DozyWannabe

As studi says, completely different type, completely different systems design. Notably the old A300/310 system had a very loud warning bell when the trim went too far out of position. Of course, those types were not FBW and as such were not designed to have a constantly-correcting automatic trim - a loud bell signifying trim movement would quickly become a nuisance with the FBW design.

With a traditional empennage design, and with all control systems functioning, it is never completely impossible to un-stall the aircraft due to aerodynamics. The limiting factor is purely time (i.e. how long you have before running out of altitude to recover), and if the PF had pushed the stick forward and held it there, the THS would have come forward and recovery would have been straightforward in a matter of a few seconds (presuming that the recovery was effected with enough altitude to spare).

By looking at the DFDR traces, it's evident that the aircraft did not stay nose-high all the way down. What happened was that the nose came down, the speed built up, but the elevator and THS position caused it to pitch back up again - just like a paper dart running out of speed.

The THS went to full-NU as quickly as it did because the PF was still pulling up as the aircraft ran out of the speed at apogee and continued pulling well into the stall. The aircraft only ever did what was demanded of it.

Remember that spoilers work as they do because of their relative closeness to the aircraft's centre of gravity. Spoilers wouldn't work on the tail because they'd cause the extreme pitch-up moment that was seen when the nose dropped in the AF447 sequence - due to being placed well aft of the aircraft's CoG.

@Organfreak - I don't know if you can see this, but I don't think I've ever even hinted that the Airbus systems design is perfect (hell, I'm a software guy and know full well there's no such thing!). All I've ever objected to is kneejerk assertions that such-and-such a change would make things better, when the people suggesting it don't fully understand the decisions behind that design - some of whom have never even tried to understand it and work from the basis that it's fundamentally wrong based on their own prejudice.

bubbers44

I think that is the reason I stuck with Boeing. Just fly it as pilots have flown for over 100 years. There are no laws, just airmanship. If you are very stupid you can stall so just don't be stupid. How hard is that?

Lyman

bubbers

Why is it do you suppose that Autotrim is kept when the Law has degraded? What advantage does it have over Direct Law, (manual reversion), such that the a/c remains at a specific Pitch incidence to work from?

This does not apply to 447, as I have pointed out, though the aircraft should have had Autotrim, it did not, and when it Stalled it did have it?

Curioser

DozyWannabe

@bubbers44 - There have been a lot of changes to how pilots control aircraft in the last 100 years, most if not all of which were necessary to progress. The very first one was going from wing-warping to aileron panels - admittedly that was more like 102 years ago now, but I suspect you were including the Wright Bros. in your timeframe. Another big one was going from taildraggers to tricycle gear, which required a significant change in methodology.

In general most of these changes were made (as were those underpinning the Airbus FBW design) to make life easier for the pilot.

As many have pointed out, it's because it's what the crew will have been used to on that type for over 99% of their time flying the thing.

Lyman

HazelNuts39

Howso? With elevators and THS deflected max NU, plus AoA, what value do you derive? Never mind, I must have had a touch of vertigo.......arse about, apologies.

Dozy:

Quote. "By looking at the DFDR traces, it's evident that the aircraft did not stay nose-high all the way down. What happened was that the nose came down, the speed built up, but the elevator and THS position caused it to pitch back up again - just like a paper dart running out of speed."

Yes, and why did the THS not trim ND?

And. Quote. "The THS went to full-NU as quickly as it did because the PF was still pulling up as the aircraft ran out of the speed at apogee and continued pulling well into the stall. The aircraft only ever did what was demanded of it."

That is just wrong. It spent 43 seconds 'parked' at three degrees NU. It did not trim NU as the climb began and continued. PF's commands were a combination of ND and NU, and some time was spent -1G. So it should have trimmed, what inhibited it?

And Quote: [B]"As many have pointed out, it's because it's what the crew will have been used to on that type for over 99% of their time flying the thing."

I was asking bubbers44 what he thought.

So why carry a 99 into the one percent? Manual should mean manual, not a 'blend'

DozyWannabe

Because it was never commanded to - none of the inputs of the PF and PNF were ever sustained long enough to make a difference, with one exception. The PNF's input at 02:13:42 would probably have been enough to move the THS - however it's a moot point for two reasons:

• The aircraft was already too low by that point.
• The PF was still pulling up - hence the "DUAL INPUT" warning.

Yes, because the elevators' authority was sufficient to meet the demand.

I've said this more times than I care to think about, but because the ND command has to be *sustained*. In the A320 sim, from THS full-NU to return to neutral required full forward sidestick input for about 8 seconds. The PF never applied corrective inputs for anywhere near long enough.

For which you'll get an answer in line with his way of thinking - i.e. that the traditional control setup is the best way to do it.

Lyman

Since when do the elevators act alone? Trim is automatic, and so quote me where it is printed that trim won't follow? Include trend please, and g references.

Quote. "Because it was never commanded to - none of the inputs of the PF and PNF were ever sustained long enough to make a difference, with one exception. The PNF's input at 02:13:42 would probably have been enough to move the THS - however it's a moot point for two reasons:"

Eight seconds w/o trimming? Reference if you do not mind....

"For which you'll get an answer in line with his way of thinking - i.e. that the traditional control setup is the best way to do it."......priceless

HazelNuts39

Lyman,

If you take a look at figure 64 of the english version of the final report, you will see that
(a) the THS did not remain 'parked' during 43 seconds, and
(b) the THS is too slow to follow quick movements of the elevator.

