447 Parted
 

Bearfoil et al
Surely the Fin/V.S. shows little sign of being ripped off sideways by aeroD forces but
lots of sign of departing by being inertially pulled off by suffering some kind of
massive whiplash ?
I dont quite understand what you are saying by, "radial forces"
I also dont follow the whereabouts or pertinence of your figure, "1.5G failure"
Thanks

OK. Now what is the explanation for the vertical load pick-up arm between the Rudder and the V/S failing at 36g with up/down shear forces and not radial ones?

http://i846.photobucket.com/albums/a...er-failure.png

IMHO the brick wall was not the 90 degree to line of flight one, but the one vertically below the line of flight, i.e. Terra Oceania. Any deformations to the left and forward of line of flight (at point of impact) are the result of small moments along those vectors that also suddenly accelerated to zero.

mm43

wilyflier

FAR 25- structural load/limit load @ 1.5 no deformation/failure.
Radial: Torsional

mm43

The Rudder is swept, and the corner of airfoil that failed loaded the mounting lug vertically as a result of its deformed ultimate plane. The pick up arm performs the function of a "strut", see above. That part of the Rudder "pushing" back on the airsteam is largest in area at the lowest lug.

"vertical" as I read the photo is the normal operating movement of the Rudder, relative to the Vertical Stabiliser, vertical as in "about" the horizontal aspect of the Hinge axis. The arm is meant to "spread" the energy at the pivot hinge, to take up some of the "vertical" stress of a deployed Rudder face. "Shear Cracks, Vertical", are indicative of the attachment's failure in its operating plane as well.

It serves to demonstrate an enormous load at the pivot, from a Rudder at some deployment in an airstream, in other words, I feel it is not impact related. We are looking at a Rudder pivot hinge destroyed by Rudder deployment beyond its limit load, i.e. aerodynamic failure.

When you say: "up and down" are you meaning "compression, tension"?
I suggest the vertical cracks in the pin's sheath at the thru-bolt are very consistent with an overloaded Rudder deflected to the right.

bear

Bearfoil, have it your way. NOW, duplicate the damage twisting to the side, eh?

It does not require severe acceleration if the tail of the plane is bent upwards. That produces a relatively speaking slow rip that pops the VS off. I am quite aware of how it is attached having seem cutaway diagrams and such. As you mention a simple sudden cessation of forward movement would not produce what is seen.

As one possible scenario, it looks like the tail cone broke off at its natural break point, the junction with the pressure vessel of the cabin. It was pushed upwards. This applied tremendous force to the trailing edge of the VS as the spar that holds the clevis joints which mount the tail is bent. The nose of the VS is held in place by the relatively strong pressure vessel. Where does the VS go? All that can happen is that you get tears approximately the same as what you see on photos of the plane. There is even a good reason for the front joint to retain part of the clevis. That's about where the spar would break anyway looking at the drawings.

Now, duplicate those tears with a sideways rip to the rear. They'll come out exactly backwards.

Methinks you are positing actions in the absence of and indeed directly contrary to the evidence, such as we have it.

{^_^}

I am relying heavily on AA 587's aerodynamic failure and loss of VS/Rudder. That occurred at less than 250 knots, ostensibly with control inputs. Considering 447 was travelling at nearly twice that speed with iffy control, well, let me say there is very little to go on, but I cannot think of a better witness to the tragic accident than a complete VS/Rudder. If it stayed with the a/c until impact, you are challenged with a two part explanation of its removal, a vertical impact, and a rebound. My surmise needs one explanation, I like the easy way, as did Occam.

Where did the rudder get the loading from? According to the BEA, when they had Airbus check the RTLU, it was found to be set at 7.9° +/- 0.1°, which is the limit in Normal Law at Mach 0.8 at FL350. The RTLU setting indicates that CAS was dropping at the time the switch to Alternate Law took place.

This means that CAS was 272 +/- 2 KTS, but we don't know what the OAT was, nor if the a/c was at its nominal M0.82, or as the CAS dropped, the A/THR was increasing that speed. So, are you proposing that overspeed could well be responsible for the V/S and Rudder damage? I would have expected to see trailing edge buffet damage if that was the case.

