FLIGHT TEST GUIDE FOR CERTIFICATION OF PART 23 AIRPLANES

(4) 20-138B Airworthiness Approval of Positioning and Navigation Systems (5) 23.629-1 Means of Compliance with Section 23.629, Flutter (6) 23-1309-1 System Safety Analysis and Assessment for Part 23 Airplanes (7) 23-1419-2 Certification of Part 23 Airplanes for Flight in Icing Conditions (8) 90-79 Recommended Practices and Procedures for the Use of Electronic Long-Range Navigation Equipment (9) 91-49 General Aviation Procedures for Flight in North Atlantic Minimum Navigation Performance Specifications Airspace (10) 121-13 Self-Contained Navigation Systems (Long Range) (11) 20-88 Guidelines on Marking Aircraft Powerplant Instruments (Displays) iii 11/16/2011 AC 23 -8C (12) 23-16 Powerplant Guide for Certification of Part 23 Airplanes and Airships (13) 23-1 7 Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships Earl Lawrence Manager, Small Airplane Directorate Aircraft Certification Service iv 11/16/2011 AC 23-8C Table of Contents Chapter 1. Subpart A--General .................................................................................................. 1 1. § 23.1 Applicability. ........................................................................................................... 1 2. § 23.3 Airplane Categories. ................................................................................................ 1 Chapter 2 Subpart B – Flight ..................................................................................................... 2 Section 1. General....................................................................................................................... 2 1. § 23.21 Proof of Compliance. ............................................................................................. 2 2. § 23.23 Load Distribution Limits........................................................................................ 6 3. § 23.25 Weight Limits. ....................................................................................................... 8 4. § 23.29 Empty Weight and Corresponding Center of Gravity. .......................................... 9 5. § 23.31 Removable Ballast. ................................................................................................ 9 6. § 23.33 Propeller Speed and Pitch Limits......................................................................... 10 Section 2. Performance ............................................................................................................. 11 1. § 23.45 General................................................................................................................ 11 2. § 23.49 Stalling Speed. .................................................................................................... 15 3. § 23.51 Takeoff Speeds.................................................................................................... 23 4. § 23.53 Takeoff Performance. ......................................................................................... 28 5. § 23.55 Accelerate-Stop Distance.................................................................................... 32 6. § 23.57 Takeoff Path........................................................................................................ 36 7. § 23.59 Takeoff Distance and Takeoff Run..................................................................... 42 8. § 23.61 Takeoff Flight Path. ............................................................................................ 45 9. § 23.65 Climb: All Engines Operating. .......................................................................... 47 10. § 23.66 Takeoff Climb, One Engine Inoperative............................................................. 51 11. § 23.67 Climb: One Engine Inoperative. ........................................................................ 52 12. § 23.71 Glide (Single-Engine Airplanes)......................................................................... 56 13. § 23.75 Landing. .............................................................................................................. 57 14. § 23.77 Balked Landing Climb........................................................................................ 63 Section 3. Flight Characteristics of 14 CFR § 23.141 .............................................................. 65 1. § 23.141 General.............................................................................................................. 65 Section 4. Controllability and Maneuverability........................................................................ 65 1. § 23.143 General.............................................................................................................. 65 2. § 23.145 Longitudinal Control......................................................................................... 67 3. § 23.147 Directional and Lateral Control. ....................................................................... 68 4. § 23.149 Minimum Control Speed................................................................................... 70 5. § 23.151 Acrobatic Maneuvers. ....................................................................................... 74 6. § 23.153 Control During Landings. ................................................................................. 75 7. § 23.155 Elevator Control Force in Maneuvers............................................................... 75 8. § 23.157 Rate of Roll. ...................................................................................................... 78 Section 5. Trim ......................................................................................................................... 78 1. § 23.161 Trim................................................................................................................... 78 v 11/16/2011 AC 23-8C Section 6. Stability.................................................................................................................... 78 1. § 23.171 General.............................................................................................................. 78 2. § 23.173 Static Longitudinal Stability. ............................................................................ 82 3. § 23.175 Demonstration of Static Longitudinal Stability. ............................................... 83 4. § 23.177 Static Direction and Lateral Stability................................................................ 86 5. § 23.179 Stability. ............................................................................................................ 87 6. § 23.181 Dynamic Stability. ............................................................................................ 87 Section 7. Stalls......................................................................................................................... 92 1. § 23.201 Wings Level Stall.............................................................................................. 92 2. § 23.203 Turning Flight and Accelerated Turning Stalls. ............................................... 95 3. § 23.205............................................................................................................................. 96 4. § 23.207 Stall Warning. ................................................................................................... 96 Section 8. Spinning ................................................................................................................... 96 1. § 23.221 Spinning. ........................................................................................................... 96 Section 9. Ground and Water Handling Characteristics ......................................................... 104 1. § 23.231 Longitudinal Stability and Control. ................................................................ 104 2. § 23.233 Directional Stability and Control. ................................................................... 104 3. § 23.235 Operation on Unpaved Surfaces. .................................................................... 106 4. § 23.237 Operation on Water......................................................................................... 106 5. § 23.239 Spray Characteristics. ..................................................................................... 106 Section 10. Miscellaneous Flight Requirements..................................................................... 106 1. § 23.251 Vibration and Buffering.................................................................................. 106 2. § 23.253 High Speed Characteristics. ............................................................................ 107 Chapter 3. Subpart D--Design and Construction ................................................................. 111 Section 1. General................................................................................................................... 111 1. § 23.629 Flutter.............................................................................................................. 111 Section 2. Control Systems..................................................................................................... 111 1. § 23.671 General............................................................................................................ 111 2. § 23.672 Stability Augmentation and Automatic and Power Operated Systems. ......... 111 3. § 23.677 Trim Systems. ................................................................................................. 111 4. § 23.679 Control System Locks..................................................................................... 113 5. § 23.689 Cable Systems................................................................................................. 113 6. § 23.691 Artificial Stall Barrier System. ....................................................................... 114 7. § 23.697 Wing Flap Controls......................................................................................... 114 8. § 23.699 Wing Flap Position Indicator. ......................................................................... 114 9. § 23.701 Flap Interconnection. ...................................................................................... 114 Section 3. Landing Gear ......................................................................................................... 114 1. § 23.729 Landing Gear Extension and Retraction System. ........................................... 114 2. § 23.735 Brakes. ............................................................................................................ 114 vi 11/16/2011 AC 23-8C Section 4. Personnel and Cargo Accommodations................................................................. 114 1. § 23.771 Pilot Compartment. ......................................................................................... 114 2. § 23.773 Pilot Compartment View. ............................................................................... 114 3. § 23.775 Windshields and Windows. ............................................................................ 115 4. § 23.777 Cockpit Controls. ............................................................................................ 115 5. § 23.785 Seats, Berths, Litters, Safety Belts and Shoulder Harnesses. ......................... 115 6. § 23.803 Emergency Evacuation. .................................................................................. 