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REFLECTOR: [canard-aviators] Re:Glass Cockpits/Computers



Folks,  I thought this "safety-related" item was worth sharing on Reflector.


>Date: Thu, 8 Oct 1998 23:24:41 -0400
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>To: timemach@telusplanet.net,
>    owner-canard-aviators@betaweb.com,
>    canard-aviators@canard.com
>Subject: [canard-aviators] Re:Glass Cockpits/Computers
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>
>[The Canard Aviators's Mailing list]
>
>THink long and hard before you tear out those instruments...
>
>The FAA has made it very clear that they will NEVER certify any primary
>flight instrument that uses a Windows operating system. There are
>several reasons, but, believe it or not, the primary one is not the
>system's propensity to fail when you need it most. Actually, the biggest
>problem has to do with the accuracy of the software code.
>
>When we in the avionics industry write code for any device, but
>especially cockpit displays, we conduct validation and verification. The
>purpose is to ensure that every line of code performs its intended
>function, that there is no potential miscalculation, and that there are
>no "extra" lines of code.
>
>An example of what happens if this were not true is the rocket that blew
>up recently when an "extra" line of code was accidentally left in its
>software.
>
>Additionally, certified displays incorporate what we call "watchdog
>timers" that continually track how long it takes to perform functions
>and update the display. Should a function get stuck in an endless loop,
>the timer send the display back to a reset mode. No laptop-based system
>has ever incorporated this function, and, given current operating
>systems, they can't with the kind of processing power currently out
>there.
>
>Given some of the brightest engineers and the most detailed series of
>cross-checks, errors still occur. For instance, about a year ago, an
>airliner accidentally stalled in flight. As it pitched and rolled, the
>flat-panel displays sensed what they thought was a failure (excessive
>roll rates beyond the design capability of the aircraft) so they went
>into their reset mode...just when the pilots needed their artificial
>horizon the most. No display is infallible.
>
>Another thing to consider: the weakest point in most computers and
>display systems are the backlights. Your computer can work just fine,
>but when the backlight fails, the laptop becomes 3 pounds you could have
>used for fuel.  Backlights in laptops are not designed to handle the
>constant vibration of a small piston airplane. Even the backlights that
>are designed to do so fail somewhere between 5 and 15,000 hours, which
>means if 100 of you had laptop-powered instrument panels, I would expect
>at least one of you per year to have an in-flight failure of your
>display. One company manufactures 95% of the world's aviation
>backlights, and even they won't guarantee their backlights much beyond
>5,000 hours in aviation applications.
>
>Additionally, the large planes that do fly with EFIS (Electronic Flight
>Instrument System) displays ALWAYS have a redundant, stand-alone backup
>for essential information, and we just don't have that kind of room if
>you use a laptop.
>
>The moral of this story: As Director of Cockpit displays for
>AlliedSignal Air Transport Avionics, I went to a lot of trouble and
>expense to install a vacuum-powered artificial horizon in my Long-EZ to
>replace a functioning electrical one. Sure, the vacuum pump has a low
>mean time between failures, but its failure will not likely be
>coincident with a total electrical failure.
>
>Single-point failures (total electrical failure) or software-induced
>display failures are just too risky for a small plane like an EZ. 
>
>Fly safely. Please.
>
>Tom Staggs
>Long-EZ N13YV
>
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