Capn Bloggs in another thread:
Fits well into our thread indeed.

The simulator experiment alone demonstrates what they didn't want to say.

Amen

So what do you think happened, and what is it you think "they" didn't want to say?

A clear restriction in the FCS that prevented the aircraft to get the optimal performance when most needed. If it is part of the normal functioning, then everything should be apparent in the decoding of the algorithms ...

So are you then suggesting that a fix was devised in secret and subsequently applied to the simulator and aircraft Bechet used for his own testing?

If so, given the timeframe, I don't think that's plausible - but as always I can't be certain. Having said that, why would there be a deliberate restriction there in the first place? It all seems a bit too cloak-and-dagger to me.

EDIT : Furthermore, in practical terms it seems unlikely - the software engineering processes made extensive use of regression testing and other techniques that maintained a record of changes made to the implementation over time. If a change was made, then every software engineer working on the project for Airbus at the time would have to have known about it, and with a team of that size it would be a massive gamble that they'd all keep their silence in perpetuity. As with all conspiracy theories, the fact that so many people would have to have known about it and subsequently keep schtum is a major roadblock to plausibility.

Additionally, if such a restriction was found and fixed, surely it would have been better PR for Airbus to tell the world that they had found and fixed the problem, would it not?

EDIT 2 : As for "decoding" the algorithms, the program source code is machine-generated from a graphical layout system - machine-generated code tends to be very difficult to reverse-engineer. You'd have better luck with the schematics, though you'd still need a qualified EE/Systems Engineer to decipher them for you.

From a software engineers' perspective I don't think that's anything out of the ordinary. Modular software design tends to inherently create "dependencies" between modules, so if a change is made in one module, then there will usually be at least some code affected in other modules - sometimes in quite surprising areas, depending on how the system architecture is laid out.

Your point also adds to why I think a surreptitious update scenario is unlikely, because it's not just Airbus's own software guys that would have to keep quiet, you've then got the sim engineers who have to install and test the update, the aircraft techs who had to do the same on the A320 Bechet used, and so on. Any one of them blowing the whistle at a later date would do far more long-term damage to the reputation of the company and the project than simply "'fessing up" to a mistake - as proven by the case of MD's DC-10 and the notorious "Gentlemens' Agreement".

Asseline had to face a restriction in the FCS that Bechet did not.
Now, suggest whatever you like ...

1. I figure Airbus has all the necessary ressources
2. It was not a time to reveal or detail any shortcoming
3. Airbus preferred propagating the myth that the envelope protection had prevented the aircraft from a catastrophic stall

No, something was different, we don't know what. We do know that Bechet's handling of the SS (emphatic and direct) was different to Asseline's (hesitant). I still think that's a better place to look than a nebulous "restriction" or "bug" in the software for which there is no evidence of it's existence or removal before Bechet came to do his tests.

The problem with Asseline is that he's been invested in this idea of a cover-up for so long that neither he nor his supporters are capable of seeing it any other way.

@DozyWannabe & CONF_itureAlgorithms need to be encoded not decoded. They describe the system in the nearest form of natural language (math included:p).Shematics already need to know System theory tools. Pilots need to know algorithms. Asseline seemed to don't know them. Did Chris Scott knew them?

The data show he's not necessarily wrong ... but Dozy has been invested in this idea for so long that no Institution and/or Corporation would ever protect their interest First that he is unable of seeing it any other way.

Not at all, but based on the complete lack of any evidence that there was anything untoward going on, no whistle blown at 25 years and counting, Dozy thinks it's a fairly unlikely possibility.

Also, it's a pretty tenuous claim that pretending there was no issue when there was one would be in the interest of the corporation or the institution involved. Bear in mind that the last company to try that ended up with their project given the nickname "Death Cruiser", and eventually went out of business - their assets becoming part of Boeing.

Obviously they got out from it pretty well as not only they managed to hide the FCS restriction but in the meantime they pushed for their favorite myth :
"the envelope protection has prevented the aircraft from a catastrophic stall"

A little bias seeping through?

Airbus was a little more astute than MD when it came to sweeping issues under the carpet. This was the lesson they learned from the DC-10s.

Nope, just a reasonable point as to why keeping things schtum is more likely to cause further problems down the line.

Sorry, I don't see what that has to do with "sweeping... under the carpet". The DC-10 got a bum rap because of the notoriety of the early accidents, but its later record was actually as good as or better than many other types. It was the damage to their reputation as a result of being caught trying to solve the cargo-door problem while avoiding an AD (and failing to fix it on the THY DC-10 that crashed) that caused the loss of confidence.