116 7. § 23.807 Emergency Exits. ............................................................................................ 116 8. § 23.831 Ventilation....................................................................................................... 116 Section 5. Pressurization......................................................................................................... 117 1. § 23.841 Pressurization Cabins...................................................................................... 117 2. § 23.843 Pressurization Tests. ....................................................................................... 117 Chapter 4. Subpart E--Powerplant ........................................................................................ 118 Section 1. General................................................................................................................... 118 1. § 23.901 Installation....................................................................................................... 118 2. § 23.903 Engines............................................................................................................ 118 3. § 23.905 Propellers. ....................................................................................................... 121 4. § 23.909 Turbo Superchargers....................................................................................... 121 5. § 23.925 Propeller Clearance......................................................................................... 121 6. § 23.929 Engine Installation Ice Protection................................................................... 121 7. § 23.933 Reversing Systems. ......................................................................................... 121 8. § 23.939 Powerplant Operating Characteristics............................................................. 122 9. § 23.943 Negative Acceleration..................................................................................... 123 Section 2. Fuel System............................................................................................................ 123 1. § 23.959 Unusable Fuel Supply. .................................................................................... 123 2. § 23.961 Fuel System Hot Weather Operation. ............................................................. 123 Section 3. Fuel System Components ...................................................................................... 123 1. § 23.1001 Fuel Jettisoning System. ............................................................................... 123 Section 4. Oil System.............................................................................................................. 124 1. § 23.1027 Propeller Feathering System. ........................................................................ 124 Section 5. Cooling .................................................................................................................. 125 1. § 23.1041 General.......................................................................................................... 125 2. § 23.1043 Cooling Tests. ............................................................................................... 125 3. § 23.1045 Cooling Test Procedures for Turbine Engine-Powered Airplanes. .............. 125 4. § 23.1047 Cooling Test Procedures for Reciprocating Engine-Powered Airplanes...... 129 Section 6. Induction System ................................................................................................... 132 1. § 23.1091 Air Induction................................................................................................. 132 2. § 23.1093 Induction System Icing Protection................................................................ 132 vii 11/16/2011 AC 23-8C Section 7. Powerplant Controls and Accessories.................................................................... 136 1. § 23.1141 Powerplant Controls: General...................................................................... 137 2. § 23.1145 Ignition Switches. ......................................................................................... 137 3. § 23.1153 Propeller Feathering Controls. ...................................................................... 137 Section 8. Powerplant Fire Protection .................................................................................... 137 1. § 23.1189 Shutoff Means............................................................................................... 137 Chapter 5. Subpart F--Equipment ......................................................................................... 138 Section 1. General................................................................................................................... 138 1. § 23.1301 Function and Installation............................................................................... 138 2. § 23.1303 Flight and Navigation Instruments................................................................ 147 3. § 23.1305 Powerplant Instruments. ............................................................................... 147 4. § 23.1307 Miscellaneous Equipment............................................................................. 148 5. § 23.1309 Equipment, Systems, and Installations. ........................................................ 148 Section 2. Instruments: Installation ....................................................................................... 148 1. § 23.1311 Electronic Display Instrument Systems. ....................................................... 148 2. § 23.1321 Arrangement and Visibility........................................................................... 148 3. § 23.1322 Warning, Caution, and Advisory Lights. ...................................................... 148 4. § 23.1323 Airspeed Indicating System. ......................................................................... 148 5. § 23.1325 Static Pressure System. ................................................................................. 149 6. § 23.1326 Pitot Heat Indication Systems....................................................................... 152 7. § 23.1327 Magnetic Direction Indicator........................................................................ 152 8. § 23.1329 Automatic Pilot System. ............................................................................... 152 9. § 23.1331 Instruments Using a Power Supply............................................................... 152 10. § 23.1335 Flight Director Systems. ............................................................................... 152 11. § 23.1337 Powerplant Instruments. ............................................................................... 152 Section 3. Electrical Systems and Equipment ........................................................................ 152 1. § 23.1351 General.......................................................................................................... 152 2. § 23.1353 Storage Battery Design and Installation. ...................................................... 153 Reserved................................................................................................................................... 153 3. § 23.1357 Circuit Protective Devices. ........................................................................... 153 4. § 23.1361 Master Switch Switch Arrangement. ............................................................ 153 5. § 23.1367 Switches. ....................................................................................................... 153 Section 4. Lights ..................................................................................................................... 153 1. § 23.1381 Instrument Lights. ......................................................................................... 153 2. § 23.1383 Landing Lights. ............................................................................................. 153 Section 5. Safety Equipment................................................................................................... 153 1. § 23.1411 General.......................................................................................................... 153 2. § 23.1415 Ditching Equipment. ..................................................................................... 153 3. § 23.1416 Pneumatic Deicer Boot System. ................................................................... 153 4. § 23.1419 Ice Protection. ............................................................................................... 153 viii 11/16/2011 AC 23-8C Section 6. Miscellaneous Equipment...................................................................................... 153 1. § 23.1431 Electronic Equipment.................................................................................... 153 2. §23.1435 Hydraulic Systems. ........................................................................................ 153 3. § 23.1441 Oxygen Equipment and Supply. ................................................................... 153 4. § 23.1447 Equipment Standards for Oxygen Dispensing Units. ................................... 153 5. § 23.1449 Means for Determining Use of Oxygen........................................................ 153 6. § 23.1457 Cockpit Voice Recorders. ............................................................................. 153 7. § 23.1459 Flight Data Recorders. .................................................................................. 154 Chapter 6. Subpart G--Operating Limitations and Information........................................ 155 Section 1. General................................................................................................................... 155 1 § 23.1501 General.......................................................................................................... 155 2. § 23.1505 Airspeed Limitations..................................................................................... 155 3. § 23.1507 Maneuvering Speed. ..................................................................................... 155 4. § 23.1511 Flap Extended Speed..................................................................................... 155 5. § 23.1513 Minimum Control Speed............................................................................... 155 6. § 23.1519 Weight and Center of Gravity....................................................................... 155 7. § 23.1521 Powerplant Limitations................................................................................. 155 8. § 23.1523 Minimum Flight Crew. ................................................................................. 156 9. § 23.1523 Minimum Flight Crew. ................................................................................. 156 10. § 23.1524 Maximum Passenger Seating Configuration. ............................................... 160 11. § 23.1525 Kinds of Operation........................................................................................ 160 12. § 23.1527 Maximum Operating Altitude....................................................................... 160 Section 2. Markings and Placards........................................................................................... 