OK465

Parked on the ground, you can hold the SS full forward for 8 seconds, 8 minutes, or 8 years and the THS will not move.....

.....because there is no change in the existing dynamic pressure.

Lyman

HazelNuts39


HazelNuts39 Lyman,

If you take a look at figure 64 of the english version of the final report, you will see that
(a) the THS did not remain 'parked' during 43 seconds, and
(b) the THS is too slow to follow quick movements of the elevator.

According to the traces of THS in IR#3, it was parked for 43 seconds.
How is a graph different due language in the accompanying text?

Too slow? So it ignores trends over time? Pretty easy to circumvent its action; so then why retain it? Bump the stick many small times so as not to wake the beast?

I trust you, as always, but here I do not believe you. For me, I would need to see the pertinent data from Airbus, re: trimming.

WAIT.... So that is why all Bus drivers stir mayonnaise? Eureka, now we know they do not like Autotrim either. Small bumps and suss... Small bumps and suss, etc. etc. fear? Or loathing? Both?

DozyWannabe

Very true - 8 seconds (or thereabouts) was the value we got in the A320 sim with THS full NU, followed by sustained full-ND on the sidestick when we attempted the AF447 scenario. Approximately 8 seconds from full-NU to neutral, controlling roll with rudder rather than ailerons (due to stalled state).

NB. I'm well aware that this experience does not necessarily reflect the behaviour of the real thing in an aerodynamic sense, but the systems are the same - no reason to think THS return to neutral would have been much different...

Organfreak

Lyman, I cannot cite this b/c I'm an airhead with few remaining memory cells, but, I am sure that I have read in an AB publication on control laws that the ND input must be definite and prolonged before the AC will trim accordingly. I'll look for it in my mahssive collection of documents. I think you should give up on this line of speculative inquiry. Ppl been telling you repeatedly that Bonin's ND inputs weren't enough to do it. No hidden conspiracy there, I accept it as fact.

Lyman

Very true - 8 seconds (or thereabouts) was the value we got in the A320 sim with THS full NU, followed by sustained full-ND on the sidestick when we attempted the AF447 scenario. Approximately 8 seconds from full-NU to neutral, controlling roll with rudder rather than ailerons (due to stalled state).

Dozy, please. Eight seconds to return to NEUTRAL..... When was it going to start its eight second journey? Or does it linger at FULL NU and then instantly return to NEUTRAL?

Skip the ailerons, why did you not think that your sim proved nothing? 447 s THS did not BUDGE, eight seconds or eight days, etc.....

More to the point, at what time did the THS start to move? Two seconds?

Are you making this up as we go along for the 'ride' ?

Hammond man


Organfreak
*

Lyman, I cannot cite this b/c I'm an airhead with few remaining memory cells, but, I am sure that I have read in an AB publication on control laws that the ND input must be definite and prolonged before the AC will trim accordingly. I'll look for it in my mahssive collection of documents. I think you should give up on this line of speculative inquiry. Ppl been telling you repeatedly that Bonin's ND inputs weren't enough to do it. No hidden conspiracy there, I accept it as fact.

Not at all, why is there no discussion on the THS as to precisely when it moves,

Why would it hesitate, to see if there is a established Pitch? What is "established pitch"?

This is not speculative, it is a demand in the wind for data to be supplied. BEA have left anyone who wants some technical back up hanging.....

Because Airbus owns the DATA? And that is important and needs to be protected exactly, WHY?

DozyWannabe

It didn't budge because it never received a command requiring it to. In the sim, the trim wheel movement and behaviour seemed akin to a curve - with full nose down it started moving after a second or two, and had returned to neutral 8 seconds later.

In the case of AF447, the only time full-ND was held on the sidestick for more than a fraction of a second came right at the end by the PNF, and was counteracted by the PF pulling full-back on his.

Remember that 8 seconds to THS neutral has the elevators commanded to full ND throughout.

bubbers44

I don't know why this is so complicated. We have all spent a lot of our lives at FL350. How many of us would pull up into a 15 degree climb? None of us, right? It wouldn't matter what warnings were going off any competent pilot would have looked at attitude and power and been just fine. For some reason they couldn't.

HazelNuts39

In IR#3, look on page 42 of the english version or page 44 of the french version. That graph was erroneously included as Figure 64 in the english version of the final report, the intended graph can be downloaded separately from the BEA site.

Organfreak

Lyman,
You're not listening, not to me nor anyone else.

But worse, why in hell did you go to the trouble of posting my personal info? Was it to underline the fact that I'm not a pilot?

Lyman

I'm so sorry, I went to copy your post and it grabbed the whole deal.

CONF iture

This is not for that reason, but just because on the ground the Law in force is Direct, so no autotrim.
But nevertheless the reason you mention could very well apply to an aircraft that is totally stalled and therefore in state of neutral balance in which no dynamic forces apply anymore ... ?

The question could be, if the sidestick is maintained full fwd, so the request is for minus 1G, would the elevators still go to the full down position, and the THS to the most positive setting, in research to satisfy anything in that direction of minus 1G ?

BEA ... all that stuff should be already in your report.

DozyWannabe

I know you don't think much of it, but in our sim sessions it certainly did.

Why? The only reason it would need to be in the report would be if they tried it in a simulated session and it didn't work as it was supposed to.