As you said - Airbus tended to be savvy and astute PR-wise. They'd have been unwise to go down the same route as MD did in the early days of the DC-10.

@CONF - *or* there was no "restriction" in the FCS, and the aircraft did indeed prevent a stall, because it didn't stall! The stall might still have happened after clearing the trees without active protection...

I'm wondering if you think that somewhere in the code, the A_MAX variable was transposed with A_PROT. Because of the way the systems were developed, this is unlikely because the unit and regression tests (both written separately from, and chronologically before, the code itself) would also have had to carry the same error, otherwise the tests would fail. The presence of regression tests also means that a later change would have shown up in the reports - something that every software engineer on the project would have seen. As OK465 says, the change would also have shown up in the sim logs, so everyone involved in the update would also have had to be sworn to secrecy. To me that's just too many potential loose ends for Airbus to consider taking the risk.

*or* one day you might understand what alpha max is ...

CONF, with all due respect - if you could just ease off on the insults and listen to what I'm saying, it might help us get somewhere.

I know what Alpha Max is, I know it wasn't reached and I suspect that the reason it wasn't has something to do with a combination of phugoid damping and Asseline's tentative stick input compared with Bechet's. I can't be certain, in fact none of us on either side of the argument can - all we can do is try to work out what's likely and what is less likely.

The assertion that the protections may have "prevented a stall" is based on Asseline's control inputs prior to impact, had they been applied to an unprotected aircraft. Without protections, full back-stick would have caused the pitch (and AoA) to increase regardless of whether there was sufficient airspeed. Without an AoA indicator to guide him, it's likely that the instinctive pull would have caused an unprotected aircraft to exceed alpha-stall (to use your nomenclature). Of course, Bechet's inputs during the test were even more immediate and positive, so he'd likely have stalled an unprotected aircraft as well.

I'm still learning about the aero side of things, but what I'm certain of is the methods used in developing the FCS software - and I'm telling you that it is *extremely* unlikely that there would have been a logical error limiting AoA to the A_PROT value, because there were around three layers of test harnessing that would have caught such an error, and each of those layers would have had to separately been developed with the same mistake - hence why I believe it's so unlikely.

EDIT:

Furthermore, whether the aircraft did or did not clear the trees is really just a footnote in terms of the investigation as a whole. Clearing the trees would have avoided the deaths, meaning Asseline would not have been prosecuted for manslaughter, but the existence of the video, whether it showed a crash or a close call, would still likely have ended his career. The investigation as a whole was more concerned with the lack of oversight from the airline and the decisions made during the approach phase than it was the mistakes made during the conduct of the last few seconds of the flight - as such, Airbus would have had no reason to cover up any technical problem. As the MD experience proved, it's far better PR for a manufacturer to put their hands up to a mistake and fix it than to risk being exposed trying to hide it.

EDIT 2: I'm surprised that you haven't picked up on the fact that I've gone from thinking phugoid damping wasn't a factor to being fairly convinced that it was. There's nothing wrong with changing one's mind if new information becomes available!

At a guess, I'd say the sim run that generated that particular data was not an attempt to duplicate the accident sequence, but to determine the limits of system behaviour. In this case they were probably trying to ascertain what difference more prompt and decisive action may have made, if any.

If I've understood previous posts on the subject, the simulator available at that time was still being refined in terms of aerodynamic response when compared to the real aircraft. If this is correct, then sim runs would really only have been of use in terms of defining systems behaviour. The real world run over the Toulouse runway would probably have been more along the lines of an attempt to duplicate the flightpath.

Take it as an insult as you wish, it was merely the observation that contrary to what you're pretending, you still don't get what alpha max is, and a stall could not have happened after clearing the trees as alpha max is not alpha stall.

Don't bother thinking for me, just read what I write, you will spare me theories I did not ask for.

Good for you ... what I was expecting is a BEA + Airbus analysis.
By the way if phugoid damping was involved, they could have detailed why Bechet was miraculously spared from it ... ?

@OK465

Actually, if you have access to a development simulator you wouldn't involve pilots at all; you would simply set up the initial conditions and feed in the actual control movements [sidestick; TLA]. This is what Aerospatiale did to produce the comparison shown on p13 Annex X of the BEA report.

The calculated response in the last couple of seconds (from just after the time where the IAS is marked as 114kt) is rather interesting - [Sidestick held fully back at -16deg, TLA at TOGA position]

A simulator stays a simulator today, since they always have commands which don't exist on the plane and use metalanguage :bored:

EDIT 1 : "real system" replaced by "plane", but it is the case too if you simulate a rocket or another computer,aso.