161 1. § 23.1541 General.......................................................................................................... 161 2. § 23.1543 Instrument Markings: General. .................................................................... 162 3. § 23.1545 Airspeed Indicator......................................................................................... 162 4. § 23.1547 Magnetic Direction Indicator........................................................................ 162 5. § 23.1549 Powerplant Instruments. ............................................................................... 162 6. § 23.1551 Oil Quantity Indicator. .................................................................................. 162 7. § 23.1553 Fuel Quantity Indicator. ................................................................................ 162 8. § 23.1555 Control Markings. ......................................................................................... 162 9. § 23.1557 Miscellaneous Markings and Placards.......................................................... 162 10. § 23.1559 Operating Limitations Placard. ..................................................................... 162 11. § 23.1561 Safety Equipment.......................................................................................... 162 12. § 23.1563 Airspeed Placards.......................................................................................... 163 13. § 23.1567 Flight Maneuver Placard............................................................................... 163 Section 3. Airplane Flight Manual and Approved Manual Material ...................................... 163 1. § 23.1581 General.......................................................................................................... 163 2. § 23.1583 Operating Limitations. .................................................................................. 165 3. § 23.1585 Operating Procedures.................................................................................... 167 4. § 23.1587 Performance Information. ............................................................................. 168 5. § 23.1589 Loading Information. .................................................................................... 170 ix 11/16/2011 AC 23-8C Appendix 1. Power Available 1. General 2. Reciprocating Engines 3. Normally Aspirated Engines with Constant Speed Propellers 4. Turbocharged Engines with Constant Speed Propellers 5. Normally Aspirated Engines with Fixed Pitch Propellers 6. Turbopropeller Engines Appendix 2. Climb Data Reduction 1. Drag Polar Method 2. Density Altitude Method Appendix 3. Static Minimum Control Speed 1. General 2. Calculation Method 3. Cautions and Assumptions 4. Sample Calculations Appendix 4 FAR-23 Manuals, Markings, & Placards Checklist Appendix 5 –Guide for Preparing Airplane Flight Manual and Pilots’s Operating Handbook Supplements 1. Introduction 2. General Appendix 6. Sample Kinds of Operating Equipment List Appendix 7. Useful Information Appendix 8. Conversion Factors Table Appendix 9. Airspeed Calibrations Introduction General Discussion of the Various Flight Test Techniques 1. Trailing Bomb or Cone Method 2. Speed Course Method 3. GPS Method 4. Pace Airplane Method 5. Pitot Static Boom Data 6. Tower Fly By Method 7. Ground Run Airspeed System Calibration Appendix 10. Guide for Determining Climb Performance After STC Modifications 1. Introduction 2. General 3. Procedure for Extending Climb Performance to Additional Airplanes 4. ‘One Only’ Airplane x 11/16/2011 AC 23-8C List of Figures Figure 1 Stall Speed ..................................................................................................................... 17 Figure A1-1 – Brake Horsepower Versus Pressure Altitude Figure A1-2 - Turbocharged Brake Horsepower Versus Altitude Figure A2-1 - Coefficient of Drag Versus Coefficient of Lift Figure A3-1 - Thrust Horsepower at Sea Level Figure A7-1 – U.S. Standard Atmosphere (1962) Figure A7-2 – Temperature Conversion Chart Figure A7-3 – Determination of Air Temperature in Relation to International Standard Atmosphere Figure A7-4 – Density/Pressure Altitude Conversion Figure A7-5 – Compressibility Correction CAS Figure A7-6 – Altimeter Error vs. CAS Figure A7-7 – Temperature RAM Rise Figure A7-8 – Stalling Speed as a Function of Angle of Bank Figure A7-9 – Vectoral Acceleration Versus Angle of Bank Figure A7-10 Figure A7-11 – Takeoff and Landing Crosswind Component Chart Figure A9-1 - Error Analysis of Ground Course Method Figure 2 Propeller Coefficients.................................................................................................... 19 Figure 3 Zero Thrust .................................................................................................................... 19 Figure 4 Thrust Effect on Stall CL ............................................................................................... 20 Figure 5 - Accelerate-Stop Time Delays ...................................................................................... 35 Figure 6 Takeoff Distance Critical Engine Failure Recognized at V1......................................... 43 Figure 7 - Takeoff Distance - All Engines Operating................................................................... 43 Figure 8 - Takeoff Run - Critical Engine Failure Recognized at V1 ............................................ 44 Figure 9 - Takeoff Run - All Engines Operating .......................................................................... 44 Figure 10 - Clearway Profiles ....................................................................................................... 45 Figure 11 - Takeoff Segments and Nomenclature ........................................................................ 46 Figure 12- Net Takeoff Flight Path............................................................................................... 47 Figure 13 - Observed Data............................................................................................................ 49 Figure 14 - Rate of Climb vs. Airspeed ........................................................................................ 51 Figure 15 - Rate of Climb and Speeds .......................................................................................... 52 Figure 16 - Landing Time Delays................................................................................................. 61 Figure 17 - Stick Force Per G ....................................................................................................... 77 Figure 18 - Static Longitudinal Stability Data.............................................................................. 80 Figure 19 - Low Speed Instabilities; Normal, Utility, and Acrobatic Airplanes .......................... 81 Figure 20 - Low Speed Instabilities; Commuter Airplanes .......................................................... 82 Figure 21 – Static Longitudinal Stability Data over Complete Speed Range............................... 83 Figure 22 - Static Longitudinal Stability Plot (Cruise Condition)................................................ 86 Figure 23 - Spin Evaluation Configuration Matrix..................................................................... 103 Figure 24 – Sample Calculation.................................................................................................. 128 Figure 25 – Corrected Cylinder Barrel Temperature.................................................................. 131 Figure 26 – Correct Cylinder Head Temperature ....................................................................... 132 Figure 27 - Carburetor Air Heat Rise Calculations .................................................................... 135 Figure 28 - Carburetor Air Heat Rise Plots ................................................................................ 136 xi 11/16/2011 AC 23-8C Figure A9-2 - Summary of PEC Test Methods Figure A9-3 - Sketches of Trailing Static Bomb and the Trailing Static Cone (not to scale) Figure A9-4 - Typical Position Error Correction Data for an Aircraft Figure A9-5 Typical Position Error Corrections Data for an Aircraft Figure A9-6 Tower Fly-By Method Figure A9-7 - Trapped Static Source Schematic Figure A9-8 - Ground Airspeed Calibration xii 11/16/2011 AC 23-8C List of Tables Table 1 - Tolerances........................................................................................................................ 3 Table A3-1 – Flight Test Data Table A3-2 - Tabulated Thrust Horsepower Available and Calculated VMC Table A9-1 - Sample Speed Course Data and Data Reduction Table A9-2 - Trapped Static (TS) Data Reduction Table A9-3 - Sample Ground Airspeed Calibration Using a Distance Measuring Unit Table 2 - Corrections to Standard Value Parameter ....................................................................... 3 Table 3 – Sample Portion of Airspeed Indicator Calibration ......................................................... 5 Table 4 - Smooth, Flat Runway .................................................................................................... 14 Table 5 - AFM Acceleration Height ............................................................................................. 39 Table 6 - WAT Chart .................................................................................................................... 54 Table 7 - Procedures ..................................................................................................................... 76 Table 8 - Trim Systems Requirements........................................................................................ 113 Table 9 – Sample of Co-Concentration Matrix........................................................................... 116 Table 10 – Light Duration........................................................................................................... 