Appendix B B-4 ARP4404, Aircraft Electrical Systems (guidance document for design of aerospace vehicle electrical systems).
ARP4754, Certification Considerations for Highly Integrated or Complex Aircraft Systems.
ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.
ARP5583A, Guide to Certification of Aircraft in a High Intensity Radiated Field (HIRF) Environment.
AS50881, Aerospace Vehicle Wiring (procurement document used to specify aerospace wiring; replaces MIL-W-5088).
AS5692A, ARC Fault Circuit Breaker (AFCB), Aircraft, Trip-Free Single Phase and Three Phase 115 VAC, 400 Hz - Constant Frequency, dated December 29, 2009.
AS6019, ARC Fault Circuit Breaker (AFCB), Aircraft, Trip-Free 28 VDC, dated June 6, 2012.
B.8 OTHER INDUSTRY DOCUMENTS.
Air Force Aero Propulsion Laboratory Technical Report AFAPL-TR-75-70, Summary of Ignition Properties of Jet Fuels and Other Aircraft Combustible Fluids, dated September 1975, http://www.dtic.mil/get-tr-doc/pdf?AD=ADA021320.
ASTM D2155-12, Standard Test Method for Determination of Fire Resistance of Aircraft Hydraulic Fluids by Autoignition Temperature, http://www.astm.org (replaced ASTM D286, Method of Test for Autogenous Ignition Temperatures of Petroleum Products, which was withdrawn in 1966).
ASTM D4865, Standard Guide for Generation and Dissipation of Static Electricity in Petroleum Fuel Systems, August 2009, http://www.astm.org.
ASTM E659-15, Standard Test Method for Autoignition Temperature of Chemicals, ASTM International, http://www.astm.org.
EUROCAE ED-107A, Guide to Certification of Aircraft in a High Intensity Radiated Field (HIRF) Environment. This document is the same as SAE ARP5583A referenced in paragraph B.7 of this AC.
NASA Report NASA/TM-2000-210077, Some Notes on Sparks and Ignition of Fuels, dated March 2000, https://ntrs.nasa.gov/search.jsp?R=20000053468.
National Fire Protection Association NFPA 77, Recommended Practice on Static Electricity, 1993 edition, http://www.nfpa.org.
Underwriters Laboratories Inc., UL 913, Intrinsically Safe Apparatus and Associated Apparatus for use in Class I, II, III, Division 1, Hazardous (Classified) Locations, dated July 31, 2006, https://standardscatalog.ul.com/standards/en/standard_913_8.
Appendix C C-1 Appendix C. Definitions C.1 ARC FAULT CIRCUIT BREAKER (AFCB).
A device that provides thermal circuit breaker protection, detects electrical arcing faults, and interrupts electrical power to the fault. (See paragraph B.7 of this AC for SAE standards for alternating current and direct current AFCB.)
C.2 AUTOIGNITION TEMPERATURE.
The minimum temperature at which an optimized flammable vapor and air mixture will spontaneously ignite when heated to a uniform temperature in a normal atmosphere without an external source of ignition, such as a flame or spark.
C.3 AUXILIARY TANKS.
Fuel tanks installed that make additional fuel available for increasing the flight range of the airplane. The term “auxiliary” means that the tank is secondary to the airplane’s main fuel tanks; i.e., the functions of the main tanks are immediately available and operate without immediate supervision by the flightcrew in the event of failure or inadvertent depletion of fuel in an auxiliary tank. Auxiliary tanks are usually intended to be emptied of usable fuel during flight and have been installed in various locations including center wing structure, horizontal stabilizers, wings, and cargo compartments.
C.4 BARRIER.
A physical partition attached to airplane structure that separates one wire or group of wires from another wire or group of wires in order to prevent arcing, fire, and other physical damage between wires or groups of wires.
C.5 COMPONENT MAINTENANCE MANUAL (CMM) DEVIATION.
1. Term used for approval of changes to CMMs that are the subject of CDCCLs or other types of airworthiness limitations adopted by a type design change.
2. Term used for the approval of changes to CMMs referenced in CDCCLs or other types of airworthiness limitations that are mandated by airworthiness directives (ADs), provided the CDCCL or airworthiness limitation includes wording that allows use of “later approved” CMMs. Otherwise, approval must first be granted as an alternative method of compliance (AMOC) to the AD. As with AMOC approvals, a CMM deviation approval must be granted by the responsible Aircraft Certification Service office.
Appendix C C-2 C.6 CRITICAL DESIGN CONFIGURATION CONTROL LIMITATIONS (CDCCLS).
Airworthiness limitations that define those critical design features of the design that must be maintained to ensure that ignition sources will not develop within the fuel tank system.
C.7 ELECTRICAL SPARKS.
A spark that is initiated by a potential difference, which causes an electrical breakdown of a dielectric such as a fuel/air mixture, produced between electrodes that are initially separated, with the circuit initially carrying no current. The term voltage sparks is sometimes used interchangeably with the term electrical sparks.
