Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF 447 Thread No. 9

Tech Log The very best in practical technical discussion on the web

AF 447 Thread No. 9

Old 8th Jul 2012, 01:13
  #141 (permalink)  
 
Join Date: May 2011
Location: BOQ
Age: 75
Posts: 488
...the jet was not in a "deep stall", but rather "deeply stalled"
This now appears to be a question of adjective versus adverb...
OK465 is offline  
Old 8th Jul 2012, 02:36
  #142 (permalink)  
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,939
Originally Posted by PJ2
What "de-confuses" the airplane is flying it like any other airplane. I don't think I was unusual in the way I thought about the A320/A330/A340...I was never "aware" that there were "protections"...it was flown like a DC8, or a Lockheed or a B767 - just never took anything for granted.
Like most of us, you never had to apply the relevant memory items in real life, but for the simulated life you have been asked to get the maximum and just rely on the protections. Anything else and you didn't follow the Published Emergency Procedure ...
CONF iture is offline  
Old 8th Jul 2012, 03:08
  #143 (permalink)  
 
Join Date: Jun 2009
Location: florida
Age: 77
Posts: 1,128
Point taken OK, and I had posted a graph of the pitch moment for the Viper a year or so ago. Flew at least two jets that could be "deeply stalled", but pushing forward and keeping wings level with rudder would enable a prompt recovery. In the Viper, we had about a ten deg AoA range that did not allow a nose down effect using full elevator. The 'bus folks claimed that the cee gee for AF447 was well forward of the allowable value, so the jet had a positive nose down pitch moment through out the drill.

I go with PJ a 100% on a few drills flying the jet without all the FD's and otto help. There's no need to be macho and "prove" your manhood/womanhood. Just demonstrate you can fly the damned jet without all the gizmos.

Finally, I re-iterate my instense dislike for the term "protection" versus "limit". For some reason, I found it easier to remember the jet's "limits" than how it was supposed to "protect" me.
gums is offline  
Old 8th Jul 2012, 06:00
  #144 (permalink)  
 
Join Date: Aug 2009
Location: Germany
Age: 63
Posts: 1,809
cjeant; Quote:
It seems that for the BEA recovery was impossible .. unless a miracle ......
On reflection, I believe the BEA have developed the Report on the basis that their mandate was to determine the actions and/or events that lead to the aircraft departing the Normal Flight Envelope. The report then covers factual information concerning the LOC through to impact.

Consequently, they are very vague on possible alternative outcomes for which no validated data is available, and it is up to the airframer and regulator to establish procedures that can be used in a LOC situation where the envelope has been "extended".
As the A330 was never tested in real life for stall and recovery ... the AF447 pilots were (against their will) promoted test pilots when the aircraft stalled
Unfortunately they do not look like they were qualified for the job ...
jcjeant is offline  
Old 8th Jul 2012, 06:59
  #145 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 76
Posts: 1,331
jcjeant;
Unfortunately they do not look like they were qualified for the job ...
If they didn't know how not to stall it, recovery was then an even bigger ask.

Not knowing you were stalled, made the outcome inevitable.
mm43 is offline  
Old 8th Jul 2012, 07:56
  #146 (permalink)  
 
Join Date: Jul 2009
Location: Sydney
Age: 74
Posts: 4
A3330 stall test

JCJEANT...are you sure they never tested A330 stall recovery? Is that possible?
geoff sutherland is offline  
Old 8th Jul 2012, 09:09
  #147 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,584
Might have taken 30s sustained ND or even more but personally I don't share the pesssimism that it wasn't technically possible.
- firstly, this is not really relevant to this accident since the crew did not have the first notion that they were 'stalled', but way back in the dark annals of the multiple threads on this I posited that 20k would be my guess at the absolute lowest recovery altitude and below that they were in yet another 'coffin corner'.

Posters talking about '30 secs sustained ND or even more' need to remember that

a) This a/c was descending at around 10,000 fpm ie from 10k, one minute to impact
b) A pitch change of around 30-40 degrees nose down would have been required to initiate unstall, which would probably have raised the r o d to around 20k fpm
c) Now pull out at xxx g?
BOAC is offline  
Old 8th Jul 2012, 09:39
  #148 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 72
Posts: 2,416
BOAC - again not to resurrect things but your numbers were about what my sim exercise produced from FL350 - one was just above FL200 - the others around FL 250 or so IIRC. Descent rates were as high as 17,000fpm. I did not try it lower and now wish I had.

