View Latest Blog Entries
Testing & Assessment Certification Standard & Regulation Aging Wires & Systems Maintenance & Sustainment Protection & Prevention Management Conference & Report Research Miscellaneous Arcing
Popular Tags
Visual Inspection High Voltage AS50881 MIL-HDBK MIL-HDBK-525 FAR Electromagnetic Interference (EMI) AS4373 Maintenance FAR 25.1707 Wire System Arcing Damage
All Tags in Alphabetical Order
2021 25.1701 25.1703 abrasion AC 33.4-3 AC 43 Accelerated Aging accessibility ADMT Aging Systems AIR6808 AIR7502 Aircraft Power System aircraft safety Aircraft Service Life Extension Program (SLEP) altitude arc damage Arc Damage Modeling Tool Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS23053 AS29606 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS6324 AS81824 AS83519 AS85049 AS85485 AS85485 Wire Standard ASTM B355 ASTM B470 ASTM D150 ASTM D2671 ASTM D8355 ASTM D876 ASTM F2639 ASTM F2696 ASTM F2799 ASTM F3230 ASTM F3309 ATSRAC Attenuation Automated Wire Testing System (AWTS) Automotive Avionics backshell batteries bend radius Bent Pin Analysis Best of Lectromec Best Practice bonding Cable Cable Bend cable testing Carbon Nanotube (CNT) Certification cfr 25.1717 Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection cleaning clearance Coaxial cable cold bend collision comparative analysis Compliance Component Selection Condition Based Maintenance Conductor Conductor Testing conductors conduit Connector connector installation Connector rating connector selection connector testing connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) corrosion prevention Cracking creepage D-sub data analysis data cables degradat Degradation Delamination Derating design safety development diagnostic Dielectric breakdown dielectric constant Dimensional Life disinfectant Distributed Power System DO-160 dry arc dynamic cut through E-CFR electric aircraft Electrical Aircraft Electrical Component Electrical Power Electrical Testing Electrified Vehicles Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) Electrostatic Discharge EMC EMF EMI EN2235 EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling environmental stress ethernet eVTOL EWIS certification EWIS Component EWIS Design EWIS Failure EWIS sustainment EWIS Thermal Management EZAP FAA FAA AC 25.27 FAA AC 25.981-1C FAA Meeting failure conditions Failure Database Failure Modes and Effects Analysis (FMEA) FAQs FAR FAR 25.1703 FAR 25.1707 FAR 25.1709 Fault fault tree Filter Line Cable Fixturing Flammability fleet reliability Flex Testing fluid exposure Fluid Immersion Forced Hydrolysis fuel system fuel tank ignition Functional Hazard Assessment functional testing Fundamental Articles Fuse Future Tech galvanic corrosion Glycol Gold Gold plating Green Taxiing Grounding hand sanitizer handbook Harness Design harness protection hazard Hazard Analysis health monitoring heat shrink heat shrink tubing high current high Frequency high speed data cable High Voltage High Voltage Degradation HIRF History Hot Stamping Humidity Variation HV connector HV system ICAs IEC 60851 IEC60172 IEEE immersion insertion loss Inspection installation installation safety Instructions for Continued Airworthiness insulating material insulating tape Insulation insulation breakdown insulation resistance insulation testing interchangeability IPC-D-620 ISO 17025 Certified Lab ISO 9000 J1673 Kapton Laser Marking life limit life limited parts Life prediction life projection Lightning lightning protection liquid nitrogen lithium battery lunar Magnet wire maintainability Maintenance Maintenance costs Mandrel mean free path measurement mechanical stress Mechanical Testing MECSIP MIL-C-38999 MIL-C-85485 MIL-DTL-17 MIL-DTL-23053E MIL-DTL-3885G MIL-DTL-38999 MIL-E-25499 MIL-HDBK MIL-HDBK-1646 MIL-HDBK-217 MIL-HDBK-454 MIL-HDBK-516 MIL-HDBK-522 MIL-HDBK-525 MIL-HDBK-683 MIL-STD-1353 MIL-STD-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-7928/5 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 MIL–STD–5088 Military 5088 modeling moon MS3320 NASA NEMA27500 Nickel nickel plating No Fault Found OEM off gassing Outgassing Over current Overheating of Wire Harness Parallel Arcing part selection Partial Discharge partial discharge at altitude Performance physical hazard assessment Physical Testing polyamide polyimdie Polyimide-PTFE Power over Ethernet power system Power systems predictive maintenance Presentation Preventative Maintenance Program Probability of Failure Product Quality PTFE pull through Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Resistance Revision C Rewiring Project Risk Assessment S&T Meeting SAE SAE Committee Sanitizing Fluids Secondary Harness Protection separation separation distance Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure shelf life Shield Shielding Shrinkage signal signal cable Silver silver plated wire silver-plating skin depth skin effect Small aircraft smoke Solid State Circuit Breaker Space Certified Wires Splice standards Storage stored energy superconductor supportability Sustainment System Voltage Temperature Rating Temperature Variation Test methods Test Pricing Testing testing standard Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Runaway Thermal Shock Thermal Testing tin Tin plated conductors tin plating tin solder tin whiskering tin whiskers top 5 Transient Troubleshooting TWA800 UAVs UL94 USAF validation verification video Visual Inspection voltage voltage differential Voltage Tolerance volume resistivity vw-1 wet arc white paper whitelisting Winding wire Wire Ampacity Wire Bend Wire Certification Wire Comparison wire damage wire failure wire performance wire properties Wire System wire testing Wire Verification wiring components work unit code

