From: "Larry Stone, United Airlines, 415-634-4725" <STONE_L@Eisner.DECUS.Org> Organization: DECUServe Date: 30 Jun 95 03:47:13 References: 1 2
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In article <airliners.1995.827@ohare.Chicago.COM>, firstname.lastname@example.org (David T. Medin) writes: > I think the main exception when compared to Airbus is that Boeing > allows pilot override of the computers, either through fighting the > control inputs or switching flight control modes, and gives simulated > tactile feedback of conventional control feel. Airbus does neither. > That is the issue... As a (light-plane) pilot, I strongly feel the need for both the feedback and to be the "final authority". There are many situations where the "long-run" optimal strategy is not the "short-run" optimal strategy and it may be for reasons that the computer can't know about (a good example is engine failure training in a single - you're taught early that best glide speed is the airspeed to fly [it may not be due to wind, weight, and other factors but let's not worry about that] - that's all well and good but if I'm descneding at best glide and notice some power lines in my way, you'd better believe I'll sacrifice some glide range to avoid those wires). But my major concern with the Airbus approach is a multiple emergency scenario that is beyond anything that might have been envisioned. I'm sure we all remember the Aloha "convertible". This was a situation that involved multiple emergencies - if I remember correctly, besides the obvious explosive decompression/structural failure, there was lost comm. (their headsets "exited" the aircraft although they later got a handhold mike out and switched to the overhead speaker), they lost an engine from FOD, the nose gear never indicated down and locked, and they had buffetting at full flaps on final that forced a less than normal flaps landing. Let's face it - the moment that incient started, the crew became test pilots flying an unproven and never before flown type. What they knew about flying a 737-200 was only a good starting point for flying what they had. They had to learn to fly this plane from scratch and fortunately, as the flap incident showed, did learn and "threw away" the book when experience showed the book no longer was right. Could a computer, programmed for a 737-200, not this new type of airplane, have done as well. What if the new configuration (with much added drag) required the controls to be positioned "outside the envelope"? The multiple emeregency aspects of this is interesting too. Due to the added drag and the failed engine, they could not climb or even maintain level flight. Therefore, when they didn't get a green on the nose gear, even after doing what part of the emergency gear extension procedure they had time for, they did the only thing could do - essentially said "screw it". Imagine a computer trying to say "you're not in the landing configuration, I won't let you land." (Note: I am not saying Airbus planes would do this, I'm just trying to point out the hazards of emergency procedures that conflict with each other or with the airplane's current capabilities. Somewhere, a judgment call has to be made to resolve conflicting instruction.) I once was looking at landing speeds cards for a 747-200. Besides the usual speeds for various "legal" landing weights, there was a shaded section marked "for use when an overweight landing is deemed the best course of action." In other words, even though the "book" says "Thou shall not land overweight", here's the information in case you have no other choice. -- Larry Stone | United Airlines VAX and HP-UX Systems Administrator | Maintenance Operations Center email@example.com | San Francisco, CA 415-634-4725 All opinions are mine, not United's.