Owain Glyndwr's numbers show a 10deg ND steady pitch attitude, for recoveries at FL350, FL200 and FL60 at 3, 2 & 1 deg/sec AoA recovery rates.

The FL350 scenario recovers between FL250 and FL220 which coincided with most but not all our exercises; the FL200 scenario recovers between FL145 and FL125 and the last scenario recovers about a thousand feet above the sea.

Last edited by PJ2; 8th Jul 2012 at 09:41.
PJ2 is offline  
Old 8th Jul 2012, 09:54
  #149 (permalink)  
 
Join Date: May 2010
Location: PLanet Earth
Posts: 801
Originally Posted by BOAC View Post
Posters talking about '30 secs sustained ND or even more' need to remember that

a) This a/c was descending at around 10,000 fpm ie from 10k, one minute to impact
b) A pitch change of around 30-40 degrees nose down would have been required to initiate unstall, which would probably have raised the r o d to around 20k fpm
c) Now pull out at xxx g?
I agree it is not really important in the given case,
just out of curiosity I had again a rough look at the physics behind.

We are probably talking about somewhere between 10 and 20kFt.

I appologise upfront for re- doing the calc.
[Assuming stall speed of ~180kts @200t, no flaps, we need 250kts IAS for a 2g recovery. At 10 kft that corresponds to ~300kts IAS. At an angle of 45 this would produce ~22kfpm (300kts x sin(45)). If we assume linear acceleration (which I admit is not 100% true) that would give us an average 16kfpm.
In 30s that would mean a drop of 8k.
Edit : At 30 - 35 RoD would be 16kfpm. Simplified average 13kfpm.
This would give us 6500ft drop.

Now the 2 g recovery:
R = v^2/a: with a = 9,81 m/s (Out of the 2g maneuver capability @300kts TAS (=250kts IAS) one g is required for Sir Isaac Newton). That gives us a radius of
2430m. At an angle of 45 the corresponding lost altitude would be (1- cos(45)) x Radius. That would gives us an additional 710m (2370ft)].
Here I err on the conservative side, as recovery in the given example would have been below 3kft and thus 250kts IAS wouldn't have meant 300kts TAS but rather 260kts.
(Edit: 1500ft at 35)

So we have lost somewhere between 6,5 and 10kft for acceleration to a speed where recovery could be executed and between 1,5 kft and 2,5kft for the recovery itself. However it would be easy to start to early with the recovery and run into the next stall.

However, from a purely theoretical PoV somewhere close to 10.000ft might have been possible.
Apologies again for beating this poor dead horse again.

But I fully agree this has no practical meaning in the given case.

Last edited by henra; 8th Jul 2012 at 10:15. Reason: Figures for 35 added
henra is offline  
Old 8th Jul 2012, 09:56
  #150 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,584
Owain Glyndwr's numbers show a 10deg ND steady pitch attitude
- I admit I cannot understand these figures - with an AoA of 35-40 degrees, and a pitch attitude of ?13-18 degrees? an instantaneous change to 10 degrees nose down still leaves you with an (admittedly improving) AoA (ball park) of between 12 and 17 degrees. ie no 'instant' unstall. How long do you wait? Are we not confusing attitude with Aoa here? Go back to ?mm's? early AoA pics and overlay a 10 degrees nose down pitch.

I am also uncertain how representative a sim exercise would be with AoAs of that value - can they even be achieved and is the software up to the job?
BOAC is offline  
Old 8th Jul 2012, 11:04
  #151 (permalink)  
 
Join Date: Jun 2011
Location: West of Offa's dyke
Age: 84
Posts: 474
I admit I cannot understand these figures - with an AoA of 35-40 degrees, and a pitch attitude of ?13-18 degrees? an instantaneous change to 10 degrees nose down still leaves you with an (admittedly improving) AoA (ball park) of between 12 and 17 degrees. ie no 'instant' unstall. How long do you wait? Are we not confusing attitude with Aoa here? Go back to ?mm's? early AoA pics and overlay a 10 degrees nose down pitch.
I was hoping to stay lurking until I had time to read the whole of the final report, but since several people have referred to my theoretical study I thought I'd better chip in.
Yeah I agree the process is not intuitive. I gave my best shot at an explanation in Thread 8 post # 175. Not an 'instant' unstall though - it takes quite a while to get the AoA down to sensible levels. I also fully agree with the statement that this represents theoretical possibilities and that the psychological pressures on the pilot might well inhibit maintaining the necessary ND attitude for long enough. And no, I think I understand the difference between attitude and AoA well enough.
As for the BEA response - I think they said they didn't know because nobody had done the sums or (certainly) any relevant flight tests. They didn't (AFAIK) say it was impossible.
Owain Glyndwr is offline  
Old 8th Jul 2012, 12:05
  #152 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
Owain Glyndwr's Recovery trajectories
HazelNuts39 is offline  
Old 8th Jul 2012, 12:17
  #153 (permalink)  
 
