Newsgroups: sci.aeronautics.airliners,rec.travel.air Path: news From: rdd@cactus.org (Robert Dorsett) Subject: Re: Airbus safety (was Re: TWAs Status) X-Submission-Date: Thu, 10 Dec 92 5:16:04 CST References: <1992Nov25.191925.27991@news.mentorg.com> <8762@lee.SEAS.UCLA.EDU> <1992Dec01.173212.27936@news.mentorg.com> Message-ID: Approved: kls@ohare.Chicago.COM Followup-To: sci.aeronautics.airliners Sender: kls@ohare.Chicago.COM X-Submission-Message-Id: Date: 10 Dec 92 16:07:03 PST In article <1992Dec01.173212.27936@news.mentorg.com> philip@mentorg.com (Philip Peake) writes: > >It wasn't unintentional - it was a deliberately (contrived) example. >The arguments I have heard so far seem to say that just because its always >been done that way, it always should be - aircraft design has changed a LOT >since the stick control was introduced - maybe this is no longer the >correct control mechanisim ? Transport aircraft design hasn't changed much at all in the last 30 years. We fine-tune various features, change the aspect ratio, develop better drag profiles, better powerplants, occasionally build a better, lighter system. Certainly improved manufacturing techniques. But the *engineering* discipline is so WELL defined that if you give three manufacturers the task of developing three different airplanes for the same mission profile, you'll now come up with almost identical airplanes. It is a discipline so evolved that we can come up with physical implementations which can match design performance objectives to within a percentage point. This is not the result of "wild-catting," or breaking the rules: it's the result of decades of working over the same problem, developing a very intimate understanding of this particular type of development problem. We should expect that the same considerations must be applied to how the pilots control the airplane. The "old" model may not be the best available, but it's well-understood, and is likely preferable to any "replacement" we are likely to produce with current technology. >If you are against the idea of insulating the pilot, maybe we should >remove servo brakes and power steering from cars too ? The pilot IS in the loop. You can complain about that, and try to eliminate that, if you want to. However, since he IS in the loop, the unique feedback requirements needed to let him do his job require a more interactive environ- ment than either contemporary glass cockpits *or*, in this case, the A320 sidestick, provide. Christopher Davis already addressed your point in his reply: *hydraulics* is the equivalent of power steering, not FBW control. However, note that we've been providing completely artificial feel to go along with this, for the past thirty years. Yet all of a sudden, on the pretext that the "FBW" in their airplane mandates it, Airbus, which is in the business of selling technology, cavalierly introduces a control device which: 1. Has no interconnect between the pilots. 2. Has no active feedback. 3. Utilizes artificial control laws in the normal and alternate flight modes. I suggest that the issue has NOTHING to do with technological "advantages" human requirements: it is completely marketing-driven. >|> In essence, my point is that standards don't exist because of happenstance. >|> They exist because it makes life easier for everyone. This is particularly >|> important when human lives are at stake. > >Standards are also perpetuated by vested interests, Yeah, that powerful yoke-manufacturer lobby. The bastards. Just because they won't retool to build sidesticks, they gotta ruin it for the rest of us. :-) Seriously, this is a tremendously conservative industry. What isn't broken, doesn't get fixed. However, when a better mouse-trap is invented, it is almost always adopted, universally. The fact that no other manufacturer is rushing to repeat Airbus' example suggests the arbitrariness of the use of the sidesticks: if there were even minor operational or material advantages in using them (and modified control laws) as interfaces to the EFCS, you could bet your last dollar every other manufacturer would be doing so, not least as the result of airline demand. We don't see that. > even when better ideas >ar around. This isn't one of them. We aren't operating in a vacuum: NASA, as one example, has been running a lot of research (over, and over) over the last 20 years, addressing precisely these issues: the Airbus implementation is arguably on the weaker of a variety of choices available. >If all new pilots were taught nothing but the side stick, >how long would the old arangementy last - and if the old arangement Why should pilots be taught nothing but a unique, *proprietary* side-stick design that no pilot had any experience with before four years ago, and which is only one of a variety of other possible designs? You imply that the sidestick's just a yoke wrapped up in a little handle. It isn't: the issue's a lot more complex, and, within that simple interface, there are *many* ways to proceed. The certification authorities, you will note, have not codified mandatory control qualities of this interface (and WON'T): thus, in a worst-case, we could have Airbus running its stick (+ control laws), Boeing running its own, MDC running its own, etc. >is so wonderful, why do military fighter aircraft, where tight control >by the pilot os ESSENTIAL use side stick controls ? Not all do: several continue to use center-sticks. In either case, the issue is in large degree driven by the need to effectively control the aircraft at high g's--but even then, it's a significantly different design than that used in the A320. I would also note that in fighter aircraft, there isn't the issue of two-pilot "peers" having to quickly and instinctively figure out who is flying the airplane. On the A320, there is no interconnect between the sidesticks: the captain can command a full-left in an emergency evasive maneuver, the F/O full-right, and the net result will be an algebraically added "zero." >The problem is the PILOTS, not the design Here we flip to cockpit integration, not sidesticks. The problem is a design philosophy which is unwilling to accomodate the human element. I also see a great deal of "stick it to the pilots" going on: a number of proponents of pilot-isolation don't even bother to cite alleged economic or safety benefits, anymore: the pilot-isolation increasingly appears to be an engineering-driven goal in itself. The Airbus approach has gone too far. Thankfully, however, it seems to be on its way out: new designs, such as the 777, are more sophisticated, yet have more conventional and interactive interfaces. And the research community is coming squarely on the side of more interactive, appropriate feedback. New designs will be more human-factors-driven, not engineering- driven. And, with luck, we'll see a return to the *evolutionary* application of high technology, rather than the *revolutionary* application of the same. And who knows, in 20 years, when we have enough underlying experience and research under our belts, we can try a *standardized* alternate interface. BTW, and for the record, I *like* the idea of sidesticks: for no other reason than to be able to see the entire instrument panel, unencumbered. I simply don't like this particular implementation, and have concerns about the human requirements any sidestick design could introduce. >Philip --- Robert Dorsett rdd@cactus.org ...cs.utexas.edu!cactus.org!rdd