View Latest Blog Entries
Close
Categories
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 Circuit Protection
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 Aluminum arc damage Arc Damage Modeling Tool Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Resistance 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 B230 ASTM B355 ASTM B470 ASTM D150 ASTM D2671 ASTM D495 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-F-5372 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 Scrape Abrasion 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

EWIS regulatory compliance with 25.1707, Part V

Certification Standard & Regulation

Each of the last four articles has focused on a subpart of the FAA 25.1707 regulation.

Because subparts e, f, g, and h are very similar, they will all be addressed here. Rather than present each of these regulations, we have combined them into one:

Combined revision of FAA 25.1707 subparts e, f, g, and h: Except to the extent necessary to provide electrical connection to the fuel/hydraulic/oxygen/water/waste systems components, the EWIS must be designed and installed with adequate physical separation from fuel/hydraulic/oxygen/water/waste lines and other fuel/hydraulic/oxygen/water/waste system components, so that: (1) An EWIS component failure will not create a hazardous condition. (2) Any fluid leakage onto EWIS components will not create a hazardous condition.

To understand the consequences of EWIS component failure, we only have to look back at the loss of an US Air Force F-22 in November 2012.

So, what does this mean from a certification perspective?

1) You must have safe separation distances defined for all of your fluid carrying system components. Not all tubes are going to fail under the same conditions. Below are a couple of articles on this topic:

2) EWIS components should be installed, so that they are above the fluid/oxygen carrying components; this will help to minimize the likelihood of fluid contamination of the EWIS.

In the figure below, there are three wire harnesses routed near a fuel line:

  1. Harness #1 is routed beneath the fuel line, but is protected by a shroud. While this can be used to protect a harness from fluid exposure, it does add to weight and potentially inspection procedures for maintaining airworthiness.
  2. Harness #2 is routed above and perpendicular to the fuel line, but the supporting clamps are too far apart to prevent sagging and chaffing on the tube. Additional clamping could be installed to resolve this issue.
  3. Harness #3 is routed horizontally, parallel to the line, which is of no issue, but in the presented system, the separation distance is less than the allowed distance as defined by a damage assessment. Redesign, separation, or protective sleeving must be considered for harness #3.
series arcing

This part of the 25.1707 regulation should also be considered in coordination with the recommended practices of AS50881 section 3.11.11 “Gas and Fluid Carrying Lines and Tubes.” Whereas the standard suggests that wiring should be routed with, “the maximum practicable separation from all fluid carrying lines,” this regulation allows for wiring to be installed in close proximity, as long as the failure consequences have been considered.

The support clamps for separation between the EWIS and fluid/oxygen lines, should be given additional consideration. Recommendation from AS50881 suggests that supporting clamps for EWIS should not be connected to fluid/oxygen components unless the separation is less than two inches.

If you are familiar with the recommendations of AS50881, then you are aware that the recommended standard practice is that wiring should, “… be installed to maintain positive separation [from gas and fluid carrying lines and tubes] of at least 0.500 inch.” First, while this separation distance may be fine for some system configurations, it is not an acceptable blanket statement for separation. Lectromec has done testing showing that tube failure can occur at an even greater distance from the arc plume generated during a wire failure event.

Second, conformity to the regulation takes precedent over industry guidance. Certification relies on data to verify the safety of design, and the recommendations of AS50881 do not provide sufficient data to support certification.

The next article in this series will cover Section ‘i’ of the 25.1707 regulations – separation with mechanical control systems.

For the past three decades, Lectromec has worked with federal agencies to make sure aircraft wiring is safe and reliable. Lectromec is responsible for testing, inspecting, and analyzing a wide range of electrical wire interconnect systems. For a white paper on “Addressing Fleet Management Needs” complete the form to the right.

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.