Join Date: Sep 2007
Location: Romford Essex
Posts: 27
More errors on BEA website.

Another (minor) error on BEA website 5 July 2012 press briefing

In the English version of the Summary, Paris time is stated to be 5 hours ahead of UTC. French, German and Brazilian (Portuguese) versions appear to be correct.

They have also transposed the links to DE and BR summaries with http://www.bea.aero/fr/enquetes/vol....let2012.br.pdf under the German flag and http://www.bea.aero/fr/enquetes/vol....let2012.de.pdf under the Brazilian flag.
kit344 is offline  
Old 8th Jul 2012, 12:34
  #154 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,271
Hi DozyWannabe,

Your comment on 19 April http://www.pprune.org/tech-log/48235...ml#post7143575 post #94
However, "following the FD" is *exactly* what the AF447 pilots had been trained to expect to do 99% of the time.
was amazingly accurate.
It explains (to me) the pitch attitudes PF attempted to follow and his errors.

Last edited by rudderrudderrat; 8th Jul 2012 at 12:38.
rudderrudderrat is offline  
Old 8th Jul 2012, 13:42
  #155 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,182
Originally Posted by aircarver View Post
Did the autopilot stall the airplane on bad airdata before it clicked off and handed over to the pilots
No - in fact it's for that very reason that the values are constantly compared and the AP will disengage if there's a discrepancy. The aircraft did not stall until it reached the apogee of the zoom climb, at which point it had been under manual control for almost a minute.

or did the PF immediately imply an overspeed, and stall it with the long period of stick back ?
That's the big question, and judging by the content of the final report there's not enough clear-cut information to provide a definitive answer there. Instead what we have is a series of possibilities, each of which has to be eliminated. Those giving the report short shrift because it does not provide a definitive answer are missing the point - it's not the fault of the investigators, it's that there was insufficient information available to provide a simple answer.

For one thing, I don't think it's a coincidence that a push for flight-deck CCTV monitoring began around the time the final report was being compiled.

Originally Posted by rudderrudderrat View Post
Hi DozyWannabe,

Your comment on 19 April http://www.pprune.org/tech-log/48235...ml#post7143575 post #94
was amazingly accurate.
It explains (to me) the pitch attitudes PF attempted to follow and his errors.
Why thank you. I feel compelled to admit I wasn't the only one pointing that out, however.

That said, I don't think the FDs alone were the cause of the PF's pitch-up commands*, just as I don't think fear of overspeed or expectation of being able to rely protections would do it in isolation. I suspect it was a combination of any or all of those factors and possibly more.

This is what irks me about some of the criticisms of the report in this thread - because if the accusations of the BEA trying to protect Airbus and AF by pinning it on the crew were true, they could easily have taken a look at the probable FD behaviour, stated that the crew contravened procedure, stalled and crashed the aircraft and left it there.

Instead what we have is a fairly exhaustive review of all the possible factors that led to the accident, inclusive of shortcomings on the part of the manufacturer, operator and the industry as a whole - there's even a whole section devoted t othe handling of the recovery operation and how to rectify mistakes made there. While there's a lot of material dedicated to how the crew mishandled the situation, the findings and conclusions only relate that factually. The implicit reprimands seem to be largely directed at the industry as a whole.

[* - The reason for this is that we don't know precisely when they re-appeared, how long they re-appeared for, we only have a theory on what they might have displayed based on systems behaviour - and probably most importantly, if the PF even saw them when they did re-appear on each occasion that they did. On its own it's an interesting rather than compelling theory, but in concert with everything else working against the crew it's definitely something that needs to be eliminated in future.]

