Appendix 2 A2-2 experience has indicated the desirability of obtaining at least 150 hours on a production configured airplane. For a previously certificated airplane, the F & R program requirement should be commensurate with the modifications or changes.
(2) When supplementary experience is not taken into account, and the airplane is conventional with regard to complexity and design features and does not incorporate engines that have not been previously certificated (including derivative engines), it has been found that function and reliability tests can be performed within 300 hours. This time may be reduced if credit is granted for certain types of component testing (see paragraph 2e(2) of this Appendix) and for supplementary experience (see paragraph 2a(3)(c) of this Appendix). However, it may be necessary to increase the 150-hour minimum F & R test requirement of § 21.35(f)(2) if difficulties are encountered or for unusual cases of complexity.
(3) When satisfactory supplementary experience is available and taken into account the following allowances should be used as a guide and applied with judgment in reducing the official flight test time. However, in any case, the official F & R test program should provide sufficient time to accomplish the objective of paragraph 1a(2) in accordance with the procedures described in paragraphs 2e(3) and (4).
(a) For Intensive Experience . When the allowance is based on the total time of any one airplane in airline crew training and similar intensive operations, two hours of such operation may be considered equivalent to one hour of official testing.
(b) For Miscellaneous Experience . When the allowance is based on the total time of any one airplane, five hours of such experience may be considered equivalent to one hour of official testing.
(c) Reduction for Supplementary Experience . Whenever a reduction of official test time is desired on the basis of supplementary experience, such experience should be adequately recorded and submitted to the responsible FAA aircraft certification office as described in paragraph 2f(2) of this Appendix.
b. Test Airplane . To facilitate completion of the type certification procedure, one airplane, in production configuration or equivalent, should be used for the official functional and reliability tests while another airplane (or airplanes) is used for the routine-type tests. In this case, the test time on at least one airplane would be sufficient to accomplish the objective of paragraph 1a(2) of this appendix.
c. Modified Types . The procedure outlined in paragraph d., below, applies to new type designs. When a design employs components (parts) identical to those used in previous designs, credit may be given for the supplementary experience available for such components. When a design is modified (e.g., several versions of the same basic type with different engines, propellers, etc.), the modified features and components should be rechecked in accordance with paragraph 2e(6), below.
Appendix 2 A2-3
d. Test Program . The project engineers of the responsible FAA ACO will propose guidelines for developing an F & R test program at the preflight type board meeting (prior to commencement of FAA certification flight tests) and coordinate this with the airplane manufacturer. Near the conclusion of the type certification tests, the FAA certification engineers will again meet with the manufacturer to review the experience gained in those tests, review changes made in the design, consider any additional supplementary experience, and revise the proposed F & R test program accordingly. In application, there is generally considerable overlap of the certification and F & R test programs, thus making a definite transition point indiscernible.
e. Planning and Execution of Test Program . The following points should be considered:
(1) The test program should be sufficiently well planned to enable its execution in an efficient manner without overlooking important items. Documentation should focus on the test objective(s) but does not necessarily require the type of detail maintained for type certification testing. The FAA project engineers will review the design features and equipment (appliances) with respect to the general objective and prepare a list showing:
(a) Components and systems to be checked in accordance with the procedures described in the below paragraph 2e(4).
(b) A brief description of the operations to be performed, where these are not obvious (referencing any necessary operating instructions).
(c) Special checks or likely critical conditions.
(d) Estimated flight time required.
(2) Allowance may be made for those functional tests whose requirements are covered by part 25 type certification tests. Allowance may also be made for qualification-type testing of new features and equipment; however, the flight test program should be planned to determine the adequacy of these tests and the accuracy of the simulated operating environment (e.g., to determine whether the actual environmental conditions such as temperature variation, etc., are covered by the test simulations) when these may be critical, and to determine whether the installation and connected systems are satisfactory. This does not imply that flight tests must be conducted under the most severe outside air temperatures likely to be encountered in service. It should normally be possible to determine the effects of extreme outside temperatures on local temperatures by extrapolation or by suitable correction factors. The FAA project engineers will then make a consolidated estimate of the total flight time required, allowing for overlapping, and adjust this in accordance with the “Test Time” outlined in the above paragraph 2a.
(3) This program will be arranged to permit the principal FAA flight test pilot to become thoroughly familiar with the operational aspects of the airplane in its anticipated service environment.
