View Latest Blog Entries
Testing & Assessment Certification Standard & Regulation Aging Wires & Systems Maintenance & Sustainment Management Conference & Report Protection & Prevention Research Miscellaneous Arcing
Popular Tags
Visual Inspection High Voltage AS50881 MIL-HDBK MIL-HDBK-525 FAR AS4373 Maintenance Electromagnetic Interference (EMI) 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 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 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 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 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

11 improvements to MIL-HDBK-522 for aircraft wire systems

Standard & Regulation

One of the best handbooks on EWIS routine inspection for aircraft wire systems is the military handbook MIL-HDBK-522, Guidelines for Inspection of Aircraft Electrical Wiring Interconnect Systems. The first version of the handbook was released in 2010 and provided a good starting point for EWIS inspection guidance. This guidance has been updated with the release of Revision A in February 2016. The MIL-HDBK-522 is a critical introduction on wire system assessment best practices and should be readily accessible to those working in any maintenance shop.

The latest revision adds several sections to the document. Here is a short overview of each of these sections:

Guideline #4 – Polyimide Wire Insulation Inspection

This section was included in the wire inspection as part of the original version of MIL-HDBK-522, but has been broken out as a separate section. Because the aging and degradation of polyimide is unique, it is important that these wires are maintained separately from other wire types.

Guideline #6 – Coaxial Cable Installation Inspection

This section has been expanded in Rev A of 522 to include more details and better visualizations of how the coaxial cables should be routed and maintained. One of the areas highlighted in the new revision is the importance of maintaining a good bend radius and good clamping to maintain the bend radius.

aircraft wire systems
Maintaining the correct bend radius is the best way to prevent premature degradation of coaxial signal quality. MIL-HDBK-522 Rev A provides inspection guidance for these components.

Guideline #14 – Critical Clamp Marker Inspection

This section of Rev A is new to MIL-HDBK-522. The importance of critical clamp markers is perfectly described in Rev A of the handbook: “Critical clamp marker labels may not be moved from their design drawing-required location. If moved beyond allowable limits, the harness may be damaged, or cut, resulting in aircraft system failure or injury to personnel.” The handbook continues with “Critical clamp markers installed on designated wire harnesses provide a means of ensuring installation clearance requirements are met. Typically, installed on very long/ branched harnesses (landing gear, flight controls) subjected to motion.”

Guideline #17 – Spot Tie/Lacing Tape/Tie String Inspection

The secondary support of wire harnesses is critical to limiting the ingress of contaminates into wire harnesses, limiting the potential for sag, and maintaining separation distances. This section provides recommendations on the spacing of secondary support and items that should be included during visual inspections.

Guideline #20 – Shield Termination Ferrule Inspection

This is another new section found in Rev A. A continuous shielding system for a wire harness is the best way to limit the potential impacts of Electromagnetic Interference (EMI). This section provides recommendations on what to look for when performing a visual examination of these components.

Guideline #22 – EMI Shielded Wrap-Around Repair Inspection

Continuing with the theme of EMI protection, guideline #22 provides inspection recommendations on EMI wrap-around protection. These products are typically Nomex® harness protection sleeving with an internal layer of platted copper braid to serve as EMI shielding. As identified in the heading, these products are typically wrapped around harnesses and can be applied in post-production. Consequently, inspections should be carried out to ensure that these components are installed correctly and do not have any protections gaps that may impact system reliability.


The degradation of connector contacts can reduce the performance of the system. To quote this new section from Rev A of MIL-HDBK-522, “Fretting is a condition where slight movement between mated surfaces occurs, which continually exposes fresh metal to corrosion.” This section includes a couple of examples of what to look for when examining connector contacts. To note: the section does not call for the removal of all connectors to inspect contacts; this is something that should be considered before connectors are re-mated after other maintenance actions.

Guideline #26 – Cold-Applied Terminal Lug Inspection

Another addition to MIL-HDBK-522 found in Rev A, is the cold applied terminal lugs, in particular, those that are the SAE AS7928/14 heatless sealing lugs. Since the cold terminals are relatively new, it is good that this guidance is available to maintainers. To supplement this information, Guideline #30 covers the cold applied splice inspection.

Guideline #29 – Heat-Applied Splice Inspection

An area that was overlooked in the original document was inspection of heat applied splices (because if you are doing repairs, you are going to be working with splices). This section provides several graphics depicting acceptable installations of splices and key points that should be examined.

Guideline #32 – Wrap-Around/Side-entry Wire Insulation Repair

In addition to heat applied and cold splices, Rev A also includes guidance on the use of wrap-around wire insulation repair. Several photos are included of acceptable and unacceptable installations of the C-wrap repairs.

Guidelines #33 through #38 – Connector and Terminal Block Inspection

This is a big new addition to MIL-HDBK-522 found in Rev A. Nearly every review of maintenance records shows that one of the most common locations for EWIS problems is at the connector. These two guidelines on EWIS inspection of connectors are great starting points for understanding some of the maintenance issues that are regularly encountered with connectors.


The MIL-HDBK-522 is a well put together handbook by the Naval Air Systems Command. Periodic review of this handbook with maintainers should be considered, to ensure the work performed meets the high expectations for preserving a reliable aircraft electrical system.

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.