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The EWIS Mandate: Changing Aerospace Electrical System Integration and Wire Harness Manufacture

Mentor3 © Mentor

Anthony Nicoli, Aerospace Director, Mentor, a Siemens business



Engineering teams developing aviation systems and aircraft strive to meet the demands of performance, quality, reliability and profitability. But most commercial aircraft will never leave the ground without strict attention to regulatory compliance. Specialized standards apply to virtually every bolt, panel, window, and wire in a modern airplane. For passenger-carrying aircraft, some of the most demanding regulations relate to the aircraft’s Electrical Wiring Interconnect System (EWIS).


Internal electrical wiring was not considered a likely source of safety risks among aircraft in the world’s passenger fleets until fairly recently. A series of fatal airplane crashes in the span of just a few years (1996-1999) quickly raised the visibility of wiring-related failures and alerted regulators, and the flying public, to the critical nature of aircraft wiring. Even though many of the initial findings from the investigation boards indicated concerns around installation and maintenance of the EWIS, it was only after these investigations had been completed that it became apparent that if EWIS mandates are considered very early in the design process, and subsequently maintained throughout the entire course of development, many of the potential concerns could be studied, modeled and analyzed. Sound engineering decisions could then be made to eliminate the concern early in the program when the cost of change is much less.


This much-publicized spate of accidents and subsequent studies became the impetus for major changes in regulators’ view of aircraft wiring development and maintenance practices. Today, companies involved in the development of transport category aircraft are required to pass the Federal Aviation Regulations (FAR) Part 25, Subpart H EWIS mandates as a precursor to type certification of the aircraft.



The EWIS mandates are very broad, open to interpretation and have an impact on an organization throughout an aircraft’s lifecycle (design, installation, and maintenance). The mandate has forced companies to re-evaluate and improve their internal business processes as well as their supplier relationships. Many OEM’s are finding themselves in the position of now having to meet the EWIS mandates for new aircraft development; whereas, in the past, they may not have had this pressure. If a company does not plan appropriately for this, the result could be costly. Also, there is more risk to a delay in the program itself. Last, but not least, the EWIS mandate can indirectly present a challenge to knowledge retention. Let’s investigate these issues in more detail.



Many of the EWIS mandates put additional pressure on the engineer during the design process. As an example, FAR Section 25.1703 (§25.1703) speaks to the need for designers to select EWIS components appropriate to their intended function. Consideration of factors such as component design limitations, functionality, and susceptibility to arc tracking and moisture are important.


While designers prior to the EWIS mandates did due diligence in this area, the mandate forces a more structured and rigid decision process for component selection. Also, consistency of decision making is paramount. For example, a part that one designer selects as being compliant should be the same part that another designer would select given the same set of design inputs. Compounding the challenge, the factors that went into the decision must be documented. They must be traceable, and in enough detail to pass the EWIS certification process. This more structured design process has the potential to lengthen overall design time. However, companies can’t simply accept an expansion of the time-to-market equation. Something must be done.



Figure 1: EWIS component selection being verified early in the design process




It is interesting that what appears to be a simple mandate can have such a significant impact. For example, §25.1711 speaks to the need for consistent methods of distinguishing EWIS components that provide easy identification of the component, its function, and its design limitations. While this mandate goes into detail about how to perform the actual identification marking of the EWIS objects, let’s focus on the identification itself. The identification must provide uniqueness in the context of the aircraft configuration and also convey important information about its role, e.g. EMC segregation, and other information.


One key issue is that, today, engineering teams rely on lengthy, manual validation processes to avoid being tripped up by the many failure points throughout the aircraft lifecycle. When considering how many EWIS components are in an aircraft and how many designers may be involved in the entire design flow, it is easy to see that managing the myriad of identifications could be a challenge. In the past, companies relied on very manual methods of determining a component’s identification. Some companies kept a book, or log, of the identifiers and, as they were used, they were manually noted. This method is risky and likely to fail because it depends extensively on people remembering to check that the book is properly updated. Given realistic rates of design change, this approach quickly becomes a potential quality, cost and time problem.  


Another area to consider is system safety analysis.  Safety is of paramount importance in commercial aircraft design. FAR §25.1709, which focuses on EWIS safety compliance, builds upon §25.1309 to provide a thorough and structured analysis of aircraft wiring and its associated components. However, §25.1309 does not adequately consider all failure conditions of EWIS components. For example, even for components covered by §25.1309, the safety analysis requirements have not always been applied to the associated wiring.


