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

AF 447 Thread No. 5

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

AF 447 Thread No. 5

Old 18th Jul 2011, 00:04
  #421 (permalink)  
 
Join Date: Jun 2011
Location: Devonshire
Age: 96
Posts: 297
Likes: 0
Received 0 Likes on 0 Posts
3holelover #407

To add to your concerns as PF... When did you last hand fly, using a SS at cruising level ?

An earlier entry from a Captain said that he had asked a number of F.O.s to look him in the eye whilst cruising and tell him what the aircraft's pitch was. He said that he got some surprising answers.

Someone else said that AB did offer an "ordinary", standby A/H, (not taken up by AF).

60 years ago Handley Page provided their Hermes 4,( which had a lot of then new(ish) and by the standards of the day advanced, electric instruments) with a standby basic, battery-powered Turn and Slip, which was fitted forward of the Captain's left knee. This may have been at the request of the original purchaser.
Linktrained is offline  
Old 18th Jul 2011, 00:13
  #422 (permalink)  
bearfoil
Guest
 
Posts: n/a
link

It is offered on the A330, and AF took a pass. It is mounted upper left, Captain's side.

(afaik)
 
Old 18th Jul 2011, 01:13
  #423 (permalink)  
 
Join Date: Aug 2005
Location: fl
Posts: 2,525
Likes: 0
Received 0 Likes on 0 Posts
Soon, hopefully, we will see if it might have helped them. Depends on what their training and experience was. It might not have helped them with their experience.
bubbers44 is offline  
Old 18th Jul 2011, 02:03
  #424 (permalink)  
bearfoil
Guest
 
Posts: n/a
bubbers44

You were here in the very first thread. Do you remember the action about the AH deselect on 447? It was a big knock on Air France, (as was the pass on BUSS) and my memory is that The FD's were gone, and the PF had no Pitch. Do you remember it the same way? The upshot was, if the PF had a horizon, his SA would have been nails, and no crash.

What I recall is that the Pilots were commanded to fly PITCH and POWER, but were helpless w/o instruments to pin that down. Am I misremembering?
 
Old 18th Jul 2011, 04:55
  #425 (permalink)  
Moderator
Thread Starter
 
Join Date: Apr 2001
Location: various places .....
Posts: 7,195
Received 110 Likes on 70 Posts
http://www.pprune.org/tech-log/45687...ml#post6573663

gums, by all means do start up a specific thread to discuss FBW things. JT
john_tullamarine is online now  
Old 18th Jul 2011, 06:06
  #426 (permalink)  
 
Join Date: Feb 2011
Location: Australia
Age: 63
Posts: 14
Likes: 0
Received 0 Likes on 0 Posts
FBW Thread

...and if you do, can you put a link here as I'd love to follow it, thanks. -A
andianjul is offline  
Old 18th Jul 2011, 08:32
  #427 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Hi Bearfoil,
Originally Posted by Bearfoil
You were here in the very first thread. Do you remember the action about the AH deselect on 447? It was a big knock on Air France, (as was the pass on BUSS) and my memory is that The FD's were gone, and the PF had no Pitch. Do you remember it the same way? The upshot was, if the PF had a horizon, his SA would have been nails, and no crash.
What I recall is that the Pilots were commanded to fly PITCH and POWER, but were helpless w/o instruments to pin that down. Am I misremembering?
I don't really follow you. What do you meant here?
1. There is no link between FD (Flight Director) and Artificial Horizon. A/H was displayed during this night on Captain and F/O's PFD (Primary Flight Display) just fine... they absolutely never lost it - there is not a single fault detected in the IR part of ADIRUs that may translate into the loss of those displays!... but also, they had a third A/H source on their large Standby Instrument (ISIS).
2. ISIS (Integrated Standby Instrument System) is an option for A330 that can replace the standard unreadable standby indicators. Hence, for AF, it was a "plus", not a "less".
.3. AF choice to not take this BUSS option is understandable as its draw backs are pretty clear (disconnection of all ADRs) and its readability not very good. It may be very useful if one loss its speed during the final descent or climb phase, but it was not designed to replace those ADRs at cruise in the middle of the South Atlantic.

