Appendix A A-5 A.3.8 Hardware Qualification.
Environmental testing—including thermal, shock and vibration, humidity, fluid susceptibility, altitude, decompression, fungus, waterproof, salt spray, and explosionproof—should be performed in accordance with RTCA DO-160G or equivalent standards. The applicant should define an insulation, dielectric, and electrical grounding and bonding standard acceptable to the FAA for the AFCB or GFI. Appropriate test categories in each section of RTCA DO-160G should be chosen based on the AFCB or GFI installation environment defined for the specific airplane. Particular attention should be given to the normal and abnormal power input tests outlined in section 16 of RTCA DO-160G. The system with AFCB or GFI installed must comply with §§ 25.954 and 25.1316 for lightning protection; §§ 25.1301, 25.1309(e), and 25.1353(a) for electromagnetic compatibility; and § 25.1317 for HIRF.
A.3.9 Airplane Tests.
The applicant should show by ground tests, flight tests, or both that all AFCB or GFIs remain armed during normal and abnormal electrical power bus and load switching as described in paragraph A.3.1.1 of this AC, and are not adversely affected by the operation of other airplane systems. The airplane tests should also show that the AFCB or GFI would not produce electromagnetic interference on other airplane systems.
A.3.10 Instructions for Continued Airworthiness (ICA).
A.3.10.1 The applicant must submit ICAs required by § 25.1529 in order to provide the necessary procedures to service and maintain AFCB or GFI installations. As required by appendix H25.4, the Airworthiness Limitations section of the ICA must include each mandatory replacement time, inspection interval, related inspection procedure, and all critical design configuration control limitations (CDCCLs) approved under § 25.981 for the AFCB or GFI installation. Inspection intervals determined from the safety analysis would be included for the detection of latent failures that would prevent the AFCB or GFI from tripping during a ground or arc fault event.
A.3.10.2 AFCB or GFIs used for showing compliance to § 25.981 requirements for preventing ignition sources are typically a CDCCL in these installations. As required by § 25.981(d), the applicant must provide visible means of identifying the AFCB or GFI as a CDCCL and should provide design features to minimize the inadvertent substitution of an AFCB or GFI with a non-AFCB or GFI device.
A.3.11 Airplane Flight Manual Limitations.
The airplane flight manual Limitations section should address any limitations related to AFCB or GFI intended function and any self-test features of the AFCB or GFI design.
Appendix B B-1 Appendix B. Related Documents The following related documents are provided for information purposes and are not necessarily directly referenced in this AC.
B.1 REGULATIONS.
The following 14 CFR regulations prescribe requirements for the design, substantiation, and certification relating to prevention of ignition sources within the fuel tanks of transport category airplanes. You can download the full text of these regulations at the U.S. Government Printing Office e-CFR website. Or you can order a paper copy by sending a request to the U.S. Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402-0001; by calling telephone number (202) 512-1800; or by sending a request by fax to (202) 512-2250.
Section 21.50, Instructions for continued airworthiness and manufacturer’s maintenance manuals having airworthiness limitations sections.
Section 25.729(f), Protection of equipment on landing gear and in wheel wells.
Section 25.863, Flammable fluid fire protection.
Section 25.901, Powerplant: Installation.
Section 25.903(b), Engine isolation.
Section 25.951, Fuel System: General.
Section 25.954, Fuel system lightning protection.
Section 25.973, Fuel tank filler connection.
Section 25.981, Fuel tank explosion prevention.
Section 25.1301, Equipment: Function and installation.
Section 25.1309, Equipment, systems, and installations.
Section 25.1316, Electrical and electronic system lightning protection.
Section 25.1317, High-intensity Radiated Fields (HIRF) Protection.
Section 25.1353, Electrical equipment and installations.
Section 25.1521, Powerplant limitations.
Section 25.1529, Instructions for Continued Airworthiness.
Section 25.1557, Miscellaneous markings and placards.
Section 25.1701, Electrical Wiring Interconnection Systems (EWIS): Definition.
Section 25.1707, System separation: EWIS.
Appendix H to part 25, Instructions for Continued Airworthiness.
