Appendix 1
AC 23-10 8/5/91 Appendix 1 APPENDIX 1 . DEFINITIONS The following definitions are applicable as used in the text of this AC.
a. Auxiliary Fuel System . An auxiliary fuel system is a system installed within the airplane which makes additional fuel available for increasing the · flight range of that airplane. The term " auxiliary " means t ha t this system is secondary to the airplane's main fuel system; i.e. , that the functions of the main fuel system are immediately available a n d operative in the event of failure or i n advertent depletion of fuel in the auxiliary fuel system (reference § 23.955(b)(2)). In essence, an airplane equipped with an auxiliary fuel system is capable of safe flight even when the auxiliary fuel system is not used, i . e. , where its fuel storage capacity is not required .
b. Main Fuel System . A main fuel system is a system installed within an airplane which is required for safe operation of the airplane. Its pri m ary function is to provide an independent, uninte r rupted flo w of fuel to each airplane engine. Main fuel tanks are those tanks which normally supply fuel directly to the engine in at least one operating mode and are necessary to satisfy the independent feed requirements of the airplane (reference§ 23.953).
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These tanks also contain the reserve fuel necessary for all flight diversions and other contingencies .
c. Fail-Safe.
(1) The FAA fail-safe design concept is a design methodology where the effect of failures and failure combinations must be considered in defining a safe design. The following basic rules involving failure events apply: (i) In any system or subsystem, a single failure of any element or connection during any one flight (brake release through ground deceleration to stop) must be assumed without consideration as to its probability of failing. This single failure event must not prevent the continued safe flight and landing of the airplane.
(ii) Additional independent failure events during any one flight following the first single failure must also be considered when the probability of occurrence is likely (i . e., those combinations of failures not shown to be extremely improbable). If a critical failure event cannot readily be detected, it must be counted as a latent existing failure in addition to the first failure. The probability of these combined failures includes the probability of occurrence of the first failure event .
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Appendix 1
AC 23-10 8/5/91 Appendix 1
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(2) The following design principles and techniques are generally utilized to prevent single failures and likely combinations of failures from jeopardizing the continued safe flight and landing of the airplane: (i) Redundancy or backup systems that provide system functio n after the first failure, i.e., two or more engines, two or more hydraulic systems , dual flight controls, etc.
(ii) Isolation of systems and components, both physically and functionally , so that failure of one element will not cause failure of the other. This is sometimes referred to as system independence.
(iii) Detection of failures or failure indication.
(iv) Functional verification, i.e., the capability for testing or checking the condition of the components.
(v) Proven reliability and integrity to ensure that multiple component or system failures will not occur in the same flight.
(vi) Damage tolerance that limits the safety impact or ( effect of the failure.
(vii) Design failure path that controls and directs the failure event by design to limit the safety impact.
(viii) Flight crew procedures following the failure event designed to ensure continued safe flight by specific crew actions .
(3) The FAA fail-safe design concept utilizes all of the above eight design principles in whatever combinations are required to produce a fail-safe design. The employment of only one of the above principles is seldom adequate; generally, two or more are used in the design to satisfy the fail-safe design concept, i.e., ensure that catastrophic failures will be extremely improbable.
d. Passenger/Cargo Compartments. All compartments specifically designed to provide a suitable life support environment for people and animals during all operating modes of the airplane. These areas may or may not be pressurized. These areas include, but are not limited to, the cockpit, passenger compartments, and cargo and baggage compartments.
e. Zero/Fuel Weight. Typically, civil airplanes are designed to carry fuel in the wings. In addition to any other advantages, locating the fuel in the wings relieves wing bending stresses and allows a higher maximum weight than would be possible with the same
Appendix 1
AC 23 - 10 8/5/91 Appendix 1 quantity of fuel located within the fuselage. For such airplanes, zero fuel weight is established as a limit to ensure that maximum wing bending stresses are not exceeded by replacing fuel in the wings with an equal weight of payload carried in the fuselage. When an auxiliary fuel tank is installed within the fuselage, the existing zero fuel weight limit is no longer directly applicable because the fuel contained in that tank does not relieve wing bending stresses. It is, therefore, necessary to reduce the zero fuel weight limit by the maximum usable fuel capacity of the auxiliary tank. Alternatively, the zero fuel weight limit may be redefined as the maximum zero fil1l9.
fuel weight limit. Any fuel contained in the auxiliary tank would then be treated as payload from a weight and balance standpoint .
