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Maintenance

EWIS and Aircraft Maintainability

The maintainability of the electrical wiring interconnection system (EWIS) is integral to the longevity of an aircraft. EWIS maintainability affects not only the EWIS itself, but any nearby system whose maintenance access is restricted by the location or function of the EWIS. Thus, high maintainability of the EWIS allows for faster, more efficient, and more precise maintenance of surrounding equipment and systems.

Original aircraft design must comply with EWIS regulations in the development stage to ensure long-term maintainability. It is important to know which regulations apply and which standards to follow when designing an aircraft to determine the appropriate maintenance requirements.

Here we will explore the requirements of some of the more common standards for EWIS maintainability in aircraft design.

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Review of EWIS for Sustainment

We measure everything that matters. In the last decade, the efforts of organizations to measure EWIS has been progressively increasing. Perhaps this is because wiring is now considered a system, or because regulations and requirements have emerged, or it may be due to a better understanding of the EWIS maintenance costs. Whatever the reason for better EWIS maintenance issue quantification, it has been a positive because there is data available to substantiate aircraft maintenance actions. The old saying is, “You can’t beat something with nothing”, and for too many years, EWIS maintainers were trying to take on EWIS maintenance without supporting data. Read more

Wire Diagnostic Equipment

Finding wire faults/damage is not an easy task; now consider that problem across an entire aircraft. In-situ testing of wires/cables has always been viewed as something of a challenge to the industry. Given the branching that most harnesses undergo, the various wire lengths, splices, and numerous termination conditions, it can be difficult. Attempts to automate some of the testing has come to the development of Automatic Wire Test Sets (AWTS [pronounced “Eh-Wits”]).

Because there are so many ways to test a wire harness, the US military sought to create a performance standard to cover the general ideas and best practices of this equipment. Here, we review the standard and some of the performance features that can be expected when using equipment in compliance with the standard

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Checking a Coaxial Cable for Damage with a Multimeter – Part II

In the last article, Lectromec introduced a damaged coaxial cable and tried three techniques to distinguish it from an undamaged cable. The standard multimeter tests (capacitance, inductance, and resistance measurements) found no appreciable difference.

The idea of this evaluation was to demonstrate that the classic multimeter, while a great tool, is not suitable for detecting damage to coaxial cables.

But we cannot run an article and leave it without a solution. In this article, we continue the testing of a damaged coax cable to see what technology, if any, can identify and perhaps locate the damaged section of cable.

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Checking a Coaxial Cable for Damage with a Multimeter

The electronic multimeter is a great tool; invented in the 1920s, the multimeter has been used by millions of technicians and engineers seeking to measure circuits and troubleshoot electrical issues. So common are these tools now that it is almost impossible to consider a toolbox complete without one. 

While these are great tools and can be employed in a million situations, they are not the magic tool that can diagnose every circuit. If only one thing is remembered from this article: multimeters are not the tool to use for coaxial cables

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New Guidance for Wiring System Inspection

Back in November 2018, the US Navy released the second revision to the military handbook on “Guidelines for inspection of aircraft electrical wiring interconnect systems” (MIL-HDBK-522). This handbook is a guide for the aircraft EWIS inspection and provides a lot of detailed examples of wiring evaluation from beginning to end of the EWIS. Read more

Impact of Wires Used as Ladders

Ideally, an aircraft’s EWIS aging is considered and monitored over time, but something as simple as gripping and pulling a wire or cable can change its electrical performance, specifically conductivity and resistance. Read more

Have we Reached the End of Aging Aircraft Wiring Systems? – Part II

At the start of the last article, the question was posed, “Is it possible that aircraft wiring reached a point where aging/degradation is a thing of the past?” In that article, four elements were identified that must be satisfied for wires/cables to be considered as age-free. The insulation and conductor aging factors were examined in the last article, and here we consider the remaining two: Design limits and random shocks. Read more

Aging Aircraft Wire

Aging aircraft wiring is a problem affecting the entire aviation industry. Lectromec’s evaluation of the 2016 service difficulty reports found that aircraft over 25 years old were more than two times likely to suffer problems with their wiring system. There are tools and analyses to get ahead of these issues. Read more

When to Pull the Component – End of EWIS Component Service Life

What is the end of life for a wire, cable, connector, or any Electrical Wiring Interconnect System (EWIS) component? This is a straightforward question that should have a straightforward answer, but often, this is an unanswered question. Regulatory guidance such as Fuel Tank Ignition Source Prevention Guidelines from the FAA think of wiring as something […] Read more