xiii Table of Contents (continued)
Appendices (continued) Appendix Page No.
Appendix 6 _______________________________________________________________ A6-1 Correction Of Air Minimum Control Speed To Standard Conditions ____________ A6-1 Theoretical Basis _______________________________________________________ A6-1 Constant Cn Method ____________________________________________________ A6-2 Graphical Method ______________________________________________________ A6-3 Equation Method _______________________________________________________ A6-6 Appendix 7 _______________________________________________________________ A7-1 Rudder Pedal Force-Limited Air Minimum Control Speed _____________________ A7-1
1 Introduction
1. Purpose.
a. This AC provides updated guidance for the flight test evaluation of transport category airplanes. These guidelines provide an acceptable means of demonstrating compliance with the pertinent regulations of Title 14, Code of Federal Regulations (14 CFR) part 25. The methods and procedures described herein have evolved through many years of flight testing of transport category airplanes and, as such, represent current certification practice. This AC is not mandatory and does not constitute a regulation. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulation(s). The FAA will consider other methods of demonstrating compliance that an applicant may elect to present. If we become aware of circumstances that convince us that following this AC would not result in compliance with the applicable regulations, we will not be bound by the terms of this AC, and we may require additional substantiation or design changes as a basis for finding compliance. This material does not change, create any additional, authorize changes in, or permit deviations from existing regulatory requirements.
b. See Appendix 1 for a list of acronyms and abbreviations used in this AC.
2. Applicability.
These methods and procedures are provided in the interest of certification approval for use during all transport category airplane flight test certification activities. This material is not to be construed as regulatory or having a mandatory effect. The procedures set forth herein are one acceptable means of compliance with applicable sections of part 25. Any alternative means proposed by the applicant should be given due consideration. Applicants are encouraged to use their technical ingenuity and resourcefulness in order to develop more efficient and less costly methods of complying with the requirements of part 25. Since these methods and procedures are only one acceptable means of compliance, individuals should be guided by the intent of the methods provided in this AC. As deviations from the methods and procedures described in this AC may occur, FAA certification personnel will coordinate what they consider to be major deviations with the Transport Standards Staff (ANM-110) of the Transport Airplane Directorate.
If in their judgment, however, a deviation is considered to be minor, coordination with ANM- 110 may not be necessary.
3. Cancellation.
AC 25-7B, Change 1, “Flight Test Guide for Certification of Transport Category Airplanes,” dated December 7, 2011, is cancelled.
4. Background.
a. Since AC 25-7 was released on April 9, 1986, it has been the primary source of guidance for flight test methods and procedures to show compliance with the regulations contained in subpart B of part 25, which address airplane performance and handling
2 characteristics. AC 25-7 has been revised several times to reflect changes in the part 25 regulatory requirements, changes in guidance and policy, and advances in technology.
b. The first revision, AC 25-7A, updated the original AC to incorporate the policy and guidance material applicable to all sections of part 25, not just subpart B. The material related to regulations outside of subpart B superseded that contained in Order 8110.8, which was cancelled when AC 25-7A was issued.
c. Change 1 to AC 25-7A added acceptable means of compliance for the regulatory changes associated with amendments 92 and 98 to part 25.
d. AC 25-7B added acceptable means of compliance for the regulatory changes associated with amendments 108, 109, and 115 to part 25, and revised guidance for expanding takeoff and landing data for airport elevations higher than those at which flight testing was conducted.
Means of compliance associated with flight in icing conditions were removed as this material is now contained in AC 25-25.
e. Change 1 to AC 25-7B added acceptable means of compliance for the regulatory changes associated with amendment 25-135.
f. This revision, AC 25-7C, is a complete revision to reduce the number of differences from the European Aviation Safety Agency’s Flight Test Guide, provide acceptable means of compliance for the regulatory changes associated with amendments 107, 109, 113, 115, 119 and 123 to part 25, to respond to FAA and National Transportation Safety Board safety recommendations, and to provide a general update to reflect current FAA and industry practices and policies.
5. Related Publications.
Certification personnel should be familiar with FAA Order 8110.4C, “Type Certification,” and FAA Order 8100.5A, “Aircraft Certification Service Mission, Responsibilities, Relationships, and Programs.” In this AC, reference is made to other FAA ACs that provide guidance on various aspects of type certification and supplemental type certification.
