1-1 CHAPTER 1. INTRODUCTION
1.1 Purpose.
1.1.1 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.
1.1.2 See appendix A for a list of acronyms and abbreviations used in this AC.
1.2 Applicability.
1.2.1 The guidance provided in this document is directed to airplane manufacturers, modifiers, foreign regulatory authorities, and Federal Aviation Administration (FAA) certification engineers, flight test pilots, and FAA designees.
1.2.2 This material is neither mandatory nor regulatory in nature and does not constitute a regulation. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulations. The Federal Aviation Administration will consider other methods of demonstrating compliance that an applicant may elect to present.
1.2.3 While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations. On the other hand, 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.
1.2.4 This material does not change, create any additional, authorize changes in, or permit deviations from, regulatory requirements.
1.3 Cancellation.
This AC cancels AC 25-7C, Flight Test Guide for Certification of Transport Category Airplanes, dated October 16, 2012.
1.4 Background.
1.4.1 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
1-2 handling 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.
1.4.2 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, Engineering Flight Test Guide for Transport Category Airplanes, which was cancelled when AC 25-7A was issued.
1.4.3 Change 1 to AC 25-7A added acceptable means of compliance for the regulatory changes associated with amendments 25-92 and 25-98 to part 25.
1.4.4 AC 25-7B added acceptable means of compliance for the regulatory changes associated with amendments 25-108, 25-109, and 25-115 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 25-25A, Performance and Handling Characteristics in Icing Conditions, dated October 27, 2014.
1.4.5 Change 1 to AC 25-7B added acceptable means of compliance for the regulatory changes associated with amendment 25-135.
1.4.6 AC 25-7C reduced the number of differences between the FAA and European Aviation Safety Agency flight test guides, provided acceptable means of compliance for the regulatory changes associated with amendments 25-107, 25-109, 25-113, 25-115, 25-119 and 25-123 to part 25, and included changes responding to safety recommendations from the FAA and National Transportation Safety Board.
1.5 Related Documents.
1.5.1 Orders.
The following FAA orders are related to the guidance in this AC. The latest version of each order at the time of publication of this AC is identified below. If any order is revised after publication of this AC, you should refer to the latest version for guidance, which can be downloaded from the Internet at https://www.faa.gov/regulations_policies/orders_notices/.
Order 8100.5C, Aircraft Certification – Organizational Structure and Functions, dated July 14, 2017.
Order 8110.4C, with Change 6, Type Certification, dated March 3, 2017.
1.5.2 Advisory Circulars.
The following FAA ACs are related to the guidance in this AC. The latest version of each AC at the time of publication of this AC is identified below. If any AC is revised after publication of this AC, you should refer to the latest version for guidance, which
1-3 can be downloaded from the Internet at www.faa.gov/regulations_policies/advisory_circulars.
AC 20-73A, Aircraft Ice Protection, dated August 16, 2006.
AC 20-124, Water Ingestion Testing for Turbine Powered Airplanes, dated September 30, 1985.
AC 20-131A, Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders, dated March 29, 1993.
AC 20-138D, with Change 2, Airworthiness Approval of Positioning and Navigation Systems, dated April 7, 2016.
AC 20-147A, Turbojet, Turboprop, Turboshaft, and Turbofan Engine Induction System Icing and Ice Ingestion, dated October 22, 2014.
AC 20-161, Aircraft Onboard Weight and Balance Systems, dated April 11, 2008.
AC 20-168, Certification Guidance for Installation of Non-Essential, Non-Required Aircraft Cabin Systems & Equipment (CS&E), dated July 22, 2010, AC 21-29D, Detecting and Reporting Suspected Unapproved Parts, dated July 12, 2016.
AC 21.101-1B, Establishing the Certification Basis of Changed Aeronautical Products, March 11, 2016.
AC 25-9A, Smoke Detection, Penetration, and Evacuation Tests and Related Flight Manual Emergency Procedures, dated January 6, 1994.
AC 25-11B, Electronic Flight Displays, dated October 7, 2014.
AC 25-12, Airworthiness Criteria for the Approval of Airborne Windshear Warning Systems in Transport Category Airplanes, dated November 2, 1987.
AC 25-13, Reduced and Derated Takeoff Thrust (Power) Procedures, dated May 4, 1988.
AC 25-15 Approval of Flight Management Systems in Transport Category Airplanes, dated November 20, 1989.
AC 25-17A, with Change 1, Transport Airplane Cabin Interiors Crashworthiness Handbook, dated May 24, 2016.
AC 25-20, Pressurization, Ventilation, and Oxygen Systems Assessment for Subsonic Flight Including High Altitude Operations, dated September 10, 1996.
AC 25-22, Certification of Transport Airplane Mechanical Systems, dated March 14, 2000.
AC 25-23, Airworthiness Criteria for Installation Approval of a Terrain Awareness and Warning System (TAWS) for Part 25 Airplanes, dated May 22, 2000.
AC 25-25A, Performance and Handling Characteristics in Icing Conditions, dated October 27, 2014.
1-4 AC 25.735-1, Brakes and Braking Systems Certification Tests and Analysis, dated April 10, 2002.
AC 25.773-1, Pilot Compartment View Design Considerations, dated January 8, 1993.
AC 25.939-1, Evaluating Turbine Engine Operating Characteristics, dated March 19, 1986.
AC 25.1309-1A, System Design and Analysis, dated June 21, 1988.
AC 25.1329-1C, with Change 1, Approval of Flight Guidance Systems, dated May 24, 2016.
AC 25.1357-1A, Circuit Protective Devices, dated October 22, 2007.
AC 25.1581-1, with Change 1, Airplane Flight Manual, dated October 16, 2012.
