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

AF 447 Search to resume

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

AF 447 Search to resume

Old 9th Apr 2011, 09:13
  #3221 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
It seems "loss of control" is now amply explained.

How about arm '36g'?
HazelNuts39 is offline  
Old 9th Apr 2011, 09:37
  #3222 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by JD-EE
But that might allow enough airspeed pickup to allow the plane to get engines started and pull out to level flight.
Using full rudder would help getting the nose down. You didn't forget to extend the flaps on the other wing to permit rolling it back to wings level?
HazelNuts39 is offline  
Old 9th Apr 2011, 10:24
  #3223 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
HN39, you asked "Using full rudder would help getting the nose down. You didn't forget to extend the flaps on the other wing to permit rolling it back to wings level?"

Um, I'd rather envisioned retracting the flap that was temporarily extended if the plane gathers too much speed to safely have flaps extended. Regardless, the concept is that once it was broken out of its "spin" you'd want to return to a symmetrical configuration. Otherwise you simply buy yourself new problems.
JD-EE is offline  
Old 9th Apr 2011, 10:57
  #3224 (permalink)  
Moderator
 
Join Date: Apr 2001
Location: various places .....
Posts: 7,181
Received 93 Likes on 62 Posts
http://www.pprune.org/tech-log/376433-af447.html links to a second locked thread on this subject.
john_tullamarine is offline  
Old 9th Apr 2011, 11:03
  #3225 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by takata
Now, that the weather alone would put suddendly this aircraft close to an "upset" attitude, while flying in automatic mode at Mach 0.82, would certainly disconnect everything the same way. Then, if this was followed immediately by the freezing of all the probes, ...
Any thoughts as to how (at FL350) "the weather alone would put suddenly this aircraft (in or) close to an "upset" attitude" in pitch, roll or yaw?

Regards,
HN39

PS1:: To illustrate what I have in mind, I have done a simple sum. In its Appendix 1 to BEA Report No.1, MétéoFrance writes:
The strongest vertical movements are observed in the "tower" of the cumulonimbus in its phase of rapid growth, that is to say before the top reaches the tropopause and the anvil is formed. The upward speeds can then reach 110 km/h and the downward speeds 50 km/h. The vertical speed can thus vary very rapidly inside of the cumulonimbus while crossing its "tower":
variations of more than 70 km/h in the space of 2 km have sometimes been observed. This intense turbulence can occur at the flight level of airliners and constitute a danger for them.
As I read this, these are extremes, unlikely the fit the CB's encountered by AF447. But let's take them as written. An aircraft encountering an increasing updraft as described by MétéoFrance will pitch up, unless the pilot or AFCS opposes that with control inputs that maintain a set pitch attitude. The tail length of an A330 is about 29.25 m. Therefore the updraft velocity seen by the wing is 0.284 m/s greater than that seen by the tail. When the aircraft pitches up at 0.56 deg/sec, that difference will be nullified by the downward speed of the tail relative to the wing. At 483 kt TAS, the 'space of 2 km' is traversed in 7.45 sec, during which time the aircraft has pitched up 4.15 deg, less the lag attributable to its mass moment of inertia in pitch (which I have no data on).

PS2:: As a result of further research into the 'mathematical model' proposed in PS1 above, I should add that, due to several attenuating factors not taken into account in the 'simple sum', such as inertia, and the natural stability that induces a pitch-down moment when AoA increases due to an upward gust, the actual pitch up will be much less than that derived in PS1. Unfortunately, I do not have the more sophisticated 'mathematical model' that would produce the correct number.

Last edited by HazelNuts39; 14th Apr 2011 at 14:33. Reason: PS2 added
HazelNuts39 is offline  
Old 9th Apr 2011, 14:09
  #3226 (permalink)  
 
Join Date: May 2010
Location: Close to LFBD - France
Posts: 22
Likes: 0
Received 0 Likes on 0 Posts
Turn radius

First, a big thank you to all contributors for this fascinating and most interesting thread.

Anyway, I'm still puzzled by the (probable) crash site being so close to LKP, so I have used an online turn information calculator to sort a couple numbers, and here is how it comes.

Supposing AF447 was at cruise speed at LKP (around 500 kts), coming back close to this point in less than four minutes supposes a constant turn bank angle of 35° at constant speed.

If I reduce the speed to 410 kts, I still come with a constant turn bank angle of 30°. Any smaller turn bank angle doesn't allow reaching LKP again in a 4 mn interval.

Another hypothesis would be that AF447 reduced her speed considerably, which would allow reaching LKP again (after a 360° turn) in 4 mn using smaller bank angle values. However, I can't see any benefit in performing a 360° turn in the middle of the ocean, and any other evolution (e.g. a 180° turn to escape from bad weather) would involve still sharper bank angles.

As far as I can say, these high bank angle values may suggest that, apart from the final stall/spin/whatever event that ended in the crash itself, AF447 first experienced a massive enough "initial upset" that resulted in a change of direction that cannot be achieved using a standard rate turn. In other words, she may have rolled/tumbled heavily because of weather or anything else.