141 xiii 11/16/2011 AC 23-8C Chapter 1. Subpart A--General 1. § 23.1 Applicability. a. Explanation. (1) Airplane Categories. Section 23.1(a) is introductory and prescribes the airplane categories eligible for certification under 14 CFR part 23. Applicants should refer to 14 CFR part 21 for certification procedures. (2) Design Data. Section 23.1(b) requires an applicant to demonstrate compliance by some acceptable means even though the FAA has previously certificated an identical alteration for someone else and has the supporting data on file. Design data submitted with an application for certification is not releasable to the public or any other applicant without the consent of the data holder. b. Procedures. None. 2. § 23.3 Airplane Categories. a. Explanation. For normal/utility category as well as for commuter category airplanes, stalls (except whip stalls) are approved maneuvers. In this context, approved stalls are to be understood to be stalls as defined in §§ 23.49, 23.201, and 23.203. b. Procedures. None. 1 11/16/2011 AC 23-8C Chapter 2 Subpart B – Flight Section 1. General 1. § 23.21 Proof of Compliance. a. Explanation. (1) Determining Compliance. This section provides a degree of latitude for the FAA test team in selecting the combination of tests or inspections required to demonstrate compliance with the regulations. Engineering tests are designed to investigate the overall capabilities and characteristics of the airplane throughout its operating envelope and should include sufficient combinations of weight, center of gravity, altitude, temperature, airspeed, and so forth, necessary to define the envelope and show compliance within. These engineering tests should define the limits of the entire operating envelope and establish compliance with the regulations. If compliance cannot be established between these points, additional testing should be conducted to determine compliance. The applicant could also apply for an equivalent level of safety (ELOS) or an exemption to the regulation if warranted by new designs or technology. Testing should confirm normal and emergency procedures, performance information, and operating limitations that are to be included in the airplane flight manual (AFM). (2) Flight Tests. Section 21.35 requires, in part, that the applicant make flight tests and report the results of the flight tests. After the applicant has submitted sufficient data to the FAA showing that compliance can be met, the FAA will conduct any inspections, flight, or ground tests required to verify the applicant's test results. Compliance may be based on the applicant's engineering data and a spot check or validation through FAA flight tests. The FAA testing should obtain validation at critical combinations of proposed flight variables if compliance cannot be established using engineering judgment from the combinations investigated. (3) Use of Ballast. Ballast may be carried during the flight tests whenever it is necessary to achieve a specific weight and center of gravity (c.g.) location. Consideration should be given to the vertical as well as horizontal location of the ballast in cases where it may have an appreciable effect on the flying qualities of the airplane. The strength of the supporting structures should be considered to preclude their failure as a result of the anticipated loads that may be imposed during the particular tests. (4) Flight Test Tolerances. The purpose of the tolerances specified in § 23.21(b) is to allow for variations in flight test values from which data are acceptable for reduction to the value desired. They are not intended for routine test scheduling at the lower weights, or to allow for compliance to be shown at less than the critical condition; nor are they to be considered as allowable inaccuracy of measurement (such as in an airspeed calibration). Where variation in the parameter on which a tolerance is allowed will have an effect on the results of the test, the result should be corrected to the most critical value of that parameter within the operating 2 11/16/2011 AC 23-8C envelope being approved. If such a correction is impossible or impractical, the average test conditions should assure that the measured characteristics represent the actual critical value. (5) Additional acceptable tolerances. Additional acceptable tolerances appear in table 1 below: Table 1 - Tolerances Item Tolerance Airspeed 3 knots or ±3 percent (%), whichever is greater Power ±5 percent Wind (takeoff and, landing tests, not for crosswind component testing) As low as possible, but not to exceed approximately 12 percent VS1 or 10 knots, whichever is lower, along the runway measured at a height of 6 feet above the runway surface. At higher wind velocities, the data may be unreliable due to wind variations and unsmooth flight conditions. (6) Corrections to a standard value. Cases in which corrections to a standard value of the parameter are normally allowed appear in table 2 below: Table 2 - Corrections to Standard Value Parameter Test Weight Density Power/ Thrust Airspeed Other Takeoff Performance X X X X Wind, runway gradient Landing Performance X X — X Wind, runway gradient Stall Speed X — — — Climb Performance X X X X Acceleration Glide Performance X X - X VMC — X X — (7) Function and Reliability (F&R) Test. Section 21.35(b)(2) specifies the requirements of F&R tests, which are required for aircraft with a maximum certificated weight over 6,000 pounds (lbs) (2730 kilograms (kg)). (Complex airplanes that include features like Full Authority Digital Engine Control (FADEC) engines, pressurization, and avionics integrated with flight 3 11/16/2011 AC 23-8C management software (FMS) and autopilot capability should consider a comprehensive F&R testing program regardless of weight.) b. Procedures. (1) Test Plan. Efforts should begin early in the certification program to provide assistance to the applicant to develop a certification plan and subsequently a test plan to ensure coverage of all certification requirements. The applicant should develop a test plan that includes the required instrumentation. (2) Instrument Calibration. Test instrumentation (transducers, indicators, and other installed instrumentation) should be calibrated (removed from the airplane and bench checked by an approved method in an approved facility) within six months of the tests. When electronic recording devices are used, such as oscillographs, data loggers, and other electronic data acquisition devices, preflight and post-flight parameter recalibrations should be run for each test flight to ensure that none of the parameters have shifted from their initial zero settings. Critical transducers and indicators for critical tests (for example, airspeed indicators and pressure transducers for flight tests to VD) should be calibrated within 60 days of the test in addition to the other requirements mentioned above. The instrument hysteresis should be known; therefore, readings at suitable increments should be taken in both increasing and decreasing directions. Calibration records, like the one shown in table 3, should be signed by the agent of the repair or overhaul facility doing the work and be available to the test pilot prior to beginning test flying. It should be emphasized that these calibrations must be accomplished at an approved facility. For example, performing a pitot-static/air data system leak check to "calibrate" an airspeed indicator, whether in or out of the airplane, is not acceptable. 4 11/16/2011 AC 23-8C Table 3 – Sample Portion of Airspeed Indicator Calibration XYZ INSTRUMENT SERVICE, INC. ABC CITY AIRPORT APPROVED REPAIR STATION - NO. 1234 8/12/80 P/N 1701DX8-04 S/N AF55-17044 A/S Indicator KNOTS Master Test Ascent Indicator Reads Descent Indicator Reads 40 38.0 39.0 50 49.0 50.5 60 59.5 61.0 70 70.0 71.0 80 80.0 81.0 (3) Use of Ballast. (i) Loading. Ballast loading of the airplane can be accomplished several ways to achieve a specific weight and c.g. location as long as the loading remains within the physical confines of the airplane. In flight test work, loading problems will occasionally be encountered, making it difficult to obtain the desired c.g. location. Those cases may require loading in engine compartments or other places not designed for load carrying. When this condition is encountered, care should be taken to ensure that local structural stresses are not exceeded or that airplane flight characteristics are not changed due to changes in moments of inertia caused by adding a very long arm (tail post, and so forth). (ii) Solid and Liquid Ballast. There are basically two types of ballast that may be used in airplane loading: solid or liquid. The solids are usually high-density materials such as lead or sandbags, while the liquid is usually water. In critical tests, the ballast should be loaded in a manner so that disposal in flight, if considered, can be accomplished and be located at a point that will produce a significant c.g. shift to a less critical c.g. location. Applicants should perform a simple structural analysis for complex load installations that have the potential to interfere with safe flight and landing if there was a failure of the supporting structure. In any case, the load should be securely attached in its loaded position. In airplanes with multiple fuel 5 11/16/2011 AC 23-8C tank arrangements, the fuel load and distribution should be considered for weight and c.g. control. (4) Function and Reliability (F&R) Tests for Airplanes over 6,000 pounds Maximum Certificated Weight. While § 21.35(b)(2) does not require F&R testing for airplanes weighing less than 6000 lbs., the Small Airplane Directorate’s policy is to require (via special conditions) a comprehensive Function and Reliability testing program regardless of weight for complex airplanes that include features like FADEC controlled engines, pressurization, and avionics integrated with FMS and autopilot capability. (i) A comprehensive and systematic check of all aircraft components must be made to assure that they perform their intended function and are reliable. (ii) F&R certification testing must be accomplished on an aircraft that is in conformity with the approved type design. Furthermore, the number of airplanes used should be limited to meet the intent of F&R testing. F&R certification testing should follow the type certification testing. This is to assure that significant changes resulting from type certification tests can be incorporated on the aircraft and successfully retested prior to the F&R tests. (a) A certain portion of the F&R test program should emphasize systems, operational conditions, or environments found particularly marginal during type certification tests. Applicants should put the aircraft in as many different environments as possible (for example, cold, hot, rain, etc.) as well as different types of airports to exercise the systems as they will be in the field. Note: It is important to perform F&R testing with the configuration the manufacturer is planning to deliver to the customer (this may be different than what is configured at the end of initial certification). This is especially important in the case of software and post-TC changes. (iii) All components of the aircraft should be periodically operated in sequences and combinations likely to occur in service. Ground inspection should be made at appropriate intervals to identify potential failure conditions; however, no special maintenance beyond that described in the Aircraft Maintenance Manual should be allowed. (iv) A complete record of defects and failures should be maintained along with required servicing of aircraft fluid levels. Results of this record should be consistent with inspection and servicing information provided in the Aircraft Maintenance Manual. 