At this point, you would probably need to go up in the air and experiment, you on the controls, what a stall is.

The answer why you do not trim up approaching the stall and certainly not further up once stalled will get obvious.

Airbus put in place some restriction to not autotrim all the way when everything works fine, but decided autotrimming all the way was the way to go when data acquisition was known as deficient … it is aberration.

Can't remember such post ... and didn't manage to locate it either ?

I did not know the FCTM replaced the instructor support manual. For the little I've seen since yesterday, the instructor support manual seemed to propose interesting stuff that I have never seen in FCTM.

What about the Technical Training manual ... Any link ?

Quote:
Originally Posted by CONF iture http://images.ibsrv.net/ibsrv/res/sr...s/viewpost.gif
Now, if it's normal by conception to autotrim under stall warning, it is aberration.

I agree with CONFiture in this regard.
The Bus has little to restrict it from autotrimming nose up in Alt2, beyond the stall AOA, and I believe this is a potentially dangerous characteristic.

I recognize the Airbus is Certificated now under EASA CS-25.

If you look at comparable language in FAA AC 25-7B, Flight Test Guide for Certification of Transport Category Airplanes http://www.airweb.faa.gov/Regulatory...FILE/25-7B.pdf

I agree with 'aberration'

Hence my suggestion from PGF days of a requirement to 'push to over-ride' a trim warning when it tries to go past a 'sensible ' limit, presumably based on something like the trim for 1.x% of Vls at forward cg? Seems it might have helped the 737 at SPL as well as the Airbus family. What are the objections?

@Machinbird

The way you describe it, less knowledgeable people would assume that the aircraft autotrimmed nose up entirely on its own without any order or prompting to do so. Of all the UAS incidents on this type only one aircraft was trimmed in this manner and that was because the PF ordered it to do so. Autotrim is "automatic" only in the sense that it responds to pilot input when under manual control - it will not trim unless there is an input for which to compensate.

The Airbus may be capable of more than the certification standards in that regard, but importantly it needs to be recognised that the trim system is a little different to conventional airliners and this needs to be acknowledged in training and certification.

And must be recalled in the worst possible scenario, even though I believe the trim, correct me if I am wrong, is NEVER used in normal operation?

Once you're in that deep manual trim might speed things up somewhat (?), however first thing that would have to be recalled is to get the nose down, and the THS would follow suit just as it did on the way up (ideally you probably wouldn't even have pulled up until the trim went to the stops in the first place).

The point of Machinbird is not the one you described (or you have not understand his post)
The way you describe it, less knowledgeable people would assume that the aircraft autotrimmed nose up entirely on its own without any order or prompting to do so
Even a less knowledgeable people will understand the Machinbird point if they read carefully the entire post of Machinbird
Please read again carefully the entire post of Machinbird

Dozy, I'd bet the test pilots never stalled the bus with full nose up trim. If so, that is not a certified condition. The only way the system would then be allowed to achieve that condition would be in some highly improbable one in a billion chance. But we definitely now know that the odds are much higher than one in a billion. I think this is an issue in the aircraft's certification that needs correction.
Now if EASA agrees, we can start fixing the problem.
Either test fly the aircraft with full nose up trim and declare it meets stall certification standards, or prevent the aircraft from autotrimming beyond the levels it was certified for.

- NO NO NO! We do not need even MORE 'system' interference in how we fly. Crews MUST have full authority on all controls such as trim, but need to know when it is 'aberrating'??. Bring back pilots.:ugh:

Relax BOAC.
I changed 'trimming' to 'autotrimming' to make it clear the type of trim we are referring to.
Do you really want your trim system quietly doing things behind your back? (Actually out of the range of your normal scan).

To me, "quietly" is the keyword, no?
I've repeatedly suggesting bringing back the 'pitch trim bicycle bell', but nobody has really picked up on that.
Yet, it's sufficiently different from the other 'bells and whistles' in the cockpit.

I still wonder why something judged to be useful on Concorde was deleted on the A330 (and presumably the other A3X0s as well ?)

