From: firstname.lastname@example.org (Terrell D. Drinkard) Organization: Boeing Date: 30 Jan 93 22:42:47 PST References: 1 2 3 Followups: 1 2
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In article <airliners.1993.66@ohare.Chicago.COM> email@example.com (Dennis Chamberlin) writes: > >In article <airliners.1993.49@ohare.Chicago.COM> firstname.lastname@example.org (Kevin Driscoll) writes: >>In article <airliners.1993.36@ohare.Chicago.COM> email@example.com.EDU (Keith Barr) writes: >>> >>>Wouldn't there be a change in attitude if the autopilot was engaged, >>>which it obviously was, and if the navigation equipment was disturbed by RF? No. Navigation equipment tells the airplane where it is, not what attitude it is in. If you have somehow convinced the airplane that it is somewhere else, it will gently guide you from where it thinks it is, to where it thinks you want to go. Large changes in attitude are not necessary. >>In this case, it is >>possible (but highly improbable) that a CD player could effect the radio >>nav (which is forward and under the cockpit). Not all of the nav boxes are under the cockpit. Some are near the antennas, some are aft under the floor. Depends on the options selected by the airline. >I guess I can't swallow the idea that a passenger's CD player is going to >find its way into nav or other avionics gear. If the manufacturer really >said this, I interpret it as straw-grasping in the absence of other >explanations. Entirely possible for reasons that I will outline below. >The most powerful components of a CD player are presumably the motor drive >and audio output. Not much there. I would think that if the aircraft systems >were so exquisitely sensitive and even if by some fault the system wiring >in the cabin area were effectively unshielded, the resulting problems would >be frequent to continuous, and emerge from many other sources than CD >players. Wiring that runs through the cabin area is not shielded, except for coaxial cables running to antennas. Shielding is heavy and is avoided if at all possible. If the passenger with the CD player is sitting next to the wire bundle, perhaps with his player leaning against the sidewall liner, it is very possible that either the digital or the analog signals from the player (which is not shielded either) could alter the data moving along the airplane's wiring. >We all live in an environment of electrical noise from multitudes of man-made >and even natural sources. Some of these are of much greater magnitude than >anything that could be supplied by the batteries in the CD player. The >normal operations of the aircraft itself emit electromagnetic energy of >considerable power. The cabin audio/video system is itself of much higher >power than the CD player, although the manufacturer does control its >installation and engineering. That last point is a key consideration. We test what we put on the airplane, part of the reason those options are so expensive, but sometimes even we make mistakes. :-) >I am sure that during development and manufacture, an expensive set of quite >sensitive measurements establish the electromagnetic compatibility (EMC) of the aircraft with itself and both known and arbitrary outside sources. I >believe that if the various and powerful internal and external sources over >a broad band were ever to start talking to the sensitive systems, we are >going to have much more to worry about than CD players. You'd be surprised at how little EMI testing has been done on commercial transports in the past. This is changing as we move to more and more complex electronic systems, fly by wire for instance. This is called HIRF testing. (High Intensity Radio Frequency I believe) HIRF tests are extremely expensive, virtually no one has the proper equipment and to my knowledge, no standards have been mandated by the appropriate regulatory agencies (FAA, CAA, JAA, etc). EMI is a major argument to move to fiber optics on airplanes. However, we have yet to certify an airplane with fiber optics. There are a lot of very senior people who have yet to be convinced that fiber optics are economically viable in the air transport industry. They don't care what the computer and telephone industries have accomplished. It is an uphill battle (you should hear their views on cables :-) but there are a few of us fighting it. -- Terry firstname.lastname@example.org "Anyone who thinks they can hold the company responsible for what I say has more lawyers than sense."