View Latest Blog Entries
Close
Categories
Testing & Assessment Certification Aging Wires & Systems Management Standard & Regulation Conference & Report Maintenance & Sustainment Research Protection & Prevention Arcing Miscellaneous
Popular Tags
Visual Inspection MIL-HDBK MIL-HDBK-525 FAR AS50881 FAR 25.1707 Electromagnetic Interference (EMI) Wire System High Voltage FAR 25.1709 Degradation Arcing Damage
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 AS22759/87 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS85485 AS85485 Wire Standard ASTM F2799 ATSRAC Attenuation Automated Wire Testing System (AWTS) Bent Pin Analysis Best of Lectromec Best Practice Cable cable testing Carbon Nanotube (CNT) Certification Chafing Chemical Testing Circuit Breaker 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 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 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 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 Testing polyimdie Polyimide-PTFE Power over Ethernet Power systems predictive maintenance Probability of Failure Product Quality Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) 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 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 white paper whitelisting Wire Ampacity Wire Certification Wire Comparison wire failure wire properties Wire System wire testing Wire Verification work unit code

Is my aircraft wiring serviceable?

Maintenance & Sustainment

Key Takeaways
  • In most cases, aircraft wiring is serviceable.
  • To determine if the aircraft wiring is serviceable, Lectromec proposes three limiting criteria.
  • Visual inspection can only do so much good in determining wiring system serviceability.

A concept employed in the civil engineering field is that of serviceability. At its core, a structure should only remain in-service as long as it is serviceable. A serviceability limit should be based on measurable performance criterion that, if exceeded, remove it from service. In limit state design, the structure fails its serviceability if the criteria of the serviceability limit state are not met during the service life with the required reliability.

This idea of serviceability is applicable to other engineering disciplines and is undoubtedly applicable to aerospace vehicles. From our perspective at Lectromec, understanding the serviceability of aircraft wiring is critical. However, to determine an aircraft wiring system serviceability state requires the limit state to be defined and assessed. Here we propose three such properties of a serviceable aircraft wiring system.

1) Performance

If a wire/cable is unable to perform the actions necessary to support the system to which it is attached, then it is performing below the required performance limit. As a starting point, the hope is that the correct wire/cable was put in place for the original design. Ideally, the wire/cable was selected to support a certain electrical current load (correct wire gauge) or to provide data within a certain frequency range and limit the attenuation below a certain threshold. There are other factors to be considered that are addressed in other Lectromec articles.

Often a wire/cable’s electrical performance degradation can be measured on an aircraft. This includes measuring the circuit resistance or signal attenuation and there are specific tools designed for these diagnostics. This should be progressively evaluated and recorded through the aircraft’s life; failure to do so will create maintenance questions like, “Do we know what a good value is?”.

Connectors should also be considered in the performance category as so many maintenance issues can be found at connectors. The degradation of contact/termination performance will also impact systems. Contact corrosion and/or contact wear often can be visually identified.

wrapback
While not definitive, a simple test to determine the wiring current condition is to take out a small section of wire and wrap it upon itself.

2) Condition

The second proposed limit state of aircraft wiring is its condition. Whereas the performance focuses on the conductor, this item focuses on the state of the wiring insulation. If the wiring cannot be reliably repaired (e.g. one repair generates more issues), then replacement is the only option. On an individual wire/cable/harness basis, this might be the case, but unlikely to be necessary for the entire vehicle.

Will some wiring age faster than others? Yes. Does this mean that aged wire is not serviceable? No.

While not definitive, a simple test to determine the wiring current condition is to take out a small section of wire and wrap it upon itself. See the photo for an example. If there is any viable insulation warping or cracking, then there may be problems.

As a reference point, Lectromec has tested wire from aircraft with more than 40 years of regular usage that have successfully passed this wrapback test.

3) Damage

The last proposed limit state is the accumulated damage to the wiring system. This asks if the wiring system endured too much damage. Have there been hundreds of repair jobs, ad hoc fixes, and collateral damage from other system failures?

There is no magical threshold after which a wiring harness/system should be replaced, but it is a contributing factor to determining sustainability. There are practical limits to how many times a single wire can be spliced. Naturally, if a wire harness has endured significant repairs, it may also require rework of a flawed design.

Is your aircraft wiring system serviceable?

Performance, condition, and accumulated damage are the three limiting factors for an aircraft wiring systems serviceability. Processes such as the US Air Force’s MIL-HDBK-525 provides thorough methods for gathering the necessary information, assessing the condition, and developing a plan of action.

If you are concerned that your wiring system has reached this point that the serviceability is a question, contact Lectromec. This is what Lectromec has been working on for 30 years and has supported numerous fleets to identify the serviceability of their wiring system through developing a proactive plan to address the wiring system. The serviceability of the wiring system should never be questionable.

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. Michael is an FAA DER with a delegated authority covering EWIS certification and the chairman of the SAE AE-8A EWIS installation committee.