Although that question is not pointed at me, i like to comment on it.
The whole FBW-system as it is designed would not work without autotrim. Fundamentally nothing is wrong with it except the point when part of the FBW logic goes down the train. At that point the system should be at least as easy to understand and be as easy to fly as a normal conventional system.

In the case we discuss here the system is excellent and far better than a conventional design when everything is online and it gets a lot more difficult when part of the system goes offline.

Holding the stick back in a stuation where the aerodynamic performance of the aircraft does not allow further pitchup due to missing lifties would leave the trim in a conventional aircraft unattended , but caused an unnecessary full NU trim state in the case of AF447.

Whoever thinks, that this built in system function is a clever design should reconsider.

It's a perfectly rational design, because what it is doing is performing in exactly the same manner it does in Normal Law. A pilot whose commercial experience consists entirely of FBW Airbus time is going to find it easier to have autotrim on when things go awry than to suddenly have to cope with manually trimming the aircraft.

Let's be honest, how hard is it to understand that one does not make large and sustained inputs - which is what these were, make no mistake about it - without a bloody good reason, even more so at altitude?

Agreed. Test pilots of Airbus gently dance on edge of the flight envelope to ensure that the a/c can return quickly. Crudely departing with high energy is undesirable as the energy/time required to return is that much greater. That way the test pilot can stay ahead of the a/c.

Dozy
Nope Dozy. In Normal Law it stops trimming at the V alpha protect if I remember correctly, but in ALT 2 it keeps on cranking away if airspeed is invalid until it hits the stops (or nearly so) as in the case of AF447.

But why make ordinary airline pilots into test pilots? Going boldly where no test pilot has gone before.

It is a certification issue. Gotta prove it meets the stall characteristic requirements with full nose up trim or stop it from autotrimming there. And for BOAC's benefit, no need to stop the pilot from doing what he needs with the trim. It is assumed that the pilots will act rationally.

Disagree
 

DW,
How could it be "rational" when nothing else does (perform in the same manner as in NL)? This "rational design" may have been part of the reason they were all killed that night. Granted, the pilots may have not known a lot of things they should, but I am entirely on the side of, and in awe of, the estimable Gretchenfrage, on all of this stuff. I think it is relatively clear (as clear as anything in these thread can be) that the AB FBW is over-designed, by and for nerds.

I may not be a real pilot, but I do have a rawther large brain! :8

Isn't that assumption somewhat at odds with the condemnation of autotrim?
AF447 didn't enter the stall in full NU trim, from then on it took over half a minute of irrational control inputs to get there. Pilots acting rationally (even if only after the stall warning) would have never gotten to that trim state.
Not saying trimming up in a stall is not a bad feature, but how could it have been a factor here if there never was any useful attempt at recovery in the first place?

An autotrimmed FBW airbus which has been held in nose up condition will now sense the new nose up condition as the new neutral in a stalled condition ie a low airspeed condition. This further aggravates the stall and the rest then,as they say, is history.
Its as simple as that.
:)

Look up the concept of "graceful degradation".

You're talking about handing a pilot who may have not flown under manual trim conditions since their last checkride (or possibly even earlier) the responsibility of handling the aircraft with manual trim (which he or she will not be used to) in the worst possible situation. How is that any better than a system which retains as much of the Normal Law handling characteristics (which the pilot would be most used to) as possible?

And with a comment like that I can't help but hope that one day, a member of the late Captain Gordon Corps' family bumps into you and gives you a well-deserved ding around the ear.

With a head that big, I'm surprised you fit through an average-sized door.

If anyone is wondering (like me) to what extent AF447 might have been different if THS had not autotrimmed beyond stall warning, look up
Owain Glyndwr's post #450, from which the following is quoted:

DW
 

Dozy,

there is no situation in cruise, where autotrim is improving a situation in ALT2 like that encountered by AF 447. If you can think of one, let me know. As we know, autotrim is inhibited in ALt1 at V-prot anyway and in direct law as well.

Then let´s look at it from the other way around.
How difficult would it be to expand the present feature from ALT1 to situations in ALT2 maybe with different and independent values? Is it rocket science?

