. Section 403(a)(1)(iv) provides methods for time interval computations using the integrated method.
EQUIVALENT PROCEDURES INFORMATION [ETM 4.2] 402(a) Subsonic Jet Airplanes [ETM 4.2.1] Page 160 402
402(a)(1) Flight test procedures [ETM 4.2.1.1] The following methods have been used to provide equivalent results to the procedures for jet airplanes described in part 36.
402(a)(1)(A) Flig ht path intercepts [ETM 4.2.1.1.1] Flight path intercept procedures, in lieu of full takeoff and/or landing profiles described in A36.9.2.1 and A36.9.2.2 of part 36, have been used to meet the demonstration re quirements for noise certification. The intercept procedures have also been used in the implementation of the generalized flight test procedures described in 402(a)(1)(B). The use of intercepts eliminates the need for actual takeoffs and landings, with significant cost and operational advantages at high gross weight, and substantially reduces the test time required. Site selection problems are reduced, and the shorter test period provides a higher probability of stable meteor ological conditions during testing. Airplane wear and fuel consumption are reduced, while greater consistency and quality of noise data are obtained.
402(a)(1)(A)(i) For takeoff [ETM 4.2.1.1.1.1] Part a) of Figure 27 illustrates a typical takeoff profile. The airplane is initially stabilized in level flight at point A and continues to point B where takeoff power is selected an d a steady climb is initiated. The steady climb condition is achieved at point C, intercepting the reference takeoff flight path and continuing to the end of the noise certification takeoff flight path. Point D is the theoretical takeoff rotati on point used in establishing the reference flight path. If thrust (power) reduction is employed, point E is the point of application of thrust (power) reduction, and point F is the end of the noise certification takeoff flight path. The distance TN is the distance over which the position of the airplane is measured and synchronized with the noise measurement at point K.
402(a)(1)(A)(ii) For approach [ETM 4.2.1.1.1.2] The airplane usually follows the planned flight trajectory while maintaining a constant configuration and power until there is no influence on the noise levels within 10 dB of the PNLTM. The airplane then carries out a go-around rather than continuing the landing (see part b of Figure 27).
For the development of the NPD data for the approach case, the speed and approach angle constraints imposed by B36.3(c) and B36.7(c) of part 36 cannot be satisfied over the typical ranges of thrust (power) needed. For the approach case, a steady speed of VREF + 10 kt (VREF + 19 km/h) should be maintained to within ±5 kt (±9 km/h), and the height over the microphone should be 394 ± 100 ft (120 ± 30 m). Within these constraints the test approach angle at the test thrust (power) should be that resulting from the test aircra ft conditions (i.e., weight, configuration, speed and thrust (power)).
The flight profiles should be consistent with the test requirements of part 36 over a distance that corresponds at least to noise levels that are 10 dB below the PNLTM (i.e., throughout the 10 dB-down period) obtained at the measurement points during the demonstration.
a) Take-off intercept
b) Approach (break-off) Time Time Intercept flight path Normal Full power take-off C C E TD K N BA F F I 10 dB 10 dB 120 m Stabilized approach flight path Noise measuring point Normal touchdown Break-off path Break-off point beyond last 10 dB-down point PNLT PNLT Intercept point prior to10 dB-down point Figure 27. Flight path intercept procedures 402(a)(1)(B) Generalized flight test procedures [ETM 4.2.1.1.2] The following equivalent flight test procedures have been used for noise certification compliance demonstrations.
402(a)(1)(B)(i) For derivation of noise-power-distance (NPD) data [ETM 4.2.1.1.2.1] For a range of thrust (power) covering full takeoff and reduced thrust (power), the airplane is flown past lateral and under-flight-path microphones according to either the takeoff procedures defined in B36.7(b) of part 36 or, more typically, the equivalent flight path intercept procedures described above in 402(a)(1)(i) . Target test conditions are established for each sound meas urement. These target test conditions defi ne the flight procedure, the aerodynamic configuration to be selected, airplane weight, power, airspeed and the height at the closest point of approach to the measurement location. Regarding choice of target airspeeds and variation in test weights, the possible combinations of these test elements may affect the airplane angle-of-attack or airplane attitude and, therefore, possibly the airplane sound generation or propagation geometry.
