42.6.2.1 Analytically assess the performance degradation of an aerodynamic configuration change by estimating the drag value and then doubling that value. The resulting degradations in takeoff performance, en route climb, and approach/landing climb capability should be determined in terms of airplane weight. For airplanes with maximum takeoff gross weights not exceeding 20,000 lbs, performance weight decrements less than
0.5 percent of maximum takeoff weight for the takeoff and en route cases (or 0.5 percent of maximum landing weight for the approach/landing climb cases) may be considered negligible. For airplanes with maximum takeoff gross weights greater than 20,000 lbs, performance weight decrements of 100 lbs or less may be considered negligible. The AFM supplement or CDL appendix should identify those type design changes or CDL items that result in a negligible performance degradation. If the performance degradation is not considered negligible, the appropriate performance penalty (in terms of a weight and/or climb gradient capability, as appropriate) should be provided. For design changes, this information should be provided as a limitation in the AFM supplement.
For CDL items, this information should be provided in the CDL appendix, along with the information described under General Limitations in paragraph 42.7.3 of this AC.
42.6.2.2 An alternative method of analytically assessing the performance degradation is to implement conservatism throughout the analysis through conservative round offs and chart readings, using worst-case assumptions, etc. The performance weight decrements are then implemented as noted in paragraph 42.6.2.1 above.
42.7 Configuration Deviation List.
42.7.1 Explanation.
The parts and/or combinations of parts permitted to be missing, and the associated performance decrements and other limitations, must be determined and presented in the AFM CDL.
42.7.2 Procedures.
42.7.2.1 The effect of the missing part should be evaluated to determine if an airplane performance decrement and/or other limitation(s) must be applied to ensure that there is no safety effect. A missing part that affects structural safety, results in damage to other parts, or causes the loss of required safety features is ineligible to be included in the CDL. For example, access panels that, if missing, could affect fire detection, extinguishing, and containment characteristics, are not eligible for listing as CDL items.
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42.7.2.2 Performance decrements should be computed as described in paragraph 42.6 of this AC. A single decrement applicable to all AFM performance limitations may be presented; or, subject to the following restrictions, performance decrements may be presented for different flight phases:
42.7.2.2.1 Only a single performance decrement for takeoff and a single performance decrement for landing will be permitted. For takeoff, the decrement should be the greatest decrement considering takeoff field length, first, second, and final segment climbs, and takeoff flight path. For landing, the decrement should be the greatest decrement considering approach climb, landing climb, and landing field length.
42.7.2.2.2 Only a single weight decrement for the one-engine-inoperative and two-engine-inoperative en route climb performance will be permitted.
42.7.2.2.3 The CDL should contain explanations of the takeoff performance decrement, the landing performance decrement, and the en route performance decrement, as appropriate for the airplane, when the three decrements are used.
42.7.2.3 No reduction in VMO/MMO will be needed if it can be shown by flight test that: (1) no significant changes of flight characteristics or other adverse airworthiness effects exist up to VMO/MMO; and (2) a rational analysis is made for speeds up to VD/MD to show no deterioration of airplane control characteristics. The rational analysis should be based primarily on the proximity of the missing part to aerodynamic surfaces. If a reduction in VMO/MMO is needed, the maximum allowable airspeed indicator and aural warning, required by § 25.1303(b)(1) and (c)(1), must be rescheduled for the reduced speed.
42.7.3 General Limitations.
The following information should be presented in the CDL appendix:
42.7.3.1 When the airplane is operated using the CDL, it must be operated in accordance with the limitations specified in the AFM, as amended in the CDL.
42.7.3.2 Any associated operating limitations (e.g., speed, altitude, or performance limitations) should be listed on a placard affixed in the cockpit in clear view of the pilot in command and other appropriate crewmember(s).
42.7.3.3 For operations using a dispatch or flight release not prepared by the pilot in command, the pilot in command should be notified of each operation with a missing part(s) by listing the missing part(s) in the flight or dispatch release.
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42.7.3.4 The operator should list in the airplane logbook an appropriate notation covering the missing part(s) on each flight.