The Port Outer Spoiler was located north and east of most other debris, but that could well be because it was not affected by wind when in the water, and its drift represented the actual near surface current without any leeway component on account of windage.

mm43

mm43

I believe failure signatures on the Rudder hinges are due to aerodynamic loading, not impact with the sea. What is the Rudder Limit in Alt Law II?
It does not matter, as the stress on the Rudder needn't have been the result of it's angle relative to the VS. Severe Yaw is sufficient to fail the rudder's hinges, even with it centered.

I've often wondered why the Rudder's hingeing system is built (overbuilt), with such care. An aircraft can fly and land without a Rudder, it cannot fly at all without a Vertical Stabiliser. Such irony in AA587, the Rudder stayed attached, the VS came off. In the case of 587, if it was indeed FO's feet that snapped the life out of his a/c, a shame the Rudder hadn't fallen off, to leave the VS attached, and take them home.

Yes, I believe the Spoiler was lost before impact.

JD-EE

Sir, would you enlarge on your statement "Swatted the a/c out of the air"? I'm not getting it.

bear

The above extract (A330 items only) from http://www.andytracy.net/files/27FLTCTL.doc was the reason I mentioned the RTLU and its measured limit of 7.9° after recovery.

mm43

Bearfoil, I mean that in a literalist sense.

mm43 has performed excellent analysis indicating that the plane hit the water about where it was four minutes before it ceased ACARS transmissions. Actual indications are North West of that point by some modest amount - at right angles to the nominal flight path. The plane was traveling at a speed that requires 25 seconds at 1 g to bring it to a stop. That's a few miles to the North East of where it was when the troubles began.

What halted its forward velocity vector and pushed it North Westwards by a goodly amount? I don't know.

One scenario, presuming mm43's work is good, has the plane making a 180 degree turn starting slightly before that last position report just before everything turned to poop. They hit the water about where such a turn would have placed them had they
managed to complete it while rapidly losing altitude. That, of course, begs the question, "But why?"

Something applied an awful lot of energy to the plane if it simply made that last position report and then sank down to the water in a flat spin with or without a vertical stabilizer and rudder. I am not sure what could have done that. I could see such a loss of control, flat spin or spinless spin, and all that scenario if the ocean tracks of the wreckage traced back to a point further to the North East along the planned flight path. In fact that is a scenario I entertained and partially accepted until the estimates of the impact point based on found wreckage started coming in. Then I put two and two together. If the VS was ripped off in the air the pattern of the rip in the tabs that fit into the clevis joints would be quite different. Damage to the sides of the VS at the bottom would be different. So I had to discard the idea in the face of data.

I am left guessing. You've heard my best guess. You don't like it. *I* would take that as a personal challenge to put the entire body of knowledge we've generated on the wreck and figure out another working scenario. Sadly, I've pretty much used up my imagination. I'm not happy with that tail cone scenario. But, it does almost fit the data. - Plane comes down tail low. Tail hits the water and is pushed upwards and applies a sudden deceleration to the plane. This leads to a water-skier's belly-flop. (This is such as you see when his skis dig into the water for some reason. Vertical person becomes horizontal person rather quickly and forward motion ceases.) The push upwards is worst at the tail. That applies a fracture stress to the tabs as the VS leading and trailing edges are pushed upwards and forward relative to the spar. I figure this all took place at a low forward speed to begin with. And it might give an impression from the wreckage of having a flatter approach to the water than actually took place. (I romantically envision the crew desperately trying to gain enough air speed to restart stalled engines. Maybe they made it. But they were too low and clipped the water trying to climb out of their dive. My cynical side says, "Prove it.")

Maybe that embellishment gets across what I see in my mind's eye better.

We have precious little data. So selecting a scenario that violates any of the data we do know becomes highly risky. But scenarios that do fit it all are risky to one's sanity, I fear.

What stopped the plane in mid air within a very short distance and threw it to the left of its track a not inconsiderable distance?

added:
I'll stop here. If this description does not do the job then continued talking past each other is counter productive.

