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AF 447 Search to resume

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AF 447 Search to resume

Old 5th Apr 2011, 01:53
  #3001 (permalink)  
 
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I think Machinbird has probably got it.

Davis talks of superstalls and T-tails (yes, I finally found my copy) but AF447 possibly got into something much more horrible than that - possibly loss of pitot info, possibly degraded FBW as a result and for all we know subsequent engine issues if the AOA got really excessive. As he/she said lets hope the info is still available.
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Old 5th Apr 2011, 04:43
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ttcse "... your basic swept wing tends to tip-stall first. "

Say what !!!????
.
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Old 5th Apr 2011, 05:14
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alph2z
Say what !!!????
Ttcse's comment is correct. Aft swept wing aircraft begin to stall at the wing tip and the stall progresses forward and inward toward the fuselage. The aerodynamics guys can twist the wing and play games with the leading edges to modify this somewhat but at high enough angle of attack it will happen.
This tip stall causes a nose up pitch moment as the lift contribution from the ends of the swept wing decreases.
I've had a lot of practice over-rotating off cat shots and I can tell you from personal experience that it used to take up to full nose down stabilator to get the nose moving back down where it belonged.
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Old 5th Apr 2011, 06:16
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Sorry if .... did they find the FDR, CVR etc ...
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Old 5th Apr 2011, 08:08
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high altitude stalls

I like this quote from the opening sentences of D.P. Davies discussion on "Stalling" (but must admit I'm taking it completely out of context):
Stalling is one of the major areas which always come up for discussion whenever responsible pilots get together. (...) Stalling appears to drive even the most rational of pilots to completely opposing points of view.
In many minds, including mine, stalling is something you get close to during takeoff and and landing, i.e. at relatively low altitude. In thirty-odd pages related to stalling, mr. Davies devotes only a single (not quite accurate) sentence to the effect of altitude:
At very high altitude the EAS stall speed occurs at a significant Mach number (180 knots = 0.61 Mach number, for example); the pressure pattern is disturbed and a higher stall speed results.
The point I wish to make is that stall at high altitude involves fundamentally different (transonic) phenomena compared to low altitude. For example, for the A330 in clean configuration, alpha max is of the order of 14 degrees up to Mach 0.275, 8 degrees at Mach 0.6, and 4 degrees at Mmo.

Regards,
HN39

Last edited by HazelNuts39; 5th Apr 2011 at 09:36. Reason: correction of amax/M.275
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Old 5th Apr 2011, 08:24
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In many minds, including mine, stalling is something you get close to during takeoff and and landing
Surely "stalling" is what occurs when you exceed alpha max, regardless of whether or not that's at low altitude (takeoff/landing), or at high altitude.

Even though the fundamental reason for the stall may be different at high/low altitude in terms of the fluid behaviour, exceeding alpha max is a stall?
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Old 5th Apr 2011, 08:27
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From this http://www.smartcockpit.com/data/pdf...light_Laws.pdf

follows that when in alternate law, all AOA protection is completely lost with dual ADR fail or ADR disagree, which was the case as we know.

HN39's numbers on AOA limits at altitude are interesting! Add to that lost AOA protection, then given the conditions they would have encountered... there's not much margin left.
 
Old 5th Apr 2011, 08:33
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Eugene, sure, exceeding alpha max will always end up in a stall. However, as all those of us know who fly, a perfect landing is a stall from an inch altitude, so that's where you want that to happen.

The trouble with the alpha max limit at altitude is that it gets so small, as HN39 has written. 4 degrees is not a lot of room in a turbulent environment.
 
Old 5th Apr 2011, 08:56
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Originally Posted by robertbartsch
...does anyone have an idea of how they would lift the wreckage to the surface from that extreme depth (+13,000 feet)? I assume the pictures have been taken by an un-manned sub; right?
Originally Posted by 500N
Question regarding the tyres in the photos. I am surprised they are not crushed / squashed by the pressure at that depth.
I recall seeing photos of the SA 295 crash in 1987, where the landing gear tyres were still intact at a depth of 4,900 metres (16,100 ft). They also successfully recovered the CVR (but not FDR) from that crash. So in 2011, it would be somewhat easier to recover parts from a slightly shallower depth of 13,000 ft and compared to 1987's technology.
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Old 5th Apr 2011, 09:02
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They also successfully recovered the CVR (but not FDR) from that crash.
Yes they did and that's where all the controversy started and still runs to this day.
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Old 5th Apr 2011, 09:32
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BEA manager interview

interview of Jean-Paul Troadec, BEA manager.05APR2011

ouest-france.fr - Rio-Paris*: un mois pour remonter épave et corps


.../...

