From: Rob Tremblay <firstname.lastname@example.org> Organization: Bell Global Solutions Date: 29 Jul 96 02:29:37 References: 1 Followups: 1 2 3
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email@example.com (John M. Hunt) wrote: > I cannot imagine any reason why total control of the aircraft on all > three axes and total throttle control cannot be trusted to the pilot > the instant he deems it desirable. I agree it would be desirable to > provide continuous trim control during autopilot operation to avoid > relinquishing control to the pilot in a seriously out-of-trim > condition, and am willing to make an exception for keeping the yaw > damper operative unless the pilot takes some simple specified overt > action to insist on rudder control independent of yaw control > assistance, but surely this is very easy and non-confusing to > implement. At least on the A320, "total control" (as you call it) is available at any time with two autoflight/autothrust disconnect buttons. The autopilot is disconnected with a red button on the sidestick, and the autothrust with a red button on the thrust levers. There are also a few other ways to disconnect said systems. As soon as the automatics are disconnected the pilot has conventional control of the aircraft- ie. Cessna 172 mode. All the protections are still in place, however. For example, if the pilot is handflying and lets the aircraft get too close to the stall, the engines will automatically accelerate to go-around mode- ie. max power. These protections are invisible to the pilot who is competant enough to keep the airplane in the normal envelope. There is no reason that I can think of why anyone would want to disconnect the built in protections. They are there for my protection- why would I deactivate them? Having said that, however, many of the protections can be disabled in different ways. If I really wanted to stall an Airbus, I could. As far as yaw authority is concerned- yaw damping is full time on all large aircraft, as far as I know. Once again, it could be disconnected- but for what reason? The yaw dampers provide stability- if for some reason I want to sideslip (x-wind landing), the yaw dampers do not fight this. Yaw damper authority can be overriden very easily. > It is inconceivable that todays pilots with their excellent simulator > training are not at least equal to pilots of an earlier era. If this > is indeed so, why the reluctance to simply trust the pilot to fly the > aircraft manually? Indeed, I have heard that Airbus now recommends that if the automation begins to overwhelm the pilot, the pilot should disconnect and handfly. The most complex computer on the Airbus is between the pilot's ears- nothing can touch the processing power of a human brain. The reluctance to fly manually is dependant on company training and indoctrination. If something needs to be done to alter a flight path rapidly (TCAS collision avoidance etc.), you can't beat handflying. > I realize that some exotic high-performance military aircraft achieve > superior performance by accepting inherent instability which is neatly > overcome by mandatory autopilot assistance, and that such aircraft may > indeed be totally unflyable by ordinary mortals without such > continuous assistance. I find it beyond belief that newly designed > airliners of the past decade are unstable, other than to Dutch Roll > and our old friend phugoid oscillations. Unfortunatly, I think you may suffer from what many others suffer from- comparing a civilian jetliner with a F-22. Two different airplanes, two different jobs. 9 G turns are simply not required in a civilian airliner. Large jets are designed to do 30 degree bank turns to final at 5 miles back- not exactly a manuever that an autopilot can't handle. > I also realize that some tiny additional increment in safety may be > achieved by automatically preventing overstressing the airframe by a > ham-handed pilot, but surely this is the classic case of a solution > looking for a problem. The Airbus has a safety feature that only allows a pilot to pull the maximum g-limit of the airplane- no more. Why would you want to overstress the airframe? Once again, we are not talking WW2 flak avoidance here- we are talking about getting passengers from point A to point B without a G-suit. > Another pet peeve is the required manual computer keyboard input of > such numeric values as rate of descent. I have no objection to this, > especially as no really graceful substitute for such data entry comes > to mind. But surely it would add very little cost to provide a > computer voice confirmation of exactly what the pilot has actually > entered, not, of course, what he THOUGHT he was entering.. Such a > service could even be provided selectively in languages other than > English to provide the greatest possible reassurance to a sizeable > portion of the world's airline pilots. It is awfully difficult to > imagine a scenario for such automated voice confirmation seriously > misleading the pilot in the event of partial and unidentified failure > of the voice feedback circuitry, since the pilot. if at all > suspicious, can easily verify the actual setting by existing numeric > displays. Rate of descent on the Airbus is not entered on a keyboard- it is done directly through the autopilot. An audible voice telling you what is going on would be totally distracting. Instead, a simple visual readout of what V/S has been selected is available on your PFD. Most of the time, V/S is not used. Instead, the airplane will calculate a perfect descent to meet altitude and speed constraints. It is really amazing to watch- especially if you have been flying an older analog airplane. It is still up to the pilot to intervene if the airplane is not doing what you want it to- this is basic airmanship. > Anyone have any thoughts in this area? > John M. Hunt > firstname.lastname@example.org > I hope I helped you out, John. Remember- don't believe everything you hear. If you have a chance, ride up front on a "glass" airplane- you will find it most enlightning. Just because something is new does'nt mean it is better. However, we must face the fact that the new technology is here to stay. It is up to airline training depts. and airplane manufacturers to make it safe.