{^_^}

Lots of pointless deliberation hereabouts about the configuration/attitude etc of AF447 at impact. I'd suggest that it's fairly obvious that it spun in in a flat spin - and that airbrakes/speedbrakes/spoilers (at least) were deployed out of desperation. It's more productive to backtrack to why/how this accident happened..... particularly as they are unlikely to ever recover the DFDR (or CVR). The effort this month is in reality a nominal and token, yet enforced, one. It has only a very slim chance of any success.
.
from the post by Noelbaba (The Last Four Minutes Of Air France Flight 447 ). This exposition is a confused mish-mash - and if it has an authoritative sourcing, it is indicative of an attempt to muddy the waters with a welter of disinformation.
.
Three critical aspects mentioned, yet hidden away (and AFAIK) not yet commented upon indepth here on Pprune, still require logically derived answers:
QUES: 1. How does this falsely high reading of TAT affect the ADIRS speed-readouts/data inflows? (if at all) i.e. before considering the Thales pitots' complications?
2. Is it possible that the TAT sensor's heating can be overpowered by an accretion of supercooled ice crystals to the same extent as the Thales pitot heads' pitot heaters?
.
ANSWERS: (probably duff, but that's why I'm asking): -
Answer: 1. If the ADIRS TAT data inflow is falsely high then that (at a constant thrust and IAS) would generate a lower TAS, but that high temp wouldn't affect the IAS (which is after all what predicates the aerodynamic stall speed). "To hold a constant Mach Number (considering that temperature is decreasing and TAS increasing thus MN increasing) you would have to raise the nose (reduce your IAS/CAS) and increase your angle of attack to climb at a constant Mach Number/hence IAS decreases?"

Again, temperature has no effect. At a constant Mach Number climb, both CAS and EAS are reducing, and increasing Angle of Attack is required. The logical extrapolation of this is that if you maintained a climb at constant Mach Number, assuming that you had a lot of excess thrust, you would climb all the way to where the AoA went all the way to the stall. What you have to remember is that the Airspeed Indicator measures Impact Pressure, which is the total sum of Dynamic Pressure (related directly to EAS) and compressibility (related directly to Mach Number). It does not measure Density, which is related to Pressure and Temperature. In fact, all of the manometric instruments on the aircraft, the ASI, Mach-Meter, Altimeter, and VSI only sense Pressure. You, the pilot, have to apply Temperature to Pressure Height to find Density Height and True Altitude, and to CAS and/or Mach Number to find TAS.

During climb, with decreasing pressure, the aircraft must fly faster, i.e. a higher TAS, to achieve the same Impact Pressure, because you're at a constant CAS. This is so, even above the Tropopause where there is no change in temperature with change of Pressure Height (except in the case under consideration here). Because the aircraft is flying faster, compressibility increases, you are experiencing an increasing Mach Number. Note this - On a very hot day, your TAS will be higher due to the lower density AS WELL AS the lower Pressure, but this temperature factor puts you not one jot closer to the speed of sound, because at the higher temperature, the speed of sound (M1.0) is ALSO higher (but, however, NOT in the false TAT case). Thus, the 'hot day effect' of a higher TAS than that due to pressure change alone, has no effect upon Mach Number whatsoever...... but it WOULD HAVE for AF447.

Consider the formula for CAS calibration -

Vc = SQR ((Y/(Y-1)) * Po/Qc * [(Qc/Po+1) ^ ((Y-1)/Y)-1]) * SQR (2 Qc / Rho0)

Where –
Vc = Calibrated Airspeed in ft/sec,
Qc = Impact Pressure in Lb/ft^2,
Rho0 = Sea Level Air Density = .0023769 slugs/ft^3,
Po = Sea Level Air Pressure = 2116.2 Lb/ft^2,
Y = A constant for air = 1.4, being the ratio of the Specific Heat of Air at constant pressure to that at constant volume (Y = Gamma, I don’t have a Greek key-board)

The Left-most portion of the equation is the ‘f’ factor, the compressibility effect –

F = SQR ((Y/(Y-1)) * Po/Qc * [(Qc/Po+1) ^ ((Y-1)/Y)-1])

At altitude, the Static Pressure, P, is substituted for Po in the left-most radical.