42.7.3.5 If an additional part is lost in flight, the airplane may not depart the airport at which it landed following this event, until it again complies with the limitations of the CDL. This, of course, does not preclude the issuance of a ferry permit to allow the airplane to be flown to a point where the necessary repairs or replacements can be made.
42.7.3.6 No more than one part for any one system (e.g., one engine pylon fairing) may be missing, unless specific combinations of parts are included in the CDL. Unless otherwise specified, parts from different systems may be missing. The performance penalties are cumulative, unless specifically designated penalties are indicated for the combination of missing parts.
42.7.3.7 No more than three parts that have each been determined to cause a negligible performance degradation may be missing for takeoff without applying a performance penalty. When more than three such parts are missing, a performance penalty of either 0.5 percent of the maximum takeoff weight or 100 lbs, whichever is less, should be applied for takeoff, en route, and landing for each missing part.
42.7.3.8 Takeoff performance penalties should be applied to the takeoff weights that are limited by performance considerations (i.e., takeoff field length, first, second, or final segment climb, or takeoff flight path). If the performance-limited takeoff weight is greater than the maximum certified takeoff weight, the takeoff performance penalties should be applied to the maximum certified takeoff weight to ensure compliance with the noise requirements.
42.7.3.9 Landing performance penalties should be applied to the landing weights that are limited by performance considerations (i.e., landing field length, landing climb, or approach climb). If the performance-limited landing weight is greater than the maximum certified landing weight, the landing performance penalties should be applied to the maximum certified landing weight to ensure compliance with the noise requirements.
42.7.3.10 En route performance penalties apply only to operations that are limited by the one- or two-engine(s)-inoperative en route climb performance.
42.7.3.11 The numbering and designation of systems in the CDL appendix should be based on an Air Transport Association (ATA) Specification. The parts within each system should be identified by functional description and, when necessary, by part numbers.
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42.8 Spare Engine Pod.
42.8.1 Explanation.
When a spare engine pod is installed, this is considered a major change to the type design. The airplane’s performance and flight characteristics that are affected by the installation should be evaluated as part of the approval process required by § 21.97(a)(2).
42.8.2 Procedures.
The drag increment due to the spare engine pod installation is normally determined by the drag polar method described in paragraph 4.9.2.1.2 of this AC. Check climbs are performed to verify the performance penalties derived from the drag data. These check climbs will normally be conducted in the airplane configuration corresponding to the limiting takeoff performance segment. Performance stalls should be conducted for a minimum of one takeoff and one landing flap setting to determine any effect of the spare engine pod installation on stall speeds and handling characteristics in the stalling maneuver. Vibration and buffeting (§ 25.251), flutter (§ 25.629), and the maximum operating limit speed (§ 25.1505) may also require flight demonstration with the spare engine and pod installed. Longitudinal control (§ 25.145), directional and lateral control (§ 25.147), and ability to trim (§ 25.161) should be demonstrated with the spare engine and pod installed.
42.9 Authorization for Ferry Flight with One Engine Inoperative—§ 91.611.
42.9.1 Explanation.
Section 91.611 provides an allowance for the ferry flight of “a four-engine airplane or a turbine-engine-powered airplane equipped with three engines, with one engine inoperative, to a base for the purpose of repairing that engine….” This allowance is provided for airplanes operated in accordance with parts 121 and 125. Section 91.611 also provides performance and operating criteria, including references to sections of part 25 that must be met to obtain a one-engine-inoperative ferry flight permit.
42.9.2 Procedures.
Section 91.611(a)(1) requires the subject airplane be flight tested to show satisfactory compliance with the requirements of § 91.611(b) or (c) for reciprocating and turbine engine powered airplanes, respectively. Deviations from the flight-tested configuration may be approved, based on a conservative analysis as described in paragraph 42.6 of this AC. An example of such a deviation would be a turbojet powered airplane with a one-engine-inoperative ferry flight approval, based on a flight test with the inoperative engine windmilling being subsequently approved for flight with a locked rotor. Though the one-engine-inoperative ferry is an operational approval and not a change in the type design, the airplane performance with the locked rotor should be treated in the same manner as a “minor design change,” and the associated drag increment computed conservatively as described in paragraph 42.6. The pertinent regulatory sections are described below.
