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EWIS: A 13-minute summary of MIL-HDBK-525

Aging Wires & Systems Management

This Lectromec presentation provides a brief summary of MIL-HDBK-525, “Electrical Wiring Interconnect System (EWIS) Integrity Program.” It provides a starting point for those involved in Mechanical Equipment and Subsystems Integrity Program (MECSIP) or those new to the EWIS service life extension efforts.

This fifteen minute presentation is a good description of Electrical Wire Interconnect Systems (EWIS) by the President of Lectromec, Michael Traskos. If you are in a position to look at the service life of an aircraft, then this is an excellent starting point.

During the presentation, Michael covers the origins of the handbook and gives a summary of the seven tasks that are part of MIL-HDBK-525.

A transcript is provided below:

My name is Michael Traskos, I’m the President of Lectromec. This is a 15 minute presentation that I gave in April 2014 on Mil-HDBK-525, which covers service life extension efforts on EWIS. This handbook is designed for MECSIP projects and any sort of EWIS service life extension effort and the work to maintain aircraft air worthiness. In this video I’ll go over where the handbook came from, why it was generated, and talk briefly about each of the seven tasks and summarize what the objectives are of each of these.

Wire failures can bring down aircraft. Here are two photos of a wire that arched against a hydraulic line, ignited the hydraulic fluid, and caused a flame thrower effect that eventually brought down an aircraft. This is just one example of the fair consequences of poorly maintained EWIS.

Why was Mil-HDBK-525 created? The Air Force research lab identified that there needs to be a clear set of recommendations for EWIS sustainment on military aerospace platforms. What they had found was that too often the fleet management offices had to develop their own set of methodologies for the EWIS sustainment or base their decisions on anecdotal evidence.

The genesis of this handbook creation came in 2008 to 2009 when a fleet was going through a life extension effort. The fleet management office went through the maintenance logs and the incidents reports and found that not a single class A event was tied to a EWIS failure, Class A events being, the loss of an aircraft or life. The recommendations where therefore to not perform any sort of EWIS sustainment or evaluation activity.

When the information was presented to the engineers at the Air Force research lab, they reviewed the results. Based on their experience with aircraft of this age and the insulation type of the wires on this aircraft, they recommended at least some level of EWIS evaluation be performed. The two groups went back and forth for a while and eventually made a final decision as to what should be done on this aircraft.

In order to avoid the standoff on what action should be taken and avoid basing decisions and recommendations on anecdotal evidence, this handbook was created. This handbook was designed to align EWIS life extension guidelines with industry recommendations and exciting military risk assessment standard practices.

The handbook did not come out of thin air. Here are a number of the standards that were integrated into the handbook. What we have here are standards from the military industry and the FAA. The information was taken from each of these to provide a clear set of recommendations for EWIS sustainment.

For you project managers out there, here is flow chart covering the overall handbook process. I will go through each of these steps here in the following slides.

Task one, physical and functional assessments. The objective here is to gather EWIS data to perform a data analysis and identify EWIS failure impacts. Here, the aircraft information is brought in covering the wire, wire specification connectors, circuit protection, harness protection, all the information that covers the wiring system. Also gathered here, is the EWIS physical data including the environmental information as to which zone this is running in, the routing within those zones, and any sort of nearby components such as fuel tanks or hydraulic lines.

Once this information is gathered, a preliminary EWIS component failure impact assessment is performed. This looks at the functional impact on the aircraft due to EWIS failure. The next assessment done during this task is an EWIS physical failure assessment. What you see down here in the bottom right corner is a chart that shows an example of an assessment of three different harnesses. The goal here is to identify the necessary separation distance in the case of a harness failure and nearby system components. For example, how far away should a harness be away from a hydraulic or fuel line before it can cause damage.

Task two, data mining. The objective here is to gather information from maintenance databases and interview support staff to direct on aircraft inspections, perform task three, and test activities performed in task four. For those that have gone through any maintenance system such as the REMUS system or the FAA service difficulty report system, you know that the information there is often miscategorized, there are misspellings, and often there’s a poor description of what is actually performed in the maintenance action. So it does take a fair bit of manual effort to take the information from that and process it into useful data.

The handbook does provide recommendations on how to process that in the most efficient manner in order to get useful data from there. If the aircraft being evaluated is a commercial derivative, the handbook recommends doing an additional analysis by going through the advisory directives that come out from the FAA.

As I mentioned at the start also part of this task, you’re looking to gather information from the engineering and support staff. They are the ones that are on the aircraft day in and day out. They’re going to have a lot of information as to where to look on the aircraft and where problems on the aircraft exist. Once all that data’s gathered, perform hot spot analysis, organize data and go through bit by bit to identify: is it a particular component, is it the system, or is it a particular zone where a lot of the maintenance activities are being performed.

Here is an example of the data analysis that was performed on an example aircraft. Over here on the left side, you see that the number of man hours is broken down by the particular work unit code or the system that the work was performed against. You see that the top three systems, which were the flight instruments, the lightening system, and electric power system, take up about 60% of the all maintenance activities. If nothing else was learned from this data, you know that if you focus maintenance and sustain activities to improving the reliability of these three systems, you would have a dramatic impact on the aircraft readiness.

