And one thing we're learning is that Airbus composites disintegrate in hydraulic fluid.
You obviously know quite a bit about this stuff, but I'm not completely ignorant either. I've got a couple of Lancairs in my hangar, and spent quite a bit of time studying composite technology, so I'm not against composites in general or anything. And I'm not some kind of "buy American" geek that's against Airbus merely because they're built in France (and other places).
One problem with composites is they're very difficult to inspect for damage. Thus the inspection on the A320 rudders was a "knock" test, where a mechanic knocks on the part and listens to what it sounds like. As far as I know, there's no automated, or objective way to do this test. Just a trained ear, and apparently the damage must be significant to show up then. I know there are methods to imbed sensors into the part and ultrasonic map it at the factory so that later damage will be detected. But I don't know how many manufacturers are doing this.
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? I'm unclear on this.
One fact we can't dodge is that if the news hit the fan that there was some kind of inherent fault in Airbus aircraft it would seriously damage the airline industry, and foreign relations with Airbus countries would be a little hot too. So there is a very large motivation to pin an unknown problem on the pilot while the real problem is quietly delt with, or even swept under the rug.
Because of the recent revelations on two Airbus incidents involving delaminations and hydralic fluid, one of which stressed the vertical stabilizer attach points nearly to the same extent as AA587, I can't completely discount the idea that things aren't all they seem to be.
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