This book was inspired by, and evolved from, the experience we gained while teaching the DO-254 class at RTCA in Washington, D.C. and at numerous companies throughout the United States and abroad. In some respects it is the logical extension of our DO-254 class, and in fact some of the material in this book shares common origins.
Most of this book, however, is a testimony of the lessons learned and wisdom gained from many years of first-hand experience in the design, verification, and approval of airborne electronics and software, including some of the very first projects in which DO-254 was applied, and also including the very first projects where DO-254 was applied at the LRU level. The early years of DO-254 were seminal to us for revealing not only the difficulties inherent in applying a comprehensive document like DO-254 to a very narrow target, but also for the labor pains endemic throughout the industry as it struggled to understand—let alone comply with—this new way of doing business. Pain is a hard but effective teacher, so by any measure those of us who experienced those years should be geniuses by now.
As we and the rest of the industry adjusted and eventually mastered both the document and its ramifications, we were able to discern the practices and techniques that complemented the processes in DO-254 and therefore worked best in this new environment. This book documents the practices and techniques that we have identified and witnessed as being compatible with the intent of DO-254, and which thus make the road to compliance and eventual approval as direct, efficient, and effective as possible. While most of the material in this book is written from the perspective of programmable logic devices (à la FAA Advisory Circular 20-152), all of it can easily be extended to encompass the rest of an electronic system in the way DO-254 was actually intended to be used.
That said, there is only so much that can be documented, let alone taught, in one book. The concepts and techniques that we introduce here are presented in their most basic and fundamental form; actually mastering the topic can only be accomplished through first-hand experience in developing an electronic system in a certification program. While this means that newcomers to the world of DO-254 compliance may experience the sometimes difficult initiation that was sustained by those who went before them, it is our fond desire that they will embrace the material in this book to minimize the cost—both literal and metaphorical—to its lowest possible level. After all, a wise person will learn from his own mistakes, but a wiser person will learn from other peoples’ mistakes. This book is built upon the mistakes and successes of many people all over the world, so it offers the wiser person the means to learn from the mistakes of a distinguished club of professionals who had to learn their lessons through experience, hardship, and even trial and error. Through this book the reader can access an enormous compendium of experiences without having to experience the associated travail first hand.
It is our desire, and our motivation for writing this book, to make that wisdom available to all of the developers of safety critical electronic hardware to minimize the needless repetition of the difficulty of those early years, and of course to make modern aircraft as safe and reliable as possible.