The airplane angle-of-attack will remain approximately constant for all test weights if the tests are conducted at takeoff reference airspeed appropriate for each test weight. For example, if the appropriate takeoff reference airspeed for the Page 162
airplane is V2 + 15 kt, then by setting the target airspeed at the V 2 + 15 kt appropriate for each test weight, while the actual airspeed will vary according to each test weight, the airplane test angle-of-attack will remain approximately constant. Alternatively, for many airplanes the airplane attitude remains approximately at the attitude associated with the takeoff reference airspeed corresponding to the maximum takeoff weight. Review of these potential airplane sensitivities may dictate the choice of target airspeeds and/or test weights in the test plan in order to limit excessive changes in angle-of-attack or airplane attitude that could significantly change measured noise data. In the execution of each condition, the pilo t should “set up” the airplane in the approp riate condition in order to pass by the noise measurement location within the target height window, while maintaining target power and airspeed, within agreed tolerances, throughout the 10 dB-down period.
A sufficient number of noise measurements are made in order to establish noise-power curves at a given distance for both lateral and flyover cases These curves are extended, either by calculation or by the use of additional flight test data to cover a range of distances, to form the generalized noise database for use in the noise certification of the “flight datum” and derived versions of the airplane type and are often referred to as NPD plots (see Figure 28). If over any portion of the range for the NPD plot, the criteria for calculating the EPNL given in A36.9.1.2 of part 36 requires the use of the integrated procedure, then this procedure must be used for the whole NPD plot. The 90 percent confidence intervals about the mean lines are constructed through the data (see 305 of this AC).
Note.— The same techniques may be used to develop NPD plots that are appropriate for deriving approach noise levels by flying over an under-flight-path microphone for a range of approach powers, using the speed and airplane configuration given in B36.7(c) of part 36 or, more typically, the flight test procedures described in 402(a)(1)(i)(B).
EPNL at a given speed Minimum distance (m) OR FN amb F1 t2 Engine noise performance parameter ( ) Figure 28. Form of noise-power-distance (NPD) plot for jet-powered airplanes The availability of flight test data for use in data adjustment (e.g., speed and height) should be considered in test planning, Page 163
as such availability may limit the extent to which a derived version may be certificated without further flight testing, especially where the effects of airspeed on source noise levels become significant. The effects of high altitude test-site location on jet source noise levels should also be considered in test planning. High altitude test-site locations have been approved under conditions specified in 403(b)(3), provided that jet source noise adjustments are applied to the noise data.
The correction method described in 403(b)(3) has been approved for this purpose.
Flyover, lateral and approach noise measurements should be corrected to the reference speed and atmospheric conditions over a range of distances in accordance with the procedures described in Appendix A of part 36. NPD plots can then be constructed from the adju sted EPNL, power and distances. These plots present the EPNL values for a range of distance and engine noise performance parameters.
The parameters are usually the corrected low pressure rotor speed ሺ ேభ ሻ or the corrected net thrust ሺ ிಿ ఋೌ್ ሻ (see Figure √ఏమ
28), where:
— N1 is the actual low pressure rotor speed;
— ߠ௧ଶ is the ratio of the absolute static temperature of the air at the height of the airplane to the absolute temperature of the air for an ISA at mean sea level (i.e., 288.15 K);
— FN is the actual engine net thrust (power) per engine; and — δamb is the ratio of the absolute static pressure of the ambient air at the height of the airplane to ISA air pressure at mean sea level (i.e., 101.325 kPa).
Generalized NPD data may be used in the certification of the flight-tested ai rplane and derivative versions of the airplane type. For derived versions, these data may be used in conjunction with analytical procedures, static testing of the engine and nacelle, or additional limited flight tests to demonstrate compliance.
402(a)(1)(B)(ii) For flight test procedures for determination of changes in airplane certification noise levels [ETM 4.2.1.1.2.2] Noise level changes determined by comparison of flight test data for different configurations of an airplane type have been used to establish certification noise levels of newly derived versions by reference to the noise levels of the “flight datum” airplane. These noise level changes are added to or subtracted from the noise levels obtained from individual flights of the “flight datum” airplane. Confidence interval s of new data are statistically combined with the “flight datum” data to develop overall confidence intervals (see 305 of this AC).
402(a)(1)(C) De termination of the lateral certification noise levels [ETM 4.2.1.1.3] The lateral full-power reference noise m easurement point for jet-powered airplanes is defined as the point on a line parallel to and 1476 ft (450 m) from the runway center line, where the noise level is a maximum during takeoff.