(Obviously, the speculations above suppose that the crash occurred at 02:14, as suggested by ACARS timeline.)

Assuming the scarce info we have is reliable, does anyone buy this theory ?
JPI33600 is offline  
Old 9th Apr 2011, 15:38
  #3227 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
More turn radius

JPI33600;

Perhaps you would like to also look at a spiral dive. For 205t, FL350, M.82 the max. available loadfactor in normal law is n=1.662 corresponding to a bank angle of 53 degrees in a coördinated (no-slip) turn. The drag coëfficient in this condition results in a flight path angle for zero thrust of 6.4 degrees down, or a rate of descent of 5425 ft/min. Radius of turn is 2.6 nm, rate of turn 3 deg/s, so 360 deg. takes 2 minutes.

Last edited by Jetdriver; 9th Apr 2011 at 18:35.
HazelNuts39 is offline  
Old 9th Apr 2011, 16:01
  #3228 (permalink)  
 
Join Date: May 2010
Location: Close to LFBD - France
Posts: 22
Likes: 0
Received 0 Likes on 0 Posts
HN39

Thanks for your thorough answer. Regarding this spiral dive hypothesis, do you suggest an intended manoeuvre ? I suppose a 1.6 load factor spiral dive would certainly call for a "fasten seat belts" emergency announce, so most of pax and cabin crew would have been strapped ? Or are you thinking of an uncontrolled spiral dive (in this case, the cause for this dive would be as acceptable as anything else for what I called the "initial upset") ?

I may be wrong, but the more I think about it, the more I guess this plane has been initially affected by something huge and totally unexpected, with all unstrapped people being instantly killed or severely injured, and the direction of the plane being radically changed in a few seconds. A subsequent spiral dive followed by a (failed) recovery attempt would fit well in this kind of scenario.
JPI33600 is offline  
Old 9th Apr 2011, 16:20
  #3229 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
JPI33600;

It's just Flight Mechanics expanding on yours. Hopefully the DFDR and CVR will tell us what happened and why.
HazelNuts39 is offline  
Old 9th Apr 2011, 17:29
  #3230 (permalink)  
 
Join Date: Jul 2009
Location: SUSSEX UK
Age: 76
Posts: 57
Likes: 0
Received 0 Likes on 0 Posts
@mm43
re your diagram of the aircraft impact (bg5kqh.jpg). I would be grateful if you could point me in the direction of the previous post it related to - date will do?
BJ-ENG is offline  
Old 9th Apr 2011, 18:18
  #3231 (permalink)  
 
Join Date: Jan 2008
Location: Blighty (Nth. Downs)
Age: 77
Posts: 2,107
Received 4 Likes on 4 Posts
Hi HN39,

Re the "could they return near to LKP in about 4mins?" issue, you write:
"Perhaps you would like to also look at a spiral dive. For 205t, FL350, M.82 the max. available loadfactor in normal law is n=1.662 corresponding to a bank angle of 53 degrees in a coördinated (no-slip) turn. The drag coëfficient in this condition results in a flight path angle for zero thrust of 6.4 degrees down, or a rate of descent of 5425 ft/min. Radius of turn is 2.6 nm, rate of turn 3 deg/s, so 360 deg. takes 2 minutes."

2 minutes allows quite a lot of "fat", so we don't even need as much as 53deg of bank. Can you or someone else confirm that deliberate bank angles beyond about 33deg (?) can only be sustained by maintaining the stick left or right of neutral throughout the turn, assuming Alternate Law (I forget which version they had) is in operation? Also that - beyond 33deg bank - the pitch-attitude would no longer be adjusted automatically to provide the vertical-axis 'g' (load-factor) appropriate to the bank angle, i.e., the aircraft would tend to fall out of the turn like a conventional aeroplane?
Chris Scott is offline  
Old 9th Apr 2011, 18:30
  #3232 (permalink)  
 
Join Date: May 2010
Location: MA, USA
Posts: 126
Likes: 0
Received 0 Likes on 0 Posts
BEA Search Summary

There is a new note from Jean-Paul Troadec posted on BEA's AF447, Phase-4 page. It summarizes the searches to-date on the occasion of terminating Phase 4, but, unfortunately, it provides no new information.

http://www.bea.aero/en/enquetes/flig...end.phase4.pdf
auv-ee is offline  
Old 9th Apr 2011, 18:32
  #3233 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes on 0 Posts
BJ-ENG;

Here is the Impact Graphic post, and you will also find related information a page or two before and after.