AC 43.13-1B, with Change 1, Acceptable Methods, Techniques, and Practices— Aircraft Inspection and Repair, dated September 27, 2001.
AC 90-100A, with Change 2, U.S. Terminal and En Route Area Navigation (RNAV) Operations, dated April 14, 2015.
AC 90-101A, with Change 1, Approval Guidance for RNP Procedures with AR, dated February 9, 2016.
AC 90-105A, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System and in Oceanic and Remote Continental Airspace, dated March 7, 2016.
AC 91-79A, with Change 1, Mitigating the Risks of a Runway Overrun Upon Landing, dated April 28, 2016.
AC 120-28D, Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout, dated July 13, 1999.
AC 120-29A, Criteria for Approval of Category I and Category II Weather Minima for Approach, dated August 12, 2002.
AC 150/5320-12C, with Change 8, Measurement, Construction, and Maintenance of Skid-Resistant Airport Pavement Surfaces, dated February 7, 2007.
2-1 CHAPTER 2. GENERAL
2.1 Applicability—§ 25.1. [Reserved]
2.2 Special Retroactive Requirements—§ 25.2. [Reserved]
3-1 CHAPTER 3. FLIGHT: GENERAL
3.1 Proof of Compliance—§ 25.21.
3.1.1 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, aft-mounted 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.
3.1.2 Section 25.21(a)—Proof of Compliance.
3.1.2.1 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.
3.1.2.2 If the airplane flight characteristics or the required flight data are affected by weight and/or center of gravity (CG), the compliance data must be presented for the most critical weight and CG position per § 25.21(a).
Unless the applicant shows that the allowable CG 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 CG.
3.1.2.3 The gross weight and CG tolerances specified in paragraphs 3.1.4.3 and
3.1.4.5 are test tolerances and are not intended to allow compliance to be shown at less than critical conditions.
3.1.2.4 Section 21.35(a)(3) requires that the test airplane be in conformity with its type design specifications. This means that the test airplane must be in conformity with its type design specification as it relates to the particular test being conducted. 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 characteristics
3-2 tests, the applicant must show that its presence would have no effect on measured airplane performance and flight characteristics.
3.1.2.5 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 B to this AC provides guidance for showing compliance with this requirement.
3.1.2.6 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:
3.1.2.6.1 In general, flight test demonstrations are the preferred method to show compliance.
3.1.2.6.2 Simulation may be an acceptable alternative to flight demonstrations in certain situations, such as the following:
1. 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);
2. The required environmental or airplane conditions are too difficult to attain, such as (1) validation of system safety analyses failure cases involving high crosswinds; (2) development of crosswind guidance for slippery runway operations; and (3) conditions involving minimum allowable weight where the minimum allowable weight cannot be achieved because of the weight of required test equipment. In case (3), simulation data can be used to supplement flight test data obtained at the minimum practicable test weight.
3. The simulation is used to augment a reasonably broad flight test program; or
4. The simulation is used to demonstrate repeatability, or to demonstrate performance of a specific scenario for a range of pilots.
3.1.2.6.3 Simulation Criteria.
If it is agreed that a simulation will be used to establish compliance, then the simulation should meet the following criteria in order to be acceptable for showing compliance with the performance and handling qualities requirements:
1. The simulation should 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?
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2. The simulation should be suitably validated by flight test data for the conditions of interest. 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. 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 non-compliant, the higher the required fidelity of the simulation).
3. The simulation should be conducted in a manner appropriate to the case and conditions of interest. If closed-loop responses are important, the simulation should be piloted by a human pilot. 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).
3.1.3 Section 25.21(c)—Proof of Compliance (Altitude Effect on Flight Characteristics).
3.1.3.1 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.
3.1.3.2 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).
3.1.4 Section 25.21(d)—Proof of Compliance: Flight Test Tolerances.
3.1.4.1 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.
3.1.4.2 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 impractical, the average test conditions should assure that the measured characteristics represent the actual critical value.
3.1.4.3 Weight Limits.
3.1.4.3.1 Table 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
3-4 configuration, particularly those tests used to establish airplane flight manual (AFM) performance information. As noted in paragraph 3.1.4.1 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 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.
Table 3-1. Weight Tolerance Limits
3.1.4.3.2 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 should be conducted on a production airplane (or other airplane on which the minimum weight can be obtained). If the instrumentation or equipment Flight Test Condition 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 and 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.
3-5 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 3.1.2.6 of this AC.)
3.1.4.3.3 For follow-on airplane certification programs involving an increase in the maximum allowable gross weight, the test weight limits of table 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.
3.1.4.3.4 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 table 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 3-1 below 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 table 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.
3-6 Figure 3-1. 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
3.1.4.4 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.
3.1.4.5 CG Limits.
A test tolerance of ±7 percent of the total CG range is intended to allow for inflight CG movement. This tolerance is only acceptable when the test data scatter is on both sides of the limiting CG or when adjusting the data from the test CG to the limit CG is acceptable. If compliance with a requirement is marginal at a test condition that is inside of the CG limits, the test should be repeated at the CG limits.
3.1.4.6 Airspeed Limits.
Normally, tests conducted within 3 percent or 3 knots (whichever is the higher) of the desired test speed are considered acceptable.
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3.1.4.7 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.
3.1.4.8 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 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:
3.1.4.8.1 Takeoff at greater than maximum takeoff weight to reach a test area at the maximum takeoff weight.
3.1.4.8.2 Landing at greater than maximum landing weights during the course of conducting takeoff tests.
3.1.4.8.3 Flights to obtain data for future approvals beyond that substantiated for the initial type design.
3.1.4.8.4 Table 3-2 below 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.