Alternative procedures using two microph one stations located symmetrically on either side of the takeoff reference track have proven to be effective in terms of time and cost savings. Such an arrangement avoids many of the difficulties encountered when using multiple microphone arrays along the lateral lines. The procedure consists of flying the test airplane at full takeoff thrust (power) at several different specified heights above a track at right angles to and midway along the line joining the two microphone stations. When this procedure is used, matching data from both lateral microphones for each fly-past should be used for the lateral noise determination. Fly-pasts where data from only one microphone are available must be omitted from the determination. The following paragraphs describe this equivalent procedure for determining the lateral noise level for jet airplanes.
a) For airplanes being certificated under Append ix B, two microphone locations are typically used, Page 164
symmetrically placed on either side of, and 1476 ft (450 m) from, the airplane reference flight track.
b) Fly-pasts are performed at constant full takeoff power, configuration and airspeed as described in B36.7(b)(3) and B36.7(b)(4) of part 36.
c) The airplane should be flown along a track that intersects, at right angles, the line joining the two microphones. A number of flights should be performed such that the height of the airplane as it crosses this line typically covers a range between 200 ft and 2000 ft (approximately between 60 m and 600 m).
d) Adjustment of measured noise levels should be made to the acoustical reference day conditions and to reference airplane operating conditions as specified in A36.9 of part 36.
e) If the adjusted noise levels show a reasonable degree of symmetry between the left and right sides, as will generally be the case for jet airpla nes, the arithmetic average of the EPNL r values for the lateral microphone pair should be plotted against either the height of the airplane opposite the microphones or the average of the sound emission heights for PNLTM. A regression curve, which is typically second order, is plotted through the data points. The reported lateral EPNL at the reference condition needed for the purpose of demonstrating compliance with the applicable noise limit is the maximum value of the curve.
f) For airplanes for which the adjusted noise levels exhibit a marked degree of asymmetry, the EPNL r values for the left and right side should be plotted against either the height of the airplane opposite the microphone location or the height at the time of emission of PNLTM. Separate regression curves, which are typically second order, are plotted through the data points for the left and right sides. The reported lateral EPNL at the reference condition (EPNL r) needed for the purpose of demonstrating compliance with the applicable noise limit is the maximum value of the curve midway be tween the left and right curves.
g) It should also be established that the confidence interval associated with the reported lateral EPNL (i.e., the maximum “regression” value of EPNLr) is within the ±1.5 dB 90 percent confidence interval specified in A36.5.4 of part 36 (see 305(b)(2) of this AC).
Note.— Exceptionally, and in order to obtain a curve fr om which a maximum value can be clearly determined, either a third order regression curve or the removal from the analysis of some outlying data points might be permitted.
Applicants will be required to provide technical justification for the use of such exceptional procedures, which will be subject to the approval by FAA Certification lateral noise levels have also been determined by using multiple pairs of laterally opposed microphones rather than only one pair. In this case the microphones must be sufficiently spaced along the lateral line to ensure that the noise levels measured at each microphone are statistically independent. A sufficient number of data points, resulting from a minimum of six runs, must be obtained in order to adequately define the maximum lateral EPNL r value and provide an acceptable 90 percent confidence interval.
Lateral noise measurements for a range of conventionally configured airplanes with under-wing and/or rear-fuselage mounted engines having a bypass ratio of more than two have shown that the maximum lateral noise at full power normally occurs when the airplane is close to 984 ft (300 m) in height during the takeoff. Based on this finding, and subject to the approval by the FAA, the airplane may be flown on a minimum of six acceptable occasions such that it passes the microphone stations at a target height of 984 ft (300 m) while staying within +328 ft, –164 ft (+100 m, –50 m) of this target height.
402(a)(1)(D) Takeoff flyover noise levels with thrust (power) reduction [ETM 4.2.1.1.4] Page 165
Flyover noise levels with thrust (power) reduction may also be established without making measurements during takeoff with full thrust (power) followed by thrust (power) reduction (see 402(a)(2)(a) for details).
402(a)(1)(E) Me asurements at non-reference points [ETM 4.2.1.1.5] In some instances test measurement points may differ from the reference measurement points specified in B36.4 of part 36.Under these circumstances an ap plicant may request approval of data that have been adjusted from actual measurements in order to represent data that would have been measured at the reference noise measurement points at reference conditions. Reasons for requesting approval of such adjusted data may be:
a) to allow the use of a measurement lo cation that is closer to the airplane flight path so as to improve data quality by obtaining a greater ratio of signal to b ackground noise; whereas 306(e) of this AC describes a procedure for removing the effects of background noise, the use of data collected closer to the airplane avoids the interpolations and extrapolations inherent in the method;
b) to enable the use of an existing, approved noise certification database for an airplane type design in the certification of a derivative of that type, when the deri vative is to be certificated under reference conditions that differ from the original type certification reference conditions; and
c) to avoid obstructions near the noise measurement points, which could influence sound measurements; when a flight path intercept technique is being used, flyover and approach noise measurement points may be relocated as necessary to avoid undesirable obstructions; lateral noise measurement points may be relocated by distances which are of the same order of magnitude as the airplane lateral deviations or offsets relative to the nominal flight paths that occur during flight testing.
