henra: thanks. :ok: ~15-20,000 fpm.

I suppose I ought to do the stubby pencil math and see how that fits in with BEA's estimated g-loads at impact.

The Recorders to Provide the details
 

“Lets wait until the recorders are recovered. Then we will know.” That statement has been made ad nauseum during this thread, and the original one.

I fear however this may not be the case.

I do agree, the recorders will provide information which will help determine the reason(s) and provide the cause(s). PROVIDED they are readable after two years at a deep submerged depth. That is a big question. Another, and more important, if they are readable, that the actual true information discovered is provided, and not altered as has been suspected in past accidents. I share the stated concern of others, and I am not comfortable with the sole custody of the recorders being granted to the BEA, who have a vested interest in the outcome of the investigation. Two French Companies and the French Government to name but three will no doubt be a great temptation to mold the cause. There seems to be a protocol being established now which prohibits any other party or government, other than the BEA, from obtaining and controlling any and all recovered info from the crash site. I don’t know if this is good or not given the results of previous investigations.

And how exactly would the pilots notice stall-related buffeting if the plane was already in the middle of major turbulence?

With all protections off could you fly it ?
 

A question from a non-pilot. Given that at some time near 2:10 the aircraft was trimmed and at an appropriate speed and altitude, and that at some time around about 2:15 the a/c was in 'line of flight' with low forward speed and high ROD but more or less level and engines at idle, is there any plausible configuration of the aircraft with limited roll excursion and plausible constant pitch angle (say less than 25 degrees) which if held which would execute the dynamics ?

If you have to invoke a multi-episode history with interludes of dramatic energy loss but with (almost) recovery of attitude at the end, the permutations must run wild. If you have to assume a turn, then the plausibility of that action in the circumstances, and the cruelty of fate which left the a/c in an ambiguous location must be accepted. If the sequence started somewhat later then the timeline gets even yet more demanding.

Quote from mm43:
A caution regarding the A/P and A/THR; an ACARS warning is not generated each time they suffer a manual disconnection. The warning is due to an automatic disconnection due to their operating parameters having been exceeded.

Your first sentence is correct. But my understanding (and experience on the A320) is that knocking the sidestick (possibly accidentally) produces the AP disconnect warning, and closing the throttles in A/THR produces the A/THR disconnect warning.

Quote:
There is one non F/Ctl warning timestamped at 0210, i.e. FCPC2 (2CE) WRG: ADIRU 1 BUS ADR1-2 TO FCPC2,HARD which is a systems warning, but we also have PROBE-PITOT 1X2 / 2X3 / 1X3 (9DA),HARD. What came first, the chicken or the egg??

I saw your discussion on wiring earlier, but haven't got my head around the implications yet. Are you suggesting that the ASIs might not have been giving erroneous indications? If they were, my argument stands; if there's doubt in that area, I'll need to review part of my argument. Please advise, mm43.

Wouldn't you need to know exactly how deep was the penetration of the sea surface? Have we any information on 'compliance' at water surfaces in these cases.

=================

Whilst we can postulate a few descent profiles, that seem to fit, there surely are too many unknown still to bother with more than say 2 or 3 basic likelihoods. Must say though, that a deliberate turn or serious wing-drop (with recovery in the same sense, being the easiest thing to do) does seem part of the picture

Quote from Mr Optimistic:
Given that at some time near 2:10 the aircraft was trimmed and at an appropriate speed and altitude, and that at some time around about 2:15 the a/c was in 'line of flight' with low forward speed and high ROD but more or less level and engines at idle, is there any plausible configuration of the aircraft with limited roll excursion and plausible constant pitch angle (say less than 25 degrees) which if held which would execute the dynamics ?

I'm inclined to think that a considerable turn or turns must have been involved, particularly in view of the alleged proximity of the debris field to the LKP. Don't follow why you stipulate a constant pitch angle, though.