3 Chapter 1 - General
1. Applicability - § 25.1. [Reserved]
2. Special Retroactive Requirements - § 25.2. [Reserved]
Chapter 2 - Flight
Section 1. General
3. Proof of Compliance - § 25.21.
a. Explanation. In an effort to provide the necessary guidelines for the flight test evaluation of transport category airplanes, without producing a cumbersome document, this AC assumes a conventional transport airplane configuration. In general, a conventional airplane configuration is one with distinct wing and fuselage elements that are joined together, aftmounted horizontal and vertical stabilizers that are attached to the fuselage, and propulsion provided either by turbojet/turbofan engines that do not provide any significant increase in lift due to their operation or engine-driven propellers. The effects of non-conventional airplane configurations (e.g., blown flaps) on the compliance methods should be evaluated and determined based on the intent of the guidelines presented for conventional airplane configurations.
(1) Section 25.21(a) - Proof of Compliance.
(a) The burden of showing compliance with the flight requirements for an airworthiness certificate or a type certificate rests with the applicant. The applicant should, at his own expense and risk, conduct such official flight tests as required by the FAA to demonstrate compliance with the applicable requirements. During the certification process, the applicant should make available the airplane, as well as all of the personnel and equipment necessary to obtain and process the required data.
(b) If the airplane flight characteristics or the required flight data are affected by weight and/or center of gravity (c.g.), the compliance data must be presented for the most critical weight and c.g. position per § 25.21(a). Unless the applicant shows that the allowable c.g. travel in one or more axes (e.g., lateral fuel imbalance) has a negligible effect on compliance with the airworthiness requirements, the applicant must substantiate compliance at the critical c.g.
(c) The gross weight and c.g. tolerances specified in paragraphs 3a(3)(b)1 and 3 are test tolerances and are not intended to allow compliance to be shown at less than critical conditions.
(d) Section 21.35(a)(3) requires that the test airplane be in conformity with its type design specifications.
1 This means that the test airplane must be in conformity with its type design specification as relates to the particular test being conducted.
2 Any deviation from conformity must be clearly shown to be of no consequence to the particular test being conducted. For example, if the slip resistant escape surface required by § 25.810(c) is not installed when conducting airplane performance and flight
5 characteristics tests, the applicant must show that its presence would have no effect on measured airplane performance and flight characteristics.
(e) Section 21.35(b)(2) requires the applicant to conduct sufficient flight testing the FAA finds necessary to determine whether there is reasonable assurance that the airplane, its components, and its equipment are reliable and function properly. Appendix 2 to this AC provides guidance for showing compliance with this requirement.
(f) Acceptable use of simulation in lieu of flight testing. It is difficult to establish guidance for using simulation in lieu of flight testing that applies in all situations. However, the following general principles can be used as guidance for determining the acceptability for using simulation in lieu of flight testing:
1 In general, flight test demonstrations are the preferred method to show compliance.
2 Simulation may be an acceptable alternative to flight demonstrations in certain situations, such as the following:
(aa) A flight demonstration would be too risky even after attempts are taken to mitigate these risks (e.g., by mock takeoffs/landings in the air at a safe altitude);
(bb) The required environmental or airplane conditions are too difficult to attain, such as in the examples listed below:
(i) validation of system safety analyses failure cases involving high crosswinds,
(ii) development of crosswind guidance for slippery runway operations; and
(iii) conditions involving minimum allowable weight where the minimum allowable weight cannot be achieved because of the weight of required test equipment.
In this case, simulation data can be used to supplement flight test data obtained at the minimum practicable test weight.
(cc) The simulation is used to augment a reasonably broad flight test program; or
(dd) The simulation is used to demonstrate repeatability, or to demonstrate performance of a specific scenario for a range of pilots.
3 Simulation Criteria. If it is agreed that a simulation will be used to establish compliance, to be acceptable for use in showing compliance with the performance and handling qualities requirements, the simulation should:
(aa) Be of a type and fidelity that is appropriate for the task. For example, is motion or an exterior view needed, or is the fidelity or customizability of an engineering simulator needed?
(bb) Be suitably validated by flight test data for the conditions of interest.
(i) This does not mean that there must be flight test data at the exact conditions of interest. The reason simulation is being used may be that it is too difficult or risky to obtain flight test data at the conditions of interest.
(ii) The level of substantiation of the simulator to flight correlation should be commensurate with the level of compliance (i.e., the closer the case is to being noncompliant, the higher the required fidelity of the simulation).
(cc) Be conducted in a manner appropriate to the case and conditions of interest.
(i) If closed-loop responses are important, the simulation should be piloted by a human pilot.
(ii) For piloted simulations, the controls/displays and cues should be substantially equivalent to what would be available in the real airplane (unless it is determined that not doing so would provide added conservatism).