Approval has been granted to applicants for the use of data from non-reference noise measurement points provided that measured data are adjusted to reference conditions in accordance with the re quirements of A36.9 of part 36 and the magnitudes of the adjustments do not exceed the limitations cited in B36.8(d) of part 36.
402(a)(1)(F) Atmospheric test conditions [ETM 4.2.1.1.6] The FAA has found it acceptable to exceed the sound attenuation coefficient limits of A36.2.2.2(c) of part 36 in cases when:
a) the dew point and dry bulb temper ature are measured with a device which is accurate to ±0.5°C and are used to obtain relative humidity, and when “layered ” sections of the atmosphere are used to compute sound attenuation coefficients in each one-third octave band in co mpliance with the provisions of A36.2.2.3 of part 36, or
b) the peak noy values at the time of PNLT, after ad justment to reference conditions, occur at frequencies of less than or equal to 400 Hz.
402(a)(1)(G) Layering equivalency [ETM 4.2.1.1.7] A36.2.2.3 of part 36 defines the procedure for layering the atmosphere and determining the sound attenuation coefficients to be used in the adjustment of aircraft noise levels. The procedure requires that the atmosphere from the ground to at least the height of the airplane must be divided into layers of 100 ft (30 m) depth. Subject to the approval by FAA, the applicant may use layers of more or less, and not necessarily equal, depth. The applicant should demonstrate that the layering procedure being proposed is equivalent to the procedure defined in part 36.
402(a)(2) Analytical procedures [ETM 4.2.1.2] Analytical equivalent procedures rely upon available noise and performance data obtained from flight tests for the airplane type. Generalized relationships between noise, power and distance (see 402(a)(1)(B)(i) for derivation of NPD plots) and adjustment procedures for speed changes in accordance with the methods of Appendix A of part 36 are combined with certificated airplane aerodynamic performance data to determine noise level changes resulting from type design changes. These noise level increments are then applied to noise levels in accordance with 402(a)(1)(ii).
402(a)(2)(A) Flyover noise levels with thrust (power) reduction [ETM 4.2.1.2.1] Flyover noise levels with thrust (power) reduction may be established from the merging of PNLT versus time measurements obtained during constant power operations. As illustrated in Figure 29, the 10 dB-down PNLT noise time history recorded at the flyover point may contain portions of both full thrust (power) and reduced thrust (power) noise time-histories. As long as these noise time-hist ories, the average engine spool-down thrust (power) characteristics, and the airplane flight path during this period (see Figure 30), which includes the transition from full to reduced thrust (power), are known, the flyover noise level may be computed.
Point of power cutback Spool-down Flyover noise time-history with power cutback 10 dB B alone Fullpower A alone Time PNLT Noise time-history Figure 29. Computation of cutback takeoff noise level from constant power tests Page 167
Noise measuring point Engine spool-down period Cutback power flight path Point of power cutback Full take-off power flight path Flight path over flyover measuring point with power cutback Figure 30. Computation of reduced thrust ta keoff noise level from constant thrust tests Where the full thrust (power) portion of the noise time history does not intrude upon the 10 dB-down time history of the reduced thrust (power), the flyover noise levels may be computed from a knowledge of the NPD characteristics and the effect of the average spool-down thrust (power) characteristics on the airplane flight path.
Note 1.— The selection of the height of an airplane within the reference flight path for initiation of thrust (power) reduction should take into account both the “average engine” spool-down time and a 1.0-second delay for flight crew recognition and response prior to movement of the throttles to the reduced thrust (power) position.
Note 2.— To ensure that the full thrust (power) portion of the noise-time history does not intrude upon the 10 dB- ܶܮܰܲܯܶܮܰܲ down noise levels, ܾ݇ܿܽݐݑܿݎ݁ݐ݂ܽ െ ݁ݎ݂ܾ݁ ܾ݇ܿܽ݁ݐݑܿ 10.5ܤ݀ .
402(a)(2)(B) Equivalent procedures based upon analytical methods [ETM 4.2.1.2.2] Noise certification approval has been given for applications based on type design changes that result in predictable noise level differences, including the following:
a) changes to the originally certificat ed takeoff or landing weight, which in turn lead to changes in the distance between the airplane and the microphone and/or reduced thrust (power) for the takeoff case, and changes to the approach power; in this case the NPD data may be used to determine the certification noise level of the derived version;
b) noise changes due to engine power changes; however, care should be taken to ensure that when NPD plots are extrapolated, the relative contri bution of the component noise sources to the EPNL remains essentially unchanged and a simple extrapolation of the NPD curves can be made; among the items which should be considered in extending the NPD are:
1) the 90 percent confid ence interval at the extended thrust (power);
2) airplane /engine source no ise characteristics and behavior;
3) engine cycle changes; and Page 168