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42.9.2.1 Section 91.611(a)(2) requires the approved AFM to contain limitations, operating procedures, and performance information, including a description of the configuration of the inoperative propeller (i.e., engine).
42.9.2.2 Section 91.611(c)(1) and (2) require flight tests to be conducted, in the propeller (i.e., engine) configuration desired for approval, to determine takeoff speeds and distances for one-engine-inoperative ferry operations.
42.9.2.3 Section 91.611(c) refers to the general performance requirements of §
25.101, the takeoff speed requirements of § 25.107, and the climb requirements of § 25.121, thus tying the one engine inoperative ferry performance to the type design criteria.
42.9.2.4 Section 91.611(c)(5) states the airplane must be satisfactorily controllable in a climb with two critical engines inoperative and the climb performance “may be shown by calculations based on, and equal in accuracy to, the results of testing.”
42.9.2.5 Section 25.21(a)(1) states the same allowance for calculated performance if it is “based on, and equal in accuracy to, the results of testing.” Based on this statement, and the previously noted references of § 91.611 to sections of part 25, it is permissible to calculate one-engine-inoperative ferry performance for a configuration that differs from that flight tested. In such cases the conservative methods described in paragraph 42.6 of this AC should be used.
42.10 Instrument Landing System Weather Minima.
42.10.1 Explanation.
The all-weather categories, as presented by the ICAO, are defined as follows:
42.10.1.1 Category I—200 feet (60 meters) ceiling, 2600 feet (800 meters) runway visual range (RVR).
42.10.1.2 Category II—100 feet (30 meters) ceiling, 1200 feet (400 meters) RVR.
42.10.1.3 Category III.
42.10.1.3.1 Category IIIA—No decision height, 700 feet (200 meters) RVR.
42.10.1.3.2 Category IIIB—No decision height, no external reference and 150 feet (50 meters) RVR.
42.10.1.3.3 Category IIIC—No decision height, no external reference for landing or taxi.
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42.10.2 Procedures.
The criteria for airworthiness certification of Category I and II all weather operations are contained in AC 120-29A. The criteria for airworthiness certification of Category III all weather operations are contained in AC 120-28D.
42.11 Takeoff Performance Credit for Alternate Forward Center of Gravity Limits.
42.11.1 Applicable Regulations.
Sections 25.23, 25.103, 25.105, 25.107, 25.109, 25.111, 25.113, 25.115, and 25.121.
42.11.2 Explanation.
42.11.2.1 In the early 1970s, approvals were granted for one alternate forward CG limit per manufacturer’s airplane model (e.g., DC-10 series 40, B737-300, A300-600, etc.). These approvals included AFM performance information that took credit for the improved takeoff performance available with a further aft forward CG limit. The effect of this was that all operators of a particular airplane model (e.g., B737-300) would have the same alternate forward CG limit, which may or may not be useable by any particular operator, depending on that operator’s interior configuration, loading, and route structure.
42.11.2.2 Since those early approvals, the commercial aviation market has changed considerably, with many transport category airplanes capable of fulfilling more than one mission requirement in an operator’s fleet. This is particularly true for modern extended range operation two-engine airplanes, most of which were derived from an earlier medium range version of the same airplane type. When these airplanes are used in long range operations, the CG can be considerably aft of the forward limit due to large fuel loadings. The advent of integral horizontal stabilizer fuel tanks has also led to a further shift aft of the CG. Some operators use these same long-range airplanes on short to medium length routes, with the CG further forward than that of the long range operations, but still significantly aft of the forward CG limit.
42.11.2.3 The operational flexibility of many of today’s transport category airplanes can be enhanced by taking credit for the improvements in takeoff performance afforded by a CG that is aft of the forward limit. The reductions in stall speeds and airplane drag result in increased takeoff weights for a given field length and takeoff flight path profile. The approval of takeoff performance for two alternate forward CG limits would provide operators with increased flexibility in operating the same airplane model on both long and short to medium range routes.
42.11.2.4 The concept of having alternate forward CG limits, with associated improvements in takeoff performance, does not conflict with any of the 42-21
airworthiness or operational requirements of the federal aviation regulations. Section 25.103(b)(5) requires stall speeds to be based on the CG position that results in the highest value of reference stall speed.