Appendix B B-2 B.2 ADVISORY CIRCULARS.
The following FAA ACs are related to the guidance in this AC. The latest version of each AC at the time of publication of this AC is identified below. If any AC is revised after publication of this AC, you should refer to the latest version for guidance, which can be downloaded from the Internet at http://www.faa.gov/regulations_policies/advisory_circulars/.
AC 20-158A, The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-Intensity Radiated Fields (HIRF) Environment, dated May 30, 2014.
AC 21-40A, Guide for Obtaining a Supplemental Type Certificate, dated September 27, 2007.
AC 25-8, Auxiliary Fuel System Installations, dated May 2, 1986.
AC 25-16, Electrical Fault and Fire Prevention and Protection, dated September 25, 1987.
AC 25-19, Certification Maintenance Requirements, dated October 3, 2011.
AC 25.954-1, Transport Airplane Fuel System Lightning Protection, dated September 24, 2018.
AC 25.981-2A, Fuel Tank Flammability Reduction Means, dated September 19, 2008.
AC 25.1309-1A, System Design and Analysis, dated June 21, 1988.
AC 25.1701-1, Certification of Electrical Wiring Interconnection Systems on Transport Category Airplanes, dated December 4, 2007.
AC 120-97A, Incorporation of Fuel Tank System Instructions for Continued Airworthiness into Operator Maintenance and/or Inspection Programs, dated May 25, 2012.
B.3 ORDERS.
The following FAA orders are related to the guidance in this AC. You can download the latest version from the Internet at http://www.faa.gov/regulations_policies/orders_notices/.
Order 8110.4C, Change 6, Type Certification, dated October 12, 2005.
Order 8110.42D, Parts Manufacturer Approval Procedures, dated March 21, 2014.
Order 8110.105A, Simple and Complex Electronic Hardware Approval Guidance, dated April 5, 2017.
Appendix B B-3 B.4 REPORTS.
The following FAA reports are related to this AC:
Report No. DOT/FAA/AR-98/26, A Review of the Flammability Hazard of Jet A Fuel Vapor in Civil Transport Aircraft Fuel Tanks, dated June 1998. This report can be downloaded from the Internet at http://www.tc.faa.gov/its/worldpac/techrpt/ar98-
26.pdf.
Report No. DOT/FAA/AR-03/61, Silver-Sulfur Deposits on Fuel Quantity Indication System and Attendant Wiring, dated October 2003. This report can be downloaded from the Internet at http://www.tc.faa.gov/its/worldpac/techrpt/ar03-
61.pdf.
Report No. DOT/FAA/AR-TN05/37, Intrinsically Safe Current Limit Study for Aircraft Fuel Tank Electronics, dated October 2005. This report can be downloaded from the Internet at http://www.fire.tc.faa.gov/pdf/TN05-37.pdf.
B.5 MILITARY SPECIFICATIONS.
The following documents are available from the Department of Defense, Document Automation and Production Service, Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094.
MIL-STD-810N, Environmental Test Methods and Engineering Guidelines, Method
511.5, Explosive Atmosphere, dated October 31, 2008.
MIL-PRF-6106N, General Specification for Electromagnetic Relays, dated September 14, 2009.
B.6 RTCA DOCUMENTS.
You can order of the following documents from RTCA, Inc., 1150 18th Street NW, Suite 910, Washington, DC 20036; telephone: 202-833-9339 or fax: 202-833-9434.
You can also order copies online at http:/www.rtca.org.
RTCA DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment, December 6, 2010.
RTCA DO-178B, Software Considerations in Airborne Systems and Equipment Certification, dated December 13, 2011.
RTCA DO-254, Design Assurance Guidance for Airborne Electronic Hardware, dated April 4, 2000.
B.7 SAE INTERNATIONAL DOCUMENTS.
The versions of the following documents are current at the time of publication of this AC. You can order copies of them from SAE International, 400 Commonwealth Drive, Warrendale, Pennsylvania 15096; or online at http://www.sae.org.
AIR1662, Minimization of Electrostatic Hazards in Aircraft Fuel Systems.
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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