Airbus crash/training flight

[Smilin_Ed]

3. Direct law. Now the plane flys direct inputs from the stick and any smoothing is gone. You can do a roll, or whatever...

Please correct me if I'm wrong but presumably the airplane would normally be in Direct Law only because of some kind of failure. If there has been a failure, what assurance does the crew have that everything else is working correctly and that the control surfaces will follow the "direct inputs from the stick"?

[NigelOnDraft]

If it flies just like a regular airplane, why weren't they able to fly it that way? They apparently had full engine power and the controls were apparently working, or were they?

All indications are that the controls were working... i.e. Ailerons and Elevators folow the stick inputs closely.

Unfortunately, unless one has experience in how an A320 flies in the stall, one cannot work out if the bahviour of the aircraft to those control inputs is as would be expected.

Would they have been able to prevent the accident it they had started at FL140?

I reckon so... in the last seconds speed was good and increasing (250K+), pitch was increasing, AoB approx 0. If the pitch increase rate was maintained it would be 0 pitch in ~5s, and another 2-3s (?)should have seen the aircraft climbing...

So from 15:45:55 the Autotrim was enabled, but no THS movement is recorded.

Same thoughts with me... but with the dynamic manouevres, and no doubt high Load Factor, it might be inhibited? I am not sure of the logic to which it works?

NoD

[DC-ATE]

NigelOnDraft -

Unfortunately, unless one has experience in how an A320 flies in the stall, one cannot work out if the bahviour of the aircraft to those control inputs is as would be expected.

May I assume that in simulator training on the A320 that the student only takes it to "recognition" of a stall and not a full stall? Is the sim able to simulate a full stall?

Same thoughts with me... but with the dynamic manouevres, and no doubt high Load Factor, it might be inhibited? I am not sure of the logic to which it works?

Are you A320 qualified?

[Clandestino]

you should not get a Stall Warning in Normal Law

There's a caveat in the FCOM: you can get stall warning in the normal law if AoA probe is damaged.

Please correct me if I'm wrong but presumably the airplane would normally be in Direct Law only because of some kind of failure. If there has been a failure, what assurance does the crew have that everything else is working correctly and that the control surfaces will follow the "direct inputs from the stick"?

FCOM says so.

If it flies just like a regular airplane, why weren't they able to fly it that way?

We'll have to wait for full CVR transcript to shed some light on it. Methinks that shock from experiencing the stall in "unstallable" aeroplane may prevent crew from noticing "USE MAN PITCH TRIM" caption on top of their PFDs and acting accordingly.

Regarding the AoA readouts it seems that we're either looking at simultaneous failure of two independent systems or perhaps failure of single AOA vane that was mistakenly crosswired to feed two GNADIRS. Slight difference in values might come from GNADIRS being differently calibrated. Whatever happened, our colleagues were extremely unlucky to experience it. However, testing stall protection at 3000ft ASL is pushing one's luck too far.

[IcePack]

Lack of elevator authority to overcome the full nose up stabilizer + the full thrust pitch couple at the speed the a/c was at. A bit of a surprise for a modern jet. Then again it was designed in the 70's, quite normal for older types. As to why it got into that position with an experienced crew well that is the question the investigation will be trying to answer.

[Lemurian]

TyroPicard :

I have been puzzling over the lack of THS movement from fully nose-up. I can't explain the lack of THS movement while in Direct law.

Yes, puzzling, isn't it ? Did they try using it, though ?

But at 15:45:40 the Pitch Law reverts from Direct to Alternate

Because of the gear retraction, I would guess. And from 15:45:13, the system had lost both FACs feeds, therefore reverting to "alternate" ( Pitch going direct because of the gear-down position, then going back to Alternate with the gear retraction.).

What is lacking in this interim report :
1- The normal load factors (I agree)
2- The instruments indications
3- A CVR transcript.
Without those, one cannot determine whether they had a jammed stabiliser, whether they had full pitch authority during the plunge, whether they knew they had a flight control mode problem...

What I personally know is - on mechanical back-up - the power of that huge piece of aerodynamics called the stabiliser is immense...can the elevator counteract its effect ? and that of the engine-induced pitch-up moment ? I doubt it.

[Lemurian]

Icepack :

Lack of elevator authority to overcome the full nose up stabilizer + the full thrust pitch couple at the speed the a/c was at. A bit of a surprise for a modern jet.

Requires the pilot to be aware of the necessity of using manual trim as there is no feeling of increased effort...I know, it's indicated on the screen...but in such a situation ?

[guiones]

"My apologies, Guiones, I only flew the thing for a few thousand hours...must have missed it altogether! I never once saw alternate or direct law except in the books, probably that's why I'm writing here in good health. And as I flew many test flights after overhauls on conventional machines, I learnt that a bit of modesty and briefings on things that are "evident" never did any harm..."

Hopefully you saw it many times in the simulator in the "few thousand" hours that you flew it. It is amber and it says: MAN PITCH TRIM ONLY. Maybe you also remember that if you are in ALT LAW and bring the gear down you get DIRECT LAW !!!!

You will still be among us in good health even if you saw it in the actual aircraft, any competent pilot can handle ALT and DIRECT LAW without any problem under non flight test conditions. Not a big deal.

100% agreement on the briefings.

G

[bubbers44]

Going back to flying basics if we found ourselves in a runaway trim or unusual attitude putting your airliner in a high nose up pitch attitude rolling into a 60 degree bank to drop the nose back down to the horizon was part of the recovery if necessary. I know the Airbus 320 has a restricted bank angle so the pilot cannot not exceed that bank. I never had to fly an airplane that wouldn't let me do what the computer disagreed with so don't know what these pilots were dealing with. They were all highly qualified pilots so must have done all they could with what they had to work with.