Section 25.117 states that compliance with the climb performance requirements must be shown with the “most unfavorable CG” position.
Historically, this has been interpreted as a requirement to conduct the associated performance flight testing at the most forward CG limit and present the resulting AFM performance for that same extreme forward CG limit. However, there is no requirement that prevents operating limitations from being used to establish multiple forward CG limits.
42.11.2.5 The primary concern in granting performance credit for forward CG limits that are aft of the extreme forward limit is the reduction in the conservative performance margin that results from usually operating with the CG aft of the extreme forward limit that the takeoff performance is based on. With the availability of alternate forward CG limits, this safety margin will be decreased, and on a statistical basis, completely eliminated more often. Consequently, emphasis should be put on maintaining accurate weight and balance records, implementing accurate loading plans, and providing the necessary training and operating procedures for ground and dispatch personnel.
42.11.2.6 Flightcrew training is also a concern for alternate forward CG limit operations. With many of today’s transport category airplanes incorporating high levels of cockpit automation, it is important that the flightcrew be aware of when an alternate forward CG limit is being used as the basis for computing takeoff performance data. This is most important when an alternate forward CG limit is used in conducting a performance-limited takeoff.
42.11.3 Procedures.
Approval may be granted for as many as two alternate forward CG limits (for a total of three forward CG limits), with associated takeoff performance data, using the following certification criteria:
42.11.3.1 No more than two alternate forward CG limits (three total) should be approved per operator-specific variant of a particular airplane type and model. “Airplane type” refers to those airplanes of similar design as identified on the type certificate; “airplane model” refers to different versions of an airplane type as reflected on the type certificate. An “operator specific variant” is an airplane type and model outfitted to a particular customer’s requirements (e.g., engine type, seat pitch, galley locations, etc.). For control purposes, airplanes that are classified as an “operator specific variant” should be clearly identifiable as such; this can be accomplished by definitive AFM document numbering systems and AFMs tied to specific airplane serial numbers.
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42.11.3.2 The alternate forward CG limits should be sufficiently different that they will be treated as discrete limits and not result in confusion when determining takeoff performance adjustments.
42.11.3.3 The CG range that results from the use of an alternate forward CG limit should be of sufficient magnitude to be practical and allow for expected variations in operational loading.
42.11.3.4 The alternate forward CG limits should be identified as such and presented on the weight and CG chart in the limitations section of the basic AFM.
That chart should also provide a reference to a separate appendix to the AFM that contains the related airplane performance adjustments.
42.11.3.5 To minimize the impact on crew training and standardization of cockpit procedures, onboard systems that use or provide weight and balance information (e.g., Flight Management Systems, Electronic Flight Bags, etc.) should include the performance and fuel management data associated with the alternate forward CG limits. If they do not include such information, a limitation should be added to the AFM that prohibits the use of such systems when using an alternate forward CG limit.
42.11.3.6 The AFM performance associated with alternate forward CG limit operations must be substantiated by flight test data per § 25.21(a)(2). This does not mean that flight test data needs to be obtained at every alternate forward CG limit; the intent is for the applicant to verify the analytical predictions of CG effect with flight test data collected at different CGs.
42.11.3.7 All affected cockpit placards and displays should be revised to reflect the alternate forward CG limits.
42.12 Airplane Backing Using Reverse Thrust.
42.12.1 Explanation.
Where compliance with applicable airworthiness requirements has been demonstrated, operational approval has been granted for the use of reverse thrust to back airplanes away from airport gates in lieu of a tug pushback. The applicable airworthiness requirements are prescribed in paragraph 42.12.2 below. Note that compliance with these requirements only demonstrates the capability of the airplane and does not constitute operational approval. Operational approval should be coordinated with the applicable FAA Flight Standards office.
42.12.2 Procedures.
To obtain airworthiness approval for reverse thrust backing, compliance should be demonstrated with the criteria prescribed below. Since operational approvals for reverse thrust backing specify the applicable airplanes, airports, and gates, some of these tests 42-23
will be site specific and should be coordinated with the applicable FAA Flight Standards office.