Last edited by mm43; 10th Apr 2011 at 01:50. Reason: fixed broken link
mm43 is offline  
Old 9th Apr 2011, 18:42
  #3234 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 81
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
CliveL
However, what seems to be missing in this discussion - at least I have never seen it mentioned, is that if you lose the complete VS you leave all the hydraulic pipes supplying the rudder open to the atmosphere. Depending on how many of your hydraulic systems go up the VS you are likely to lose all hydraulic power and hence control in either axis.
Exactly. And none of the ACARS messages referred to hydraulic failure, and a hydraulic failure would definitely be the subject of a maintenance ACARS message.
Therefore the VS was on until water impact. Please, no more "They lost the VS before water impact." It is a lunatic theory.
Machinbird is offline  
Old 9th Apr 2011, 18:59
  #3235 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes on 0 Posts
Chris Scott;

A330/A340 - Flight Laws , a HTML adaption of an original document by Andy Tracy may help. Note:: The summary table is also scrollable.

Last edited by mm43; 9th Apr 2011 at 20:19. Reason: fixed broken link
mm43 is offline  
Old 9th Apr 2011, 19:04
  #3236 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Chris Scott
Can you or someone else confirm that deliberate bank angles beyond about 33deg (?) can only be sustained by maintaining the stick left or right of neutral throughout the turn, assuming Alternate Law (I forget which version they had) is in operation?
Hi Chris;

As I replied to JPI33600, it's basic flight mechanics, nothing more. I didn't look into the aspects you mention and expect that others, more qualified than I am in those things, will do that.
HazelNuts39 is offline  
Old 9th Apr 2011, 19:31
  #3237 (permalink)  
 
Join Date: Aug 2007
Location: Brazil
Age: 71
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
meeting

According to brazilian press, a meeting will be held in Paris monday (11th) to discuss the next step, whitch is the recovery of the bodies (and wreackage?).

A person representing the families of the victims will be allowed to attend this meeting and also allowed to be an "observer in site" when the recovery of the bodies begins.

All bodies will be transported to France, where DNA examinations will occur.
Rob21 is offline  
Old 9th Apr 2011, 20:41
  #3238 (permalink)  
 
Join Date: Jun 2009
Location: florida
Age: 81
Posts: 1,610
Received 55 Likes on 16 Posts
Salute!

Long time between posts, but frequent lurker. This the best site on the 'net for good poop and inputs from knowledgeable folks.

- I wish to point out to some folks that roll inputs that command a rate are not all that different from Champs, Cubs, Luscombes, P-51's, F-86's, F-4's and the Viper. Even if you must physically move the control that has direct/hydraulic connections to the ailerons or other surfaces such as I had in the F-102, you are not commanding a bank angle. Once you center the control or relax pressure you get whatever you are trimmed for, and the bent wing jets may continue to roll just a bit. Big deal. Unlike the Airbus, our Viper stick did not move at all until a year or so after initial operational jets were on the flightline, and thereafter about 1/8 inch to help feeling you had commanded max roll or gee command. No kidding. It was all pressure, and relaxing the grip stopped roll/pitch command instantly. About 17 pounds of pressure was max roll command to the computers. Biggest thing we had to get used to was "roll ratcheting", as the inertia of our arm woul reduce the pressure and the roll would slow or even stop, heh heh. Watch the T-birds versus the Blues. You will note that the Viper freezes after a roll and sometimes the Hornet will wobble a bit. In the Viper letting go of the stick by opening your hand stopped the roll instantly.

So the fact that the Airbus control moves is not a big deal. Only time I ever physically moved a stick for 30 years was in a violent maneuver, and not day-to-day flying, especially in close formation. I watched many great pilots in the T-33 and A-37 that had mechanically connected dual controls. Was very hard to tell where the stick was most of the time.

Thing that haunts me is the plethora of "control laws" that the Airbus employs. Shows the difference between the commercial planes and the ones I flew, I guess, but still don't understand the rationale.

- I would still not rule out the vertical stab coming off just prior to impact. Seem to remember the PIO on the Airbus at New York 10 years ago when the pilot exceeded the limits of the doofer. The recorders will tell us.
gums is offline  
Old 9th Apr 2011, 21:21
  #3239 (permalink)  
 
Join Date: Aug 2009
Location: Germany
Age: 67
Posts: 1,777
Likes: 0
Received 0 Likes on 0 Posts
Cool

Hi,

Machinbird
Exactly. And none of the ACARS messages referred to hydraulic failure, and a hydraulic failure would definitely be the subject of a maintenance ACARS message.
Therefore the VS was on until water impact. Please, no more "They lost the VS before water impact." It is a lunatic theory.
Do you know (are you sure) that the sending of ACARS message ended just a second before the aircraft made contact with water?
After the end of ACARS message ... who know if more was to be send .. but not send for any reason ?
Where in reality is the aircraft at the time of the end of ACARS message ?
Are that lunatic questions ?
jcjeant is offline  
Old 9th Apr 2011, 23:04
  #3240 (permalink)  
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 748
Likes: 0
Received 0 Likes on 0 Posts
jc theory

So, jc, you're indicating you think that the VS came off quite a long way into the incident and thus was not an initiating nor early failure?
HarryMann 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.