Originally Posted by
L337
Because of the Airbus A/T design, the thrust would have gone to full power. A fundamental design flaw, imho, and one that will never be admitted to by Airbus.
Er, I'm pretty sure this was discussed on the previous thread - some time ago they not only "admitted" that it was a problem, they changed the behaviour so that when A/THR kicks out, the thrust remains at the last setting the A/THR commanded. The thrust setting does not change until the pilots touch the thrust levers.
As it is we seem to be discussing three scenarios here. Note that what follows are largely my
opinions, for what they're worth.
Svarin postulates that some hitherto undiscovered software bug caused the FCU components to slip in and out of Normal Law, causing intermittent activation of protections forcing the aircraft nose-up. Personally I find this the least likely explanation, based on the specification and design of the systems as I understand them, coupled with the fact that the A330 has been flying for nearly two decades without such a scenario presenting itself, despite numerous documented failures of the pitot system. I'm not saying it's impossible, just pretty remote based on the information I have.
Chris Scott wonders if the "G-Loading" mode of the FCU would have ordered up elevator and consequent nose-up THS movement via the autotrim system. Personally I think this scenario slightly more credible than Svarin's, because it is more of an edge case in terms of specification and design. That said, I'd be very surprised if the engineers overlooked this consequential failure mode given how thorough they were with everything else.
Finally we have the scenario I consider the most likely, which is that the autotrim was responding directly to the pilot's consistent nose-up sidestick commands, but this in itself opens a can of worms because it is perceived in some quarters (incorrectly IMO) as an attempt to "blame the pilot" and get Airbus/AF off the hook. For a start, Airbus and AF are already on the hook to some extent because of the known pitot problem, and AF's response to the service bulletin not being expedited in the wake of the numerous cases where these failures led to near loss of control incidents. The old aerospace chestnut of a "failure of imagination" comes into play here, because most of the previous events occurred in daylight, where pilots had an external reference from which to aid their recovery of the aircraft. Prior to the accident, few seem to have taken into account how much more dangerous a failure of this nature would be in adverse weather conditions in the dark hours of night, which would suggest that the lessons of Birgenair and Aeroperu were not heeded as well as they should have been.
For my part, I agree with PA 18 151 in the sense that this case is far from closed and we should respect the abilities of the investigators to get on with it. To clarify my position as referred to by BOAC, I mentioned that another poster (I believe it was Smilin'_Ed) seemed to be proposing a drop to Direct Law in the case of air data failure, and bypassing Alt 2 entirely. Indeed, it would appear that is indeed what Smilin'_Ed is proposing ginven his recent posts. Personally I disagree and think that Alt 2 has a purpose in this kind of incident, although it can be argued that the outcome of this particular scenario doesn't reflect well on the design. As I've said many times before, the ability to manually control trim is available in any law, including Alt 2, provided via the trim wheels sitting right next to the inboard hands of both pilots. Indeed I think it was PJ2 who stated that as part of his training he was required to land the A320 simulator using rudder and pitch trim only.
BOAC, I find it interesting that you acknowledge that your background information on FBW airliners is limited, yet you feel qualified to state that a drop to Direct Law is "anathema to the FBW world", by which I presume you mean mentality. I think that this is a fundamental misunderstanding. Part of the FBW rationale was certainly to reduce the cost of operations by using lightweight componentry in aircraft controls, however another purpose of the design was to
assist pilots - not hinder or eventually replace them, no matter what some of the more lurid scaremongering on this forum from time to time suggests. The designers and engineers asked pilots what they wanted when the requirements were gathered, and built a system that implemented the specification drawn up from those requirements. The whole idea was to build something that *worked*. If the decision is taken that a drop to Direct Law in this scenario would be preferable, then I'm sure they will make that change.
As I stated, I'm of the belief that Alt 2 serves a purpose, and that a lot of thinking will be done based on the evidence gathered in the investigation of this accident. I'm sure that scenarios were considered that make Alt 2 a much better fit than Direct Law in this set of technical circumstances, and eventually they will have to weigh up those hypothetical scenarios against this real one before they make that decision. Birgenair proved that a more "conventional" FCS is no protection against the "loss of air data" scenario, and just for the record on this thread I will state again that the Birgenair Captain was a *highly experienced ex-military pilot* and even he was thrown (even as his two F/Os were repeatedly feeding him suggestions that might have helped). He didn't seem aware that the situation was being made worse by the actions he took all the way down to the ocean.
There seems to be an undercurrent on here occasionally that some pilots are not only distrustful of technology, but also have a dim view of the engineers that built the aircraft they are flying - seemingly thinking that because the protections were implemented by engineers, therefore the engineers must in turn have a dim view of pilots' abilities. I can't speak for engineers in general, but I must say that I think this view is blinkered. It is in the interests of pilots and engineers to make aircraft as safe and as comfortable to fly as possible. Ultimately pilots are responsible for the lives of everyone on the aircraft with them and additionally pay the price if something goes wrong. But another way to look at it is that engineers are responsible for *every* person riding on the aircraft they design, *every single time* one of those aircraft takes to the skies. Think for a second of the Boeing engineers that carried out the faulty repair on the aircraft that became JAL 123. Think of the price that the JAL engineer who signed off that repair paid (I believe he took his own life).
Thinking in these adversarial terms is not only counter-productive in my book, it is also dangerous. We are all in this together in a very real sense - I may not agree with what Svarin, Chris Scott, BOAC and some others are saying, but it would be churlish and short-sighted of me to not take it on board and at least accept that there is a possibility they're right. I think any engineer worth their salt would feel the same way, even if only to provide the data that contradicts (or even backs up) the theories and ideas put forward. At this point I am out of data, so I'm back-seating this for a while and hoping that the report when it comes is thorough and well put together.
Let's be safe out there, people.