Last edited by takata; 18th Jul 2011 at 08:42.
takata is offline  
Old 18th Jul 2011, 09:12
  #428 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes on 0 Posts
Hi takata,

It seems better to have in this case a pitch Alternate rather than direct, certainly because autotrim (inop in direct law) will permanently deal with fuel transfers (the pitch law is mostly based on CG computation by fuel computers). It will also damper pitch sensitivity if CG is aft, while roll axis should be trimmed by rudder and the aircraft is supposed to fly in straight line hands off.
Is the reason that AB FBW don't have the option for the pilots to deliberately select Direct Law (unlike B777) because the allowed CofG can be so far aft and the subsequent handling characteristics?

I agree that rudder should be used to trim out any roll tendency - maybe if the aircraft had been perfectly in trim at the time of AP disconnect, then the PF could have just left the controls centred and continued at FL 350.
rudderrudderrat is offline  
Old 18th Jul 2011, 09:45
  #429 (permalink)  
 
Join Date: Aug 2005
Location: London
Posts: 78
Likes: 0
Received 0 Likes on 0 Posts
HN39,

Agreed, I should have just said that whatever 'protection' was responsible for the Turkish zoom climb event, it couldn't apply to AF447 if, as we are told, none of the protections other than g were active in ALT 2. The brief description given by the BEA suggest that it was indeed PF who commanded the climb, which just makes it all the more important to figure out what persuaded him this was a good plan, or prevented him from stopping it.
gonebutnotforgotten is offline  
Old 18th Jul 2011, 10:00
  #430 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Hi Rudderrudderrat,
Originally Posted by Rudderrudderrat
Is the reason that AB FBW don't have the option for the pilots to deliberately select Direct Law (unlike B777) because the allowed CofG can be so far aft and the subsequent handling characteristics?
CG set at max envelope aft should not be an issue for handling in direct law if one is carefull about not over controlling (elevators are really powerfull at high altitude). In any circumstance, with full aft CG, (beside some related FCMC faults) Airbus state that no forward fuel transfer is needed (turbulences, whatever...). Nonetheless, direct pitch is loosing autotrim and, during normal operation at cruise, there is a constant displacement of the CG due to fuel transfers (by +/- 0.5%) . Hence in direct law, one would have to retrim constantly in pitch or disable the fuel transfer function.

Originally Posted by Rudderrudderrat
I agree that rudder should be used to trim out any roll tendency - maybe if the aircraft had been perfectly in trim at the time of AP disconnect, then the PF could have just left the controls centred and continued at FL 350.
Right. They had just completed a virage before AP disconnected. It's then possible that ailerons were still adjusting in autoflight when AP kicked off and PF had to correct this roll tendency. It certainly played its part as the attention of the PF was then attracted by this correction of the roll rate rather than keeping his pitch in range. As the roll axis was direct, it was much more sensitive than previously and he certainly over-controlled for some time. This could also happen if pitch would be translated directly into direct law, especially at this altitude where the aircraft was flying.
takata is offline  
Old 18th Jul 2011, 10:13
  #431 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes on 0 Posts
Hi takata,

Thanks for the reply.
As the roll axis was direct, it was much more sensitive than previously and he certainly over-controlled for some time.
In ALT LAW, if pitch remains attitude stable, what's the reason for having roll direct? Why can it not be designed to be roll attitude stable, (but still with no protections)?
rudderrudderrat is offline  
Old 18th Jul 2011, 10:55
  #432 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Rudderrudderrat
In ALT LAW, if pitch remains attitude stable, what's the reason for having roll direct? Why can it not be designed to be roll attitude stable, (but still with no protections)?
Good question. For sure, there is a reason linked to the change of flight law that would limit an EFCS function, but I don't know which one precisely. What you are loosing is the ability to maintain a bank angle, hence, you are left with a limited coordination in turn, and a different feeling in control.
takata is offline  
Old 18th Jul 2011, 11:09
  #433 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by takata
Nonetheless, direct pitch is loosing autotrim and, during normal operation at cruise, there is a constant displacement of the CG due to fuel transfers (by +/- 0.5%). Hence in direct law, one would have to retrim constantly in pitch or disable the fuel transfer function.
- heavens! What have we come to? Is it too much to ask of an AB pilot - I mean, like FLY an aeroplane, man??
BOAC is offline  
Old 18th Jul 2011, 11:52
  #434 (permalink)  
 