Lonewolf 50
There was a briefing given to the Royal Aero Society by Boeing Chief Test Pilot Capt. Frank Santoni regarding progress in certification programs for Boeing 748 and 787.
It is an hour long briefing and for you television addicts-contains no video :p but some very interesting audio. Among the topics discussed was stall testing of these aircraft. I have not re-listened to the briefing, but I recall the description of testing the stall characteristics of these aircraft. From my recollection, he described stall behavior of these aircraft as a low frequency vibration with increasing motion on the flight deck until it reached the point that was mandatory that the crew be strapped in or else they would be thrown from their seats. This type behavior would likely be also relevant to the A332.
Boeing Flight Test Update on the 747-8 and 787 | Aero Society Channel | The Royal Aeronautical Society

Agreed. One other point that came to mind was that they located the wreckage after about a week. The original estimate was, I think 16 weeks.

This suggests they found it nearish their starting point.

I would have assumed they would start south, since that was the "red" (most likely) area in both their "everything taken account of" search area (fig #32) and their "everything except ping-only searches taken account of" search area (fig #33) (to paraphrase somewhat inaccurately).

I would assume that only once you had finished there, would you search the area north, since (a) that area had already been searched (albeit "ping-only") and (b) it would only be necessary to go there if both pingers had not activated AND nothing turned up in the south.

However mm43 noted this a while back:
So if that's right, again suggests possibly in the north?

Occam's razor: they might not have realised it was active the first time (or publicly available enough), and so disabled it this time (because they want to keep the location secret)? ie a simple oversight?

sensor_validation;
If for any reason the engines rolled back, level flight is not possible, but forward flight is, and at the same airspeed as before or, more likely a slower, gliding speed. The A330 glides extremely well, far better than any Cessna, (but at a lot faster speed in the glide - best L/D for the A330 at 205T would have been about 245kts), and a heavier aircraft glides further than a light aircraft and takes longer to get down. A glide from FL350 to sea level with no engine power would take about 20 - 25 minutes and cover from 80 to 120nm depending upon weight, wind and some other factors. For comparison, under idle thrust, 30 - 35 minutes, 110 to 150nm to lose 35,000ft. The shorter distance with engine failure is due in part to the large windmilling frontal surfaces presented to the airflow by the N1's.

With dual engine failure you still have pitch of course so you have speed control, (governed, really, by AoA). The QRH Unreliable airspeed drill has the pitch-for-airspeed tables, and the QRH Dual Engine Failure (With Fuel) has airspeed to glide at. The ditching would be done with Config FULL, if available, (windmilling engines will power the hydraulics to some extent) and gear up and, as Sully showed us all, could be survivable under the right conditions.

I'm pretty sure this didn't occur and have written what I thought happened, but the recorders may mock us all...

wes_wall;

Regarding altering the SSFDR and SSCVR to suit certain interests, can you describe for me how that could be done and how it would avoid detection by those who do flight data analysis and sound spectrometry in their sleep? Thanks.

Are you still uncertain as to the approximate location of the debris? The plan was to work north to south across the area not searched in Phase 2/3 that is within the 20nm radius, then to proceed outward, as required. I believe Metron Figure 33 is the appropriate reference, as there are sufficient reasons to discount the pingers (produce a weak signal at high frequency, obscured by debris or mud, etc.), searching the remaining north sector doesn't take a long time (2 weeks?) and they would then be better positioned to expand the search south, without having to run north, again.

In any case, the BEA has drawn a nice picture of the approximate location (last page, below), in the abyssal plain to the north and west of LKP, and they said that the debris field was within this (dark blue) area; though their arrow identifies the abyssal plain, not the wreck within it.

http://www.bea.aero/fr/enquetes/vol....4avril2011.pdf

No, not uncertain - just responding to a question. I think it is north, slats11 said he originally thought more likely to south - just setting out some of my reasoning & the assumptions on which it is based. (Trying to keep an open mind.)

Makes sense; thanks.

One other thing I had missed until now (and I don't recall seeing it in the thread already) -- look at the sonar image in the BEA 4/4 report (p2):

http://i.imgur.com/qFkfv.png

The red arrow at the top points north. I'm no expert on sidescan sonar, but doesn't it look like the wreckage & the debris field runs approximately along the east/west axis?

Would correlate with being left of planned course - but I suppose there may well be little correlation between final resting orientation and orientation at impact for such a deep descent?

Thats mighty generous auraflyer. While not suggesting a conspiracy, I certainly don't believe many things have been left to chance in this whole process.

