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EWIS Instructions for Continued Airworthiness

Maintenance & Sustainment

Key Takeaways
  • Aircraft wiring system maintenance has come a long way in the last 20 years.
  • Operators must now have Instructions for Continued Airworthiness (ICA) for the aircraft wiring system.
  • The FAA has established several supporting Advisory Circulars (ACs) to assist in the development of ICAs.
  • Listen to the podcast here.

Aircraft are delicate creatures. They can be very finicky when not treated right and the design of an aircraft can only go so far to ensuring that the aircraft has a long, successful life. Without a doubt, many of Lectromec’s articles address the design and manufacturing phases of an aircraft’s life. As highlighted in the last article, technological and engineering hurdles must be overcome for aircraft electrical wiring interconnect system (EWIS) to achieving a fault-free life.

While that last article looked at the degradation elements around wiring and where the industry must improve upon, here we look at the last 95% of an aircraft life: operation and maintenance. In this, we review the regulatory requirements around EWIS instructions for continued airworthiness (ICA) and some of the resources that can be used to ensure a smooth certification process for your wiring system.


instructions for continued airworthiness are a fundamental part of aircraft design. Most operators expect to use an aircraft for more than 20 years and it is expected that maintenance procedures for these vehicles are well-established. For operators, understanding the required routine maintenance is part of the original cost calculation and scheduling needs for the organization.

Example EZAP
Many parts of the EZAP development process are straight forward, but there are others that require a through understanding of the wire system routing and failure modes. Lectromec can help to simplify this process.

While most aircraft systems had ICAs, until 2007, there was no specific regulation requiring wiring system ICAs. The industry/government push for the creation of these regulations was the output from the Aging Transport Systems Rulemaking Advisory Committee. In particular, working group #9 of the ATSRAC was tasked to provide recommendations and develop guidance for enhanced maintenance criteria for systems and recommend wire systems instructions for continued airworthiness.

The work of the ATSRAC working groups informed the FAA and EASA’s final decision on the EWIS regulations. After years of work, the regulation pushing for specific instructions for the wiring system instructions for continued airworthiness came out in 2007. The ICA regulation was part of the overarching EWIS regulations captured in the 25.1700 series regulations. Specifically, regulation 25.1729 states:

“The applicant must prepare Instructions for Continued Airworthiness applicable to EWIS in accordance with Appendix H sections H25.4 and H25.5 to this part that are approved by the FAA”.

Like many regulations, this one leaves much to the imagination. A first read of this regulation would lead anyone to generate dozens of questions and feel a sense of uncertainty as to what might be necessary to satisfy a regulator’s expectations.

Best Aircraft Wire Test Lab

Thankfully, the FAA released an advisory circular (AC) along with the regulations. Captured in advisory circular 120-102A, “Incorporation of Electrical Wiring Interconnect Systems Instructions for Continued Airworthiness into an Operator’s Maintenance Program”, in AC25.1701-1, and lastly in AC25 – 27A “Development of Transport Category Airplanes Electrical Wiring Interconnect Systems Instructions for Continued Airworthiness Using Enhanced Zonal Analysis Procedure”.

It is these three documents that coordinate the framework in which EWIS ICA can be created. As identified in this Lectromec article, the starting point for this work is to identify the specific zones within the aircraft, evaluate the environmental conditions within the zone, identify the components and systems within the zone and use that as a set of input data for the flowcharts provided in AC 25-27A.

Beyond this, the additional documents provide additional factors for review and integration with the overall maintenance/ICA framework.

What to Evaluate

Often there are a wide variety of configurations for single aircraft. As specified in AC 120-102, the instructions for continued airworthiness are required for a representative aircraft according to regulation 26.11. Specifically, the advisory circular provides this guidance:

“a. TCH. The TCH is required to develop EWIS ICA for the “representative airplane” in accordance with § 26.11(b). The purpose was to ensure that all variations of EWIS used in production were reviewed and appropriate ICA were developed. These EWIS ICA were developed in accordance with H25.5(a)(1) and (b), in effect on December 10, 2007 for each affected type design. The TCH submits those ICA for review and approval by the FAA Oversight Office.”

To fill in what is required in 26.11(b), we have the following:

“…For purposes of this section, the “representative airplane” is the configuration of each model series airplane that incorporates all variations of EWIS used in production on that series airplane, and all TC-holder-designed modifications mandated by airworthiness directive as of the effective date of this rule. Each person specified in paragraph (d) of this section must also review any fuel tank system ICA developed by that person to comply with SFAR 88 to ensure compatibility with the EWIS ICA, including minimizing redundant requirements.”

Next Up

This is a starting point for the elements informing and impacting EWIS ICAs. In the next article, Lectromec will continue to expand on these areas and the associated impact.

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.