Electrical Fault and Fire Prevention and Protection

Certification Protection & Prevention

The prevention of electrical fires is a common goal for most aircraft systems. Advisory Circular (AC) 25-16, “Electrical fault and Fire Prevention and Protection”, released in 1991, can be considered one of the precursors to the Electrical Wiring Interconnection System (EWIS) regulations. Although the document is now 25 years old as of last month, AC 25-16 provides a wide variety of recommended practices that are commonplace in the EWIS design and installation. Here we review some of the key points addressed in AC 25-16 and considerations with modern EWIS design with respect to electrical fault and fire prevention and protection.


When FAA released Amendment 25-32 in May 1972, this added new requirements for aircraft EWIS flammability. Up until that time, aircraft wiring was not deemed as a necessary component for flammability testing. This was the regulation that required flammability testing for wire components. In effect, this was the regulation that ended the inclusion of PVC insulated wires, an insulation with a propensity to sustain fire, in aircraft.

In particular, the flammability requirement of wiring is clearly captured in the FAA EWIS regulation 25.1713-part C stating, “Insulation on electrical wire and electrical cable, and materials used to provide additional protection for the wire and cable, installed in any area of the airplane, must be self-extinguishing when tested in accordance with the applicable portions of Appendix F, part I, of 14 CFR part 25

Wire flammability testing is a critical part of the component certification.
Wire flammability testing is a critical part of the component certification.

Hot Stamping

Among the practices that were recommended against in AC 25-16 include the practice of hot stamping. Hot stamping often caused damage to wire insulation and frequently found as a culprit in wire fires and electrical shorting. Although this practice is strongly discouraged, there is guidance available for those that choose to use this method of wire identification. Thankfully alternatives to hot stamping, such as UV marking, have proven their ease of use, maintaining the insulation integrity, and mark durability to common aircraft environmental and mechanical stresses.

Circuit Protection

The requirements on circuit protective devices became codified in FAA regulation 25.1717 on "Circuit Protection Devices". This regulation states, "Electrical wires and cables must be designed and installed so they are compatible with the circuit protection devices required by §25.1357, so that a fire or smoke hazard cannot be created under temporary or continuous fault conditions." The basic idea is the circuit protection should match the electrical load of the circuit, the wire gauge, and the ability to handle over-current conditions. This recommendation from AC 25-16 is partially included under the EWIS risk assessment requirements of FAA regulation 25.1709. As specified in the AC 25.1701, "The following factors must be considered when determining the separation distance [between wire harnesses and/or equipment]: … The maximum temperature generated by adjacent wire/wire bundles during normal and fault conditions."

Although standards like the AS50881 do provide ampacity guidance on handling steady state conditions for wire harnesses, transient or over-current conditions are not addressed. From a risk assessment perspective (such as showing compliance with 25.1709), one must consider the case where a properly electrical current derated wire harness in a high-temperature zone. Consider a scenario where the design pushed the limits of the wire temperature rating. In the application of this scenario, there is a 10C margin between maximum wire harness operational temperature and the maximum temperature rating of the components. Now, what would be the impact if two of the wires short together? There would be additional heat generated on both wires, which, because they are already near their maximum temperature rating, will easily exceed that temperature. The question is of course, what is the potential damage to the system? To ensure the safe design, factors like this must be considered.

Aged Recommendations

Although AC 25-16 is a good supporting reference document, some of the information included in the AC is out of date as would be expected with a 25-year-old document. An example of this is Paragraph D.4 which advises that, "wires having significantly different insulation hardness, or abrasion characteristics, should be routed in separate bundles" was found to not be necessary. The FAA-funded research in 2004 found that there was no appreciable difference in wire longevity if it were routed in a wire harness with the same or different wires.

Aerospace Wire Testing

Section d.5 of the AC focuses on the impact of insulation damage caused by "liquid spillage". Thankfully, most wires now must undergo fluid resistance testing before they can be considered for air vehicle installation. Although these fluid exposure tests identify different fluids, they typically include fuel, oils, hydraulic fluids, and cleaners (link to test).

This is an important factor to keep in mind when reviewing FAA recommendations. Many of the FAA advisory documents are written, forgotten, and rarely updated. It is therefore important to seek out modern recommendations for design, installation, and maintenance for not just EWIS, but any system that is covered by an AC.


AC 25-16 does provide a snapshot of how the FAA and the industry were beginning to consider the importance of EWIS, but does not tell the whole story about EWIS. The recommendations that are included in the AC show the understanding of wiring at the time and how much further the industry has come since the publication of the document. Flammability, circuit protection, and wire identification all have changed since 1991 and are continuing to evolve today. The concern with these advisory circulars is that, although they addressed some deficits in wire system design, it is important to work with those who understand the requirements and demands of modern EWIS design and certification.

Michael Traskos

Michael Traskos

President, Lectromec

Michael has been involved in wire degradation and failure assessments for more than a decade. He has worked on dozens of projects assessing the reliability and qualification of EWIS components. In September 2014, Michael was appointed as an FAA DER with a delegated authority covering EWIS certification.