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 that should remain reliable throughout the airplane’s operational life.
When other components are considered, there are life-limits and assessments utilizing tools and techniques to identify when replacement is necessary. Looking at a vehicle’s tires, there are signs when they are no longer viable for use, and based on typical usage and tire wear, it is possible to predict when the tires will need to be replaced. Why is this not done more often with EWIS components? Too often the technologies that are available for EWIS to predict the future reliably are ignored.
As a framework to establish the end of EWIS component service life, Lectromec has prepared this article covering the factors that often create the end of life condition and how they can be assessed. This follows the considerations outlined in AS50881 on the prioritization of EWIS design and installation principles.
This life-limiting factor considers the economic impact of wire system failures and seeks to determine if the EWIS can no longer be maintained in an economic fashion. In this case, EWIS issues appear so frequently that the cost of patchwork maintenance actions becomes a burden for the maintainer. The maintenance cost is then combined with the loss of aircraft availability and rescheduled flights. This maintenance element of this cost determination would be straightforward if the maintenance data correctly identified all the wire system issues (see NFF), but all too often it is not.
A review conducted by the Air Force on the maintenance codes used found that a high percentage were assigned to the incorrect system. These data entry errors create a heavy burden on those looking to identify the EWIS costs and are likely to need either advanced analysis or additional time and effort to correctly identify the frequency of maintenance issues.
If cost calculation is used as a means to determine the wiring system’s end of service life, then this also acknowledges that the wiring system has degraded to the point that wire failures are a common occurrence. This also admits the vehicle is not airworthy; that is not an acceptable condition for any aircraft.
What about Risk?
Should the wire system component end of life be based upon its risk to the vehicle? A wire failure is not just a wire failure when it is supporting flight controls. A degraded connector does more than just complete a circuit, it is a critical factor in sending signals to the communications equipment. Thinking of the EWIS degradation and the aircraft level impact helps to identify where the risks may rest.
There are established procedures for assessing the risk of an aircraft’s EWIS. Military handbook 525 outlines and thoroughly discusses seven tasks for the performance of the EWIS evaluation. The overall structure of the handbook is to provide a customizable framework for EWIS assessment and an assessment can be expanded or contracted to the particular needs of the platform being assessed. But the assessment should not be done haphazardly. While some assessment is better than none, blindly selecting a task for the assessment is analogous to reaching into a bag full of marbles and hoping to get the best one. A thoughtful consideration of what the available inputs are, and the expected outputs are important for any project. With careful selection and direction that Lectromec can offer, the greatest value of the wire system assessment is possible. And with a valuable assessment, it is possible to determine the risk of the aging wiring system to the vehicle and identify specific actions that can be taken to return it to an airworthy condition.
Does it Work?
What about performance? Should wire system components be replaced and be considered to have reached the end of life if their electrical or mechanical performance has degraded? The subsequent question to that is how much performance degradation should be permitted?
There is natural variability in the performance of wires/cables from different manufacturers. Some manufacturers produce wires that consistently exceed the minimum performance requirements while others barely pass. If the performance criteria for end of life is the original product performance, then the end of EWIS component life of Company A’s product could potentially be years longer than that of Company B.
While this approach of limiting the component use to its original performance specifications is useful, many have identified this as impractical. Often, this line of thinking into a more fundamental question about any component performance; if a component is in a condition that would not be placed into a new aircraft design, why leave it on an existing aircraft?
Thankfully, most components placed in the aircraft will never be stressed to their maximum performance capabilities. The performance capabilities of many of these EWIS components will be stressed about 30 to 50% of their capabilities, and as such, there is significant leeway for component degradation.
End of Life
The end of component life can be assigned by economic, risk, or performance considerations. Each of these have their merits and potential benefits. One area that was not considered during this assessment or the review of these methods, was the future performance of the system. Each of these looked at the current condition for actions in the terminations. But if the goal is for the aircraft to be flown for another 10 or 20 years then additional assessment to determine the degradation and performance is necessary.
Lectromec has developed the technical capabilities to predict the remaining service life of EWIS components. By doing these assessments, it becomes possible to not only see the cost and risk of wire system issues today but also predict how those will evolve as the aircraft ages. By doing this assessment, it becomes possible to predict the operational costs and maintenance costs in the years to come.
The challenge of maintaining a reliable aircraft electrical system is a great challenge for maintainers. The aging aircraft systems work against maintainers repeated efforts, and this is a difficult uphill battle. Lectromec has been solving EWIS degradation problems for more than 30 years and we have helped numerous fleets proactively address their problems. With the assessment of the wiring system providing a clear path and costs for handling EWIS degradation, actions can be taken, and data-based decisions can be made.
Lectromec has produced a white paper covering past efforts. This is the first step to understanding how an EWIS can be evaluated which will help reduce decision uncertainty and ensures the decision you make for maintenance is the right one. To take the next step, set up an appointment with Lectromec.