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TESTING 1, 2—Part 1: Enduring Challenges

by George Novacek

Start • A Bit of Background • Hard-Won Experience • What’s the Worst That Can Happen? • Finding a Solution • Sources

A BIT OF BACKGROUND

In the good old days, flight controls consisted mainly of cables and pulleys with some hydraulic valves and actuators. Because there wasn’t much sophistication and very little to go wrong, reliability wasn’t a major worry. However, today’s sophisticated flight controls comprise electronic servo systems (collectively referred to as "fly-by-wire") with many parts that might fail, as well as software, and—unlike in the PC industry—cannot solve its problems with the three-finger salute. This same trend towards a higher level of technology exists in all areas of our daily lives. Part of the price we pay for sophistication and system intelligence is in more design effort to achieve reliability.

No matter what an electronic device is expected to do, its functional design is only a small part of the entire design process. Even when we can demonstrate it working flawlessly on the bench, we’re still asked how we know that our circuits will continue to work in the real world. The question for us becomes: what do we have to do to ensure that our device maintains its precision and reliability, despite temperature variations, lightning storms, or when all hell breaks loose (see Photo 1)?

Photo 1— To protect an electronic controller from the effects of harsh environment, its package looks like a brick, yet it is deceptively light because it is usually machined out of a solid piece of aluminum. You can drive over this baby with a truck or dunk it in the water and it won't lose a beat.

Before we start testing our equipment in a wide range of environments, it’s a good idea to define a standard or a composite of conditions the product is likely to encounter. It’s not surprising that the military is on the forefront of defining standardized operating conditions. In North America, MIL standards set the pace. Although we love to hate them, they are well thought out and, for that reason, have served as a template around the world.

For many years, the MIL standard was the only standard of the aerospace industry, but because they had been designed to apply to a great variety of military hardware, from submarines to missiles, commercial standards were developed by the RTCA specifically for aeronautical applications. There are many similarities between MIL and RTCA standards. Today, RTCA standards are accepted around the world and, in many instances, have been accepted by the military in place of their own, more traditional MIL-STD.

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