Temperature does not even get a mention (except in establishing standard Sea Level Density for calibration purposes, and then it's a constant). However a falsely high temperature might induce the ADIRS to assume a lower thrust and/or TAS/Mach and so cause the autothrust to incrementally offset the (ADIRS) perceived under-performance. Net effect would be to cause AF447 to fly faster than "indicated" (to the pilots) - and thus, in TAS terms, even closer to the coffin corner envelope. You then only need the Thales pitot clog-up over time to create a coffin corner encounter (see theShadow's post at link http://www.pprune.org/rumours-news/3...ml#post5537109 for the outcome of that cumulative {over time} additive error). The conclusion is that a freeze-over of the TAT sensor would have put them, courtesy of the ADIRS, at a higher actual TAS. Usually the temperature isn't a factor or a consideration, except when it's a "phony" one.
.
Also, in this regard, the article claims fairly authoritatively that AF447 was heavy (i.e. cargo and pax-laden) so went early direct to best height (FL350) looking for optimum SFC (i.e. to "make" fuel and avoid any enroute drop-short of destination reserves requirements.). That in itself would have quite early put a heavy AF447 closer than normal to the upper RH edge of the operating envelope and that much closer to a Mach Crit encounter. The fact that they never reported "Level FL350" - but only read-back that final cleared height - may indicate that they levelled and soon thereafter accelerated straight into a compressibility encounter..... having already accumulated some of the icing-induced errors on climb.
____________________________________
Answer: 2. Once again depends (as theShadow points out with respect to the pitot heaters) upon the heating capacity of the sensor's protection. Having atmospheric precipitation freeze upon impact to form ice is quite a different thermal proposition in aviation to accumulating an agglomeration of already formed supercooled ice crystals over time during a relatively smooth cruise in Cirrostratus/Cirrocumulus. But in the Thales pitot head, by contrast, the tendency was to "collect" the ice crystals inside a tube and thus gradually (insidiously) clog the pneumatic flows and sensed pressures. An assumption can be made that a false high TAT (and consequent high undetected TAS), due to a thickening sensor ice-coating, was a possibility.
____________________________________
QUES: 3. I sorta beg to differ here - entirely. I agree with theShadow that the effect was in fact quite insidious and that all three pitot heads were affected simultaneously and thus never "differed" - (thus no alert to pilots and nil breach of triple redundancy disagreement rules as far as the ADIRS was concerned). See ASW article on the A346 double flame-out due to fuel computer programming: "THRICE ALMIGHTY, the Virtues of Triple Redundancy" (at link
Thrice Almighty - The Virtues of Triple Redundancy | Air Safety Week | Find Articles at BNET
________________________________- Over to others who may be better informed/educated.
.

May I remind the people that NASA used triple redundancy on the Apollo program, if no others. But they did not use three of the same computer. They used two IBM computers and one Rockwell International computer. That way if the code was bad in IBM it could still be good in the Rockwell computer, and of course the other way around holds true as well.

If the interface description is up to snuff for the computers there could and should be two different designs and a rule that both had to be in use on any given plane. And with CPUs being what they are TODAY any new design should feed all sensors to all computers through interfaces that don't fail if one of the computer input interfaces dies.

This sort of thing has been done before. NASA, if nobody else, has shown how.

I've run the failure analysis process looking for single point of failure events, I've used triple redundancy before. Specifically it is what keeps the GPS satellites on the "desired" frequency while on orbit despite Rb and Cs standard drift. And it should be noted that sometimes 'desired' is not nominal so that it's harder to plonk a missile down Jimmy Carter's toity when he was in the White House using GPS. (That was when it was initially designed and the chief reason for it. GPS accuracy enhancement is a fallout of the design.)

{o.o}

This has been posted on Flightglobal, if it's of interest:

Complexity of AF447 crash probe to dominate ICAO discussion

JD-EE

Consider that the Auto Pilot dropped as a result of its being "unable" to control the a/c with its set of limited control commands.