Join Date: Nov 2006
Location: SoCalif
Posts: 896
Likes: 0
Received 0 Likes on 0 Posts
I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.
Graybeard is offline  
Old 18th Jul 2011, 12:11
  #435 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes on 0 Posts
Hi BOAC,

If AB pilots had conventional control columns, I'm sure they would cope. I think the problem lies with the side sticks. They are good at telling the the computer what attitude you'd like, but they are hopelessly lacking in tactile feed back.

The only feel is the centring spring in the box, they lack the conventional back driven clues. The control forces required is measured in ounces rather than pounds. It would be like driving your car with the steering wheel replaced by a joy stick. Ok in a straight, but would feel horrible at speed through tight bends.

takata is correct, I think they would be far too sensitive for manual direct law flight at altitude.
Edit - unless the "sensitivity" could be manually selected by the pilots.

Last edited by rudderrudderrat; 18th Jul 2011 at 12:17. Reason: edit
rudderrudderrat is offline  
Old 18th Jul 2011, 12:20
  #436 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Hi gonebutnotforgotten,
Originally Posted by gonebutnotforgotten
A month ago on the preceding thread I asked for a good explanation or a comment on my own hunch that it was a reaction to the initial decrease in indicated altitude after the start of the UAS event (due to the loss of appropriate Mach number correction). No one took me up on the challenge then, though HN39 took me to task for suggesting that the pull up was very robust, saying that even 0.2g would produce 7000 fpm in 18 secs; true, but 0.2 g is not exactly gentle controlling, it would normally only be exceeded by a TCAS RA (ideally 0.25g) or a GPW, and I don't believe I ever experienced such hamfisted inputs in my 35 years up front. So the question is still unanswered.
Your point that a sharp altitude decrease on PF display seems to me a fairly possible explanation of his initial imputs, including his roll correction. It will depend on what displayed information he was looking at... then, to which one he first (over)reacted.

Everything in the fault sequence analysis makes me think that the PF display was the first affected. The PROBE fault recorded imply that the 3 probes readings were different as well as out of range with previous median values. Hence, no single ADR could be rejected but the three altogether. We are also told of the recorded sequence implying PNF speed decrease followed by ISIS: the first value then to drop should have been the one on the PF display.

There is also an indirect proof of an altitude drop and range: the following reported TCAS fault by ACARS. AFS/FMGES (autoflight system) ADR altitude monitoring fault treshold is set at 400 ft instead of 3,000 ft at EFCS level (flight control monitoring). Hence, TCAS should have faulted because of that. So, could it be that uncorrected static pressure was dropping to the point of displaying an over 400 ft of instantaneous altitude change, Mach going down from 0.81 to about 0.18? Could it be that static pressure was also affected by icing?

If this was the first information taken by the PF in addition to the roll at AP disconnection, he could have effectively feared that some kind of spiral dive could follow. Likely, his pitch rate wasn't his first concern, then without speed, after ignoring the first stall warnings as spurious, he might have lacked the correct info necessary to understand how much energy was lost during the climb with an altitude under reading, then he also would be spatially disoriented. There was also no mention of thrust change during this climb and this would rather fit with a PF trying to slow down than one fearing of stalling.

Nonetheless, I don't think that the climb took as much as 18 seconds to be engaged. BEA prose is somewhat hard to follow. It is hard to deduce the correct chronology of the flight events that may be different from what is induced by their description. Language is ambiguous enough as to make one believe that some events were following each other, as it is written, while basically, they could have occured almost at the same time.
Anyway, we'll check that in next report.