Task three, on aircraft EWIS inspection. This is where you get your hands dirty and perform a physical inspection to determine the EWIS condition and identify areas for EWIS component removal done in task four. The information from task one identified those areas that are of critical importance. They have a high failure severity. Task two identified those areas that have a high probability of failure. By combining the results of those two tasks you can identify which areas on the aircraft should have a higher prioritization during on aircraft assessment.

Did You Know? Lectromec’s EWIS component test lab is an ISO 17025:2005 certified facility. Lectromec’s has a wide range of wire and cable testing services.

Before going onto the aircraft, a checklist should be created for what components should be evaluated for at that time. The checklist should be based on existing maintenance documents, as well as integrating information from the Mil-HDBK-522; also industry standard AS50881. This checklist should include such items such as looking for exposed conductors, any sort of contamination, sort of fuel or fluid exposure, overheating, excessive splicing, any sort of, evidence that indicates a reduction into the reliability of the system components.

During this on aircraft inspection there are three different levels of inspection recommended, the first one being a detailed visional inspection. This is what you want to do in those areas that have the high failure severity or a have a high probability of failure. This task recommends the use of magnifying glasses, flashlights, mirrors, anything that’s necessary in order to get a better visual examination of the EWIS components.

Those areas within an aircraft that are identified as being benign should be visually inspected at a general level. This is where you’re at least within arm’s reach and looking for any sort of obvious physical damage to the components. For those areas that are not benign, but are not failure level one, it’s a mix approach, which is called a zonal inspection, should be used.

Task four, EWIS agent analysis. The objective here is to perform an in laboratory assessment of the EWIS components that are removed from the aircraft. Task one, two, and three identify where the biggest problems are on the aircraft. During this task, task four, the components are removed and mechanical, electrical, chemical, or destructive testing is performed on these components. The objective here is to determine where in the lifecycle the component is and how much longer it can remain on the aircraft.

Over here on the right side we see three different models for degradation, the top two were developed by Lectromec for XL-ETFE and Polyimide and the bottom one was developed by the FAA for Composite construction. The benefit of using degradation models is that it can provide a means of identifying where in that lifecycle that component is and how much longer it could be used on that aircraft. For those components without degradation models, the objective of the testing is to answer the question: would you be comfortable putting this component back on the aircraft?

Task five, overall EWIS risk assessment. The objective here is to perform an EWIS risk assessment and identify the areas, systems, and components posing the greatest risk to the aircraft. Here, the information from task one through four is combined in order to do this. Task one provides information on the failure severity, and task two through four provide information on the probability of failure. Here, this is combined to generate that assessment.

For those familiar with MIL’s Standard 882, the chart on the top right should be very familiar. Here, we generate a numerical representation of the severity of failure and the probability of failure, combined to generate a single numeric value. Based on this, the prioritization of any sort of sustainment activities can be performed.

In the bottom right, there’s an example of a component degradation impact on risk, for four different areas. Examining only the leading edge wiring, the current risk level is a three, which may or may not be acceptable, depending on the particular platform. As stack component ages, you see after five years, it still remains at the same risk level, but somewhere between the five and ten year mark, the degradation to the system components has increased and changed the risk level. This information provides a way to do a phased approach to replacement or any sort of maintenance activities. This is the benefit of having degradation models for the EWIS components.

Task six, action plan. This is not just an engineering study, but actually looking to identify what can be done on the aircraft in order to improve the aircraft air worthiness. For those areas that have a high risk, there are three mitigation techniques that are recommended in the handbook. The first one is design change. Here, look to identify and develop a mitigation strategy for the components with a high failure severity values. Mitigation strategies developed and a second risk assessment is performed, where you go back to task five and identify if your mitigation strategy has reduced the risk to an acceptable level.

An alternative mitigation strategy is replacements. This method is not ideal, but it should only be considered when design changes cannot provide the desired failure severity values. Replacement should be based on the individual platform needs and constraints.

The last option presented for reducing the risk are maintenance changes. Here, the EWIS inspection program developed in task three should be integrated in with the existing maintenance practices for that aircraft.

Lastly task seven, a periodic reassessment of the aircraft. In order to ensure that the recommendations have been acted upon, here, you look to set up monitoring to maintain aircraft air worthiness. This is an iterative EWIS assessment used to track the degradation of EWIS components and update any sort of replacement or retirement actions. This is done by going back through task one through six, but given that that information has already been gathered, it should be a far more rapid process. Based on the outcome of the degradation assessment, changes may need to be made for the aircraft sustainment.

That covers all seven task of MIL-HDBK-525. If you’re interested in reading the whole handbook you can download it from the assist website at quicksearch.dla.mil. If you’re interested in finding out more about what Lectromec can do to help you through this sustaining project, contact us at info@lectromec.com. Thank you for your time today.

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.