At one level I can understand not disclosing the location right now. It would inevitably promote more speculation about what caused the crash - while such speculation is happening anyway, I can appreciate they have no desire to encourage it. It would almost certainly generate criticism of the previous search efforts if they were seen to be fairly wide of the mark (yes such criticism would be unwarrented and would be ignorant of the substantial difficulties involved, but we all know that such criticism would be forthcoming).

I hope that this is the only reason, and that there are not other agendas at play. I believe we should give the authorities the benefit of the doubt that justice is being done. Equally, those authorities need to be realistic and understand that justice also has to be seen to be done. Fairly or unfairly, there are already plenty of questions being asked about many aspects of this investigation. Against that background, the authorities need to appreciate that the lack of of communication and insufficient transparency do not help this cause.

And I am still not convinced about the location. On balance, I suspect the graphic produced is honest. But the language used is loose enough to be ambiguous - possibly deliberately so.

Agreed, that is the correct interpretation. At this resolution, I can't tell which end of the field has the heavy parts, but it looks like the eastern side.

Some of the distribution of debris will be caused by scattering of the parts at the surface from the initial impact, and some (I think more) by the differential drift of heavy and light parts as they descend in the water column. [By heavy/light, I am simplifying by combining the effects of submerged weight and drag.] IF the A/C had low forward speed at impact (I'm not proposing a theory, just using as an example what I take to be the prevailing one), then I would be ( am prepared to be?) surprised if parts were scattered more than 100-200m before sinking. I think the E-W spread says more about the current than about the direction of travel at impact.

wes_wall,

As part of a post wherein you expressed doubt as to the objectivity of the BEA, you said the BEA has "a vested interest in the outcome".

Can you explain what you meant?

Just a minor point but actually for a ditching with all engines flameout, the QRH procedure is to limit the selection to FLAP 1 only. It must be something to make sure that the limited hydraulic capacity is dedicated to the main flight controls, even if at this point the electrical hydraulic pumps could be running as well thanks to the APU and the RAT would be extented.

Blame?
 

It's a nominally French airplane flown by a nominally French airline certified and investigated by a French authority, with nominally French pitot probes that are suspect..

Who would they blame - Brazil?

No, I don't expect a coverup.

Ice
 

Is it possible that the failed pitot tubes where actually a symptom of what was going on and not the cause of the crash? If the pitot tubes were coated in ice would it be possible for other parts of the A330 to be coated in ice as well, causing the flight upset (stall?)?

WRG
 

I had doubts about that definition of WRG, and PJ2 negated it, but perhaps too politely, losing impact. On 12 Apr at 14:09 he wrote that WRG means the fault is not correlated by another computer of the FWS.

This does not make it a wiring fault, although that's a possibility. It was much more likely an issue with erratic airspeed being captured at slightly different times by two computers.

Mr. Optomistic - you have me scratching my head. I'm not and never have been a pilot. (Near Mr. Magoo eyes pretty much guaranteed that. But I could focus on 1 mil gold wires on integrated circuits just fine.)

Seriously, discussions in this forum and one of its predecessors has led me to believe that one of the people in the cockpit is supposed to have his mask on at all times. Is that an incorrect understanding on my part?

JD-EE;

Going from memory as it was a long time ago...in Canada and I believe the US, if one crew member left the cockpit while the aircraft was cruising at 410, the remaining crew member was required to don his mask. Above 410 one crew member had to wear his mask at all times. Below 410 there was no requirement to wear the mask under normal operations.

Hope this helps.

Lonewolf 50, your finding the drop rate of a stalled airliner raised a DUH factor in me.

If I remember the BEA report it heavily implied more vertical component than horizontal to the oceanic impact as deduced from damaged elements to which they had access.

We're talking of 100 to 150 MPH fall rate. Therefore the plane was not in anything close to a flying status when it hit. It may have had some forward velocity, but it would have been well below any known stall speed unless surface winds were hurricane force.

If the plane was NOT stalled it's vertical velocity would have had to be on the order of 200MPH to be noticeable as an effect on the wreckage, I suspect.