Last edited by takata; 18th Jul 2011 at 12:38. Reason: syntaxe
takata is offline  
Old 18th Jul 2011, 12:31
  #437 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Hi Graybeard,
Originally Posted by Graybeard
I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.
They say 29%. Either a typo, either it means that the aircraft was loaded with a heavy nose, hence, target CG could not be moved aft, even with a fully loaded THS.
takata is offline  
Old 18th Jul 2011, 12:32
  #438 (permalink)  
 
Join Date: Jun 2009
Location: Germany
Age: 71
Posts: 776
Received 3 Likes on 1 Post
CG-travel

takata
CG set at max envelope aft should not be an issue for handling in direct law if one is carefull about not over controlling (elevators are really powerfull at high altitude). In any circumstance, with full aft CG, (beside some related FCMC faults) Airbus state that no forward fuel transfer is needed (turbulences, whatever...). Nonetheless, direct pitch is loosing autotrim and, during normal operation at cruise, there is a constant displacement of the CG due to fuel transfers (by +/- 0.5%) . Hence in direct law, one would have to retrim constantly in pitch or disable the fuel transfer function.
Greybeard
I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.
Found this reference some time ago about CG travel due to fuel
Getting to grips with weight and balance

A330 /340 starrts at page 49, inflight CG-travel page 59.

The mentioned CG from BEA makes me wonder as well, itīs that far forward form desired target CG

Aft target cg would be around 39% MAC (see page 60 of above reference) and how it is influenced by the trim-tank shows page 63.

CG target:
In flight, the FCMC controls the position of the center of gravity. It calculates the CG position and compares it to a target value, which depends on the aircraft weight. According to this calculated CG position compared to the target, the FCMC determines the fuel quantity that needs to be transferred aft or forward.
The FCMC determines the fuel quantities to be transferred to maintain the aircraft CG in a control band limited by the CG target position and CG target position +/- 0.5%. Takata, are those the 0.5% you mentioned as fuel transfer cg shift?
RetiredF4 is offline  
Old 18th Jul 2011, 12:36
  #439 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by rudderrudderrat
If AB pilots had conventional control columns, I'm sure they would cope. I think the problem lies with the side sticks. They are good at telling the the computer what attitude you'd like, but they are hopelessly lacking in tactile feed back.

The only feel is the centring spring in the box, they lack the conventional back driven clues. The control forces required is measured in ounces rather than pounds. It would be like driving your car with the steering wheel replaced by a joy stick. Ok in a straight, but would feel horrible at speed through tight bends.
If what you're suggesting is that the sidestick response goes from balanced and gradual to "squirrelly" with law degradation, that is apparently not the case, and if I recall correctly it was PJ2 who gave the lie to that particular idea. He said the difference can be noticed, but is not that great that it would either cause trouble or could not be corrected for very quickly. I'm told the spring response is actually quite dynamic - this is not like your computer or video game controller in that it exerts more counteracting force the further you deflect the stick.

As I said before regarding modern back-driven FBW controls a la B777, if you've got a triple-pitot failure and UAS scenario, how do you know that the computer is applying the correct column/yoke backdrive?

As for BOAC's question, I don't think takata's point is a case of Airbus pilots not being able to fly an aircraft so much as it is the question of whether you'd want to have to suddenly take over manual pitch trimming - in turbulence, at night, with no speed indications and the fuel transfer system causing the need for regular adjustments.
DozyWannabe is offline  
Old 18th Jul 2011, 12:45
  #440 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Hi Franz,
Originally Posted by RetiredF4
The FCMC determines the fuel quantities to be transferred to maintain the aircraft CG in a control band limited by the CG target position and CG target position +/- 0.5%. Takata, are those the 0.5% you mentioned as fuel transfer cg shift?
Yes. I also posted above the informations and tables (not up to date) concerning the A332. CG is constantly moving forward, aft by this margin at cruise, providing fuel transfer is taking place. If the THS tank is full, but target CG can't be achieved (possible AF447 case), then no such transfer is taking place until later during the flight.
takata is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.