[alph2z]

NOD - All indications are that the controls were working... i.e. Ailerons and Elevators folow the stick inputs closely.

It seems to me that in the last few seconds that the 2 elevators (green* line on p. 34) reversed to what the stick input (blue) was.

Anybody have any idea why ?

This occurs around the time that they are at their max nose-dwn pitch-angle and are commanding full nose-up, but the elevator is giving full nose dwn !??

* also blue line hidden by green line.

RIP
.

[TyroPicard]

alph2z

It seems to me that in the last few seconds that the 2 elevators (green* line on p. 34) reversed to what the stick input (blue) was.

The Pitch Law is Alternate, with load factor protection. The sidestick demands load factor - neutral =1g, the pilot was demanding maximum positive g with full back stick. The limit is 2g with flap, 2.5 g clean, provided the wing can produce that load factor.

It appears that with the a/c out of trim, full nose-up, the elevators were working to reduce/control the load factor. But without the Load Factor readout we don't really know. And the THS position readout requires physical confirmation.

The pitch rate at the end was about 5°/sec - can anyone convert that to "g"?
TP

[Tarq57]

The pitch rate at the end was about 5°/sec - can anyone convert that to "g"?
TP

(From page 21 of the report) last recorded airspeed=263kt.
For anyone who wants to do that sum.

[Bis47]

g at 263 kts and 5° rot speed

That is barely 1.1 g or 1.2 (given the - lack of - accuracy of the pitch up rate).

Somebody has any hints about the position or movement of the stabilizer during the final dive?

Any chance that the stabilizer has moved from full up to full down somewhere in the process of "law changes" that took place (perhaps?).

[bsieker]

Originally Posted by TyroPicard

The pitch rate at the end was about 5°/sec - can anyone convert that to "g"?

Originally Posted by Bis47

That is barely 1.1 g or 1.2 (given the - lack of - accuracy of the pitch up rate).

Yes between 1.1G and 1.2G is what I got, assuming it was doing a perfect circle at 5 degrees/s and 263kts.

Add to that some uncertainties and the 1G standard earth gravitation, you may be close to 2.5G. So it's plausible that they were at load limit.

And at the correct altitude (FL100+) it would have been an "exciting" upset, but with plenty of altitude to recover.


Bernd

[DozyWannabe]

Going back to flying basics if we found ourselves in a runaway trim or unusual attitude putting your airliner in a high nose up pitch attitude rolling into a 60 degree bank to drop the nose back down to the horizon was part of the recovery if necessary. I know the Airbus 320 has a restricted bank angle so the pilot cannot not exceed that bank.

In Direct Law those restrictions do not apply and you can roll the A320 into a spiral dive straight into the ground should you so desire. Even in Normal Law you can get a bank angle of up to 67 degrees, so the maneouvre you describe above is perfectly do-able in the A320.

[IcePack]

Lem.
Yes manual pitch trim would be required. That is if it was working at the time. As I said still surprised that the elevators do not have enough authority.

[NigelOnDraft]

May I assume that in simulator training on the A320 that the student only takes it to "recognition" of a stall and not a full stall? Is the sim able to simulate a full stall?

Our training is firstly the "Normal Law" charateristics of Approach to Stall, and the "protections" and the recovery actions. Secondly the Alternate / Direct Law where you now get a Stall Warning (audio) and the Recovery Actions. You do not, IIRC, "stall it" fully, and doubt the sim would reproduce this accurately?

Are you A320 qualified?

My First Officer's would probably say not. 5 years command... and current now.

you should not get a Stall Warning in Normal Law

There's a caveat in the FCOM: you can get stall warning in the normal law if AoA probe is damaged.

My reading of the FCOM is that the "Stall Warning" is still available, just in Normal Law the protections should avoid you getting to that stage. In this case, some Normal Law malfunction (?) AoA Probes? seems to have led to a genuine Normal Law Stall Warning (maybe from the 3rd AoA probe not on the FDR?)

Methinks that shock from experiencing the stall in "unstallable" aeroplane may prevent crew from noticing "USE MAN PITCH TRIM" caption on top of their PFDs and acting accordingly.

One would hope that people flying Test Profiles are suitably briefed and trained... for what eventualities are possible with each test area...

It seems to me that in the last few seconds that the 2 elevators (green* line on p. 34) reversed to what the stick input (blue) was.

Anybody have any idea why ?

My guess is to limit the pitch rate / 'g' as per Altn Law demands...

NoD

[bsieker]

Originally Posted by DozyWannabe

In Direct Law those restrictions do not apply and you can roll the A320 into a spiral dive straight into the ground should you so desire. Even in Normal Law you can get a bank angle of up to 67

For anyone not wanting to do the math: 67 degrees bank angle corresponds to a co-ordinated turn at the load limit of 2.5G normal (i. e. downwards relative to the aircraft) acceleration.

(The 33 degree limit, to which the bank angle returns from higher angles at stick release corresponds to a comfortable 1.2G turn.)


Bernd

[TyroPicard]

Which means...
At 67°AOB your pitch-up capability is nil
At 33° AOB you can pitch up at 1.3G

Initial AOB during the final pitch-up was 45° ....

[bsieker]

Originally Posted by TyroPicard

Which means...
At 67°AOB your pitch-up capability is nil
At 33° AOB you can pitch up at 1.3G

Initial AOB during the final pitch-up was 45° ....

... which only corresponds to 1.4G, leaving 1.1G for pitch-up.


(Although the values for 33 and 67 seem to imply otherwise, the relationship is not linear. At 84.26 degrees the load is 10G, at 90 degrees it becomes infinite.)


Bernd