PPRuNe Forums - AF 447 report out

PPRuNe Forums (https://www.pprune.org/)

- Rumours & News (https://www.pprune.org/rumours-news-13/)

- - AF 447 report out (https://www.pprune.org/rumours-news/489790-af-447-report-out.html)

HWell Bobn, can you provide some more detail on what you did?

Quote:

In the Boeings you have to work at it to keep it stalled, but we were doing a falling leaf, descending at 11000 ft/min, 10 degrees nose up at firewall thrust.

Would the recovery have been easier without thrust ?, it depends on geometry but those underwing engines are likely to generate a nose up tendency.

Would the recovery have been easier without thrust ?, it depends on geometry but those underwing engines are likely to generate a nose up tendency.

most assuredly yes...

Let's say you have a properly trimmed airplane that for some reason gets into a nose-high attitude and begins to fall as AF447 did. Is there a regime in which you just cannot get out of it? Will the nose always come down if you have proper trim and take the thrust down to idle if necessary? Is there a danger of entering a flat spin? How to avoid that?

I keep thinking some sort of emergency reaction control to push the nose down might work. Some small solid rockets just for emergency use.

Quote:

I keep thinking some sort of emergency reaction control to push the nose down might work. Some small solid rockets just for emergency use.

That might be a little extreme. I think a better avenue would be for AB to work with the key stakeholders (sorry if that sounds cliche) to review the software and AP policies and notification methods therein.

Is there a regime in which you just cannot get out of it?

some t-tail jets, the BAC-1-11 had a famous one during flight testing, have deep stall tendencies, where the horizontal stab is rendered useless...in an airplane with a conventional horizontal stab, it seems impossible, provided sufficient altitude is available to recover...even the 727 was found to NOT be prone to deep-stall tendencies...in the AF crash, it appears no positive effort was made to recover from the stall...simply lowering the nose down 5deg is not sufficient to reduce angle of attack to below stall when the aircraft flight path is much greater..Airborne Express DC-8 on a test flight is another example of flawed stall recognition and recovery training...

Trying to avoid the dreaded Pprune edit nonsense, but I would like to append my earlier post to reinforce that there still needs to be a greater focus on training and making sure the pilots really know how to fly the airplane by hand and understand basic aerodynamics. I've seen so many industries lose their way on fundamentals, and I would like to see the aviation industry avoid that. Too many lives are at stake.

At the risk of waking the Oozlum bird who has managed the odd 5 minutes sleep here:

As far as we know:

447 was kept in a nose-high attitude by

a) a nose up demand on the sidestick
b) TOGA
c) Full nose-up THS delivered by the software and sidestick demand.

Whenever either a or b was relaxed, the nose appeared to drop. I think it is safe to assume that had the stick been held forwards and the power reduced it would have recovered (given sufficient altitude). This appears to have been a 'foreign' concept to AB pilots at the time.

Quote:

I keep thinking some sort of emergency reaction control to push the nose down might work. Some small solid rockets just for emergency use.

I suspect rockets would cause all sorts of regulatory problems (they've been suggested for ejecting flight recorders, but faced similar issues). I seem to recall that at least one of the T-tail airliners had a booster in the rear during test flights just in case.

Quote:

Originally Posted by BobnSpike (Post 7296817)

In the Boeings you have to work at it to keep it stalled

Same with the Airbus - remember the PF was holding between 50-100% back stick for the majority of the sequence.

In the sim experiments we did, you had to really hold the stick back to keep the nose where the crew had it - because as the speed bled off, the nose clearly wanted to come down. Even with the THS all the way back, it was possible to recover using forward sidestick alone - which we did as we came back down through FL320, during which time the trim wheel obediently rolled back forward - and come out of the descent at around FL180.

Quote:

Originally Posted by BOAC (Post 7297129)

c) Full nose-up THS delivered by the software and sidestick demand.

The software aspect isn't really relevant - it was only doing what was asked of it by the pilot, as any other aircraft would.

AF 447 crashed because the pilots allowed it to stall. The pilots allowed it to stall because they pulled back on the stick. They pulled back on the stick because they were confused. They were confused because the automation left them in the lurch. The automation left them in the lurch because of a mechanical problem with the speeder tuber thingies. The speeder tuber thingies failed because they got clogged up with frozen water particulates commonly called "ice". The ice was formed because the pilots didn't go far enough left right up down backwards forwards sideways to avoid the storm. The pilots didn't avoid the storm because the captain failed to take the crossing of the ICZ seriously and instead went to sleep in his bunk with a woman. The captain didn't take the crossing of the ITZ seriously because he was complacent due to his vast experience. The captain achieved this vast experience by flying the plane too much. The captain flew the plane too much because Air France allowed the plane to take off from the ground. Air France allowed the plane to take off from the ground because the passengers payed them money. THEREFORE The passengers are to blame for the crash of AF447 and the proper judicial verdict is one of mass suicide by airliner.