2. § 23.23 Load Distribution Limits. a. Explanation. (1) C.G. Envelope. The test tolerance of ±7 percent of the total c.g. range (given in § 23.21) is intended to allow some practical relief for in-flight c.g. movement. This relief is only acceptable when the test data general scatter is on either side of the limiting c.g. or when c.g. 6 11/16/2011 AC 23-8C correction from test c.g. to limit c.g. is acceptable. Sufficient points inside the desired weight and balance envelope should be explored to ensure that the operational pilot will not be placed in an unsafe condition. Should unsatisfactory flight characteristics be present, the limits of the envelope should be reduced to ensure safe margins. Where variation in the c.g. position may have a significant effect on the result of a test (for example, spins and VMC), the result should be corrected to the most critical c.g. position within the operating limits to be approved. If such a correction is impractical or may be unreliable, the actual test should ensure that the measured characteristics represent the critical value. (2) Narrow Utility C.G. Envelope. Some utility category airplanes, for which spin approval is sought, may have a very narrow c.g. range. If a limited fuel load is required to achieve the narrow c.g. envelope, the test pilot should ensure that loading instructions or aids (such as fuel tank tabs) will enable the operational pilot to stay in the approved c.g. envelope. (3) Gross Weight Effects. The test pilot is expected to determine the effect that gross weight, including low-fuel state, may have on the airplane's flight characteristics. If it is found the flight characteristics would be adversely affected, tests should be performed for trim, stability, and controllability including VMC, stalls, and spins under the most adverse weight condition. Separate loading restrictions may apply to certain flight operations, such as spins. (4) Lateral Loads. If possible loading conditions can result in a significant variation of the lateral c.g., this lateral range of c.g. must be established by: (i) The limits selected by the applicant; (ii) The limits for which the structure has been proven; or (iii) The limits for which compliance with all the applicable flight requirements has been demonstrated. The demonstrated weight and c.g. combinations should consider asymmetric loadings. When investigating the effects of asymmetric lateral loads, the following sections in this flight test guide (FTG) represent applicable flights requirements: (a) § 23.143 Controllability and Maneuverability, General. (b) § 23.147 Directional and lateral control. (c) § 23.149 Minimum control speed. (d) § 23.151 Acrobatic maneuvers. (e) § 23.157 Rate of roll. (f) § 23.161 Trim. (g) § 23.201 Wings level stall. (h) § 23.203 Turning flight and accelerated turning stalls. (i) § 23.221 Spinning. (j) § 23.233 Directional stability and control. (k) § 23.701 Flap interconnection. b. Procedures. None. 7 11/16/2011 AC 23-8C 3. § 23.25 Weight Limits. a. Explanation. (1) Maximum Weight Limits. The maximum weight may be limited in three ways: at the election of the applicant, by structural design requirements, or by flight requirements. (2) Maximum Weight Exceptions. The regulations concerning design maximum weight allow an exception that some of the structural requirements may be met at a lesser weight known as a design landing weight, which is defined in § 23.473. (Refer to Advisory Circular (AC) 23-7 if the airplane is being modified for an increase in maximum weight.) Due to changes in the operational requirements of an owner/operator, in many cases the need arises to modify and substantiate the structure for an increase in maximum weight and maximum landing weight. Any one of these increases affects the airplane's basic loads and structural integrity, and they could affect the limitations and performance. (i) If an airplane was certificated with maximum landing weight equal to maximum weight, some applicants take advantage of the five percent difference between design landing and design maximum weight permitted by § 23.473(b). These applicants use the STC process. In these cases, re-substantiation of the landing gear for landing loads is not required when increasing the maximum weight by as much as five percent. For those programs involving more than a five percent increase in maximum weight, some re-substantiation of the landing gear should be accomplished. (ii) Other applicants are replacing piston engines with turbopropeller engines, thus requiring that gasoline be replaced with jet fuel, which weighs as much as 17 percent more. In some cases, the quantity of fuel is being increased at the same time as engine replacement, but the maximum zero fuel weight remains the same. (iii) All the above types of modifications should be investigated to verify that critical loads have not increased or that those loads that have increased are capable of being carried by the existing or modified structure. (3) Weight, Altitude, Temperature (WAT). For all airplanes with a maximum takeoff weight exceeding 6,000 pounds and turbine engine airplanes, a WAT chart may be used as a maximum weight limitation. (4) Ramp Weight. The applicant may elect to use a "ramp weight" provided compliance is shown with each applicable section of part 23. Ramp weight is the takeoff weight at brake release plus an increment of fuel weight consumed during engine start, taxiing, and run- up. Generally, this increment of fuel should not exceed one percent of the maximum permissible flight weight up to 125 pounds. The pilot should be provided a means to reasonably determine the airplane gross weight at brake release for takeoff. A fuel totalizer is one way of providing the pilot with fuel on board. Alternately, a mental calculation by the pilot may be used, if the pilot is provided the information to make the calculation and the calculation is not too complex. Normally, fuel for engine start and run-up will be sufficiently close to an amount fixed such that taxi can be considered as the only variable. If the pilot is provided with taxi fuel burn rate in 8 11/16/2011 AC 23-8C pounds per minute, then the resulting mental calculation is acceptable. The pilot will be responsible to ensure that the takeoff gross weight limitation is complied with for each takeoff, whether it is limited by altitude, temperature, or other criteria. The maximum ramp weight should be shown as a limitation on the TC Data Sheet and in the AFM. (5) Lowest Maximum Weight. Sections 23.25(a)(2)(i) and 23.25(a)(2)(ii) require that each of the two conditions, (i) and (ii), must be considered and that the maximum weight, as established, not be less than the weight under either condition. This has to be shown with the most critical combinations of required equipment for the type of operation for which certification is requested. (6) Placarding of Seats. When establishing a maximum weight in accordance with § 23.25(a)(2)(i), one or more seats may be placarded to a weight of less than 170 pounds (or less than 190 pounds for utility and acrobatic category airplanes). An associated requirement is § 23.1557(b). The AFM loading instructions, required by § 23.1589(b), should be specific in addressing the use of the placarded seats. b. Procedures. None. 4. § 23.29 Empty Weight and Corresponding Center of Gravity. a. Explanation. (1) Fixed Ballast. Fixed ballast refers to ballast that is made a permanent part of the airplane as a means of controlling the c.g. (2) Equipment List. Compliance with § 23.29(b) may be accomplished with an equipment list that defines the installed equipment at the time of weighing and the weight, arm, and moment of the equipment. b. Procedures. For prototype and modified test airplanes, it is necessary to establish a known basic weight and c.g. position (by weighing) from which the extremes of weight and c.g. travel required by the test program may be calculated. Normally, the test crew will verify the calculations. 5. § 23.31 Removable Ballast. a. Explanation. This regulation is associated only with ballast that is installed in certificated airplanes under specified conditions. The ballasting of prototype airplanes so that flight tests can be conducted at certain weight and c.g. conditions is covered under § 23.21, paragraph 3, of this AC. b. Fluid Cargo. For those airplanes configured to carry fluid cargo (such as agricultural chemical tanks, minnow tanks, slurry tanks, and so forth), airplane handling qualities should be evaluated for controllability and non-exceedance of the limitations at the full and the most critical partial fluid loads. When so equipped, the effects of in-flight jettison or dumping of the 9 11/16/2011 AC 23-8C fluid load should be evaluated to establish that the pilot is able to exercise sufficient control to prevent unacceptably large flight path excursions or exceedance of operational/structural limits. 6. § 23.33 Propeller Speed and Pitch Limits. a. Explanation. Section 23.33(a) requires that propeller speed and pitch be limited to values that will ensure safe operation under normal operating conditions. b. Procedures. (1) Fixed Pitch Propellers. (i) Maximum Revolutions per Minute (r.p.m.). The regulation is self-explanatory. (ii) Static r.p.m. Determine the average static r.p.m. with the airplane stationary and the engine operating at full throttle under a no-wind condition. The mixture setting should be the same as used for maximum r.p.m. determination. If the wind is light (5 knots or less), this static r.p.m. can be the average obtained with a direct crosswind from the left and a direct crosswind from the right. (iii) Data Sheet r.p.m. Determination. For fixed pitch propellers, the static r.p.m. range is listed in the TC Data Sheet: for example, not more than 2200 r.p.m. and not less than 2100 r.p.m. The allowable static r.p.m. range is normally established by adding and subtracting 50 r.p.m. to an average no-wind static r.p.m. Applicants should account for altitude and temperature effects in the TCDS. An applicant may desire to obtain approval for one or more additional propellers and retain only one r.p.m. range statement. An applicant may also choose to extend the propeller's static r.p.m. range. (a) Lower r.p.m.. The static r.p.m. range may be extended on the low side by obtaining approval for a propeller with a lower static r.p.m. In this case, the approval must be accomplished with due consideration of performance requirements. The airplane with the new propeller installed must be able to meet the minimum climb performance requirements. (b) Higher r.p.m.. If the static r.p.m. range is to be extended upward, the new propeller would have to be tested to ensure that it did not cause an engine speed above 110 percent of maximum continuous speed in a closed throttle dive at the never-exceed speed. It must not exceed the rated takeoff r.p.m. of the engine up to and including the best rate of climb speed of the airplane. An engine cooling climb test may also be required due to the additional power produced by the faster turning propeller. (2) Controllable Pitch Propellers Without Constant Speed Controls. (i) Climb r.p.m. With the propeller in full low pitch, determine that the maximum r.p.m. during a climb using maximum power at the all-engine(s)-operating climb speed does not exceed the rated takeoff r.p.m. of the engine. 10 11/16/2011 AC 23-8C (ii) Dive r.p.m. With the propeller in full high pitch, determine that the closed throttle r.p.m. in a dive at the never-exceed speed is not greater than 110 percent of the rated maximum continuous r.p.m. of the engine. (3) Controllable Pitch Propellers With Constant Speed Controls. (i) Climb r.p.m. With the propeller governor operative and propeller control in full high r.p.m. position, determine that the maximum power r.p.m. does not exceed the rated takeoff r.p.m. of the engine during takeoff and climb at the all-engine(s)-operating climb speed. (ii) Static r.p.m. With the propeller governor made inoperative by mechanical means, obtain a no-wind static r.p.m. (a) Reciprocating Engines. Determine that the maximum power static r.p.m., with the propeller blade operating against the low pitch stop, does not exceed 103 percent of the rated takeoff r.p.m. of the engine. (b) Turbopropeller Engines. Although this rule references manifold pressure, it has been considered to be applicable to turbopropeller installations. With the governor inoperative, the propeller blades at the lowest possible pitch, with takeoff power, the airplane stationary, and no wind, ensure that the propeller speed does not exceed the maximum approved engine and propeller r.p.m. limits. Propellers that go to feather when the governor is made inoperative need not be tested. (iii) Safe Operation Under Normal Operating Conditions. (a) Reciprocating Engines. Descent at VNE with full power, although within the normal operating range, is not a normal operating procedure. Engine r.p.m., with the propeller on the high pitch blade stops, that can be controlled by retarding the throttle may be considered as acceptable in showing compliance with § 23.33(a). (b) Turbopropeller Engines. Perform a maximum r.p.m. at maximum torque (or power) descent at VMO to ensure that normal operating limits for the propeller are not exceeded. (4) Data Acquisition and Reduction. Outside air temperature and altitude needs to be considered for the ground tests. The observed r.p.m. data in each case must be corrected for tachometer error. The airspeed system error must also be taken into consideration to determine the proper calibrated airspeed. True airspeed may also need to be considered because propeller angle of attack is a function of true airspeed. Section 2. Performance 1. § 23.45 General. a. Explanation. 