And one thing we're learning is that Airbus composites disintegrate in hydraulic fluid.
That's really overstating the case rather strongly. (It's the equivalent of responding to Aloha 232 by saying "Bonded 737s come unglued and fall apart" -- an element of truth in it).
One problem with composites is they're very difficult to inspect for damage.
Right, I was getting at that when I mentioned that we're still discovering ways to inspect these materials -- and failure modes we hadn't anticipated. That's routine engineering.
I've heard the story about the rudder reversal on AA587. The problem is there was supposed to be some type of control system to prevent this from occuring. The airplane is fly-by-wire. Did this system fail?
The National Transportation Safety Board determines that the probable cause of this accident was the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design that were created by the first officer’s unnecessary and excessive rudder pedal inputs. Contributing to these rudder pedal inputs were characteristics of the Airbus A300-600 rudder system design and elements of the American Airlines Advanced Aircraft Maneuvering Program.
To answer some of your specifics, you ought to look at some of the reams of .pdf on the Flight 587 Docket Website. But since you may not have time, and I'm familiar with this stuff, let me spin you up.
The airplane is not fly-by-wire. It has a very conventional rudder control system -- pushrods to bellcranks to cables running the length of the fuselage, hydraulic boosted. Absolutely bog-standard. So any pilot inputs are transmitted (within the limits of a conventional cable and boost system) to the rudder.
The DFDR does track rudder and rudder pedal position (and IIRC, also rudder-pedal strain). There was nothing anomalous there.
Finally, there was no delamination in the vertical stabilizer or rudder (while the main wreckage area was badly burnt, these parts were recovered, unharmed but for their separation, from the bay). The stab is held on by pins through six attachment lugs and three separate transverse-load lugs. All of these, or the metal where they attached, failed in overload. (I'm sure you understand the engineering facts of life here -- once one lets go it's curtains, because the remaining lugs only have say 5/6 the strength of the system that just started failing).
One thing we can do is distinguish an overload failure from a contamination-driven delamination. In the same vein that we can tell an overstress failure from a fatigue failure in an aluminium structure. The damage looks different, under a scope if not to the naked eye.
[I]f the news hit the fan that there was some kind of inherent fault in Airbus aircraft it would seriously damage the airline industry...there is a very large motivation to pin an unknown problem on the pilot
While it's true that the accident investigation profession usually looks at the pilot first and hardest, it's not prejudice.. it's profiling. Mostly, planes don't crash, pilots crash planes. And I thought that the judgment here was fair to the pilot flying, FO Sten Molin -- he didn't know that tails are only required to bear 1.5G. I mean, did you? I didn't. He did what he was trained to do. Turned out to be the wrong thing. We can best honor his memory by making sure that mistake doesn't get repeated.
And... while I hear what you're saying... on the 737 rudder hardovers, why didn't they point out that those planes were recoverable (at least two of them were -- one of which was successfully recovered, and one wasn't). If they are so concerned about keeping up appearances, why pin the blame on a design feature of every 737 flying?? But they did.
In every investigation, the parties get to say their piece. The union sends a guy, Pratt or Rolls or CFM sends an engine guy, the airline sends an operations guy, and everybody spins it his own way, not because they're liars by any means, but because they're captive of their frames of reference. Out of this, the IIC and staff have to make a report that is a coherent narrative and provide a decision memo to the full board.
The full board is political to the nines, but the investigators are not. They call 'em as they see 'em. Are they right? Usually. Are they sometimes wrong? Hey, they're human, of course they are. Just like us pilots. Mechanics. And engineers.
Also, one last thing. Not all Airbusen have the composite stab. Most 300s don't (this was a 300-600, its only the 300-600 and, ISTR, 310 that have this tail).
d.o.l.
Criminal Number 18F
It's hard to overstate the fact that a hydraulic fluid drenched rudder disintegrated in flight on March 6, 2005 on an Airbus A310-300 climbing out of Cuba. The FAA report claims that this applied nearly the same loads on the rear Vertical attach lugs as AA587 and I'm thinking it claimed there was damage to the lugs.
If the AA587 rudder was found undamaged, well then that shoots my hypothesis, but you must admit that there would be *significant* motivation to cover up any structural defects in the part.
My experience with Air Force fighters tells me that there's no way an airplane can be kept clean, and that once drenched in hydraulic fluid there's no way to determine how much damage will occur in the future, and probably no way to completely clean all traces of fluid from all voids in the part.
I'm sure existing airframes can be maintained, even if they have to replace contaminated parts. My main concern is that Boeing has learned from this for the 787, and will choose a resin system that eliminates this problem. And/or reformulate hydraulic fluid to eliminate it. It will be impossible to change the fuselage should a line leak, and repair may be impractical.