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.