Concerning your graceful degradation explain this degradation with autotrim of the THS:

In Normal LAW autotrim (a rally nice feature)
In ALT1 Law autotrim prohibit at VC-prot (looks sound to protect from entering unknown territory)
In ALT2 Law autotrim (that is your part to explain)
In Direct LAW autotrim off (looks sound to protect from entering unknown territory)

I would name that one non linear degradation (far off from gracefull).

Concerning your naming manual trim again, please do not push aside the inputs made to that issue from Clandestino. http://www.pprune.org/6770409-post394.html
Quote:
.

That should straighten up the manual trim option once and for all. It´s even worse, because the functioning autotrim in ALT 2 prevents manual trim in its original sense of implementation.

There might be pilots insane enough to pull on the yoke or sidestick in conventional and FBW aircraft until the aircraft stalls, but no one would trim while pulling.

To understand that above statement let me explain normal trim behaviour. With the intention to climb the pilot uses the yoke to change the pitch, once that change is reached he uses the trim to get rid of the pressure on the yoke. The trim comes into play when the change is achieved and not in the timeframe, where the change takes place.

In case of AF447 without autotrim the pilot would never ever have tried to achieve the desired flight path change with manual trim, because that is not the way to do it.

Personal insults
 

Mr. Wannabe said,
I'm already familiar with it, thanks for the advice anyway. I left your period where you put it, out of courtesy.

Assuming facts not in evidence, sir. I never said that I did. In fact, my cranium is so large I've been confined to the barn for years.

It is not ALT2 in itself that causes the loss of low speed stability and the uninhibited travel of the THS. It is only the loss of 2 or more ADRs that causes this specific condition. It is possible to be in ALT2 with a THS that behaves as in ALT1.

To say that no pilot would trim nose-up while pulling is a bit presumptious i think. I do not find it inconceivable at all that the PF would have trimmed nose-up, perhaps even to the same extent the autotrim did, if he had the means to do so. He was after all back to mechanical stop on the stick for a full 30 seconds.

Not much a what he did was the way to do it, but he did it nonetheless.

Franzl,

The FCU has no concept of "cruise", as far as I am aware. It is a real-time processing system that does the job it was designed to do very well, but it is intentionally quite a simple beast in terms of design (because the simpler a system is, the less things there are to go wrong).


You have to look at this from a systems perspective to understand. Autotrim as a system is never "inhibited" in any law other than Direct and Manual Trim Only - it is the *protections* that prohibit the aircraft from leaving the flight envelope by preventing any commands - either manual or automatic - from doing so, and if necessary providing corrective commands to keep the aircraft within the flight envelope. The protections are a completely discrete subsystem that is loosely-coupled to the others that make up the FCU system.


Again, that is not correct if you look at the architecture as a whole. I'll repeat for clarity - Autotrim as a system is not "prohibited", nor "turned off" in any other mode or Law than Direct or Manual Trim mode. If the protections are active, then the autotrim commands will be treated as any other command that takes the aircraft out of the flight envelope and corrected accordingly. Think of it as two separate processes running alongside each other rather than as an integrated whole.

Put even more simply, imagine two people on either side of a wall that has a two-handled saw poking through it. The person on one side (let's call him Otto Trim) is told to push the saw forward and the person on the other side (who is physically stronger and called Pete Tection) is told to not let the saw through past, say, two-thirds of it's length. Pete will always stop the saw at the limit and will try to return it to the prescribed position if it goes past, but he is not explicitly aware that Otto's on the other side trying to push it because the wall is in the way, and as such does not interfere or communicate with Otto directly - all Pete knows is that he mustn't let it through past a certain point.

What do you mean by "original sense of implementation"? Using manual trim to set the THS to a certain degree of pitch and letting go will cause the autotrim to try to hold that pitch, unless a demand is then made on the sidestick for which the autotrim will try to compensate. It doesn't "remember" what it was doing X number of seconds or minutes ago, it simply tries to hold the trim set by the autoflight or pilot commands.

In any case, using manual trim and then holding on to the wheel will prevent the autotrim from re-engaging.

"No pilot would ever..." is an impossible statement to prove.

