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
Appendix A Table A-1. Terms and Definitions (continued)
Term Definition dB Decibel DER Designated Engineering Representative DFDR Digital Flight Data Recorder DG Directional Gyros DH Decision Height DME Distance Measuring Equipment ECAM Electronic Centralized Aircraft monitor EFCS Electronic Flight Control System EGT Exhaust Gas Temperature EICAS Engine Indicating and Crew Alerting System EMC Electromagnetic Compatibility EMI Electromagnetic Interference EPR Engine Pressure Ratio ESDU Engineering Sciences Data Unit F Fahrenheit F&R Function and Reliability FGS Flight Guidance System FMEA Failure Modes and Effects Analysis FMS Flight Management System FOD Foreign Object Damage FS Longitudinal Control (Stick) Force A-3
Appendix A Table A-1. Terms and Definitions (continued)
Term Definition FSB Flight Standardization Board FS/g Stick Force per g ft Foot or Feet FWC Flight Warning Computer g or G Acceleration Due to Gravity at the Earth’s Surface GLS GNSS Landing System GNSS Global Navigation Satellite System HF High Frequency HGS Head-Up Guidance System HQ Handling Qualities HQRM Handling Qualities Rating Method HSI Horizontal Situation Indicator HUD Head-Up Display Hz Hertz (cycles per second) IAS Indicated Airspeed ICAO International Civil Aviation Organization IFR Instrument Flight Rules IKE Initial Kinetic Energy ILS Instrument Landing System IMC Instrument Meteorological Conditions INS Inertial Navigation System IRS Inertial Reference System A-4
Appendix A Table A-1. Terms and Definitions (continued)
Term Definition ITT Interstage Turbine Temperature IVSI Instantaneous Vertical Speed Indicator KE Kinetic Energy lbs Pounds LF Low Frequency LFE Limit Flight Envelope LNAV Lateral Navigation LODA Letter of Design Approval M Mach Number MAC Mean Aerodynamic Chord MCS Master Caution System MCT Maximum Continuous Thrust MD Design Dive Mach MDA Minimum Descent Altitude MDF Demonstrated Flight Diving Mach MEL Minimum Equipment List MF Medium Frequency MFC Maximum Mach for Stability Characteristics MFD Multi-Function Display min Minute(s) MLRC Long Range Cruise Mach A-5
Appendix A Table A-1. Terms and Definitions (continued)
Term Definition MLS Microwave Landing System MMEL Master Minimum Equipment List MMO Maximum Operating Mach MSL Mean Sea Level MWS Master Warning System MUH Minimum Use Height N1 Rotational Speed of Low Pressure Compressor (Turbine Engine) N2 Rotational Speed of High Pressure Compressor (Turbine Engine) NAS National Airspace System NAV Navigate NM Nautical Mile(s) NFE Normal Flight Envelope OAT Outside Air Temperature OEW Operating Empty Weight OFE Operational Flight Envelope PA Public Address PFC Porous Friction Course PIO Pilot Induced Oscillation Q Dynamic Pressure R/A Radio Altimeter RFI Radio Frequency Interference A-6
Appendix A Table A-1. Terms and Definitions (continued)
Term Definition RPM Revolutions per Minute RMI Radio Magnetic Indicator RNAV Area Navigation RNP Required Navigation Performance RTO Rejected Takeoff RVP Reid Vapor pressure RVR Runway Visual Range SAS Stability Augmentation System SAT 1. Static Air Temperature
2. Satisfactory (when used with the handling qualities rating method) SATCOM Satellite Communications secs Seconds SELCAL Selective Calling System S/F Slow/Fast SR Special Regulation STC Supplemental Type Certificate STOL Short Takeoff and Landing SWC Stall Warning Computer TAT Total Air Temperature TAWS Terrain Awareness and Warning System TCAS Traffic Collision Avoidance System TCDS Type Certificate Data Sheet A-7