CHAPTER 6 - USER INSTRUCTIONAL REQUIREMENTS.
17. AIRPLANE PLACARDS AND INSTRUMENT MARKING EVALUATION.
a. Location of Placards, Markings, Gauges, Switches, etc. ($ 25.1557(a) and (b)).
(1) Cockpit and tueling station placards, markings, annunciator lights, gauges, switches and controls for the auxiliary fuel system should be located in suitable areas with sutticient illumination to assure they are easily readable during day and night operations. The switches and controls must be easily accessible to the ground or flightcrews as required by the applicable regulations.
(2) Special placards, located in the cargo compartment, or adjacent to the auxiliary fuel tank installation may be necessary to infor or caution the ground crew about certain aspects of the installation. These placards may, or example, state certain cargo compartment loading limits or restrictions, lexible cargo barrier tensioning requirements or cautionary flammable fluid requirements as required. Also suitable markings on the airplane exterior surface are required, identifying drain access doors, masts, etc.
Instrument, Instrument identitication, Leghting and Calibration $§ 25.1305, 25.1337, 25.1381, 25.1541, 25.1543, 25.1553, 25.1555 and 25.1583).
(1) A fuel quantity indicator should be installed for each independent auxiliary fuel tank which provides indication to the flightcrew of the quantity, in gallons or equivalent units, of usable fuel in each tank during light (see also chapter 4, paragraph lib(4)). indicators should De as accurate and compatible with the existinq airplane fuel quantity indicators as possible and calibrated using the same units of volume (metric or English).
(2) Instrument and switch markings should be easily readable with instrument lights.
(3) Each instrument, indicator and switch must have markings/placards which permit the crew to easily identity it. Markings and placards shall be displayed in conspicuous places and shall be such that they cannot be easily erased, disfigured or obscured.
(4) If the instrument markings are on the cover glass of the instrument, inere must de means to maintain the correct alignment of the glass cover with the face of the dial.
(5) Each fuel tank selector control, if used, must be marked to indicate the position corresponding to each tank.
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18. AIRPLANE FLIGHT MANUAL (AFM) ($$ 25.1581 through 25.1587).
Auxiliary fuel tanks installed after initial certification of the airplane require an FAA-approved AFM supplement or an appendix to the existing basic AFM to provide appropriate operating information, procedures and limitations. Generally, an appendix to an AFM is appropriate when written by the manufacturer of the basic airplane, and a supplement is appropriate when the applicant for an auxiliary fuel tank installation is other than the manufacturer.
appendix which will be incorporated into the basic AFM. The operating The applicant is responsible for preparing the AFM supplement or procedures and limitations will be evaluated by the FAA flight test crew as part of the flight test evaluations prescribed by the Type Inspection Authorization (TIA). Crew workload also will be evaluated to determine whether it is still acceptable with the addition of an auxiliary fuel system. Crew workload should be considered early in the design of the system, with FAA participation, to ensure that all considerations are properly coordinated.
Sufficient information and data should be provided in the AFM to assure that the flightcrew will be able to understand and operate the system during normal, abnormal, and emergency operations of the airplane.
d. Abnormal procedures are those that are not normal procedures and also are not emergency procedures. They include procedures for foreseeable failure situations in which the use of special systems, or the use of regular systems, may be expected to maintain an acceptable level of airworthiness. Immediate action is not usually required. Since most auxiliary fuel systems are add-on systems, which are not included in the flight training syllabus of the airplane, the AFM supplement or appendix must be complete in providing the required information. To assure completeness of the AFM supplement (or appendix) the following discussion and format are provided as a guide for the type of information that should be considered.
(1) Limitations.
(1) Weight Limitations. Maximum zero fuel weight changes and weight and center of gravity limits should be specified. It should be emphasized that when fuel is loaded into fuselage auxiliary tanks, the maximum zero fuel weight must be reduced by the weight of the added fuel.
(ii) Fuel Loading Limitations. The maximum allowable fuel in each auxiliary tank should be specified. Loading limitations may be required co maintain weight/c.g. within limits, i.e., certain main fuel tanks may be required to be loaded before the auxiliary tanks and the auxiliary tanks may be required to be loaded in a particular sequence depending on the design of the system.
(iii) Fuel Management Limitations.
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(A) Specific fuel usage procedures may be required to maintain the weight and balance of the airplane within limits. Additionally.
right planning limitations may be required it a single failure can trap fuel in the auxiliary fuel system; the main fuel system must still provide sufficient fuel to the engines for the remainder of the flight, i.e., to reach the airport (B) A specific sequence of transferring auxiliary fuel may be required as a result of fuel flow rates.
(C) If auxiliary fuel is used for ballast, a placard indicating the amount of ballast fuel is required in the cockpit.
(iv) Operating Limitations.
(A) Maneuvering limitations should be specified.
(B) Tank pressurization or transfer of fuel during takeoff and landing are usually prohibited because of the crashworthiness fire hazard.
(C) Transfer of fuel during climb or descent may be prohibited because of usable fuel considerations.
(v) Miscellaneous Limitations. Cargo and floor loading restrictions may be required due to the auxiliary fuel tank installation.
(2) Emergency Procedures.
(i) Ditching. If applicable, procedures must be provided regarding transfer of fuel from auxiliary fuel tanks and placement of controls and switches prior to ditching.
(ii) No Fuel Transfer. Should fuel not transfer and become trapped in the auxiliary tanks, procedures should be included to regain transfer capability. If transfer is still not available, management procedures should specify how to maintain weight/c.g. within limits.
(iii) Engine Inoperative. In the event of an engine failure, auxiliary fuel systems which use engine bleed air for fuel transfer may lose cranster capability. In order to restore transfer, procedures must be includec which define the steps required for obtaining bleed air from the remaininc These procedures should also define engine operating restrictions, if required, which apply during transfer following engine-out Continued use of bleed air for fuel transfer may be affected by the engine-out enroute climb performance requirements of Part 25.
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(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.
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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