Bear, that is brilliant.

I agree...apart from the last bit.

Quote:

AF 447 crashed because the pilots allowed it to stall.

Correct

Quote:

The pilots allowed it to stall because they pulled back on the stick.

No. Because they made totally incorrect control demands.

Quote:

They pulled back on the stick because they were confused.

No. Because they were completely incompetent and had received utterly inadequate training.

Quote:

They were confused because the automation left them in the lurch.

No, it didn't. The AFS acted correctly and disconnected with a clear annunciation. The idiots at the helm didn't follow the QRH, let alone commonsense.

Quote:

The automation left them in the lurch because of a mechanical problem with the speeder tuber thingies.

By 'speeder tube thingies', I presume you mean pitot tubes. They failed, it is true. However, all that did was to cause an entirely recoverable situation for properly trained pilots.

The rest of your post is utter tripe. An ill-disciplined, poorly trained crew killed themselves and everyone on board through their own inadequacy.

"The captain ... went to sleep in his bunk with a woman".

It's outrageous that you say such a terrible thing. Do you have any proof that he slept?

@BEagle:

I don't think MountainBear was being entirely serious. :}

I read somewhere they were all knackered because of too much bonking in Rio.

Pulling back on the side stick sounds totally correct to me. Without stall protection any aircraft will stall with the stick way back. The reason for the loss of control is obvious. Why these two couldn't fly an airliner with one failure, AS, which caused the AP to disconnect is beyond me. Experience level is still my guess. Monitoring an autopilot again does not count for quality experience.

I still don't have an answer to this question - if they are in this very low forward-air-speed, very high nose-up situation, is it easy with the right inputs to bring the nose down in time? How long does it take? That seems very important. You are falling, and the solution is to hold the stick/yoke forward and trim the stabilizer to help and reduce thrust, even if it takes 30 seconds to get a result. That would require a lot of discipline. To do that, you'd have to be damn sure that it was going to work. So would it?

Another thought is - have we found the Achilles heel of the modern wing? The unspoken factor in this crash is the wing design. Does it have this ability to fall like a leaf in honey because otherwise it is so very efficient?

Quote:

Originally Posted by deSitter (Post 7297619)

http://www.pprune.org/tech-log/46062...ml#post6793521

Quote:

The first experiment involved setting the conditions to night IMC with CBs in the vicinity, having set the autoflight to take us to 35,000ft and hold us there. We had a friend of his who is a TRE sitting in the LHS to provide guidance and monitor what we were doing. He then failed the ADCs, leading to autopilot disconnect and a drop to Alternate (without speed stability) and we tried to follow through and maintain a 15 degree pitch angle. Things we noted:

I'd suspected it would involve considerable effort to hold the sidestick there for a significant amount of time, but I was genuinely surprised at just how much.
The zoom climb occurred exactly the way we expected
The Alternate Law (no speed stability) on the A320 seems to have a hard trim limit of 3 degrees nose up
It was definitely possible to hold the aircraft in the stall with 3 degrees of nose-up trim and full back stick, but it required effort
The aircraft wanted to nose down and recover itself, and with about 10 degrees of nose-down maintained with the sidestick at the moment we passed about 30,000ft, we managed to effect a recovery with the speed coming back up to a point where we could level out safely at about 20-25,000ft judging by the standby altimeter.

The second experiment was the same as the first, but as my pal had noted, the A320 has a hard limit of 3 degrees NU trim available via autotrim in the secondary Alternate Law. We tried again, this time winding in full nose-up trim manually just prior to the point of stall. This time:

The aircraft seemed more willing to hold pitch with the trim at full-up, but to hold it at 15 degrees still required considerable effort
We had to add a touch of rudder (on the TRE's advice) to control the roll.
Despite full nose-up trim, we elected to start a recovery as we came down through about 35,000ft this time, just to see if it was possible using sidestick only
Following the same 10 degree nose-down sidestick demand as before, the trim rolled forward with the sidestick demand, returning to around neutral within about 5-8 seconds, and we came out of the stall as before.

Based on this, as far as the A320 is concerned at least, recovery is possible using autotrim via sidestick only even when the trim has been manually wound fully nose-up. Given more time we'd have liked to see what happened attempting recovery at lower altitudes, but the general take-away seems to be that with sufficient forward sidestick demand it is possible to recover from stall even with trim forced to where it's not supposed to be.

Hi,

DeSitter

Quote:

How long does it take? That seems very important. You are falling, and the solution is to hold the stick/yoke forward and trim the stabilizer to help and reduce thrust, even if it takes 30 seconds to get a result. That would require a lot of discipline. To do that, you'd have to be damn sure that it was going to work. So would it?

One thing the pilot know (or must know) :
That's keep pulling on the stick will not help for recovery
So why not take the chance to push on the stick .. and pray ..
At least .. better try to recover instead the contrary .. !