11 11/16/2011 AC 23-8C (1) Atmospheric Standards. The purpose of § 23.45(a) is to set the atmospheric standards in which the performance requirements should be met. The air should be smooth with no temperature inversions, mountain waves, and so forth. This is essential to obtaining good data and repeatable results. Non-standard conditions of temperature, pressure, and so forth, can be corrected to standard, but there are no corrections to compensate for poor quality data due to turbulence or poor pilot technique. A thorough knowledge of the limitations of the testing procedures and data reduction methods is essential so that good engineering judgment may be used to determine the acceptability of any tests. (i) Reciprocating Engine-Powered Airplanes Below 6,000 pounds (2730 kg) Maximum Weight. Performance tests will normally be conducted in non-standard atmospheric conditions, but ideally for accuracy in data reduction and expansion, tests should be conducted in atmospheric conditions as near those of a standard atmosphere as possible. Accounting for winds and non-standard conditions requires testing procedures and data reduction methods that reduce the data to standard atmospheric conditions. (ii) Reciprocating Engine-Powered Airplanes of More Than 6,000 pounds (2730 kg) Maximum Weight and Turbine-engine Powered Airplanes. Performance tests should be conducted in the range of atmospheric conditions that will show compliance with the selected weight, altitude, and temperature limits. Refer to § 23.53 of this AC for guidance on extrapolation of takeoff data and § 23.75 for extrapolation of landing data. (2) Standard Atmosphere. The Standard Atmosphere is identical to the International Civil Aviation Organization (ICAO) Standard Atmosphere for altitudes below 65,000 feet. Appendix 7, figure 1, gives properties of the Standard Atmosphere in an abbreviated format. (3) Installed Power. The installed propulsive horsepower/thrust of the test engine(s) may be determined using the applicable method described in appendix 1, based on the power approved during airplane certification. The methods in appendix 1 account for installation losses and the power absorbed by accessories and services. Consideration should also be given to the accuracy of the power setting instruments/systems, and the pilot's ability to accurately set the power/thrust. (4) Propeller Cutoff. In general, if the airplane will be approved with an allowable cutoff for the propeller, then the performance flight testing should be done using the most critical propeller diameter. In most cases, this is expected to be the minimum diameter propeller allowed. (i) For normal, utility, and acrobatic category airplanes only, a two percent margin was the allowed reduction in propeller diameter. Historically, the two percent margin was selected as being the maximum permissible reduction in diameter of a given propeller that will not noticeably reduce performance. Service history has shown this to be an acceptable margin without additional flight testing. 12 11/16/2011 AC 23-8C (5) Flight Procedures. The flight procedures must not be unduly sensitive to less than ideal atmospheric conditions. The atmospheric conditions "reasonably expected to be encountered in service" may be different depending on the class of aircraft, but should cover at least the maximum demonstrated crosswind component established in compliance with § 23.233(a). (6) Flight Test Data. For calibrated engines, test day power is the calibrated test day power. For uncalibrated engines, an acceptable method is to assume that the test day power is the upper tolerance chart brake horsepower; however, the upper tolerance chart brake horsepower for reciprocating engines using 14 CFR part 33 tolerances of +5 percent, -0 percent may lead to unrealistic performance. Historically, the two major reciprocating engine manufacturer’s engines have tolerances closer to +2 percent, -0 percent. Refer to appendix 1 for further information. The performance data required by § 23.1587 is dependent on the horsepower assumed for the various temperature and altitude conditions. Refer to appendix 1, which deals both with test data reduction and expansion. (7) Humidity Correction. Refer to appendix 1. b. Procedures. Refer to appendix 1. c. Operation on Unpaved Runways. (1) Small airplane operations from grass runways. For airplanes less than 6,000 pounds (2730 kg) maximum weight, the factors given below may be quoted in the flight manual, as an alternative to the scheduling of data derived from testing or calculation. It should be noted that these factors are intended to cover the range of airplane types in this category and are necessarily conservative. Manufacturers are, therefore, encouraged to produce and schedule their own data in accordance with (1) and (2) above to obtain optimized performance for their airplane. 13 11/16/2011 AC 23-8C Table 4 - Smooth, Flat Runway Takeoff Landing Dry Grass 1.2 1.2 Wet Grass 1.3 1.6 Note: If the runway is not smooth, the grass is very long or very short, higher factors may be warranted. Very short grass = golf course length Very long grass = unmowed field or high interstate highway median grass length (2) Airplanes with 6,000 pounds (2730 kg) maximum weight or more. The following guidance was developed to include high performance multiengine airplanes. The level of detail should be scaled back to that appropriate for the airplane. Simple, single-engine turbine bush airplanes, for example, do not need the level of detail discussed here. Operations on other than smooth, dry, hard runway surfaces may require specific approval and the scheduling of information on the effect of those surfaces on takeoff and landing distances in the flight manual. Applicants may use the factors for grass runways in paragraph (1). These factors would, in many cases, result in such conservative distances that operational utility may be compromised. Applicants may propose their own factors if accompanied with supporting data. To obtain approval for takeoff and landing operations on unpaved runway surfaces, compliance with the following should be shown: (i) Each type of surface must be defined so that it can be recognized in operations in service including conditions such as day or wet. (ii) It must be determined that the airplane can be operated on each defined surface without hazard from likely impingement or engine ingestion of any foreign objects that constitute parts of the surface. (iii) If any special procedures or techniques are found to be necessary, these must also be determined and scheduled. (iv) The takeoff and landing performance on each defined surface must be determined in accordance with §§ 23.53 and 23.75, as modified in (3) below. (3) Takeoff and Landing Data. Takeoff and landing data must be determined for each type of unpaved surface for which approval is requested. (i) The test runways on which the takeoff and landing distance measurements are conducted should be chosen to be representative of the worst characteristics (that is, high rolling friction, low braking friction) of each of the types of runway under consideration. 14 11/16/2011 AC 23-8C (ii) In establishing the operation limitations for a particular type of unpaved runway, the runway’s load bearing characteristics, rolling and braking friction, and impingement and ingestion characteristics, should be considered. e. Wet and Contaminated Runways. Reserved. 2. § 23.49 Stalling Speed. a. Explanation. (1) 61 Knot Stall Speed. The 61 knot stalling speed applies to the maximum takeoff weight for which the airplane is to be certificated. (2) Background. Since many of the regulations pertain to performance, handling qualities, airspeed indicator markings, and other variables that are functions of stall speeds, it is desirable to accomplish the stall speed testing early in the program so the data are available for subsequent testing. Because of this interrelationship between the stall speeds and other critical performance parameters, it is essential that accurate measurement methods and careful piloting techniques be used. Most standard airplane pitot-static systems have not been found to be acceptable for stall speed determination. These tests require the use of properly calibrated instruments and usually require a separate test airspeed system, such as a trailing bomb, a trailing cone, or an acceptable nose or wing boom. The stall speed determinations necessary for marking the airspeed indicator are in terms of indicated airspeed (IAS) corrected for instrument error. The other stall speeds are in terms of calibrated airspeed (CAS). Thus, a production airspeed system should be available during stall speed measurements to determine stall speeds in terms of IAS. (3) Stall Definition. Section 23.49(d) requires the VS0 and VS1 speeds to be determined using the procedures specified in § 23.201. Refer to 14 CFR part 1 and § 23.49 for definitions of VS0 and VS1. “Landing configuration” in part 23 is gear down and full flaps. Section 23.201(b) defines when the airplane can be considered stalled for airplane certification purposes when one of three conditions occurs, whichever occurs first. The conditions are: (i) Uncontrollable downward pitching motion; (ii) Downward pitching motion resulting from the activation of a device (for example, stick pusher); or, (iii) The control reaches the stop. (a) For those airplanes where the control reaches the stop, VS is considered to be the minimum speed obtained while the control is held against the stop. Elevator limited airplanes may or may not develop a minimum steady flight speed. Refer to figure 1 for a graphic representation of stall speed time histories for various configurations. The time the control is held against the stop for stall speed determination should be a minimum of two seconds and consistent with the time against the stop for stall characteristics testing in § 23.201. 