42.12.2.1 Both the airplane and engine manufacturer should determine the applicability of the maneuver and provide appropriate limitations for the procedure. These limitations should include:
Engine power or thrust setting and operating parameter limits, Minimum and maximum allowable weights, CG limits, Ramp slope limits, Use of wheel brakes, Atmospheric conditions (see Note below), and Any other factor unique to the proposed operation.
Note: The use of reverse thrust backing with snow, ice, or slush on the ramp, or during periods of heavy rain, is not considered good operating practice.
42.12.2.2 All limitations, and any normal or abnormal operating procedures, associated with reverse thrust backing should be included in the AFM.
Any procedures related to ground crew functions should also be included in the AFM.
42.12.2.3 Testing should be conducted to verify that the reverser efflux does not have a detrimental effect on the powerplant installations. Items to be considered include:
Foreign object damage (FOD), Effects on engine cooling, Inlet flow distortion, Re-ingestion of exhaust gases, and Any effects on engine mounted accessories.
42.12.2.4 Testing should be conducted to verify that the reverser efflux does not have a detrimental effect on other airplane systems such as air conditioning system inlets, APU inlets and exhausts, overboard drains, etc.
42.12.2.5 It should be verified that cockpit and cabin air will not be contaminated.
Note: It is acceptable to have a limitation prohibiting the operation of the air conditioning packs during reverse thrust backing to avoid cockpit and cabin air contamination.
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42.12.2.6 Reverse thrust backing demonstrations should be conducted to evaluate the associated procedures. These demonstrations should be conducted at:
Maximum ramp weight with the CG at the aft limit, and Any other weight that may be critical with the CG at the aft limit.
42.12.2.7 The reverse thrust backing demonstrations of paragraph 42.12.2.6 above should be evaluated to determine:
42.12.2.7.1 The amount of aft pitching moment, including its effect on nose wheel steering;
42.12.2.7.2 The effect of inadvertent heavy/emergency braking action;
42.12.2.7.3 Adequate cockpit visibility and ground crew function;
42.12.2.7.4 An area around the airplane that should be free of ground crew personnel and ground support equipment throughout the reverse backing maneuver;
Note: This evaluation should also consider the effects of the reverser efflux on airplanes at adjacent gates.
42.12.2.7.5 The adequacy of procedures for transitioning from reverse to forward thrust;
42.12.2.7.6 The effect of thrust asymmetry due to failure of an engine to enter reverse, or recover forward thrust mode;
42.12.2.7.7 The effects of low tire pressures;
42.12.2.7.8 The effect of ramp slope and surface condition;
42.12.2.7.9 The effects of ambient atmospheric temperature; and
42.12.2.7.10 The effect of flap/slat configuration.
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Appendix A APPENDIX A. ACRONYMS, ABBREVIATIONS, SYMBOLS, AND DEFINITIONS Table A-1. Terms and Definitions
Term Definition AC Advisory Circular ACARS Aircraft Communications Addressing and Reporting System ACO Aircraft Certification Office ACN Aircraft Classification Number ADC Air Data Computer ADF Automatic Direction Finder ADQ Adequate AEO All-Engines-Operating AFM Airplane Flight Manual AGL Above Ground Level AHRS Attitude and Heading Reference System AOA Angle of Attack APU Auxiliary Power Unit AR Authorization Required ARSR Air Route Surveillance Radar ARTCC Air Route Traffic Control Center ASR Airport Surveillance Radar ATA Air Transport Association ATC Air Traffic Control ATCRBS Air Traffic Control Radar Beacon System A-1
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AC 25-7D Appendix A Table A-1. Terms and Definitions (continued)
Term Definition ATS Automatic Throttle System ATT REF Attitude Reference ATTCS Automatic Takeoff Thrust Control System C Celsius CAR Civil Air Regulations CAS Calibrated Airspeed CAT Category CAWS Central Aural Warning System CBR California Bearing Ratio CDL Configuration Deviation List CDU Cockpit Display Unit CFR Code of Federal Regulations CG Center of Gravity CL Lift Coefficient CMM Component Maintenance Manual CN Yawing Moment Coefficient COM Communications CON Controllable CRT Cathode Ray Tube CVR Cockpit Voice Recorder CWS Control Wheel Steering A-2