Some regulations or standards apply to almost every bolt, panel, and wire in a modern aircraft. Some of the most demanding regulations are related to Electrical Line Interconnection Systems (EWIS). If these conformance requirements are not predicted at the beginning of the aircraft design project, it can have a significant impact on costs. By taking EWIS regulations into account early in the project and making wise design decisions, most of the later design changes can be avoided. Postponing a consistency check can mean making the most costly changes.
EWIS is now part of the Federal Aviation Regulations (FAR) Part 25 regulations and is therefore a certification requirement for all new commercial aircraft. â€œEWIS Thinkingâ€ has been extended to other industries such as rotorcraft and defense platforms. We may wish to study some of the main concerns and explore ways in which commercial off-the-shelf (COTS) electronic design automation tools can help designers achieve EWIS consistency.
FAR 25.1711 describes the types of authentication and information that an EWIS component must carry, including component functionality, redundancy considerations, isolation requirements, and uniqueness. In an aircraft, each component has and has only one corresponding identification, which must be adhered to throughout the life of the aircraft.
For example, assuming the wire name consists of the harness identification, the isolation category, the harness-specific count, and the wire size, the wire number is W238-FC1-101-22. According to the uniqueness requirement, another wire numbered W238-FC1-101-22 cannot appear in the wiring harness or other parts of the vehicle. Today, the many EWIS components in the aircraft, different aircraft configurations and lifecycle change management challenges make this job very difficult and error prone. This requires a more systematic and automated approach.
A simple solution is to electronically check the component name for duplicates at different stages of the design cycle. But this can make the wrong tricks spread through the process and affect connections or archiving elsewhere in the aircraft. .
In contrast, advanced COTS tools use the â€œcorrect buildâ€ approach. The software eliminates the occurrence of errors from the source, rather than relying on subsequent checks to find out where the problem is. When designers create design data, the COTS tool uses wire naming rules to ensure EWIS targets are met, automatically meeting FAR 25.1711 requirements.
FAR Part 25.1709 focuses on the security of the EWIS system. These requirements ensure that catastrophic failures are almost impossible and are not caused by a small failure, and that the probability of each possible dangerous failure is almost zero.
The failure tree analysis (FTA) and failure mode and impact analysis (FMEA) illustrate the virtual modeling capabilities used here. Software tools that perform this type of analysis require the use of current design data, and it is a huge challenge to take action at any time based on changes. Electrical designers must strictly adhere to delivery times and try to make these data more complete, because security engineers don't have time to re-enter new data for each analysis.
The best way to solve this problem is to use a complete set of security analysis tools that meet the needs of the design environment. This makes it easy to reuse information and apply design data to applications that serve larger projects. Ideally, the security analysis tool not only provides â€œdataâ€ about security implementation, but also provides a way to quickly assess the impact of the analysis and help the design engineer make changes.
Recently, most analytical tools have given analytical results in text form, and security engineers need to identify the most critical issues based on these results. But the modern COTS design and analysis toolset has been integrated into a seamless environment. The latest electrical design data can be reused for a variety of purposes, including EWIS safety conformance analysis that targets the current state of the design data. In addition, the data can graphically indicate where the problem might be.
Figure 1 shows several related analysis windows for the Mentor Capital Design Suite, with annotations for the ability to display graphics.
Figure 1 - Graphical display of FMEA results
This example shows various faults ranked by risk factor (RPN). An RPN value of 60 indicates that this error is causing attention; a fault can cause the warning panel (CAP) to fail to display information in the cockpit.
From the highlight of this diagram, you can directly see where the errors in the design are and how they are affected. The green line in the circuit indicates power up and the blue line indicates circuit interruption. Engineers can easily see that a breaker failure causes a current interruption in powering a particular device.
The EWIS regulations include a set of rules that express requirements. E.g. Each component must "...have its basic functionality in terms of type and design"; "Independent power supplies must not share a ground wire." Such instructions can be met within the COTS toolset by capturing core requirements for similar design rules and constraints.
Design tools enforce rules and constraints to assist and automate most decisions. This approach has obvious advantages:
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