I know you're not intending to patronise me, but I am fully aware of how trim works in the conventional sense - I even did it once or twice in the Chippy. Here there is no tactile feedback, so "trimming to the pressure" is impossible, and performing the same thing visually using the ADI as reference would be physically exhausting on a day-in, day-out basis. This was part of the reason autotrim was developed because the flight control design was a completely new paradigm.

The only way you could possibly know that is with a Ouija board. The last time he trimmed manually would have either been during type conversion training, recurrent training or even back when he was flying trainers - because the Airbus FBW flight control paradigm does not require it except in case of major failure.

If all goes to plan I'm going to be doing some exciting research this weekend and I'll be able to argue from a much surer footing. If it turns out I've been wrong about anything you guys will be the first to know.

@Organfreak - Those were not intended to be personal insults, but I must confess I was flabberghasted with the throwaway manner in which you described the Airbus system design and those who developed it. I emphatically request you find out who Gordon Corps was, what he accomplished and how he died - and if you have the time, have a browse through the Flight International archives relating to A320 development (in which he figures very prominently) before you put your foot in it again.

takata re: SPIKES.

The Airbus has this elegant escape from CFIT? NON?

Max power, roll full, and pull back max.

A max effort, 'at the limits' safety manuever. During which the a/c nibbles at Stall? and wing drop? No sweat, the Bus knows SPIKES.

The Pilot doesn't. As above, for Alternate Law, the STALL WARNING needs some looking into.

Hamburt Spinkleman. Howdy. Isn't STALL WARN inhibited in Protection?

G Prot? Vc Prot? Load Factor Prot? The pilots did not hear the STALL WARN at the top of climb, Right? It shows in the trace, but where is the SV Cricket inhibited? On which side of the FDR? Is it silenced at the panel?

Thanks, hope you can help.

The Stall Warning and "cricket" annunciation is on the d*mn CVR - if they were picked up on the CAM or the hot mikes, it was audible in the flight deck. Must try harder.

Radio silence resumed.

They clearly did not hear the WARN, and I do believe that the WARN is inhibited in prot, but you would know that?

Did you hear it?

You have been given one of three things, the 'annunciations'.

You are entirely willing to accept two absurdities to believe the one.

1. They did not hear it.

2. They heard it, but ignored it, without comment.

This is acceptable to you, because you are wanting to stop at what makes your position correct.

You have no desire to hear or see further, your mind is made.

There is one mind that will foreclose all doubt, the one that will be correct at all costs, even prior to investigation.

A new paradigm? Perhaps that is the real issue. As for pilots trimming into a stalled situation, of course that is ridiculous. If you don't discount that, then you'd have to say there is no place in the cockpit for pilots becuase they are too incompetent.

Au contraire, sir - I'd *love* to know why they didn't hear it - and if it didn't sound then I'd be the first to say that would be a major problem. But unless you're accusing the BEA of falsifying evidence, then the presence of the Stall Warning alarm on the CVR is a documented fact, which closes that line of enquiry and this conversation.

@Capn Bloggs - As with any work, on the line I'm sure you'll encounter super-competent pilots, pilots who shouldn't be allowed in a flight deck and pilots of every level inbetween, with most hovering around an average competency level (which in most cases requires more general competence than a lot of jobs). However, you'd think that "No pilot would...":

• Take off without permission
• Retract LE devices below a safe speed
• Fail to deploy high lift devices at all prior to take-off
• Fail to turn on engine anti-ice when taking off into a blizzard
• Shut down a healthy engine and leave the damaged one running

and yet pilots have done all of those things, and some pilots have repeated the same mistakes made by their predecessors. This is not to say I think pilots are incompetent, far from it - because of the staggering number of flights that get to their destinations safely every day - but "No pilot would..." turns out to be a demonstrably false assertion. "No pilot *should*..." on the other hand, and you won't hear me arguing. :)

To go back to your question, the change in paradigm was based on a desire to start from a "clean sheet" when it comes to flight deck ergonomics based on the technological leaps made during the Space Age, not because of any desire to impugn pilots as a whole.

For pitys sake.

If a pilot is holding the yoke full aft, that tells a story.

If a pilot is holding his wrist half-cocked back ,in a pocket in the corner of the cockpit, at night. that's another story.