Last edited by DozyWannabe; 8th Jul 2012 at 14:10.
DozyWannabe is offline  
Old 8th Jul 2012, 14:10
  #156 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,271
Hi DozyWannabe,
The reason for this is that we don't know precisely when they re-appeared, how long they re-appeared for,
the times and modes are here
http://www.bea.aero/docspa/2009/f-cp...nexe.02.en.pdf
I hope Airbus changes the FD logic. If the FDs are withdrawn automatically, then they should remain withdrawn until the pilots reselect them.
To have them reappear automatically in a different mode to that which the pilots originally engaged them, can be very confusing.
rudderrudderrat is offline  
Old 8th Jul 2012, 14:24
  #157 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,182
Originally Posted by rudderrudderrat View Post
Hi DozyWannabe,
the times and modes are here
http://www.bea.aero/docspa/2009/f-cp...nexe.02.en.pdf
I hope Airbus changes the FD logic. If the FDs are withdrawn automatically, then they should remain withdrawn until the pilots reselect them.
To have them reappear automatically in a different mode to that which the pilots originally engaged them, can be very confusing.
Agreed. That behaviour is far from optimal and should be altered regardless.

That said, while the times and modes are displayed in the annex, that still only provides an estimate of what might have been displayed. Taking a look at the timeline, the FDs reappeared twice during the climb phase of the accident sequence - first in ALT CRZ* mode, and subsequently in VS/HDG mode. They then reappeared during the descent phase several times.

Here I need a bit of clarification - in this mode, will the FDs lock to the current vertical speed or the selected vertical speed?
DozyWannabe is offline  
Old 8th Jul 2012, 14:35
  #158 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,271
Hi DW,
The reference to "vertical speed selected" is what the FDs automatically acquired on automatic re-engagement.
The reference to "vertical speed" is what the aircraft is actually doing.

Last edited by rudderrudderrat; 8th Jul 2012 at 14:39.
rudderrudderrat is offline  
Old 8th Jul 2012, 15:14
  #159 (permalink)  
 
Join Date: May 2011
Location: BOQ
Age: 75
Posts: 488
I am also uncertain how representative a sim exercise would be with AoAs of that value - can they even be achieved and is the software up to the job?
Level D simulators generally have a touch screen instructor station display. On the systems/flight diagnostic page there is an icon labeled "INPUT GUIDANCE".

Selecting this page allows you to choose a specific internal software parameter, such as ALPHA, and have it 'artificially' displayed on the ND where VOR DME would normally be. This function allows two different parameters to be selected at any given time, i.e. VOR 1 DME & VOR 2 DME could be set to display ALPHA & BETA. (A poor man's AOA )

The ALPHA values at any point are very consistent with those from the FDR, a credit to the Sim manufacturers and the value of the 'predicted' data provided with the software 'flight package'. (BETA is another story)

I believe the mathematical analyses of recovery altitudes assumed a constant average nose down pitch rate (based on actual pitch rates generated for short periods from the FDR data) and a specific constant 'G' applied at a given speed on the pull-out. Correct me if I'm wrong.

This is all well and good if the FCS is 'agreeable' to providing those pitch rates over the extended period of time encompassing the full exercise. In other words, the analysis is, at least partially, independent of the specific flight control system as the SS is held forward for longer and longer periods, the 'assumed' long term pitch rate being extrapolated from short periods.

It may be entirely representative...
OK465 is offline  
Old 8th Jul 2012, 15:26
  #160 (permalink)  
 
Join Date: Jun 2011
Location: West of Offa's dyke
Age: 84
Posts: 474
I believe the mathematical analyses of recovery altitudes assumed a constant average nose down pitch rate (based on actual pitch rates generated for short periods from the FDR data) and a specific constant 'G' applied at a given speed on the pull-out. Correct me if I'm wrong.
This is correct for the entry and exit manoeuvres, but for by far the longest time the aircraft was assumed to be held at constant pitch attitude - in most cases 10 deg ND but other attitudes were looked at. The thinking was that attitude was about the only thing he could rely on and hold easily. 10 deg was a "for instance" value which might not have been too extreme to be believable, and was held for a long time just to see if it would have been effective. So your next point is OK - the sums did not depend on the ability to hold specific pitch rates over an extended period and weren't really any sort of function of FCS except insofar as the entry rate of pitch was concerned, and even there one could show that the entry rate did not significantly affect the outcome.

Last edited by Owain Glyndwr; 8th Jul 2012 at 15:31.
Owain Glyndwr is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.