Q : Cette zone proche de la dernière position connue n'avait pas été explorée. Pourquoi ?
A:- Entre la dernière position connue et l'impact, il s'est écoulé cinq minutes. Le Rio-Paris aurait pu parcourir une distance très importante. Au départ, nous n'avions pas de raison de penser qu'il était pratiquement à l'aplomb de cette dernière position.

Q : This area near the last known position was not explored. Why ?
A: Between the last known position and the impact, five minutes elapsed. The Rio-Paris flight could have cover a very important distance. At the beginning we had no reason to think that he was almost straight above this last position.

Est-on certain qu'il n'y a pas eu explosion en vol, mais décrochage ?
- L'explosion paraît très peu vraisemblable. Les débris légers retrouvés à la surface indiquaient déjà, par leurs positions symétriques, que l'avion avait touché l'eau en ligne de vol et en étant entier. Il n'était pas préparé à l'amerrissage car les passagers n'étaient pas équipés de gilets de sauvetage. Quant à l'hypothèse d'un décrochage, il est trop tôt pour se prononcer.

Q : Are we sure that there was no in-flight explosion, but stall.
A : An explosion seems very unlikely. Light debris found at the surface already indicated, with their symmetrical positions, that the airplane had touched the water in line of flight and was entire. It was not prepared for a sea landing because passengers were not wearing life jacket. About the stall hypothesis, it is too early to give an opinion.

Remonterez-vous tous les corps des passagers ?
- L'identification des victimes, quand elle est possible, s'impose à nous. Certaines familles le souhaitent, d'autres pas. Mais l'on ne peut pas remonter les corps de façon sélective. Les familles vont être associées à cette ultime phase des recherches. Nous allons les réunir prochainement et leur détailler la façon dont cette mission va être conduite.

Q: Will you retrieve all passengers bodies.
A: Victims identification when possible is essential to us. Some families wish this, others no. But we cannot retrieve bodies in a selective manner. Families will be associated to this last searches phase. We will meet them together soon and detail them the way this mission will be managed.
.../...

The wreckage is at 3900 meters depth. Three boats are considered for this operation:
René Descartes owned by France Télécom Marine, based at Brest, France. Another based in Cyprus and a third owned by Alcatel Lucent. The selected ship will be on the scene in one month.
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Old 5th Apr 2011, 10:44
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A: Between the last known position and the impact, five minutes elapsed. The Rio-Paris flight could have cover a very important distance. At the beginning we had no reason to think that he was almost straight above this last position.
Here is the main point that is almost ruling out an upset at 02.10 causing the crash where the wreckage is actually lying.

It certainly doesn't take 5 minutes to "deep stall" from cruise level to sea level, when in the meantime, the aircraft is circling at the same spot and will keep this attitude at impact.
Something else happened in that sequence that we still don't know.
CVRs and FDRs are really the key to fully understand it.

I'll bet that they will recover the engines.
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Old 5th Apr 2011, 10:46
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I think, this are the windows in seat row 29...31 the first behind the emergencydoor, grity
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Old 5th Apr 2011, 10:51
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Interesting discussions about deep stalls, but do the revelations of the last 48 hours change anything?

Machinbird,
For the benefit of this pedestrian pilot, what is a "cat shot", and are you talking about a F-102/ F-106 (delta-wing)?

Quote from SaturnV (post #3000):
"...there was no lightning with this particular complex; none detected by satellite, nor by ground stations. Apparently lightning is infrequent in the ITCZ."

Before anyone gets the idea that sub-Saharan Africans (for example) know little about lightning (!), my understanding and experience suggest ITCZ lightning is less likely over the oceans.

I'm interested in the idea that some serious atmospheric changes may have been experienced if they got far enough to emerge from the north face of that Cb. As I've said before, this would have left them very poorly placed if they were already trying to fly thrust/attitude with unreliable airspeed indications.

Chris

PS (Edit):
takata,
Maybe the five minutes involved a tear-drop?
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Old 5th Apr 2011, 11:04
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From takata's list, here are the three recovery ships that are being considered. EDT ARES is presently off Alexandria Egypt.

Rene Descartes
RENE DESCARTES - 9248100 - Vessel's Details and Current Position

Île de Bréhat
ILE DE BREHAT - 9247053 - Vessel's Details and Current Position

EDT ARES
EDT ARES - 9130755 - Vessel's Details and Current Position

EDT ARES aircraft recoveries:

EDT and Phoenix Recover Yemenia Flight Debris

Aug 20, 2010

EDT Ares assists with search - Offshore Shipping Online
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Old 5th Apr 2011, 11:45
  #3016 (permalink)  
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@takata: Let's look at what we know.