(4) All components of the airplane should be intensively operated and studied under all operating conditions expected in service and obtainable within the time and geographical
Appendix 2 A2-4 limitations of the tests. Intensive operation means repeated operation of components in various sequences and combinations likely to occur in service. Particular attention should be given to potential sources of crew error, excessive crew workload or coordination, and the procedures that would be required in the event of malfunction of any component. The testing should also include an evaluation of operations with various MEL items declared/simulated inoperative.
This intensive type of testing should be conducted in all cases, but the length of time for which it is continued will depend upon the supplementary experience available for the particular type, as outlined in the above paragraph 2a, “Test Time.”
(5) Ground inspections should be made at appropriate intervals during the test program to determine whether there are any failures or incipient failures in any of the components that might be a hazard to safe flight. The normal maintenance procedures should be employed during the F&R Program and carefully documented for review.
(6) When design changes are made during the course of the test, or when the official test airplane differs from those on which supplementary experience is obtained, the modified items will be rechecked in accordance with the above procedures. Every effort should be made to include such items in the program in such a way as to avoid unduly extending the overall test time. To this end, the Administrator may accept, in lieu of additional flight tests:
(i) Special tests of the original and revised components in which the conditions causing failure are intensified.
(ii) Ground qualification tests of differi ng components when the test methods have been validated as being representative of actual flight conditions.
f. Reports and Records .
(1) A log should be kept of all flights, and accurate and complete records kept of the inspections made of all defects, difficulties, and unusual characteristics and sources of crew error discovered during the tests, and of the recommendations made and action(s) taken. Items for which design changes may be required will be reported to the manufacturer and the appropriate FAA ACO.
(2) If supplementary experience is to be taken into account, similar records of such experience should be kept and submitted to the responsible FAA ACO, together with a list of the differences between the airplane on which the experience was obtained and the official test airplane. When supplementary experience is obtained on a large fleet of airplanes (for example, military operations) of the same or a comparable type (see the above paragraph 2e(6)), these records may consist of statistical summaries in lieu of complete records for each individual airplane.
(3) At the conclusion of the official tests, a summary report should be prepared by the participating pilots, engineering specialists, and manufacturing inspectors and made a part of the type inspection report.
Appendix 3 A3-1
Appendix 3
Correction of Air Minimum Control Speed To Standard Conditions
The following analysis presents three methods of correcting a flight test derived value of air minimum control speed to standard conditions. These methods are applicable only to rudder deflection limited VMCA, for either jet or propeller driven airplanes. The effect of banking into the operating engine is accounted for, and the method will work with either fixed pitch or constant speed propellers, including the effects of windmilling drag. For rudder pedal force limited VMCA, see Appendix 7.
1. Theoretical Basis
a. Given the static lateral/directional equations of motion for straight line, unaccelerated flight:
Fy Cy ay aC Cyrr = CL · sin
Mx Cl Claa Clrr
Mz Cn Cnaa Cnrr Cna
where:
CL = 2952WVSe Cna = 2952 FlVS bna ee
W = weight - lbs
V e = equivalent airspeed - kts
S = wing area - ft 2
F na = asymmetric net thrust - lbs
F na = (Fn + Dw) for engine inoperative
F na = (Fn + Fi) for engine at idle
F n = net thrust of the operating engine - lbs
F i = idle engine net thrust - lbs
Appendix 3 A3-2 D w = windmill drag - lbs
l e = distance from aircraft center line to engine thrust line - ft
b = wingspan - ft
2. Constant C n Method
a. For the case where full rudder deflection is achieved, r is a constant, and the system of equations can be resolved to an identity which shows that Cna is a linear function of CL sin .
Cna = A·CL sin + B (4)
b. If it is assumed that test and standard day V MCA occur at the same angle-of-attack and bank angle, the asymmetric yawing moment coefficient will be constant, and VMCA can be corrected to standard conditions by the relationship:
VMCAs = VMCAt · F F na na s t for Turbojets
VMCAs = VMCAt · THPTHPsstt 1 3 for Propeller driven
where:
THP s = Maximum AFM scheduled Brake/Shaft horsepower multiplied by standard day propeller efficiency.