15 11/16/2011 AC 23-8C Additionally, for airplanes with a stall barrier system, stick pusher operation has been considered as the stall speed. The term "uncontrollable downward pitching motion" is the point at which the pitching motion can no longer be arrested by application of nose-up elevator and is not necessarily the first indication of nose-down pitch. (4) Reciprocating Engine Throttle Position. For reciprocating engine airplanes, the stalling speed is that obtainable with the propellers in the takeoff position and the engines idling with throttles closed. As an alternative to "throttles closed," the regulations allow the use of sufficient power to produce zero propeller thrust at a speed not more than 10 percent above the stalling speed. The regulations do not allow any alternative to the use of "propellers in the takeoff position," nor is any alternative intended except that the use of a feathered propeller in certification stalling speed tests is acceptable only when it has been determined that the resulting stalling speed is conservative (higher). If the stalling speed tests are to be conducted with the propellers delivering zero thrust, a dependable method of determining inflight thrust, such as a propeller slipstream rake, should be available in flight. The practice of establishing zero thrust r.p.m. by calculation is also acceptable. One calculation method is given in paragraph (5) below. Analytical corrections may be acceptable if satisfactory accounting is made for the effects of propeller efficiency, slipstream, altitude, and other pertinent variables. (5) Zero-Thrust r.p.m. Calculation. (i) Zero-thrust r.p.m. can be calculated by using the propeller manufacturer's propeller coefficient curves. The thrust will be zero when the propeller thrust coefficient is zero for the particular propeller blade angle. Using the propeller coefficient curves, obtain or construct a chart like figure 2, where: CT = thrust coefficient CP = power coefficient ß = blade angle setting J = advance ratio 16 0 w UJ a.. V') ~ < ·- ·· l · ·:· t · ::: TRIM SPEED -··-- ----- TRIM SPEED -- -·- ----- ,__ _. 1----· t- . - · -· ... - . . - :::::: __::::: ·- :-_ :::- :::-::- .. - ...... ·- ... - . - .. ......... =:: - .... ... -··. :: : : ::__:. : : : : . --- .. - -----· :=: =:: i-: -:-~: ::.:: ... : :..:: :::.:. :::...:: :::.: .. ·-- ~ -- .-.- : :.-= : ::: ..:. ....: ···- :t:::::r,,.;__· ·. :::: ::: :-:::: . ·- · ·- ···- ·- - ···· t---- ELEVATOR REACHES STOP ,-_-+_ --+--+--ELE VATOR ~ '::. .:::· =:: ---_;_ ._::::.: CONTROL ::-:-:- LIMITED* ::::: - . . :'"'"-1. •• - 1·. . .. .. . ·-. ::.. ,.: ·-. 1-"'. ~= : -·- .... .. .. :::; :::: :::: :::: :::: ~ ~~6:. ·:: :::: :::. ···- ........ ·-:: :::·: :::-:- ::.:f--:-;: ::: . :·:: :::: :::: :·· · 1,~ . . ·- · ·- -···. __,._ . - . .. . 1 .... 1 .. 1 .• •• j •••• , .. .. ::~: ::: =11:·. ~~ : ·: :: ::: :. ·c:-r =--~ ::-:.~ :::: ARTIFICIAL BARRIER ·-·- ;:;i ~j ~ ~i .·!j ?-:~~ ;~ -~~ ~~~ _:: :: :::: . \_~USHER SY~! ~ )__ : :: :. ::: : ~ ~-- :t.· : :· 7." ::: ENTRY .:- ..:....:.~: ~ :: .:.;. .. : :::: ::--:- :::: :: : : : : : : - .. - - .. RATE - SLOPE - ~ ~ --- l- ... .. I- -- --- - ·-·- . : :: r.-;.... : I-- ---· ... . ·-. -- '-_-_·':"-:-.: :.::: ~: : ::.:.: : PUSHER 1-:::__ .;.;.i~4"-+ -+---i-:-:-:-+:-:--:-±: -:-:: ::-:-_~t-:.::_:-_.•± :-:-:t _:-:-_-::__:t FI RED ~ --1--- 4---- -+-· _._. ·+ .-.-_-_+-f--.-.-.+-- -+-:-:-:~ ~: :~ ~ ~~ : . . . • : - . I - -' -i _ ... --i .:::-: . ·-- ---- -·- -1-- - · -.. - .. . - . TIME - SECONDS --·- . -. ··- -- . - ... : ::-:. :.:::-: ___ _ .__ __ . -·- .. . ... .::_ :::.: 11/16/2011 AC 23-8C Figure 1 Stall Speed 17 11/16/2011 AC 23-8C (ii) The propeller blade is usually against the low pitch stop position, in the speed range of interest. Knowing the blade angle setting, the advance ratio J can be determined to give zero-thrust for the particular propeller under consideration. Knowing the value of J for zero- thrust, the propeller r.p.m. for various velocities can be calculated as follows: Propeller r.p.m. = 101.27 V JD Where: V = airplane true airspeed in knots J = advance ratio D = propeller diameter in feet (iii) The calculated velocities and propeller r.p.m. for zero-thrust can be plotted as shown in figure 3. (iv) Another approach is to use the prop rake method. In some cases this may be easier to use and more accurate. (6) Turbopropeller Thrust. For turbopropeller airplanes, § 23.49(a)(2) requires the propulsive thrust not be greater than zero during stall speed determination or, as an alternative to zero thrust, if idle thrust has no appreciable effect on stall speed, stall speed can be determined with the engines idling. If the airplane has a flight idle position, this would be the appropriate throttle position. Flight test experience has shown that some turbopropeller-powered airplanes may demonstrate a relatively high positive propeller thrust at the stall speed with the engines at flight idle. This thrust condition may yield an unconservative (lower) stall speed; therefore, just as for piston-powered airplanes, some dependable method to determine zero thrust should be available for comparison of zero thrust stall speed and flight idle stall speed or for determination of zero thrust stall speed. Residual jet thrust should be considered. Comparisons of zero thrust stall speed and flight idle stall speed should be investigated at high and low altitudes. Use of feathered propellers is acceptable if the feathered stall speeds are found to be conservative (higher). (7) Fixed Shaft Turboprops. Experience on some fixed-shaft turboprop installations indicates that stall speeds can be evaluated at mid-altitudes and appear to be totally conservative. However, if stalls are conducted at altitudes of 5,000 feet or below, the stall speed can increase dramatically. This occurs because the propeller drag characteristics are a function of true airspeed, and as true airspeed decreases, the drag goes up substantially and the flow behind the propeller on wing-mounted engines causes premature inboard wing airflow separation. (i) In addition, if the horizontal tail and the elevator are exposed to the same flow, the elevator power is decreased and tends to compound the problem. It is recommended that stall speeds be re-evaluated at low altitudes on all fixed shaft turboprops to assure that the stall speeds have not increased. 18 11/16/2011 AC 23-8C Figure 2 Propeller Coefficients CP - POWER COEFFICIENT J - ADVANCE RATIO C T =.10 CT =.08 C T =.06 CT =.04 CT =.02 CT =0 B=10 O B=15 O B=20 O B=25 O B=30 O Figure 3 Zero Thrust P R O P E L L E R R P M V-TAS IN KNOTS 19 ---- 11/16/2011 AC 23-8C (8) Turbojets and turbofans. (i) Stall speeds are normally defined with the thrust levers at idle; however, it is necessary to verify by test or analysis that engine idle thrust does not affect stall speeds to an extent that they are appreciably lower than would be experienced at zero thrust. Negative thrust at the stall, which slightly increases stall speeds, is acceptable. (ii) To determine whether thrust effects on stall speed are significant, at least three stalls should be conducted at one flap setting, with thrust set to approximately the value required to maintain level flight at 1.6 V S in the selected configuration. (iii) These data may then be extrapolated to a zero thrust condition to eliminate the effects of idle thrust on stall speeds (refer to figure 4). If the difference between idle thrust and zero thrust stall speed is 0.5 knots or less, the effect may be considered insignificant. Figure 4 Thrust Effect on Stall CL ENGINE THRUST STALL CL THRUST EFFECT ON STALL CL IDLE THRUST THRUST FOR 1.6 Vs IN LEVEL FLIGHT ZERO THRUST b. Procedures. (1) Instrumentation. (i) Test Systems. As previously mentioned, the production airspeed system is normally not sufficiently predictable or repeatable at high angles of attack to accurately measure the performance stall speeds of an airplane. However, a production airspeed system should be installed during stall speed tests to define the airspeed indicator markings required by § 23.1545. 20 11/16/2011 AC 23-8C (a) The performance stall speed test system utilized in a type certification program should be calibrated to a minimum speed at least as low as the predicted minimum stall speed anticipated on the test airplane. Test systems that have been utilized to accurately define the performance stall speeds include, but are not limited to the following: 1. Boom Systems. Swivel-head, boom-mounted, pitot-static systems with sufficient free-swivel angle to cover the stall angle-of-attack range of the airplane have been found to be acceptable. Some angle-of-attack compensated fixed pitot heads have also been found to be acceptable over a wind tunnel defined angle-of-attack range. Another way to make the fixed pitot work for stall speeds is to mount the boom at a negative incidence angle biased for the stall angle of attack. In all wing-mounted boom systems, the boom mounted static source should be at least one chord length ahead of the wing leading edge. On nose-boom mounted systems, it has been generally accepted that the static source should be at least one and one-half fuselage diameters ahead of the nose. All boom systems should be installed in a manner which assures that the boom and boom pitot-static head are structurally sound (both static and dynamic) within the proposed operating range. 2. Pitot-Static Bombs. Pitot-static bombs that are stable through the stall maneuvers have been found to provide acceptable data. 3. Trailing Cones. A trailing cone static source dynamically balanced with a swivel head pitot source, or dynamically balanced with a fixed pitot source of proven accuracy in the stall angle-of-attack range has been acceptable. The stability of the cone should be verified during stall tests and throughout its intended operating range. The length of the cone may need to be adjusted on individual airplane installations to assure cone stability. (ii) Lag Equalization. All of the systems described in paragraph (i) could involve the use of long lengths of pressure tubing, and the associated pressure lags then occur whenever either speed or altitude, or both, are changed. Probably the most important consideration in these installations (on most small general aviation airplanes) is that the test pitot-static systems should be dynamically balanced. This is easily accomplished experimentally by putting both the total head and static orifices in a common chamber and varying the pressure in the chamber at a rate corresponding to a 2,000 to 3,000 feet-per-minute rate of descent. Various volumes are inserted in the total head line until the airspeed indicator has no tendency to move in either direction from zero during the simulated rate of descent. This method results in approximately the same volume in both systems, and, for the same size tubing, the Reynolds Number of the flow through both lines will be the same. A dynamically balanced airspeed system has equal lag in both the total and static sides. Use of a balanced system simplifies the interpretation of recorded stall time histories. (iii) Lag Correction. When a balanced test airspeed system is used, it is often unnecessary to determine the actual amount of lag present. When such a determination is necessary, a method of accounting for lag errors is described in NASA Reference Publication 1046, "Measurement of Aircraft Speed and Altitude," by W. Gracey, May 1980. A lag correction is unnecessary if it can be shown that the system lag is small enough to be considered insignificant. 