Business & GA, Commercial, Military

The Hardware Link

By Vance Hilderman | February 1, 2009
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Quiz: In our increasingly numerical world, which of the following standards has rapidly become the focal point for the silicon in avionics hardware?

  1. Mil-Std-1553

  2. AS9100

  3. DO-178B

  4. DO-254

If you said 3 — DO-178B — you are close. But the correct answer is 4, DO-254. In just four short years, DO-254 has become the de-facto standard for almost all avionics hardware just as DO-178B is the de-facto aerospace software standard.

Why was hardware formerly perceived as the "weakest link?" And what are the scope, challenges, and costs of DO-254? If you are involved with avionics hardware, you are at risk of becoming the weakest link unless you take heed of the answers to these questions.

Commercial avionics software is certified according to the strict DO-178 standard. Over the past decade, the world’s military and space industries have followed suit and adopted DO-178 or its variants for their software. But hardware was immune from such certification requirements and gradually became the dumping ground for added functionality: avionics vendors could freely move functionality from software to hardware in order to avoid onerous certification. Meanwhile, that very silicon was rapidly increasing in complexity and functionality. What was the result of this evolution? Increasingly complex "hardware" that contained millions of lines of logic, all devoid of the very certification that similar "software" required. Avionics hardware became the weakest link.

So DO-254 was quickly put in place to address this loophole. Must all avionics hardware be developed and certified to DO-254? No: DO-254 is only for "complex hardware." Officially, this refers to "hardware which is not simple." Then, what is "simple" hardware? Simply put, simple hardware is avionics hardware for which exhaustive testing can deterministically verify all outputs over the range of possible inputs. In most cases, avionics hardware containing silicon must have that silicon certified to DO-254. Most of your silicon is too complex to be exhaustively tested, so you must follow a DO-254 development and certification process.

Which avionics silicon must now be certified to DO-254? Most custom avionics ASICs, FPGAs, PLDs and IP cores must be developed per DO-254. What does DO-254 require? DO-254 is 80 percent the same as DO-178B for software, but has crucial differences. DO-254 requires detailed safety analysis, planning, processes, requirements, traceability, deterministic design, validation, verification, archival and configuration tracking, production assurance, and certification-entity approval. In just four short years since the mandate for DO-254, a plethora of tool vendors has arisen to address this market. Any Internet search for "DO-254" will reveal dozens of tools and services from over 40 vendors addressing this nascent need. None of these existed just five years ago.

Has DO-254 adoption been easy or cheap? Hardly. HighRely Inc. has found that most companies spend an extra 70 percent to 90 percent in development costs on their first DO-254 deployment. But that is more than double the amount that an efficient DO-254 process should incur.

How do you avoid having DO-254 become your weakest link? Like meeting other technical challenges, you need to procure training, tools, checklists, and a DO-254 process prior to starting. Chances are you already comply with 50-to-60 percent of the DO-254 requirements without realizing it. You need to formalize your existing hardware development to obtain credit for the good engineering activities you are already doing, and then close the DO-254 gap in your remaining activities.

The new DO-254 Industry Group ( is a good starting point. DO-254 white papers are available online and a book on DO-254 has been published. There is also a dedicated DO-254 blog at with threads for the most common DO-254 issues.

Is DO-254 a one-time cure for all avionics hardware imperfections? No: DO-254 is a life-long regimen. When properly applied, DO-254 can remove one more "weak link," making all aircraft safer. Safe skies.

Vance Hilderman is co-founder of HighRely Inc., headquartered in Phoenix.

To contribute to Avionics magazine’s Perspectives column, contact Bill Carey, Editor in Chief, at (301) 354-1818 or [email protected].

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