(2) Section 25.21(c) - Proof of Compliance (Altitude Effect on Flight Characteristics).
(a) Any of the flying qualities affected by altitude, including controllability, stability, trim, and stall characteristics, must be investigated at the most adverse altitude conditions approved for operations.
(b) Consideration should be given in the test program to any aerodynamic control system changes that occur with changes in altitude (e.g., maximum control surface displacement or auto slats that may be inhibited by Mach number above a specific altitude).
(3) Section 25.21(d) - Proof of Compliance (Flight Test Tolerances).
(a) To allow for variations from precise test values, acceptable tolerances during flight testing must be maintained. The purpose of these tolerances is to allow for small variations in flight test values of certain variables from the targeted value. They are not intended for compliance tests to be planned for other than the critical condition, nor are they to be considered as an allowable measurement error.
(b) Where variation in the parameter for which a tolerance is allowed will have an effect on the results of the test, the results should be corrected to the most critical value of that parameter within the approved operating envelope. If such a correction is impossible or
7 impractical, the average test conditions should assure that the measured characteristics represent the actual critical value.
1 Weight limits. Figure 3-1, below, presents weight tolerances that have been found acceptable for the specified flight tests. Many flight tests need to be conducted at or very near the maximum operating weight for the airplane configuration, particularly those tests used to establish airplane flight manual (AFM) performance information. As noted in paragraph
(a) above, the purpose of the test tolerances is to allow for variations in flight test values, not to routinely schedule tests at less than critical weight conditions or to allow for compliance to be shown at less than the critical weight condition. In addition, the tolerances can be used to help determine when to interrupt a series of test conditions in order to refuel the airplane if necessary to remain within the acceptable weight tolerance.
Figure 3-1. Weight Tolerance Limits
Flight Test Conditions Weight Tolerance Limit ±5% ±10% Stall Speeds X Stall Characteristics X All Other Flight Characteristics X Climb Performance X Takeoff Flight Paths X Landing Braking Distance X Landing Air Distance X Takeoff Distance & Speed X Accelerate-Stop Distance X Maximum Energy RTOs X Minimum Unstick Speed X Minimum Control Speed X
NOTE: A -5 percent tolerance limit means that the weight for the particular test may be up to 5 percent less than the test target value. A +5 percent tolerance limit means that the weight for the particular test may be up to 5 percent higher than the test target value.
(aa) It can be difficult or impossible to conduct testing at the airplane’s minimum allowable weight with an airplane configured for conducting a flight test program. If the minimum weight cannot be obtained (within the specified tolerance limit) and compliance at the minimum weight cannot be clearly deduced from the results at the tested weight, the testing
8 should be conducted on a production airplane (or other airplane on which the minimum weight can be obtained). If the instrumentation or equipment needed to conduct safe testing cannot be installed on the production airplane configuration, or the weight of such instrumentation still prevents the minimum weight from being obtained, consider the use of simulation to extend the results obtained at the minimum practical test weight. (See paragraph 3a(1)(f).)
(bb) For follow-on airplane certification programs involving an increase in the maximum allowable gross weight, the test weight limits of Figure 3-1 have been applied as extrapolation limits on the original test data in order to minimize additional testing. For the test weight tolerance limits to be applied in this manner, the original test data must be from an existing certificated database for an aerodynamically similar model of the same airplane type.
The tolerance limit should be applied to the maximum weight at which the original testing was conducted, not to the maximum certified weight.
(cc) Equivalent weight extrapolation limits. For follow-on airplane certification programs where it is desired to increase a maximum operating weight based on existing certified performance parameters that have weight as one of their independent terms, those parameters should be examined for equivalent compliance with the weight tolerance limits of Figure 3-1. An example would be the reduction of an airplane’s landing flap position, to one approved on a similar model of the same airplane type, which would incur an increase in landing speeds and brake energy, relative to the original certificated landing flap, at any given weight.
The brake energy, at the maximum certificated landing weight, should be calculated for the reduced landing flap. This brake energy should account for the increased landing speeds and reduced aerodynamic drag associated with the reduced flap setting. It should then be determined what equivalent gross weight would have rendered that brake energy with the original landing flap. (See Figure 3-2 for an example of how this can be done.) If the resulting equivalent gross weight does not exceed the certificated maximum landing weight by more than the five percent weight extrapolation limit specified in Figure 3-1, the reduced flap certification may be eligible for a reduced flight test program (e.g., limited to stall speed verification, handling characteristics, and a qualitative landing demonstration). Further limitations may be imposed by the criteria of technical standard order (TSO) C135a (“Transport Airplane Wheels and Wheel and Brake Assemblies,” dated July 1, 2009).