21 F 11/16/2011 AC 23-8C (iv) Transducer Location. The instrumentation should account for any difference in the installed location of the pressure transducers used in the cone, boom, or bomb and the aircraft system. (2) Test. (i) Stall Speed. The actual test should be commenced with the airplane in the configuration desired and trimmed at approximately 1.5 VS1 or the minimum speed trim, whichever is greater. The airplane should be slowed to about 10 knots above the stall, at which time the speed should be reduced at a rate of one knot per second or less, until the stall occurs or the control reaches the stop. Where exact determination of stalling speed is required, entry rate should be varied to bracket one knot per second, and data should be recorded to allow the preparation of time histories similar to those shown in figure 1. The indicated airspeed at the stall should be noted, using the production airspeed system. Both the IAS and the calibrated stall speeds may then be plotted versus entry rate to determine the one knot per second values. (ii) Bomb. When using a bomb, caution should be used in recovering from the stall so that the bomb is not whipped off the end of the hose. (iii) Weight and C.G. The stalling speed should be determined at all weight and c.g. positions defining the corners of the loading envelope to determine the critical condition. Data should be recorded so that the weight and c.g. at the time of the test can be accurately determined. This can often be done by recording the time of takeoff, time of test, time of landing, and total fuel used during the flight. (iv) Power and Configuration. The stall should be repeated enough times for each configuration to ensure a consistent speed. If a correction is to be made for zero thrust, then the stall speed and power at several power settings may be recorded for later extrapolation to zero thrust. (v) Control Stops. The elevator up stop should be set to the minimum allowable deflection. Flap travels should be set to minimum allowable settings. (3) Data Reduction. The correction involves: (i) Correction for airspeed error. IAS to CAS (correct for instrument as well as position error) when CAS is required. (ii) Correction for weight. Multiply the test calibrated stall speed times the square root of the standard weight divided by the test weight. WS VS = VST WT 22 11/16/2011 AC 23-8C Where: VS = Stall speed (CAS) VST= Test stall speed (CAS) WS = Standard weight (pounds) WT = Test weight (pounds) (iii) The correction for weight shown above applies only where the c.g. is not also changing with weight. Where c.g. is changing with weight, such as between forward regardless and forward gross, stall speed should account for this. A straight line variation between the measured stall speeds for the two weight and c.g. conditions has been found to be an acceptable method. 3. § 23.51 Takeoff Speeds. a. Explanation. The primary objective of this section is to determine the normal takeoff speeds for non-weight, altitude, and temperature limited airplanes. For WAT limited airplanes, the objective is to determine the takeoff speed schedules for all takeoff configurations at weight, altitude, and temperature conditions within the operational limits selected by the applicant. b. Procedures. For normal, utility, and acrobatic category airplanes, the rotation speed, (VR) in terms of calibrated airspeed, must be selected by the applicant. VR is constrained by § 23.51(a), as follows: (1) For multiengine landplanes. VR must not be less than the greater of 1.05 VMC or 1.10 VS1; (2) For single-engine landplanes. VR must not be less than VS1; and (3) For seaplanes and amphibians taking off from water. VR may be any speed that is shown to be safe under all reasonably expected conditions, including turbulence and complete failure of the critical engine. c. Procedures. For normal, utility, and acrobatic category airplanes, the speed at 50 feet should be determined by: (1) Multiengine 50-foot Speed. For multiengine airplanes, § 23.51(b)(1) requires the speed at the 50-foot point to be the higher of the following: (i) A speed that is shown to be safe for continued flight (or land back, if applicable) under all reasonably expected conditions, including turbulence and complete engine failure; or (ii) 1.1 VMC; or (iii) 1.2 VS1. 23 11/16/2011 AC 23-8C (2) Single Engine 50-foot Speed. For single-engine airplanes, § 23.51(b)(2) requires the speed at the 50-foot point to be the higher of the following: (i) A speed that is shown to be safe under all reasonably expected conditions, including turbulence and complete engine failure; or (ii) 1.2 VS1. (3) Takeoff Speed Investigations - General. Investigation of the acceptability of the takeoff speed and of the associated takeoff procedure should include a demonstration that controllability and maneuverability in the takeoff configuration are adequate to safely proceed with the takeoff in turbulent crosswind conditions and maximum approved lateral imbalance. (4) Single-engine Airplane Takeoff Speeds. The takeoff speed investigation should include a demonstration that controllability and maneuverability following engine failure at any time between lift-off and the 50-foot point are adequate for safe landing. (5) Multiengine Airplane Takeoff Speeds. For multiengine airplanes, the investigation should include a demonstration that the controllability and maneuverability following critical engine failure at any time between lift-off and the 50-foot point are adequate for either safe landing or for safe continuation of the takeoff. There will be some combinations of weight, altitude, and temperature where positive climb at the 50-foot height with one engine inoperative is not possible. Because of this, a satisfactory re-land maneuver should be demonstrated. Rotation speed should be scheduled so that the speed at 50 feet is in accordance with § 23.51(b)(1). (6) Multiple Takeoff Weights. For those multiengine airplanes for which takeoff distance data are to be approved for a range of weights, and for which the takeoff distance is based upon takeoff speeds that decrease as the weight decreases, the investigations of paragraph (3) of this section also should include consideration of the minimum control speed, VMC. The 1.2 VS design limit imposed on VMC by § 23.149 is intended to provide a controllability margin below the takeoff speed that is sufficient for adequate control of the airplane in the event of engine failure during takeoff. Hence, to maintain the intended level of safety for the lower takeoff speeds associated with the lighter takeoff weights, investigation of the acceptability of such speeds for compliance with § 23.51(b)(1) should include demonstration of acceptable characteristics following engine failure at any time between liftoff and the 50-foot point during takeoff in accordance with the established takeoff procedures. (7) Complete Engine Failure. The term "complete engine failure" has been consistently interpreted to require that, for multiengine airplanes that meet the powerplant isolation requirements of § 23.903(c) in the takeoff configuration, only one engine needs to be made inoperative in the specified investigations. 24 11/16/2011 AC 23-8C d. Jets Over 6,000 Pounds Maximum Weight and Commuter Category Airplanes. (1) Takeoff Speeds. The following speed definitions are given in terms of CAS. The AFM presentations are required, by § 23.1581(d), in IAS. (i) Section 23.51(c)(1) - Engine Failure Speed (VEF). The engine failure speed VEF is defined as the CAS at which the critical engine is assumed to fail and must be selected by the applicant. VEF cannot be less than 1.05 VMC, as determined in § 23.149. Ground controllability should also be determined to be adequate at VEF to ensure meeting the requirements of § 23.51(c)(1), that is, speed adequate to safely continue the takeoff. During the demonstration, the airplane's ground run should not deviate more than 30 feet from the pre engine-cut projected ground track. VMCG determined under 14 CFR part 25, § 25.149(f) is acceptable in lieu of 1.05 VMC. At the applicant's option, in crosswind conditions, the runs may be made on reciprocal headings or an analytical correction may be applied to determine the zero crosswind deviation. If nose wheel steering is an integral part of the rudder system and is required to be operative, then nose wheel steering may be active. Otherwise, control of the airplane should be accomplished by use of the rudder only. If the applicant elects to use VMCG, then the nosewheel steering must be disconnected as required in § 25.149(d). All other controls, such as ailerons and spoilers, should only be used to correct any alterations in the airplane attitude and to maintain a wings level condition. Use of those controls to supplement the rudder effectiveness should be avoided. (ii) Section 23.51(c)(l) - Takeoff Decision Speed (V1). The takeoff decision speed V1 may not be less than VEF plus the speed gained with the critical engine inoperative during the time interval between VEF and the instant at which the pilot recognizes the engine failure. This is indicated by pilot application of the first decelerating device, such as brakes, throttles, spoilers, and so forth, during accelerate-stop tests. The applicant may choose the sequence of events. V1 should include any airspeed system errors determined during accelerate- takeoff ground runs. Refer to the requirements of § 23.1323(c). (iii) Section 23.51(c)(2)- Rotation Speed (VR). (a) The rotation speed, VR in terms of in-ground effect CAS, must be selected by the applicant. VR is constrained by § 23.51(c)(2) as follows: 1 V1; or 2 1.05 VMC determined under § 23.149(b); or 3 1.10 VS1; or 4 The speed that allows attaining the initial climbout speed, V2, before reaching a height of 35 feet above the takeoff surface in accordance with § 23.57(c)(2). 25 11/16/2011 AC 23-8C (b) Early rotation, one-engine inoperative abuse test. 1 In showing compliance with § 23.51(c)(5), some guidance relative to the airspeed attained at a height of 35 feet during the associated flight test is necessary. As this requirement dealing with a rotation speed abuse test only specifies an early rotation (VR-5 knots), it is assumed that pilot technique is to remain the same as normally used for an engine- out condition. With these considerations in mind, it is apparent that the airspeed achieved at a height of 35 feet can be somewhat below the normal scheduled V2 speed. However, the amount of permissible V2 speed reduction should be limited to a reasonable amount, as described in paragraphs 2 and 3 below. 2 In conducting the flight tests required by § 23.51(c)(5), the test pilot should use a normal/natural rotation technique as associated with the use of scheduled takeoff speeds for the airplane being tested. Intentional tail or tail skid contact is not considered acceptable. Further, the airspeed attained at a height of 35 feet during this test is required to be not less than the scheduled V2 value minus five knots. These speed limits should not be considered or utilized as target V2 test speeds but rather are intended to provide an acceptable range of speed departure below the scheduled V2 value. 3 In this abuse test, the engine cut should be accomplished prior to the VR test speed (that is, scheduled VR-5 knots) to allow for engine spin down. The normal one engine-inoperative takeoff distance may be analytically adjusted to compensate for the effect of the early engine cut. Further, in those tests where the airspeed achieved at a height of 35 feet is slightly less than the V2-5 knots limiting value, it is permissible, in lieu of re-conducting the tests, to analytically adjust the test distance to account for the excessive speed decrement. (c) All-engines-operating abuse tests. 1 Section 23.51(c)(6) requires that there not be a "marked increase" in the scheduled takeoff distance when reasonably expected service variations, such as early and excessive rotation and out-of-trim conditions, are encountered. This is considered as requiring takeoff tests with all engines operating with: 26 11/16/2011 AC 23-8C (aa) An abuse at rotation speed, and (bb) Out-of-trim conditions, but with rotation at the scheduled VR speed. Note: The expression "marked increase" in the takeoff distance is defined as any amount in excess