Sometimes units translations help. It didn't really dawn on me what speeds were likely involved until I made that translation.

I also got to thinking that the plane was making headway on the order of 4 to 5 miles per minute. In a little over 4 minutes it could not be much further from LKP than 10 miles if it also had to traverse the vertical distance as well. The BEA must have been out of its mind to search way out where it invested so much time and money.

I much admired Hazlenut's description of stalls. With nearly all training now being done on simulators few airline pilots ever experience genuine stalls, or even the approach to the stall on the types for which they are qualified. I am now retired but used to be a training captain on VC10s (T-tailed), 707s and 747s, and did C of A test flights on all 3 types.

The stalls both in training and on C of A flights were always, wings level, slow deceleration (1kt/sec) to the 1G stall (or stick push in the case of the VC10). I have no experience of stalls in banked flight, or accelerated stalls when pulling G. The aerodynamic buffet in all cases was distinct from the turbulence felt in clear air near jet streams and from the turbulence in the vicinity of thunderstorms.

The 747 was an interesting case since the stall speed clean was defined by the maximum acceptable buffet, D P Davies describes it as a violent vertical bounce, sometimes with a lateral component. To the best of my knowledge the 747 has not been stalled in the clean configuration. In each of the flaps down configurations the stalls were immaculate with good natural buffet, good controllability and a good margin between the buffet and the 1G break, followed by a classic nose drop.

The VC10, being a T-tail aircraft, required a stick shaker and stick pusher, and on C of A flights was always fitted with an incidence meter above the coaming. If the stick push had not occurred before 14deg incidence you pushed like mad!

I relate all this because of the discussion in previous posts about whether the pilots could have distinguished between pre stall buffet and the turbulence associated with thunderstorms. I think the answer is in most cases 'yes', the two are distinguishable. However, in heavy turbulence it is highly probable that the pre stall buffet would be 'lost' in the general ambient turbulence. And in really heavy turbulence one's brains feel rather 'scrambled' which would make it even more difficult! In which case it is quite possible that the pilots on AF447 would not have been able to discern the pre stall buffet.

Bergerie1, thank you for an enlightening contribution. I haven't stalled a transport category aircraft but have done so in a D - level simulator which is required to replicate the behaviour of the aircraft (in a stall) as part of its certification.

During discussions, stall and high speed buffet came up. I would be interested in hearing if you believe it is possible to differentiate between high speed buffet and low speed buffet at cruise altitude. The question came up as the enquiry into "coffin corner" arose, (in the analysis it was determined that the aircraft was a long way from either boundary).

PJ2
I have only once been to the aerodynamic ceiling and that was on a VC10. I was young co-pilot at the time and the training captain took it up to 46,000ft. Where he demonstrated the low speed buffet and the high speed buffet and I was permitted to do so too. There was about 5kts between the two. As I remember, the high speed buffet was of a sharper quality and at a slightly higher frequency - but memory does play tricks. I also suspect that each aircraft would exhibit slightly different qualities. For example, the heavy low frequency vertical motion of the 747 clean is quite different to the VC10 and 707.

Perhaps some of our test pilot colleagues could enlighten us on the stall characteristcs of different types under different conditions.

I quote from the 2nd BEA report:

"The reappearance of the flight directors on the PFD when two air speeds will
be calculated that can lead the crew to rapidly engage the autopilot. However,
these speeds, though of the same order, can be erroneous and weak and thus
lead the autopilot to command movements of the flight control surfaces that
are inappropriate for the real speed of the airplane.
In case of automatic disconnection of the autothrust with activation of the
thrust lock function, the absence of appropriate manual adjustment of thrust
can present a risk of an attitude/thrust mismatch, especially when this
disconnection occurs with a low N1 value."

The same report, speaking of 13 cases of A330 airspeed anomalies:
"In seven cases, the autopilot was reconnected during the event. In two of
them, the re-connection occurred when the two speeds were consistent
with each other but were erroneous".