- The last position received was at 02:10:34. That's 20 seconds after the AP switched off and problems obviously had begun.
- At 02:12:51, ADR disagree triggered, with concurrent loss of AOA protection

- Assuming they had taken evasive action shortly after 02:10:34 by initiating a left turn, they would now (~2.5 minutes later, at 02:12:51) be just about overhead where the wreckage was found and would probably be just about coming out of the left hand course reversal

- Enter a deep stall / flat spin at that point, facilitated by lack of AOA protection, pitch and power flying in turbulent conditions in a turn

- Assuming ~350ft/s descent rate in flat spin, impact with water would have happened ~1m40s later (if still at FL350 when entered)

- time predicted for impact: 02:14:31, that's 6 seconds off from when transmissions ceased. Very close.
 
Old 5th Apr 2011, 12:07
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Originally Posted by ZeeDoktor
@takata: Let's look at what we know.
- The last position received was at 02:10:34. That's 20 seconds after the AP switched off and problems obviously had begun.
- At 02:12:51, ADR disagree triggered, with concurrent loss of AOA protection

- Assuming they had taken evasive action shortly after 02:10:34 by initiating a left turn, they would now (~2.5 minutes later, at 02:12:51) be just about overhead where the wreckage was found and would probably be just about coming out of the left hand course reversal

- Enter a deep stall / flat spin at that point, facilitated by lack of AOA protection, pitch and power flying in turbulent conditions in a turn

- Assuming ~350ft/s descent rate in flat spin, impact with water would have happened ~1m40s later (if still at FL350 when entered)

- time predicted for impact: 02:14:31, that's 6 seconds off from when transmissions ceased. Very close.
My understanding is that the system switched to "Alternate law 2" from the begining at 02.10. Then, "AOA protection" was lost from the start of the sequence anyway.

Why would they initiate such an "evasive action" at 02.10 while they had to keep flying "pitch and thrust"?... this would not be very smart without a real need to do so. During all the similar sequences documented so far (more than 36), not a single crew did take such an initiative to make an "evasive action" only due to unreliable airspeed data.

Nothing is telling us for sure that the aircraft impacted at the end of the ACARs transmition (02.15). In fact, without engine power, no more ACARs would be sent anyway.
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Old 5th Apr 2011, 12:31
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Only alpha floor is lost in alternate law 2. AOA is still monitored and protection now applies to stall speed rather than AOA. Protection is lost only if VSG1 can no longer be calculated (which I think was not the case, happens when slat/flap information is not available and GWT is no longer known), or when dual ADR fail or disagree is triggered.

In our case, it looks as if at least stall protection was available until ADR disagree triggered.

I agree evasive action in the form of a turnaround is virtually unheard of (in fact it's usually discouraged for reasons we can discuss in another thread). But we don't know what picture was painted on the radar. Nor what went on with the aircraft, maybe a something evolved that prompted them to return to the nearest landing opportunity which would have been behind them (I think?)
 
Old 5th Apr 2011, 12:35
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At first, I would like to thank you all for this really interesting thread !

After reading your posts I was thinking of an unrecovered spin as there is not much distance between LKP and crash site.

But ZeeDoktor did the maths and found 350ft/s... Not likely to be a spin...
That makes it 21.000ft/min almost a 200kt vertical speed (free-fall?). What about the fact that BEA hypothesis is a close to horizontal water contact.

I have further questions some people following this thread might answer :

What are the consequences of a high speed stall ? On a swept back wing ?

My guess are : First you lose altitude then static pressure rise and compressability effects are weaker.
Assuming this, would the airfoil recover lift by itself after a high speed stall ?

What if only one wing enters a high speed stall ? Self destruction might be more likely than spin at that speed isn't it ?
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Old 5th Apr 2011, 12:53
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Originally Posted by ZeeDoktor
Only alpha floor is lost in alternate law 2. AOA is still monitored and protection now applies to stall speed rather than AOA. Protection is lost only if VSG1 can no longer be calculated (which I think was not the case, happens when slat/flap information is not available and GWT is no longer known), or when dual ADR fail or disagree is triggered.

In our case, it looks as if at least stall protection was available until ADR disagree triggered.

I agree evasive action in the form of a turnaround is virtually unheard of (in fact it's usually discouraged for reasons we can discuss in another thread). But we don't know what picture was painted on the radar. Nor what went on with the aircraft, maybe a something evolved that prompted them to return to the nearest landing opportunity which would have been behind them (I think?)
Well. but the late triggering of "ADR disagree" at 02.12 is obviously what caused ALT2, Autopilot OFF, Autothrust OFF, Rudder limiter control, etc. And this is what happend in the first place at 02.10 because of those Pitots reading errors... There is not so much possibility for the system to switch to ALT2 in any case.

The fact that this maintenance message was transmitted much later in the ACAR sequence doesn't mean that the system was not already in error before its maintenance time stamping or you'll have to find an explanation why ALT2 was already triggered at 02.10.

Last edited by takata; 5th Apr 2011 at 13:03.
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