THP t = Test day brake/shaft horsepower where VMCA was achieved multiplied by test day propeller efficiency.
s = Atmospheric density ratio at standard conditions.
t = Atmospheric density ratio at test conditions.
c. Windmilling shaft horsepower is not considered, because the current part 25 takeoff requirements for propeller driven airplanes result in such large performance penalties with a windmilling propeller that all part 25 turboprops to date have had autofeather installed.
d. Since both net thrust and shaft horsepower vary with speed, use of these equations will require an iterative solution. Because this constant Cn method does not consider the effect on
Appendix 3 A3-3 VMCA due to variations in bank angle, weight, sideslip angle, or adverse yaw, its use is limited to corrections of 5% or less in asymmetric net thrust or power.
e. For corrections beyond 5%, the relationship shown in equation (4) should be used, and enough flight test data should be obtained to define the correlation between Cna and CLsin.
3. Graphical Method
a. In theory these data could be obtained by varying any combination of asymmetric thrust, airspeed, weight, and bank angle that would provide a representative variable set.
However, since VMCA and stall speed are nearly coincident for most airplanes, there are some severe constraints on most of the variables. Typically, any reduction in maximum asymmetric thrust will cause VMCA to decrease below stall speed, and any increase in weight will cause stall speed to increase above VMCA; therefore, the only parameter that can reasonably be varied is bank angle.
b. To maximize the spread between stall and minimum control speed, V MCA tests are normally done at the lightest possible weight, at the maximum allowable asymmetric thrust (even with a short duration overboost, if the engine manufacturer will agree). At typical test altitudes (2000-3000 feet) and prototype gross weights, it will usually still not be possible to define VMCA with the full 5° bank, because of stall buffet.
c. To obtain the data necessary for extrapolation to the 5° bank limit, and to maximum asymmetric thrust, testing at three bank angles is required for the definition of the Cna vs CL sin relationship. These data should be obtained by shutting down the critical engine (normally the left), setting maximum allowable thrust on the operative engine, and slowing down while maintaining constant heading until full rudder deflection is achieved. The first point, a wings level condition, is easy to set up, and results in a speed well above stall buffet. A second point, at zero sideslip, will be achieved at approximately 2° - 3° bank (flown with a yaw string, or instrumented sideslip vane) and will provide an intermediate speed, still above buffet. The third data point is flown with as much bank angle that can be used without excessive buffeting (no more than would be accepted as the minimum level of stall warning). If necessary, an additional point can be obtained by banking 2° - 3° into the inoperative engine.
d. To use this method, instrumentation is necessary for the determination of net thrust/shaft horsepower, and an accurate calibrated airspeed system is required, as well as engine/propeller charts for windmill drag, charts for propeller efficiency, and the ability to measure bank angle to at least a tenth of a degree.
Appendix 3 A3-4
e. Data obtained using this method with a typical business jet and a large jet transport are shown in the following two graphs:
2-ENGINE BUSINESS JET 0
0.01
0.02
0.03
0.04
0.05
0.06 -0.04 0 0.04 0.08 0.12 0.16 CLsin C K=0.20
4-ENGINE TRANSPORT 0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08 0 0.05 0.1 0.15 0.2 CLsin C K=0.14
Appendix 3 A3-5
f. These plots represent the capability of the airframe to produce yawing moment by a combination of rudder deflection (full, in this case), and the sideslip which results from the bank angle. In order to determine the limiting condition for VMCA, it is necessary to know what the applied yawing moment is (due to the engine-out moments), and to plot the applied moments on the same plot, in a similar form. It is possible to do this by choosing a gross weight to be used to calculate CL, and since standard bank angle will be 5°, the only remaining variable in CLsin is Ve. By choosing the appropriate values of Fn available versus Ve, a plot of Cna versus CLsin can be made which represents the applied yawing moments. If the weight chosen represents some standard minimum weight, and the available net thrust values represent the maximum allowable thrust scheduled in the AFM, the intersection point of the airframe curve and the engine curve will be the desired standard day values which can be used to calculate VMCA.
g. As an example, the following values of net thrust plus windmill drag have been extracted from a typical corporate jet engine spec. The data represent a maximum thrust engine, and have been corrected for ram drag and minimum accessory bleed and electrical load. The CLsin values are based on a gross weight of 9000 lbs.