The A330 stall recovery procedure is to apply takeoff thrust and full aft stick, relying on the computer to maintain maximum allowable AOA. Without FBW, no pilot uses full aft stick to recover from a stall (this is usually reserved for entering a spin!). This practice is unique to an aircraft with FBW and essentially puts the pilot in a position of relying on the computer to prevent the stall (because the pilot's control input is actually trying to cause the stall). In this case, the computer may have been relying on airspeed and altitude data from 2 consistent but erroneous air data inputs and computed a maximum allowable AOA that corresponds to a lower altitude. This would be a higher AOA than should be allowed at FL350 and if full aft stick were applied would lead to a full stall. Depending on the aircraft's actual indications of a stall (something the pilots would not have experienced in training since the aircraft is "unstallable") and the fact that it was night in IMC and turbulence the crew may not have recognized the nature of the full stall and believed that the computer was preventing a full stall. I think this could have set up the situation of a deep straight-ahead stall all the way down. By the way - in the stall the drag is much higher than normal and lift much lower. This combination creates a very high sink rate, much higher than an idle power nose down descent from cruise. I think a rate of >10,000 fpm is very possible. Someone calculated a rate of 18,000 fpm from the reported information.

On the Pitots: Icing is assumed (with good reason) to be an issue - but thinking about it - if an aircraft enters extreme weather with massive changes in pressure, wind direction etc etc - is that a possibilty of giving 'erroneous' data to the aircraft from the pitots - IE the will correctly detect a large variation in one pitot, while another MIGHT get a differing reading - or simply that massive changes were read as an error, not the actual 'aispeed' changing vastly?

Is there any thought that the airpseed data was lost for the duration of the inceident?

I know it's a 'silly' question, just wondering if system failure or ice aside, a pitot system could be 'fooled' or more precisely the computer monitoring them could think that number changes beyond a given range is incorrect?

Who did the TWA800 investigation to avoid any cover-up? The Chinese? :ugh::ugh:

Wreck orientation
 

Looking at the sonar image in the BEA report there is, to my mind,
a large piece of wreckage in the north east of the debris field that is high enough to produce a sonar shadow. I would hazard a guess that it is the very front part of the fuselage.

Theres another scenario to consider then isn't there, that the aircraft was turning, perhaps they considered the best way out of a storm cell that they didn't know was there is the way they came in, a turning aircraft with the handling pilot trying to reduce speed that appears not to be whilst the aircraft is descending due to downdrafts may have been attempting to trade off speed to maintain some height, only speed is not reducing, with thrust at idle, nose attitude high, severe turbulence, and bank angle,(perhaps exaggerated by turbulence) how long to stall now?

Quote techgeek
What rubbish.
It is "stallable" in Alternate Law.
The stall warning (computer voiced STALL, STALL) is AOA generated, and a certain indication of the aircrafts AOA exceeding the stall AOA.
Techgeek, your previous post exposes your total lack of knowledge of the A330 flight control systems.

PJ2 and Bergerie1;

I believe that the aerodynamic 'mechanism' that I described in post #3447 is the same for high speed buffet and low speed buffet. The curves in the buffet boundary graph produced by mm43 a little while ago are continuous across the maximum at about M=0.82. That is even more apparent if you reduce these curves to a lift-coëfficient. Therefore I wouldn't expect a discontinuity in 'feel' across that maximum. EDIT: That said, it may well be that when looking at a range of Mach, say from .75 to .86, that the frequency content of buffet felt at the pilot's station changes with Mach.

Regards,
HN39

PS: The graph linked above combines in a continuous curve FCOM 3.01.20 Page 4: Buffet Boundary for 0.5<M<0.86 and Page 7: Stalling Speeds for 0.2<M<0.425 .

Certainly on a 737 high and low speed buffet are distinguishable as Bergerie1 says, but I would hesitate to guarantee that identification in a CB!

All this talk of descent rate and 'impact at 0215' - we do not know, do we? Until the FDR and CVR are (hopefully) read, we can 'surmise', but we don't know when impact occurred. If for any reason ACARS had stopped transmitting they could have been flying for a while!

Speculation, hypotheses, fine with me, as long as they make sense and open new perspectives on what might have happened. If they just go around in circles, repeating 'ad nauseam' what has been suggested many times before, it becomes somewhat boring.