You can yarn it however you like , but that's how it is.

@BarbiesBoyfriend

The ending of the story (aircraft pitches up to an attitude that has no business being achieved in cruise) is the same in both cases however. The proper response to the story ("That's not right - are you really doing that? I have control.") is the same.

Why such additional layer of uncertainty that yokes would naturally prevent ?
Also, pilots do silly stuff, let them do those by themselves, automation is here to help not to put you deeper in the mud.
Let him trim by hand if that's really what he wants.

Because someone above either of our paygrades on both the pilot and engineering side decided that the benefits outweighed the drawbacks.

Think about it logically - the difference between looking over at the yoke to confirm what you're seeing on the ADI or out the window (unless you're watching your colleague's inputs like a hawk, which I suspect isn't the case given the average PNF workload) and asking them directly is what - a second, maybe two?

And the autotrim does help - specifically it helps a pilot who is in manual control maintain the attitude he is requesting, and if the protections are available they keep the attitude within the flight envelope. Lose the protections and the autotrim will do it's best to keep up with demand, even if that demand is inappropriate.

As part of the research I was talking about, it is possible that the A320's equivalent of Alt 2 (Alternate with no speed stability) may function differently when it comes to trim, I'll keep you updated.

Which he (or she) can do by holding on to the trim wheel if he or she does not like what the autotrim is doing (although I have yet to hear of autotrim behaving inappropriately due to a software or hardware failure).

Easier to build, saves money. That's it! Oh, and SS give you unimpeded access to your dinner tray. :cool:

Those who think yokes should be the cure-all for what the other guy is doing should look at this accident originally posted by Netstruggler in the current Rumors & News AF447 thread.
http://libraryonline.erau.edu/online...s/AAR97-05.pdf
An interesting mix of Perpignan and AF447 on a DC-8 airframe. No loss of airspeed, but a stall warning failure combined with a PF who didn't let the nose down promptly at the stall and two staff pilots + a FE on a Post Maintenance Check Flight.
The guy in charge (PNF) didn't apparently realize that they were still stalled and allowed the PF to continue to hold the Yoke too far back to recover.
When the wings started rocking-it was like they had both forgotten all they should know.

Oh yes, PF had trimmed too far nose up. Do you see a possible pattern?:hmm:

Though it should be noted that according to the NTSB this has not been a factor...
Some of the conclusions sound quite familiar:

Refocus?
 

There seems to be a tendency to let the mass of opinion become fact...

- Autotrim did not stall the airplane, the PF did that quite successfully and then held the SS NU for a good long time, resulting in the NU trim eventually. The stall would have occurred with or without autotrim. My opinion is this is a distraction and something for the anti-Airbus brigade to fixate on. That the PNF did not notice the eventual trim demand seems to be a topic that has received scant attention - I believe those trim wheels would have been rotating for a good while. But no comment???

- The stall warning system worked and sounded at one point for, what was it, 53-54 seconds continuously, with no comment from PF or PNF? Eventually the damn thing gave up since the airspeed dropped below the 60kt cutoff, but come on!!!... From then on the vertical speed and pitch attitude should have told ANYONE with half an understanding of the basic laws of aerodynamics that the airplane was no longer flying in the true sense and was stalled.

- I am also surprised that the PNF never seemed to really comment on the initial zoom-climb? Why not? Nothing like "Hey, we're at FL380 what are you doing?"

There seems to a lot that the PNF didn't do? Question the climb, question the stall warning, the pitch/VS combination. Unfortunately, he seems to have been somewhat fixated on the necessity to call the Captain back to the cockpit, just at the time when his full attention should have been on what the aircraft was doing.

Machinbird Zorin_75

It is a fascinating report netstruggler gave us the opportunity to read.
It is a reminder that stalling an airliner, intentionally or not, is a very serious matter.

You are correct, it cannot be the miraculous solution.
But it is one of the great piece of equipment that a multicrew has in its toolbox.
It is free non verbal communication between all in the flight deck.
The yokes have the merit to make that information available.
The sidesticks have the default to supress it.

In my book, an aft control column, is the best shot to wake me up.