Regardless of which procedure is used, the AFM must clearly state the limit and its meaning.
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Appendix 2
AC 23-10 8/5/91 Appendix 2 ADVISORY CIRCULARS APPENDIX 2.
The advisory circulars listed below can be obtained from the U.S.
Department of Transportation, Utilization and Storage Section, M - 443 . 2, Washington, D.C. 20590: a. " Qualification of Fuels, Lubricants, and Additives for Aircraft Engines ," Advisory Circular 20-24B, Federal Aviation Administration, December 20, 1985.
b. " Aircraft Fuel Control," Advisory Circular 20-43C, Federal Aviation Administration, October 20, 1976.
c. " Protectio n of Aircraft Fuel systems Against Fuel Vapor Ignition Due to Lightning, " Advisory Circular 20- 53A, Federal Aviation Administration, April 12, 1985 .
d. " Composite Aircraft Structure, " Advisory Circular 20 - 107A, Federal Aviation Administration, April 25, 1984.
e. " Fuel Drain Valves," Advisory Circular 20-119, Federal Aviation Administration, February 7, 1983.
f. " Water in Aviation Fuels, " Advisory Circular 20-125, Federal Aviation Administration, December 10, 1985.
g. " Design Considerations for Minimizing Hazards Caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor and Fan Blade Failures," Advisory Circular 20-128, Federal Aviation Administration, March 9, 1988.
h. "Flight Test Guide for Certification of Part 23 Airplanes," Advisory Circular 23-8A, Federal Aviation Administration, February 9, 1989.
i. " Substantiating Flow Rates and Pressures in Fuel Systems of Small Airplanes, " Advisory Circular 23.955-1, Federal Aviation Administration, June 10, 1985.
j. " Unusable Fuel Test Procedures for Small Airplanes," Advisory Circular 23.959-1, Federal Aviation Administration, January 14, 1985.
k. " Procedures for Conducting Fuel System Hot Weather Operation Tests, " Advisory Circular 23.961-1, Federal Aviation Administration, January 14, 1987.
1. " Procedures for Determining Acceptable Fuel/Oil Ratio as Required by FAR 23.lOll(b)," Advisory Circular 23.1011-1, Federal Aviation Administration , November 14, 1983.
Appendix 2
AC 23-XX-16 8/5/91 Appendix 2
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m. "Installation of Fuel Flowmeters in Small Airplanes with Continuous - Flow, Fuel-Injection, Reciprocating Engines," Advisory Circular 23 . 1305 - 1, Federal Aviation Administration , December 21, 1984.
n . " Certification of Non-oxygenated Automobile Gasoline (Autogas) Instead of Aviation Gasoline (Avgas) in Part 23 Airplanes with Reciprocating Engines, " Advisory Circular 23.1521-lA , Federal Aviation Administra t ion, January 2, 1991 .
o. " Acceptable Methods, Techniques and Practices -- Aircraft Inspection and Repair, " Advisory Circular 43.13 - lA, Federal Aviation Administration, April 17, 1972.
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Appendix 3
AC 23 - 10 8/5/91 Appendix 3 APPENDIX 3. RELATED READING MATERIAL a. U.S. Army Aircraft Cr ash Survival Design Guide, USARTL TR - 79 - 22A b. MIL-C-6136 - Conduit; Electrical, Flexible Shielded, Aluminum Alloy for Aircraft Installation, Types I or II c . MIL- HDBK - 5 - Metallic Materials and Elements for Aerospace Vehicle Structures d . MIL-HDBK- 17 - Plastics for Flight Vehicles \ 1 ( and 2) 'U.S. Government P rin ting Office: 1991 - 282 · 653155506 US Department BULK MAIL of Transport ation POSTAGE & FEES PAID FEDERAL AVIATION Feder al Aviation ADMINISTRATION PE RMIT NO . G-44 Administration 800 Independence Ave ., S. W.
Washington. D.C. 2059 1 FOR WA RDING AND RET U RN POSTAGE GUARANTEED Official Business Pena11y for Priva1e Use $300
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