Ve Fna Cna CLsin 70 2,846 0.079 0.204 90 2,798 0.047 0.123 110 2,764 0.031 0.082 130 2,737 0.022 0.059 150 2,710 0.016 0.044
Plotting both the airframe and engine yawing moment curves on the same graph looks like:
Airframe .048 Engine .124 0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09 0 0.05 0.1 0.15 0.2 0.25 CLsin Cna
h. The intersection of the airframe and the engine curve shows values of:
Appendix 3 A3-6 C na = 0.048 C Lsin = 0.124
i. Since the engine C n curve was based on W = 9000 lbs, the standard day value of VMCA can be determined from:
C Lsin= 0.124 = 295 WVSe2
0.12490000.1108V2e
V MCA = 89.7 KEAS
j. If the airframe data is obtained from flight test, there are no assumptions or simplifications, and the value of VMCA derived from this method includes all the effects of bank angle, sideslip, adverse yaw, angle-of-attack, etc. Also, since the standard day value of Cna will always be less than the test value, no extrapolation is required, and there is no restriction on the value of standard day thrust that may be used.
Appendix 3 A3-7
4. Equation Method
a. A single test day value of V MCA can also be corrected to standard conditions (using all the appropriate variables) without using this graphical method, provided either the slope of the Cna vs CLsin relationship is known (from wind tunnel, or analytical estimates), or one is willing to use a default (conservative) value. Thrust extrapolation using slope values not based on flight test is limited to 10% of the test day thrust. The following analysis shows the derivation of this single-point correction equation:
b. If the test day engine C na curve was added to the previous plot, it would be possible to see how far, and in what direction, the correction from test to standard day was made. Assuming that a single value of VMCA was determined at 3000 feet at a weight of 9000 lbs, a test day engine Cna curve could be plotted using the same technique used for the standard day curve, except substituting the 3000 ft thrust values from the engine spec:
Ve Fna Cna CLsin 70 2,634 0.073 0.204 90 2,589 0.043 0.123 110 2,554 0.029 0.082 130 2,528 0.02 0.059 150 2,510 0.015 0.044
c. The following C na vs CLsin plot shows the airframe curve, the standard day engine curve, and the test day curve:
Airframe .048 .052 Standard Day Engine Test Day Engine .124 .147
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09 0 0.05 0.1 0.15 0.2 0.25 CLsin Cna
From the airframe/engine curve intersections:
Appendix 3 A3-8
C nt = 0.052 C ns = 0.048
C Lsint = 0.147 C Lsins = 0.124
VMCAt = 82.4 kts VMCAs = 89.7 kts
d. This is a thrust correction of approximately 8%. If the constant C n method had been used, the test value of .052 would have applied, and the corresponding VMCAt would have been
85.7 kts, an error of 4 knots (5%) in the non-conservative direction.
e. Noting that the correction from test day to standard day is along the C n vs CLsin curve, which is a straight line, and denoting the slope of the airframe curve as K the intersection of the standard day thrust line with the airframe curve as Cns and CLsins, and the intersection of the test day thrust line with the airframe curve as Cnt and CLsint, the following equation can be derived:
Given the point-slope form of a straight line,
Y 2 - Y1 = m(X2 - X1)
Correspondingly,
C ns - Cnt = K (CLsins - CLsint )
C ns - K CLsins = Cnt - K CLsint
Fl qS b na e s s - K Ws i nqSsss FlqS bna et t K Ws i nqSttt
Substituting q = V295e2 and then multiplying through by VS295e2S
Fnas lbe - KWs sins = VVe 2 e 2 s t F lb KW s i nnat e tt
Appendix 3 A3-9
and finally,
VMCAs = VMCAt F lb KW s i n F lb KW s i n na e ss na e tt s t 1 2 for Turbojets
VMCAs = VMCAt 326 SHPV lb KW s i n 326 SHPV lb KW s i n SS S MCA e ss tt t MCAt e tt s 1 2 for Turboprops
In the simplified form of the lateral directional equations, K is CCny which is the directional static margin. The value of K typically varies from approximately 0.14 to 0.19, depending on the lateral/directional characteristics of the airplane being tested. As with the graphical method, if K is determined by flight test, thrust corrections to VMCA are based on an interpolation of flight test defined airframe capability, and there is no limit on the amount of the thrust correction to VMCA. A somewhat conservative default value of 0.20 for K may be used if flight test data is not available; however, in this case, any thrust extrapolation is limited to 10% of the test day thrust. To assure that corrections for bank angle and weight do not result in standard day VMCA values at or below stall speed, the corrections made by either the graphical or equation method should not result in a VMCA which is based on a CLsin that is greater than CLMAX sin5.