C.8 ELECTRICAL ARCS.
Electrical arcs occur between electrodes that are in contact with each other and carry excessive current, which results in melting at the contact points. This may result in electric arc plasma and/or ejection of molten or burning material. The term thermal sparks is used interchangeably with the term electrical arcs.
C.9 EXPLOSION PROOF.
Components designed and constructed so they will not ignite flammable vapors or liquids surrounding the component under any normal operating condition and any failure condition. Further information on possible failure conditions that should be considered is specified in § 25.981(a)(3).
C.10 FAIL-SAFE.
As defined in the preamble to amendment 25-102, “the FAA’s policy has been to require applicants to assume the presence of foreseeable latent (undetected) failure conditions when demonstrating that subsequent single failures will not jeopardize the safe operation of the airplane.” Section 25.981(a)(3) incorporated the fail-safe principles of §§ 25.901(c) and 25.1309. (66 FR 23087) C.11 FILAMENT HEATING.
The heating of a small diameter conductive material when exposed to electrical current.
C.12 FLAMMABLE.
Flammable, with respect to a fluid or gas, means susceptible to igniting readily or to exploding (14 CFR 1.1, General definitions). Further information on flammable fluids used in airplanes may be found in the documents identified in paragraph B.8 of this AC.
Appendix C C-3 C.13 FLASH POINT.
The flash point of a flammable fluid is defined as the lowest temperature at which the application of a flame to a heated sample causes the vapor to ignite momentarily, or “flash.” The test standard for jet fuel is defined in the fuel specification.
C.14 FRICTION SPARK.
A heat source in the form of a spark that is created by mechanical contact, such as debris contacting a rotating fuel pump impeller.
C.15 FUEL SYSTEM AIRWORTHINESS LIMITATION.
Any mandatory replacement time, inspection interval, related inspection procedure, and all critical design CDCCLs approved under § 25.981 for the fuel tank system identified in the Airworthiness Limitations section of the ICA (as required by § 25.981(d) and section H25.4 of appendix H to part 25).
C.16 GROUND FAULT INTERRUPTER (GFI).
A device that provides thermal circuit breaker protection, detects an electrical power short circuit-to-ground condition, and interrupts electrical power to the ground fault.
C.17 HOT SHORT.
Electrical energy introduced into equipment or systems as a result of unintended contact with a power source, such as bent pins in a connector or damaged insulation on adjacent wires.
C.18 IGNITION SOURCE.
A source of sufficient energy to initiate combustion of a fuel/air mixture. Hot surfaces that can exceed the autoignition temperature of the flammable vapor under consideration are considered to be ignition sources. Electrical arcs, electrical sparks, and friction sparks are also considered ignition sources if sufficient energy is released to initiate combustion.
C.19 INSTALLATION APPRAISAL.
A qualitative appraisal of the integrity and safety of the installation.
C.20 INTRINSICALLY SAFE.
Any instrument, equipment, or wiring that is incapable of releasing sufficient electrical or thermal energy under normal operating conditions, anticipated failure conditions (see § 25.981(a)(3)), and environmental conditions, which could cause an ignition source within the fuel tank.
Appendix C C-4 C.21 LATENT FAILURE.
A failure whose presence is not apparent to the flightcrew or maintenance personnel. A significant latent failure is one that would, in combination with one or more specific failures or events, result in a hazardous or catastrophic failure condition.
C.22 LINE REPLACEMENT UNIT (LRU).
Any components that can be replaced while the airplane remains in operational service.
Examples of fuel system LRUs include components such as flight deck and refueling panel fuel quantity indicators, fuel quantity system processors, and fuel system management control units.
C.23 MAXIMUM ALLOWABLE SURFACE TEMPERATURES.
As defined in 14 CFR 25.981(a)(1) and (2), the surface temperature within the fuel tank (the tank walls, baffles, or any components) that provides a safe margin under all normal or failure conditions, which is at least 50 °F (27.8 °C) below the lowest expected autoignition temperature of the approved fuels. The autoignition temperature of fuels will vary because of a variety of factors (ambient pressure, dwell time, fuel type, etc.).
The value accepted by the FAA without further substantiation for kerosene fuels, such as Jet A, under static sea level conditions, is 450 °F (232.2 °C). This results in a maximum allowable surface temperature of 400 °F (204.4 °C) for an affected component surface.
C.24 QUALITATIVE.
Those analytical processes that assess system and airplane safety in an objective, non-numerical manner.
C.25 QUANTITATIVE.
Those analytical processes that apply mathematical methods to assess system and airplane safety.
C.26 TRANSIENT SUPPRESSION DEVICE (TSD).
A device that limits transient voltages or currents on wiring to systems such as the fuel tank quantity, fuel temperature sensors, and fuel level switches, etc., to a predetermined level.
Appendix D D-1 Appendix D. Advisory Circular Feedback If you find an error in this AC, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by (1) emailing this form to 9-AWA-AVS- AIR-DMO@faa.gov or (2) faxing it to (202) 267-1813.
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