(3) Normal Procedures/Abnormal Procedures.
Fuel Loading. Instructions necessary to enable loading of the airplane within the established limits of weight and center of gravity, and to maintain the loading within these limits in flight must be provided.
(ii) External Preflight Check. Detailed procedures should be specified.
(iii) Cockpit Preflight Check. Detailed procedures should be specified.
(iv) Fuel Management and Transfer Procedures.
(A) Detailed procedures should be specified for each fuel transfer schedule approved and should include normal fuel transfer rates for use.
(B) Flow Check. Procedures to determine that auxiliary fuel transfer is available should be specified, where required.
(C) Fuel Jettison. (If installed). Procedures should be established to dump fuel, if desired, listing airspeed, altitude, and configuration.
(v) Usable Fuel. Maximum usable fuel should be specified.
(vi) Unusable Fuel. The unusable fuel should be specified.
(4) Performance. Any change in airplane performance should be provided. For instance, if engine bleed air is used to pressurize the auxiliary fuel system, its effects should be accounted for.
(5) Auxillary Fuel System Description. A detailed description and functional arrangement schematic should be provided. This information may be provided in an unapproved section of the AFM supplement (or appendix) or may be included in the approved SECTION 3, NORMAL PROCEDURES. A suggested outline includes the following:
(i) Fuel Transfer System.
(ii) Control Panel.
(111) Refueling System.
(iv) Electrical System.
(v) Schematics.
19. WEIGHT AND BALANCE MANUAL INFORMATION. Weight and loading distribution information including loading instructions must be presented either in the AFM Chap 6 44 Par 18
supplement or in a separate weight and balance control and loading document which will be referenced in the AFM. Reference § 25.1583(c).
MAINTENANCE MANUAL (9 29.1529). The inspections, tests, repairs and related intervals upon which compliance with the applicable certitication basis is based should be included in a maintenance manual supplement supplied by the applicant. The manual should also contain complete servicing information for the auxiliary tanks and systems. If the applicant proposes to have a system where a tank (s) may be removed or made inoperable for maintenance purposes and the remainder of the system remains airworthy (as where more than one tank configuration is an approved configuration) or where the entire system is classified as removable, complete maintenance instructions should also be provided detailing the methods of system modification or removal, resealing and restoring the compartments, and other considerations necessary to make the airplane airworthy. The applicant should refer to Part 25, Appendix H, Instructions for Continued Airworthiness, when providing maintenance instructions.
Chap 6 Par 19 45 (and 46)
Appendix 1 APPENDIX 1 DEFINITIONS. The following definitions are applicable as used in the text of this AC.
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 that this system is secondary to and backed by the airplane's essential fuel system, i.e., that the functions of the essential fuel system are immediately available and operative without immediate supervision by the flightcrew in the event of failure or inadvertent depletion of fuel in the auxiliary fuel system (reference in essence, an airplane equipped with an auxillary tuel 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 for short range flight.
b. Essential Fuel System. An essential fuel system is a system installed within an engine powered airplane which is required for safe operation of the airplane. Its primary function is to provide an independent, uninterrupted flow of fuel to each airplane engine. Essential (or 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 § 25.953). These tanks also contain the reserve fuel necessary for all flight diversions and other contingenices.
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
(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:
Redundancy or back up systems that provide system function 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 assure 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) Designed failure path that controls and directs the failure event by design to limit the safety impact.
(viii) Flightcrew procedures following the failure event designed to assure continued safe flight by specific crew actions.
(3) The FAA fail-safe design concept utilizes all of the above eight design principles in whatever combination is 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., assure that catastrophic failures will be extremely improbable.
d. Fuselage Break Points. Fuselage break points are points along the fuselage where accident data has shown the fuselage shell structure has tailed.
It can be a partial failure in which the structure across the break remains attached or a complete failure resulting in two separate pieces. These are generally attributable to two types of conditions:
(1) Cutouts and stress concentrations.
(2) Points of maximum load, either point loads by the landing gear or maximum bending moments, such as, at the juncture of the wing and body.
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.
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Appendix 1 These areas include, but are not limited to, the cockpit, passenger compartments, galleys, and all classes of cargo and baggage compartments.
f. Zero Fuel Weight. Typically, transport category airplanes are designed to carry the fuel supply 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 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 1s, 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 wing fuel weight limit. Any fuel contained in the auxiliary tank would then be treated as payload from a weight and balance standpoint.
the limit and its meaning.
Par 1 3 (and 4) * U. S. GOVERNMENT PRINTING OFFICE: 1986 491-828/54716