We have to look at the failure modes of the EWIS components at the airplane, or platform, level and evaluate whether the EWIS specific failures could have an impact on the safe operation of the aircraft. The cost impact of §25.1709 appears in the increased time necessary to conduct the safety assessment. Couple that with the trend in newer aircraft to become “more electric”, and the program time to ensure sufficient safety analysis only increases further.




Figure 2: Automated failure analysis accelerates time to EWIS compliance




Another example of a cost driver is system separation. As aircraft become more electric, the challenges of system separation become more acute. FAR §25.1707 looks at system separation and details what separation must be maintained to eliminate unintended EMI and HIRF induced crosstalk and other effects. 



Figure 3: Electrical system and MCAD integration enables platform level EWIS separation assessment





Companies have always struggled with how to capture, maintain and proliferate the “tribal knowledge” of engineers to help increase the efficiency of the larger organization and to ramp up the training of new engineers. The EWIS mandate compounds this challenge by calling for more consistent and repeatable design processes, regardless of the level of experience of the engineers involved. It has forced companies to look at ways to institutionalize their engineering process intellectual property, leveraging it across the organization. Knowledge retention presents both an opportunity and another potential cost contributor that must be controlled.



With the exception of power plant manufacturers, suppliers aren’t responsible for the EWIS compliance. Compliance is the OEM’s responsibility. However, the advent of the EWIS mandates has forced OEMs to improve their supplier relationships. For example, let’s consider an externally supplied wire harness that fits into the overall vehicle and exists with other wire harnesses manufactured by the OEM. The decisions about part selection and other design parameters used by the supplier must agree with the design guidelines used by the OEM. The level of collaboration required between the OEM and the supplier to make and validate these decisions force a situation where communication using the typical exchange of emails and paper documentation will no longer suffice. Process improvement gains have come from embracing a digital communications thread between the companies involved. This provides a much more error-free and decision-traceable environment that both the supplier and the OEM can leverage to implement the certification process more effectively.




Mentor recognizes the challenges the EWIS mandates place on aircraft OEMs and suppliers. It has responded with the advanced capabilities of its Capital electrical systems integration software platform. Let’s consider just a few of these.


Capital enables companies facing the EWIS mandates head-on to take a much more “correct-by-construction” approach. This approach takes multiple design parameter inputs, captures them in an algorithmic form, and then uses these to drive an automated design decision. In this way, the design decision, guided by predefined functional, logical and physical constraints, is made correctly at the time the design feature is authored.  No separate checking or validation step is needed in the process. In addition, any engineer using the same inputs would get the same answer, which helps ensure decision consistency, as required by the EWIS mandates.


Recall the example above regarding the challenges associated with identifying objects, as outlined in the FAR 25.1711 explanation. Capital addresses these challenges by providing ways to manage the object names via algorithmic rules. The object naming rules are defined one time for the project. As the engineers do their design work, the next available name for that particular aircraft configuration is made available automatically by the software. Not only does this directly address this particular mandate, but this method also provides more time for the engineer to do design work instead of having to deal with non-value added, manual data tracking tasks.


Finally, Capital provides a platform-based approach, which means the designer can and should evaluate design decisions in the context of the entire platform. Traditionally, evaluation of large amounts of data took excessive time, and the actual evaluation of the data was decoupled from the design tools. The result was that it was time-consuming and difficult to evaluate a design decision in the platform context. It was also difficult to evaluate the relative contributions to the result from the various inputs.  By employing Capital’s ability to assess and depict the impact of design inputs in the context of the full platform EWIS, evaluation and validation is simplified thereby addressing negative impacts to cost-of-compliance and to time-to-compliance before they occur.



Complying with the EWIS mandates requires far more rigorous design and verification processes. Companies using traditional design approaches, relying on nonintegrated tools and manual processes, find that achieving EWIS compliance is costly and delays EWIS certification, extending platform time-to-market.


Both tools and design-to-certification processes must evolve in order to make significant strides forward in addressing the challenges of EWIS compliance, while retaining present levels of profitability. Capital’s innovative capabilities and digital data continuity throughout the EWIS value chain enable customers to meet these business objectives.



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