wolit@alice.UUCP (Jan Wolitzky) (03/07/85)
> The airliner is on autopilot and the crew is flying with brains disengaged. > Power is lost on one of the outer engines. The obedient autopilot maintains > altitude by raising the nose. Air speed drops, plane stalls. The asymmetric > thrust rolls it into a spin. Plane drops, goes transonic in the dive. The > plane reaches denser air and the autopilot pulls it out if the dive at 9500 > feet. During the pull out, the G force drops the gear and the doors fly off > and hit the tail. After the pull out, the crew finally gets their act > together and disengages the autopilot. Interesting possibility, but 747's are generally equipped with autothrottles as well. It's true, though, that at 40,000 feet the margin between maximum cruise speed and stall speed isn't very wide -- maybe 20 - 40 kts or so. Maybe the autothrottles are programmed not to exceed a certain thrust level during cruise (remember that the Air Florida 737 that went into the Key Bridge in DC did so mainly because the crew refused to put the throttles to the firewall because of a faulty high thrust readout, even when their fate was obvious, a mistake no new student pilot would ever make). At any rate, some of these planes are also equipped not only with stick shakers, which literally start shaking your hand (if you have them on the yoke, of course) when you're approaching a stall, but with stick pushers that actually push the stick forward if you get close enough to one. No, given the redundant systems and just plain nice flying characteristics (from what I've read) of a 747, I'd guess that "benign neglect" would not have been enough to cause what happened on the China Airlines flight: sheer stupidity seems to have been necessary. Maybe deploying some slats or dropping gear at Mach 0.8 (gear doors fly off FIRST, hit tail, knock off much of horizontal stabilizer and some of elevators, with resulting loss of pitch authority), when you meant to push in the cigarette lighter or something... -- Jan Wolitzky, AT&T Bell Laboratories, Murray Hill, NJ; (201) 582-2998
peterb@pbear.UUCP (03/09/85)
Actually you have hit on a point that was all to evident in a 727 mishap a while ago. I don't remember the airline or the year, but a mysterious accident occured when for no apparent reason the 727 rolled over and dived straight down from about 35000-40000 feet shortly after entering cruise. Another 727 did the same thing a while later and this time they figured out the reason. 727's were not originally designed to fly at such high altitudes so when they do they tend to plow along in a nose up attitude since the thin air does not create enough lift in a level attitude. this was no real problem until the fuel crunch, and pilots and airlines realized it. Somebody came up with an illegal brainstorm: put out 2 degrees of flap and the wing now generates enough lift to fly level and lower feul consumption, reduce air time, redice time to cruise, etc. This was great(apparently) but there was a minor flaw in it. On the 727, the flap and slat circuits operate together under one control. So at 3XX00 feet, in order to put out 2 degree of flap without having the slats open they pop the circuit breaker to the slats. In the incidents the bozos doing this either didn't pop one of the breakers or forgot or whatever. But the end result is rather astonishing. Opening a slat at about 300-400 knots on a 727 is self-destructive. Apperently one slat deployed and quickly disintigrated. This caused a highly asymmetric lift condition(with an entire leading edge gone, there's no choice) which was so bad that FULL aileron/spoiler deflection could not overcome the imbalance, and hence the plane barrell rolled over into the ground. The FAA inspectors were puzzled when they found that the flaps were out a little, and that the slats were gone. There was no way to determine of they were deployed or not, they were just ripped out, actuators and everything. When they rebuilt the cockpit and examined it, lo and behold one of the slat breakers was popped. Through some deductive reasoning they figured the rest. The incident with the China 747 sounds a little fishy to me, I wouldn't be suprised to find that they pulled a real stupid move. Peter Barada ima!pbear!peterb
hgp@houem.UUCP (#H.PAGE) (03/11/85)
<...> 'Just returned from a trip to Seattle. On the way their, our departure was delayed do to some problem with the baggage handling equipment. So I walked up to the flight deck and asked the pilot what he thought happend on the China Air Lines flight. His guessed that the crew members probably all fell asleep, and the dive started when the engines flamed out due to fuel starvation when it was time to switch tanks. Does this sound plausible? Howard G. Page ..!ihnp4!houem!hgp