Regards,
HN39

Indeed. As I set up two sides of the equation to get the units to match, I realized that I didn't have a figure for deceleration, and more explicitly, a time from V max to V zero. So I was dead in the water. (No pun intended).
Thanks. I'll have a listen to the link this weekend, over a coffee or two.
Many thanks.

techgeek, if I may critique your presentation:
If you stall, you have already exceeded max allowable AoA, yes?

If I am correct in understanding how pilots are trained, what you are calling stall recovery is actually recovery from approach to stall, then full power and Max Allowable AoA ... which will keep you from stalling, and get you out of near occasions of stall. ;)

Once you actually stall, you have to REDUCE AoA (or you will remain stalled) which probably can't be done with aft stick, unless you are flying inverted ... which I don't think you'll find people doing in the A330. ;)

You appear to have mixed and matched stall recovery and stall prevention.
Agreed, however, I don't think you are correctly interpreting what the procedure is to be applied to.
Stall prevention and stall recovery are not the same thing.

Do you see from the bolded bits why I think you are mixing apples and oranges?

More to the point, I disagree with your assertion that using max power and high (but not stalled) AoA is confined to FBW aircraft.

I used to teach a recovery from an approach turn stall (practiced at altitude, gear and flaps down) in which you deliberately enter a stall in a balanced turn, and you then ...

lower the nose (AoA) and level the wings
max power
raise nose to high AoA
eventually establish a rate of climb

I also used to do the following in the landing pattern to test stall prevention on safe for solo checks:

I'd hit the AoA test button briefly, to get the rudders to shake. In that training plane rudder shakers (like stick shakers in some commercial transport aircraft) was a warning of impending stall (AoA at about 26 units, stall typically at 29 units) . I would look for the following response (stall prevention): wings level, full power, climbing attitude ... with the idea being that if your approach to landing was close to stall, it was time to wave off (go around) and try again.

HazelNuts pointed out a few posts back that if AF 447 were stalled, the A330's robot voice would have been advising the pilots (with annoying repetition) that they had stalled. So my concern about "would they recognize the stall," and Bergerie1's point about what heavy turbulence might do to body senses, have already been answered by the aircraft's designers by using AoA to trigger "You are stalled!!!!" warnings in unambiguous terms. You'd think that stall recovery would begin with a move to reduce AoA, yes? The FDR's will hopefully tell us if that is true or not, in due course.
[/QUOTE]
You posit a flight crew putting the engines at idle and trying to maintain altitude with the stick. Why? If the engines are at idle due to a failure or ice or something, would not the crew be cued, and would not the crew maintain airspeed and in descent try to get the engines started again? I'd think that is covered in training, and as noted previously, this was not a rookie crew.

Your event chain leaves me scratching my head.

This is of great interest especially when you realize that no latter that last december, Airbus has published a RED Operating Engeneering Bulletin on that matter ...

CONFitureIs there reason to believe that AF 447 was operating at a low N1 value? :confused:

From the excerpt techgeek cited, my instinct was to presume (perhaps incorrectly) that the risks of this problem would tend to be greater during landing.

That said,

... thus lead the autopilot to command movements of the flight control surfaces that are inappropriate for the real speed of the airplane.

appears to be what Svarin was alluding to a few dozen posts back.

The prospect is scary, be ye pilot or be ye pax.

If at the time of the automatic disconnection of the autothrust with activation of the thrust lock function, the A/THR had lowered the EPR to reduce the speed to the selected mach for turbulence, it is possible that the N1 were in a lower range than usual for cruise.

*Click*

The lightbulb just went on.

Thanks. :)

force of 100 g-load`s
 

@Lonewolf and HarryMann

if you stopp a falling pelvis with a vertical speed of 15000 ft/min (15000*0,3/60 =75 m/sec) with a constant force of 100 g-load`s (100g=981m/sec²) it stopps to zerro after 75/981= 0,076 sec and a way of less than 3m !

water is nearly incompressible at this speed, (within 0,07 sec it can not move much to the side), it makes not realy a grate difference if you crash into concrete or water with 75m/sec !

and this very short stoppway is plausible:
ca. 3m will be the sum of the compressible space between the pelvis and the water, (the space under the seat, the airspace into the baggage compartment, and the construction space in the lower fuselage.....)

grity