9 Figure 3-2. Equivalent Weight Extrapolation
∆ G.W. Not greater than 5% Gross Weight - Pounds ∆ KE Max. Landing Wt.
“Equivalent” Gross Wt.
Flap Brake Energy Ori ginal Reduced Flap
2 Wind Limits. A wind velocity limit of 10 knots (from any direction) or
0.11 VSR1 (whichever is lower) is considered the maximum acceptable for obtaining valid takeoff and landing flight test data. Takeoff and landing performance data obtained under runway wind conditions greater than 5 knots may be inconsistent and unreliable because winds of that magnitude are likely to be unsteady. However, performance data obtained with winds between 5 and 10 knots should not necessarily be discarded. Their validity should be checked against data obtained in conditions with lesser winds. Wind velocity should be measured at the height of the wing mean aerodynamic chord (MAC), as determined with the airplane in a static ground attitude. When measuring test wind velocity at the wing MAC height, a height of six feet above the ground should be considered as a minimum measurement height to avoid possible measurement inaccuracies due to surface interference.
3 C.G. Limits. A test tolerance of +7 percent of the total c.g. range is intended to allow for inflight c.g. movement. This tolerance is only acceptable when the test data scatter is on both sides of the limiting c.g. or when adjusting the data from the test c.g. to the limit c.g. is acceptable. If compliance with a requirement is marginal at a test condition that is inside of the c.g. limits, the test should be repeated at the c.g. limits.
4 Airspeed Limits. Normally, tests conducted within 3 percent or 3 knots (whichever is the higher) of the desired test speed are considered acceptable.
5 Thrust/Power Limits. Thrust critical tests, such as minimum control speeds, should be conducted at the highest thrust (or power) allowable on the engine given the constraints of temperature and altitude. It is then permitted to calculate further corrections to allow extrapolation of data to cover the entire operating envelope. These thrust (or power) corrections should be limited to 5 percent of test day thrust (or power), unless a detailed analysis is performed.
(c) It is not the purpose of these tolerances to allow flights at values in excess of those authorized in the type design. If such flights are to be conducted, adequate structural
10 substantiation for the flight conditions should be available. These flights should always be conducted under controlled conditions and with the flight test crew’s full knowledge of the situation. Examples of such flights are:
1 Takeoff at greater than maximum takeoff weight to reach a test area at the maximum takeoff weight.
2 Landing at greater than maximum landing weights during the course of conducting takeoff tests.
3 Flights to obtain data for future approvals beyond that substantiated for the initial type design.
(d) The table in Figure 3-3 indicates the cases for which corrections are normally allowed. Any corrections to flight test data should be made by methods that are agreed to by the FAA.
Figure 3-3. Test Parameters That Normally Can Be Corrected
Flight Test Condition Correctable Parameters Wt. C.G. Airspeed Altitude Power/ Thrust Wind Airspeed calibration X --- --- --- --- --- Stall speeds X X --- --- X --- Climb performance X X X X X --- Landing performance X --- X X --- X Takeoff performance X X --- X X X Accelerate-stop perf. X X --- X X X Minimum control speed --- --- --- --- X --- Minimum unstick speed X X X --- X --- Buffet boundary X X --- X --- ---
(e) All instrumentation used in the flight test program should be appropriately calibrated and acceptable to the FAA test team.
(4) Section 25.21(f) - Proof of Compliance (Wind Measurement and Corrections).
The relationship between the wind measured at one height and the corresponding wind at another height may be obtained by the following equation:
11 VW2 = VW1(H2/H1)1/7
Where: H = Height above the runway surface VW2 = Wind velocity at H2 VW1 = Wind velocity at H1
This equation is presented graphically below. Values of H less than 5 feet should not be used in this relationship.
0 10 20 30 40 50 60 70 0 10 20 30 40 50 60
WIND VELOCITY - KNOTS
HEIGHT ABOVE FIELD ELEVATION - FEET 10 meters
Figure 3-4. Wind Profile Variation
(5) Wind Profile Variation for Test Data. The performance data of airplanes should be obtained in such a manner that the effect of wind on the test data may be determined. The test wind velocity should be corrected from the recorded height above the test surface to the height of the airplane wing mean aerodynamic chord. If the wind profile variation is not measured, the variation may be calculated using the equation in paragraph (4) above. The following examples are methods of handling wind profile variation data. Other methods have also been found acceptable.
Example: Test Data
Given: