CONF iture;
Agree, thank you for the catch and correction.

Sigh, going from memory isn't working as well as it used to.

are not valid. Flashes for 9s then is steady."

FBW design goals and aircraft performance
 

The following quote is taken from a document comparing B777 and A330 flight control design vis a vis aircraft performance limitations and pilot authority developed during the recent USAF tanker competition (emphasis is mine):

"The Airbus design allows the pilot to obtain, in a repeatable fashion, a consistent level of aircraft performance. However, the pilot may be prevented from obtaining maximum aircraft aerodynamic performance. The procedure for the CFIT escape maneuver in the Airbus aircraft as recommended by Airbus, is for the pilot to pull full back on the stick and apply TOGA thrust. Speed brakes if extended, will automatically retract. Control laws either stabilize the AOA at an optimum value or adjust pitch rate to obtain maximum allowed g. With the Airbus CFIT escape maneuver pilots can quickly and easily achieve a repeatable consistent level of performance allowed by the envelope limiting system. This ease of handling might, in certain cases, result in optimum CFIT escape performance, even though full aerodynamic performance may not be achieved. The argument can be made that pilot authority is limited in the “hard” design by the fact the pilot is prevented from exceeding the limits of the flight envelope. The Airbus design allows the pilot to rapidly obtain maximum allowed aircraft performance to avoid ground contact. However, the pilot is prevented from obtaining all possible aircraft aerodynamic performance. That last bit of available but not attainable performance may be all that is necessary to avoid ground contact."

For those so willing to cast doubt upon the flight crew you should give thought to the more likely event that they were trained to take specific actions on the assumption of control laws being in operation with valid inputs. The aircraft may well have betrayed the best intent and effort of the pilots in this circumstance.

Thanks to Chris and JD-EE

Trying to look at this through inexperience eyes, and with as little speculation as possible, another few questions:

ACARS Timings: are they accepted as mirroring the duration of the event?
(As in from first signs to or near impact - if any doubt - 'no')

If above is 'yes' then is it accepted the aircraft went very rapidly from normal flight to rapid descent?

Weather: is this ABSOLUTELY determined to be THE or merely a contributory factor?

The Aircraft:
As the commander has final authority for the safety of the aircraft - we have no indication of diversion or messages RECEIVED (or sent) regarding any such action. Regardless - is this in any way relevant to events? (That is IF a turn was implemented, or an intentional descent would this have ANY material bearing on events in terms of any contribution - or if it is a concurrent event demanded by the situation is it irrelevant to the outcome?)

Crew awareness: Assuming all crew alert - and weather a factor - is there any relevance to saying the crew 'should' have noticed via weather radar any anomolies, or were the general conditions not a factor of concern until 'too late'? (That is, there was no reason to be concerned and possibly no way to know what lay ahead?)

Finally: assuming rapid descent - again irrespective of the ACARS messages - if the pilots had a non respoding aircraft - there are obviously countless variations on the theme - but the question would seem to boil down to;

Is there a possibility or indication of 'loss of control'?

If control was lost or reduced - what is MORE responsible - mechanical action (by ice or any other damage) - or the Airbus computer system?

@ techgeek :

I'm not sure the statement you posted apply to an A330 under ALTN 2 FBW law ?

Furthermore, accepting the conclusion (based on hard evidence - floating debris analysis) that the aircraft impacted water with a high vertical speed and a low forward speed (i.e. stalled), what would a bit more performance have changed ? It's not a CFIT situation, as far as we know...

'BOAC, discussions here led me to believe it was standard practice for one of the cockpit crew to have his mask on so that if something went wrong with the air supply he'd still be alert enough to fix it.

{^_^}'

Is this a coded message pilot to pilot or can it be read literally ? The only alternative is that there is some scuttlebutt on what the rov's have seen ?

Where did you read that?

Hi,

Podrían haber encontrado las cajas negras del Air France que cayó al Atlántico en 2009 – RT

cuddieheadrigg,

Forgive me, but I can't help feeling as if we're being asked to take part in some kind of consumer survey by an organisation that has only a passing interest in the subject, that has insufficient time/inclination/ability to phrase all its questions with intelligible syntax, demands yes/no answers, and which may have an agenda it is unwilling to reveal.

Am I being uncharitable?

JD-EE,

Re "gentle descent unlikely": yes, admittedly I do occasionally lapse into tongue-in-cheek understatement.

@ HN39 : High vertical speed is from the BEA. Low forward speed is my interpretation of BEA's Report 2 data (*) + declarations following the wreckage found + photos showing a relatively intact frame (compared to SW111).

(*)Am I misleaded, here ? Any other reasonnable interpretation I cannot see ?

- - - - - -

@ techgeek : After checking : g protection still in effect in ALTN 2 law, so you're right, then. :)
I still can't see that (correct) info as relevant to AF447, though.

Was the A330 actually certified for the flight plan it filed?
 

It seems based on the first BEA report that at FL350 the temperatures were EXPECTED to be lower than. -40C and there is nothing unusual about that I assume, yet according to Appendix 4 of the second (interim) report this was the very limit of the Certification of the Pitot tubes.

So, if the pitot tubes are not certified below -40C, then how can the A330 be, or are we just relying on "Ice will not be a problem below -40C" ?

After all the previous examples of Incorrect Airspeed, below -40C, why did we have to wait for this loss before recommending that the certification needed adjusting to encompass what is after-all a fairly routine temperature range?

Chris Scott:
Forgive me, but I can't help feeling as if we're being asked to take part in some kind of consumer survey by an organisation that has only a passing interest in the subject, that has insufficient time/inclination/ability to phrase all its questions with intelligible syntax, demands yes/no answers, and which may have an agenda it is unwilling to reveal.

Am I being uncharitable?

I would say so.

I've actually followed all these threads for a long time - I have not added to them as I have nothing to input - but as the threads expand, it becomes difficult to see any comments that are either not theorising, and are 'simple' to understand.

I shall try and put into words how the events appear to me (with no technical knowledge). I have no interest other than A: finding the various theories difficult to comprehend and B: being an occasional air traveler.

So: in terms I understand, you need lift and thrust to move an aircraft through the air. If either of these factors change or are lost then the aircraft will not fly correctly.

From reading and rereading the events seem to point to an incident which lasted a short period of time - indicating that the aircraft descended rapidly.

The ONLY relevance to the type (Airbus) that I can possibly see in terms of the accident is IF the computer shut down or operated in some way as to either stop or inhibit control inputs being corectly applied, or the computer sent the aircraft into a dive.

Otherwise, disregarding the weather, the only other possibilities are that the aircraft lost thrust - how? or it lost lift - how? - or - it lost one or a combination and did not descend as rapidly as may be believed, and ditched.

If the aircraft lost thrust it will descend rapidly even if full control is available elsewhere. If it breaks up midflight then it will plummet. If control is lost then it has to be exceptionally severe if thrust and minor controls cannot restore any form of controlled flight - so ultimately, the questions have to be - short of the aircraft being pitched down deliberately - if an aircraft stalls, and has diminished controls, is it really not possible to get some measure of control back in 30 odd thousand feet? Can weather totally disable an aircraft?

It seems otherwise, that it could in theory be anything from engine to system failure, or even fuel starvation. There are no posts which say, for instance 'if the computer failed then all control would be lost' (that I can find) - which may give a clue. All we know is it fell or flew from the sky.

Fair to say I left out an important point, particularly considering that on this forum, copilot and captain experience is frequently raised as a troubling issue for the current state of the airline industry. (See the Hudson River Landing, two experienced pilots did well in a tough situation ... the Buffalo crash / icing rather the inverse ... )

There was an old Aviation Safety Maxim that goes something like this:@cuddieheadrigg:
Probably not. I'd be careful in attempting to correlate too closely a text based maintenance message system (with a comparatively low baud rate) with a flight data system. You are asking for more than what that system is designed to give.

To give you some perspective: if the "wait in line" message interval is six seconds, a number of things can happen all at once (let's say four) and it takes 24 seconds to get all of the faults transmitted to the maintenance system. In the meantime the pilots have been busy dealing with malfunctions. For perspective: I could enter a training spin, let the aircraft spin for a few revolutions, and recover, in less than 24 seconds, (altitude reduced by a few thousand feet) when I was an instructor in T-34C's. I could also, in the same aircraft, in six seconds or less, be at the 90 (base) in the landing pattern, get into a skidded turn stall, and be dead on impact with the ground. A whole lot more than error messages would have gone on in the interim for both of the above events.
"Merely a contributory factor?" Weather is a contributory factor to a lot of what happens in flight, for fair and foul. You question makes zero sense as phrased.
That might be due to the CVR and FDR not having been found yet. Info from ACARS is intended to assist the maintenance crew in their trouble shooting and remedy of faults to some aircraft systems. Also, the protocol when flying, the iron rule of the sky, is Aviate, Navigate, Communicate. If and when things went all wrong, the last thing the crew is going to do is talk. They'll first address getting the plane flying, then getting on course/speed/altitude/route, etc, and then talk about it.
This question makes no sense. Increasing your Angle of Bank will change your stall margin, but people turn aircraft left and right every day with no ill effects. You can stall from straight and level flight, or in turning flight. I did both with some frequency as an instructor pilot. It was a controlled situation, however. What has become clear to me in this family of threads and posts, in re AF 447, is how difficult it is to handle a big passenger jet that has actually stalled, rather than approached stall, and how many thousands of feet it requires to recover from that stall, if recovery can be managed. It has been a real eye opener.
The reason weather radar is on modern transport aircraft is to allow a crew to avoid surprise, damage, and worse as a consequence of running into severe weather. How one uses that tool is a factor of training and practice. How one arrives at decisions based on info from the weather radar is a function of airmanship. "Should have" is a vague assessment, when lacking data. Numerous posts in AF 447 threads, and a few recently here, point out some of the nuances and limitations of weather radar.

People have keyed on weather as a contributing factor for a variety of reasons (see references to other posts on this topic about a pitot tube issue over the Pacific a few years ago) but the major reason is as follows: without significant phenomenon influencing AF 447, and given how well modern aircraft can be trimmed for level flight at altitude, and given the system redundancy designed into modern passenger aircraft, there is little rational reason for AF 447 to have done other than maintain altitude and course selected to eventually arrive in Paris. Something interrupted that, and given the weather in the area, and other flights using course deviations to avoid significant weather, that factor has been considered as a key to solving the mystery of AF 447's loss.
The aircraft hit the water. An aircraft in control most likely won't do that when the selected altitude is 35,000 or 37,000 feet. Between the pilots and the aircraft systems, being "in control" would avoid unintended water impact. How and why controlled flight was compromised is the great unanswered question of this crash.
The answers to that question are pending retrieval of the CVR and FDR. Attempting to attribute a major cause by guesswork (as has been going on in the various speculative posts in this extended discussion, including mine) has limited utility.

The facts available to date do not lend themselves to the terse summation you require without FDR and CVR confirmation.

I should also have mentioned: on the face of it weather, human factors (bad design, negligence, human error etc) an 'unforeseen circumstances' (which could be a combination of the above) always seem to factor highly in any accident, aviation or not.

Now, if weather alone was a primary cause in the case of AF447, then has avaiation been incredibly lucky, or did we see unknown weather in the area? If not, then surely logic will say that such events should be more common: how many windshear events have caused incidents at airports, even when known about? If similar weather events could cause total loss of conrtol then surely statistically there would be more cases even if the particular area sees less traffic? I don't know.

I also do not think crew incompetence or absence or whatever has much if anything to do with AF447 - but as we are told it did not break up in mid air, it really leaves only the options previously mentioned - which may or may not have much in common with the prevailing weather.

I am going to be a bit of a nitpicker here. The intent is to assist with understanding.

"If weather alone was a primary cause"

If weather alone was the cause, weather being the sole cause, then there is no resort to primary, secondary, or tertiary causes ... but I think that the way your framed that isn't the right lens through which to view this aviation accident.

For what it's worth, I have learned over the years to look at aviation mishaps and crashes as being shaped by contributing factors, some with greater weight than others, but all being linked together in combination to provide a combined cause for the effect, which is a crash or other mishap.

I invite you to consider the infamous Swiss Cheese model.

Colorado Firecamp - HFACS, the "Swiss cheese" model, Introduction

What you might be looking at is the issue of being necessary and or sufficient.

"Without the Wx as the trigger, would this mishap event chain have been broken?"

That is one way to look at it. Weather has been around us (and a hazard) since Orville and Wilbur took to the skies. How we mitigate the numerous risks that weather provides to the flying environment is one of many factors in flying safely. (You alluding to wind shear is a well placed example).

Quoting from HazelNuts from way back last August (hope he doesn't mind)

'So, based on the ACARS messages alone, the ROD in the final seconds could have been anywhere between 2463 and 16320 fpm, while the average ROD in the preceding descent was of the order of 7850 fpm: 35000 (2:10:10) - 2176 (2:14:21).

I also believe that the airplane probably stalled one or more times in those final minutes. Is it certain that it was stalled in the final seconds?

Quote:
some juggling of a flight termination time could give a v/s that fits with the BEA reports (high vertical speed, 'en ligne de vol', and 'arm 36 g' etc..).
The 320 ditched in the Hudson at 780 fpm, 125 kt, 9.5 deg pitch. Its fuselage received substantial damage but stayed in one piece.

The Turkish 737 in Amsterdam impacted stalled at 3000 fpm, 100 kt, 22 deg. pitch, its fuselage broke into three sections.

AF447's stall speed (Vs1g; V_alphamax) was 158 kCAS; 162 kTAS; 274 fps. The corresponding alphamax can be estimated as 14.5 degrees. Interpreting "avec une assiette positive, une faible inclinaison et avec une vitesse verticale importante" as 2.5 degrees nose-up, leaves an FPA of 12 deg. down, or 3418 fpm.

So was it stalled?'

Based on straightforward kinematics, an impact at 20000m from LKP within 300 seconds assuming constant ROD gives an average ground speed of about 140 kts, about 65 kts vertically, flight path angle -26 degrees, average speed about 170 kts and with linear deceleration gives a starting speed of 340 knots.

Are these figures that unlikely ?

Agreed, and not unreasonable too, but not a fact,

Lonewolf

Many thanks, that is a superb link.

Also, thanks for the input to the questions I put. I think in retrospect they are all 'worse' than speculating that the Captain was on the lavatory or whatever. Your answers actually highlight the speculative nature of the questions, even if they 'demand' yes or no answers.

I think, as you mention, with a combination of events almost always to blame for such things, it may well be something no one has thought of is in the mix somewhere, rather than one 'key'.

My thoughts too, since Svarin pointed out the WRG: WRN: difference

About stalling, generally speaking
 

Since we're likely to get into this again and again, a few words on stalling (apologies to all those for whom the following contains nothing they don't already know, several elements having been posted earlier).

One way to stall an airplane is to gradually reduce airspeed at approximately 1g. The speed at which the airplane then stalls is called the 1g-stall speed, or Vs1g. In the conditions of AF447, such deceleration would take of the order of 1.5 - 2 minutes. When the load factor is greater than 1g, the airplane stalls at a higher speed. That is because stall is not solely a function of speed, but occurs when the airplane exceeds a certain angle of attack, AoA, or alpha.

For the A330, alphamax is an AoA slightly below the AoA at which the airplane stalls aerodynamically, as illustrated schematically in FCOM 1.27.20. It is the highest AoA that can be obtained in normal law by gradually pulling the sidestick fully back and keeping it there. Thus it defines the minimum steady flight speed obtainable with this airplane, variously referred to as V_alphamax or Vs1g. At high altitude alpha-max corresponds to the onset of perceptible buffet.

Loadfactors greater than 1 can result from control inputs (maneuvers such as pull-ups or turns), gust encounters, or a combination of both. This graph shows the relation between between alpha, load factor and gust velocity for a rigid body encountering a sharp-edged gust. Real-life gusts cannot be sharp-edged, but are always surrounded by a mixing zone that 'softens the blow'. Other attenuating factors are structural flexibility, unsteady aerodynamics, and longitudinal stability, all not taken into account in this graph. Per regulation, the highest discrete gust velocity assumed in the design of the structure at this altitude is about 60 ft/s TAS.

Finally, it should be said that a stall is a temporarily uncontrolled, but usually recoverable condition, provided the pilot recognizes it and takes the right actions. The stall is identified by buffet of increasing intensity, usually becoming so intense that, in regulatory language, it is an effective deterrent to further reduction of speed or increase of load factor. To 'unstall' the airplane, the AoA must be reduced below that at which it stalls.

All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.

Funny how you ask a few questions and something pops up that seems to make a little sense: IE - normally speaking, one would expect an aircraft to avoid weather likely to be very uncomfortable or dangerous.

Any issue with the aircraft resulting in a flight proflle that is not ideal would only incease any risk from bad weather - irrespective if the issue cropped up before or during the worst of the weather - BUT if the weather 'alone' was not enough to be the decisive influence without any other problem, then any potential issue arising independently or because of (Turbulence) would certainly explain subsequent events.

Out of interest, if icing is a potential cause of the airspeed inconstencies is it equally possible a wiring fault could casue the same thing?

Looking at a whole, it seems more plausible than some of the other ACARS messages since some appear unrelated (directly) to having problems with the pitots and probes - or perhaps that was the cause alongside a seperate fault unrelated?

AF447
 

Maybe a much more useful device - inview of the fact that the earth is 72% water - would be a CVR that was stored in the top of the fuselage above the passenger cabin that ejects on contact with water and maybe with a pressure sensor after a certain depth - bright orange flashing strobes and powered by sunlight, floats to the surface for retrieval by rescue units. (too simple?) PE

paul
you have a vivid imagination
keep taking the pills

Just for clarification, would you say that it is unlikely that the airplane stalled at all, or that it is unlikely that the airplane BOTH stalled AND remained that way to the surface?

It seems to me, unencumbered as I am by much knowledge of Airbus FCL, that it isn't surprising at all for an airplane with unreliable airspeed information in rather rough weather to reach a critical AOA.

From that point, however, no plausible explanation as to how the aircraft reached it's present position has presented itself (to me), even after several hundred pages of more-or-less educated speculation. :confused:

It won't descent more rapidly than usual as most of the time engines are kept to idle for normal operation descents.


Would you futher elaborate ... ?

The point I was trying to make (or be corrected on) is does it seem plausible that the a/c went from A to B without the need to deviate off course to make the sums work. Since the opinion seems to be that the engines were producing thrust, that the a/c remained structurally intact and that a turning manoeuvre would be avoided in the circumstances, was hoping to establish that such was possible without 'hand of God' stuff.

On another point, is it confirmed on the 'WRG: WRN' definition ? 'Wiring' seems and odd way to express a connectivity fault which could be a connector or board coming away from a backplane.

For Hazelnuts:

You raise a couple of questions:

1) Could stall buffet be mistaken for turbulence associated with a CB? :confused: If so, how long would it take an aircrew to realize "Hey, this is a stall, not heavy turbulence" and begin to initiate corrective action?

2) What if, worst case, crew is riding/fighting buffet for quite a while ("Blast it, we are in the storm, it's really rough!") not realizing they are stalled ... due to A/S input being unreliable ... you then arrive at an altitude where the A/S input (pitot tubes no longer iced?????) gets sorted out and crew need X seconds to recognize "Hey, that ain't turbulence, we are stalled!" and get on with corrective action ... (this recalls to mind a post over a year ago about stall training, not sure who posted it)
OK, with that in mind, and the above as a possible way events play out, a stalled A330 typically falls at what rate? What you suggest is that with a high rate of descent, instrument conditions, and a crew playing catch up to a stalled heavy, by the time of stall recovery, Rate of Descent and altitude at time of recovery were insufficient to avoid water impact ... or,

crew had to do a recovery from unusual attitude as well as stall recovery, so by the time they were able to recover, get level, and try to arrest rate of descent ... water impact occurred.

Is that what you had in mind when you suggested that the aircraft did not remain stalled all the way down to the surface?

EDIT: I went back and finally found your post in the other thread, where you commented on "Flying the Big Jets" and the vertical velocity figures of 9,000 to 14,000 fpm for a stalled heavy.

Not surprising perhaps, but 'maintain pitch and power' is designed to avoid that, and usually does.

Forward motion
 

In the second BEA report under the section on pathology, there is a statement that forty-three of the victims, spread between business class and the rear of the aircraft, had fractures to the spinal column, the thorax and the pelvis. Pelvic fracture is one of the classifications used by accident investigation pathologists (Naval Flight Injury Manual) to correlate the most serious injury sustained against deceleration and corresponds to a deceleration force in the range 100G to 200G. Interestingly, although thoracic injuries are mentioned, there is no mention of any facial or head injuries, normally associated with forward motion impacts, nor any reports of limb fractures - thoracic injuries are often attributed to forward collision, but could also be explained as a result of contact with seat arm rests during a vertical descent. Of course, the absence of any mention of head or facial injuries may be because the BEA just wanted to present the most significant injuries, or simply that they are refraining from a more detailed description until the final report. The alternative is that there were none, and the forward velocity was minimal.

In clear air, with visual references (including your PFD), I think so too.

At night, in or surrounded by turbulent CBs, it seems less straightforward and I imagine you could exceed your critical alpha. I still don't see how they get from stall onset to the bottom of the ocean, within spitting lateral distance of where they were in the flight levels, while impacting pancake-like (as opposed to some sort of dive). But that a stall occurred at some point does seem likely--at least plausible-- to me.

asc12: a thought on stall and directional control, if we go forwrad on the assumption that at some point aircraft was stalled.

When stalled in turbulent air, is there not the risk of asymmetric lift on the wings inducing a rolling moment? Once such a roll is begun, how does one stop it until the control surfaces are once again effective? (On some aircraft, maybe rudder opposite direction of roll, but that's type dependent, and may be limited to small/light aircraft).

This leads me to the attitude gyros (which feed the PFD) used in the A330: if your aircraft is not designed as an aerobatic machine, would you install a 3D gyro?

I ask because I flew a trainer that we used for VFR spin training and VFR aerobatics training. The attitude gyro typically tumbled, during spins and aerobatic flight, unlike the gyros in high performance jets that allowed "on instrument scan" aerobatic maneuvers (like a barrel roll) with no degradation to the gyro's ability to provide reliable attitude reference.

I have no idea how much 3-axis disturbance it would take to cause such havoc in the A330's attitude reference system, but if such disturbance occurred, that's one more difficult flying task to undertake, recovering from a 3 axis upset using a partial panel scan, that even when one is prepared can be difficult.

I don't envy the BEA and the various search parties their search problem before much was found, since establishing datum rested on assumption, rather than facts, regarding track over ground.

Quote from HN39:
All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.

Agreed. Perhaps I can chip-in to offer a few related observations I've been chewing over for a while, at risk of re-stating the obvious (or needing correction).

Prior to 0210z
(a) A/THR was supposed to be controlling speed, and may even have been used by the PF to slow the A/C to turbulence speed. Partial (subtle) loss of thrust seems unlikely, though not impossible.
(b) Alpha-Floor was available, looking at alpha (not speed), and its intervention would have generated warnings.
(c) AP was controlling the selected pressure-altitude: probably still FL350.

Between 02:10:00 and 02:10:59 (selected events – sequence unclear)
(1) Inconsistencies may be apparent on individual ASIs or between the 3 ASIs (although the relevant failure message later transmitted by ACARS would not have been displayed to the crew).
(2) Duty AP disconnects: either due to a system failure or a sidestick forced off-centre.
(3) A/THR disconnects: either due to a system falure or PF closing the throttle levers. If the former, Thrust-Lock would have maintained the N1 at time of disconnect.
(4) Flight controls degrade to Alternate Law (thought to be be ALTN 2). On both pilots' PFDs, therefore, speed protection bands and indices re-configure on ASIs, and "Speed Lim" flags appear; bank-angle protection marks on attitude indicators change to amber Xs.
(5) Alpha-Floor protection is lost (meaning the crew would have to order TOGA thrust for any stall recovery).

I think most of us believe that an upset sequence started between 0210z and 0211z, or very soon after: perhaps while the crew started to realise that they had no reliable speed indication, and were attempting to establish a thrust/pitch regime; perhaps due to severe vertical windshear during this change of modus-operandi. As I think HN39 has stated, the aeroplane would have taken a long time to slow down to the stall.

Prior to 0210z, it seems unlikely the speed would have fallen seriously except in the event that the crew were not monitoring AND all 3 pitot-heads iced-up in concert to produce false, but similar, over-readings. The latter seems implausible.

To sum up: it seems unlikely that the initial upset involved a stall.

Chris

Not mentioned for a while - but if initial problem was caused by icing - what about the effect of ice crystals on the engines, did they somehow "roll back" meaning level flight with "pitch and power" not an option? This phenomena still subject to research

Flights To Gather Data On Jet-Engine Core Icing | AVIATION WEEK

Lonewolf_50;

The purpose of my post was to dispel a few popular misperceptions about stalling. As to what did happen, I adopt PJ2's wise words that we simply have to wait for CVR and DFDR to tell us.

As to your first question: "Could stall buffet be mistaken for turbulence associated with a CB?", the stall buffet is preceded (in alternate law) by stall warning, a synthesized voice calling "STALL, STALL, STALL" that continues until the AoA is reduced below that at which it starts. I have no personal experience with stall buffet, but believe that it is unmistakably different from "turbulence associated with a CB". I am aware that the training syllabus of airline pilots does not expose them to anything beyond stall warning (simulators are not representative in that regime), but would expect that an experienced pilot is familiar with the turbulence encountered in CB's.

I do not have the quantitative data that you ask for in the remainder of your post. Some very rough estimates have been made many pages back in this thread.

I'm with you in the camp that agrees that the poop really left its pile (as you say, "the upset sequence started") at or after 0210. None of the available alternatives make sense-- really, including a stall. It's obviously shocking enough to all of us to have inspired this much discussion.

I guess I have always thought of severe turbulence as being the physical force instigating the upset, with recovery complicated by unreliable or unavailable airspeed information. With autothrottle set at turbulence penetration speed (or Mach?) the commanded thrust varying all over the place to cope with gusts, lateral shear, and vertical shear-- this seems like a phenomenally bad time to have to very suddenly "pitch and power" fly the plane... especially with temperature shears in my assumed CB affecting recorded Mach. But then it's hard to figure out how the plane got from penetration speed to stall speed (or even within, say, 50kts of stall speed) so fast.

I suppose I settle meekly back in to the "wait for the recorders" group. It's like we got every 10th page of a 100 page mystery.

Quote:

---

Lonewolf_50;

The purpose of my post was to dispel a few popular misperceptions about stalling. As to what did happen, I adopt PJ2's wise words that we simply have to wait for CVR and DFDR to tell us.

---

*tips cap* :)

Understood. If AoA detection/measurement is compromised (as it appears airspeed was was compromised) ... I'd need to understand the AoA system in the A330 before asking further questions on that. I'll see if I can find something on that.
My experience with stalls is from small aircraft, not heavies. Even when dealing with accelerated stall (happened twice, me not at controls) it does feel different from moderate clear air turbulence ... and as I avoided CB/thunderstorms like the plague, I've no "feel" for how that feels. Thunderstorm penetration wasn't an option.
Roger.
As above, I went back to an older thread where you cited "Flying the big jets" and am happy with the "9000-14000 fpm RoD" for a heavy. It at least puts a boundary on my question, which is good enough.

Thanks. :)

You gave a list of events that may have been contributory to what actually happened from 0210 and onwards. 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. 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??

Depending on how you interpret what could have caused what, the outcome could be completely different in each case.

During which time the Aircraft would travel a distance of roughly 10 - 15nm i.e. way beyond where it is supposed to have been found now.

On the other hand this would leave roughly 2,5 - 3 minutes for the descent to the sea which sounds quite plausible for a fully stalled A330 at cruise weight.

That is the mysterious part about it: why would they let it get into a fully developped stall. In an Aircraft of the momentum and mass of the A330 going from normal flight via incipeint stall to fully developped stall is unlikely to happen in a fracture of a second.
At least in straight and level flight this process takes time.
And leaves time to react.
(we are not talking about a Cessna here)

I strongly tend to agree.
Given the fact that it took overall 5 minutes and brought the plane effectively ~6nm down and ~5nm forward from LKP, I strongly tend to agree.
In a straight line this amounts to ~8nm in 5 mins which equates to net ~100kts if it were to go down in a straight line starting at 2:10 at LKP.
Impossible in an airliner where both min horizontal (~350kts at 35k going down to ~200kts at S/L) and min vertical speed (~200kts at 35k going down to ~140kts at S/L) alone are much higher. This simplification even ignores the fact that it started probably at ~450kts at LKP, so the net average speed towards the end would have to be even lower.

My conclusion: The way down must have been significantly more complex.
A multi stall scenario seems more likely.

I still see the possibility of certain decelleration following the loss of Airspeed Information followed by an accelerated stall e.g. due to vertical gusts leading to a massive wing drop as a potential entry scenario into the disaster.

Lonewolf_50;

I believe pre-stall buffet at high altitude is (at least in part) a cyclic phenomenon. The airflow becomes locally supersonic in the 'peaky' part of the pressure distribution on the upper surface of the wing, shock waves form, causing (local) separation of the boundary layer, that changes the pressure distribution, causing the shock wave to move , and so on.

For my taste these figures seem a tad too low for an A330 @210t.

Light GA Aircraft usually spin at a vertical rate constantly surprisingly close to 6000ft/min. You can see that in most accident reports of NTSB where a light GA Aircraft spun to the ground.

Wing loading of these tends to be around 100kg/sqm.
Drag rises roughly to the square of the speed.
so 4 times the wing loading should give very roughly twice the RoD. Looking at the TU154 we find that it had a wing loading of ~400 kg/sqm. RoD prior to impact given by the accident report was ~12000 ft/min. So exactly as could be expected.
In our given case the A330 had a wing loading of ~580 kg/sqm. That would result in ~14500 ft/min at S/L and ~20000 ft/min at altitude.

CNN: Missing tail section found