Stardate 20011114.0705 (On Screen): Daniel writes to say that investigators of the latest jet crash in NYC (how it pains me to have to put it that way) have found no apparent damage to the engines and no important evidence of bird strikes. There doesn't appear to be any bomb damage, so the puzzle is deepening. The one obvious anomaly was that the rear stabilizer fin broke off the jet, which is unprecedented and extremely puzzling. The A-300 is "fly-by-wire", which means that the pilots have no direct control over the air surfaces (i.e. no cables). Rather, their controls are simply inputs to a computer system, which then makes the airframe do all the right things. When this was first proposed there was considerable fear about the possibilities of software bugs bringing planes down, but in fact all military jets have been fly-by-wire for decades and the Shuttle is, too, and the programmers appear to have taken very great care. However, in a case where one of the primary control surfaces of the jet is gone, it's likely that the software was not programmed to deal with a jet crippled that way. So if the stabilizer did come off the jet, then the jet was doomed. That part's completely understandable, the puzzle is just why the stabilizer did actually come off?
It seems to me now that it may be that there was some sort of previously-undiscovered weakness in the airframe. It's happened before. All aircraft design is a tradeoff; you cannot put as much in as you'd like because it would never leave the ground. They design them to be strong but not over-strong because overdesign is parasitic weight, and all aircraft must be light. (Proportionally speaking, of course.) Under the stress of flight, a small weakness can cascade and result in a catastrophic failure.
The DC-10 cargo-door failure was an example of that. In some circumstances, the door on the cargo hold of a DC-10 could fail in flight. It was holding cabin pressure in, and would blow out. That caused the cargo hold to depressurize, but the passenger cabin remained at higher pressure, which put immense stress on the flat floor separating them. The floor then collapsed in a few places, and this severed a channel through which cables ran which controlled the rudder and elevators, causing the pilots to lose control of the aircraft, resulting in catastrophic loss of the jet. This happened at least twice in the 1970's, and once they diagnosed it they then strengthened the door and the DC-10 has been a reliable and safe aircraft ever since. The chain of events is straightforward in retrospect, but the idea that a failure of a cargo hold door could cause loss of the aircraft seems incredible on the face of it. Equally, it may turn out that the loss of this A-300 was caused by what seems to be a minor failure which cascaded. The "rattling" noise reported on the cockpit voice recorder is not inconsistent with a progressive mechanical failure of the airframe. (discuss)
