View Latest Blog Entries
Testing & Assessment Certification Aging Wires & Systems Management Standard & Regulation Conference & Report Maintenance & Sustainment Protection & Prevention Research Arcing Miscellaneous
Popular Tags
Visual Inspection MIL-HDBK MIL-HDBK-525 AS50881 FAR High Voltage FAR 25.1707 Electromagnetic Interference (EMI) Maintenance Wire System Arcing Damage FAR 25.1709
All Tags in Alphabetical Order
25.1701 25.1703 Accelerated Aging ADMT Aging Systems Aircraft Power System Aircraft Service Life Extension Program (SLEP) arc damage Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS83519 AS85485 AS85485 Wire Standard ASTM D150 ASTM F2799 ATSRAC Attenuation Automated Wire Testing System (AWTS) batteries Bent Pin Analysis Best of Lectromec Best Practice bonding Cable cable testing Carbon Nanotube (CNT) Certification Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection Coaxial cable cold bend comparative analysis Compliance Component Selection Condition Based Maintenance Conductor conduit Connector connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) Cracking D-sub data analysis data cables degradat Degradation Delamination Derating diagnostic dielectric constant Distributed Power System DO-160 Electrical Aircraft Electrical Component Electrical Testing Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) EMC EMF EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling ethernet EWIS Component EWIS Design EWIS Failure EWIS Thermal Management EZAP FAA AC 25.27 FAA AC 25.981-1C Failure Database Failure Modes and Effects Analysis (FMEA) FAQs FAR FAR 25.1703 FAR 25.1707 FAR 25.1709 fault tree Fixturing Flammability fleet reliability Flex Testing fluid exposure Forced Hydrolysis fuel system fuel tank ignition functional testing Fundamental Articles Future Tech Green Taxiing Grounding Harness Design Hazard Analysis health monitoring heat shrink tubing high current high Frequency high speed data cable High Voltage History Hot Stamping Humidity Variation ICAs IEC60172 Instructions for Continued Airworthiness Insulation insulation resistance IPC-D-620 ISO 17025 Certified Lab Kapton Laser Marking life limited parts life projection Lightning Maintenance Maintenance costs Mandrel Mechanical Testing MECSIP MIL-C-38999 MIL-C-85485 MIL-DTL-17 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-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 Military 5088 modeling MS3320 NASA NEMA27500 No Fault Found off gassing Outgassing Overheating of Wire Harness Parallel Arcing part selection Performance physical hazard assessment Physical Testing polyimdie Polyimide-PTFE Power over Ethernet Power systems predictive maintenance Presentation Probability of Failure Product Quality Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Rewiring Project Risk Assessment SAE Secondary Harness Protection Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure Shield Shielding signal cable silver plated wire smoke Solid State Circuit Breaker Space Certified Wires Splice stored energy supportability Sustainment Temperature Rating Temperature Variation Test methods Test Pricing Testing Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Shock Thermal Testing Tin plated conductors Troubleshooting TWA800 UAVs verification Visual Inspection voltage white paper whitelisting Wire Ampacity Wire Certification Wire Comparison wire damage wire failure wire properties Wire System wire testing Wire Verification work unit code

Aircraft wire failure and incident investigation, Part II


A couple of weeks back, we wrote the Wire Failure and Incident Investigation article that reviewed some of the characteristics of wire failure and the means to detect them in a post aviation incident investigation. That article focused mostly on the conductor failure mechanisms. The three failure mechanisms that will be covered in this article are:

  • Insulation Fracture
  • Thermal Damage to Insulation
  • Conductor Discoloration

Insulation Failure

This actually covers a wide variety of aircraft wire failure mechanisms. The general idea behind the insulation failure mode is that through one mechanism or another, there is a reduction in the insulation dielectric strength.

This reduction in dialectic strength may be caused by:

  • Mechanical strain stretching the insulation (as can be seen at locations with tight bends)
  • Poor wire construction leaving weak points in the insulation (more susceptible to voltage breakdown or mechanical failure)
  • Insulation degradation (exposure to higher temperatures or more severe environmental conditions)
  • Chaffing (rubbing against another wire bundle or against structure)

More often than not, these types of failures (with the exception of chaffing) will have other indications of similar degradation elsewhere in the aircraft. Lab analysis of the wire construction and level of degradation are possible.

Thermal Damage to Insulation

wire failure
Even under magnification, cracks in wire insulations are hard to find.

Thermal damage to the insulation can provide information as to the temperature, duration, and location of a failure event. Wire insulations have a low thermal conductivity meaning that the damage is usually restricted to areas near the heat source. The signs of thermal damage include:

  1. Gradual discoloration, usually darkening
  2. Loss of insulation flexibility and cracking
  3. Loss of electrical resistance (dielectric) properties

The thermal damage will start at different temperatures based on the polymer. Depending on the insulation, this can be as low as 105oC for PVC (not common on aircraft) or as high as 600oC for polyimide based insulations. The level of discoloration can provide information as to the temperature as well as the duration of the event. Some polymers will have a different insulation color based on the exposure temperature.

Conductor Discoloration

Conductor discoloration is another sign indicating exposure to high temperatures. More often than not, exposure to high temperatures leads to either conductor plating diffusion or chemical reactions that result in conductor discoloration.

For silver-plated copper conductors, the silver and copper will diffuse into one another at temperatures above 200oC. This is identifiable by seeing a reduction in the conductor surface luster. A similar process occurs with tin-plated copper conductors above 150oC.


These tips only provide a starting point for identification of wiring failure. Available power, wire gauge, wire specification, and environmental conditions are some of the other factors that modify the potential damage from a wire failure. To get to the root cause, sometimes it is necessary to recreate the scenario in a lab environment. Careful control and monitoring under laboratory conditions can provide insights.

Lectromec’s laboratory is equipped with a variety of power conditioning stations and environmental chambers to sufficiently represent the most common aerospace environments.

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.