Remanded to "Manual", the pilots have a serious challenge, again as the result of what I propose is the a/p's "long leash". Given that the a/c is oscillating inside an envelope of prescribed parameters, and its cruise (.82 Mach) speed, whatever caused the ap to retreat is now in the hands of a man whom we assume is at Cruise, SA-wise. A hyper-vigilant Chief Pilot would be challenged as he never had been in his life.

Now consider another possibility. The a/c was not under threat at all.

As the micro-crystalline Water Ice packs up the pitots and hobbles the OAT sensor, the a/p "reads" the flight status as dynamic, rather than static. It doesn't think, and it can't hear, so it makes inputs to "correct" what is becoming a rapidly deteriorating (to it) situation. It is likely reading slowing a/s, so lowers the nose a titch, and perhaps augments thrust, just to "smooth and speed" the "recovery". But it isn't working. It's only plan is to correct, not stop and assess. Sometimes doing nothing is better than doing something. But the autopilot soldiers on. How quickly did the limits cause the a/p to shut down? Let's hope it didn't allow the Pitch and speed to get too wack, but one thinks it did.

Energy. At a high velocity, "slowing down" takes time. The a/c is clean, and the descent devices are not available for quite awhile, they would be battered to bits. What caused this a/c to slow rapidly? If, as mm43 proposes, the a/c was in a turn and Impacted not far from its "onset" position, there are only unpleasant suppositions.

Small and sharp things leave first, wingtips, tail bits, skin that is disturbed by the departure of objects of ever increasing size, which exacerbates the deceleration and donation of parts to the air and sea below. At some point the velocity is low enough and the relative strength is high enough that a "balance" is achieved, and the airframe settles into its likely flat spin to the Sea.

Nothing about this is proposed to be certain, there is too much missing from the puzzle. It is minimally informed supposition. Guesswork.

587 lost an engine (as in separation) almost immediately, wake turbulence is a beast, low and slow. Primary failure at altitude and close to the speed of sound? Somehow (someway) 447 recovered to impact the Sea on the verge of complete recovery?? Not saying it's impossible, but....

So that is one answer to this aircraft's having been "swatted from the sky". I tend to agree that velocity was lost quickly, and disastrously.

bear

I like your analysis, but would like to offer a comment on triple redundancy, which may be pertinent to the discussion.

JD-EE has already dealt with the NASA approach to the subject. However, I would have to say that the tried and proven saying of "garbage in equals garbage out" is important here. If two components of the equation (pitot & temperature senors) can fail because of one cause, e.g. ice, then there needs to be an alternative means of measurement.

In respect of the FL350 level time, I am not sure exactly when they levelled, but on transfer to Recife Center at 23:19:27z (50 minutes after take off) they reported level at FL350. Curitiba Center cleared them to FL350 at 22:55:41z and it would be interesting to know from what level, and the time they actually levelled. This means that they had been at FL350 for at least 2 hours 50 minutes prior to the upset.

mm43

Redundancy, or replication, is of less use in critical systems than parallel but anomalous systems. BA038 satisfied all ETOPS requirements, but in hind sight and to this day, critical systems tend to replicate each other as the destination of each system is approached, rather than continue to supply, meter, or control critical systems in independently engineered ways.

Taken to an extreme, BA 038 could have been fitted with separate but similar powerplants, ie. one GE and one Trent. As silly as it sounds, it represents what I feel is a neglected discipline.

Redundancy depends on reliability, and as we know, in Aviation, reliability is a frequently "balanced" consideration.

If one device has a freckle, two more will also. In 2003, Thales researched and recommended a separate sensing system for airspeed.

mm43

As the RTLU was found in its Normal Law setting, what is the implication regarding travel? Was the Rudder free to travel stop to stop, was it pinned in a centered position? Etc. I am extremely impressed with your contributions to this thread. What of the initial reports that bodies were recovered in "two separate areas, separated by fifty miles?" What do you make of the found positions re: VS, Galley, wing bits, aileron, Elevator, Spoiler, et al?

bear

Bearfoil
Once the maximum allowable rudder angle is computed, the RTLU stop screw turns incrementally to implement the angle.
Much of the information released by the Brazilian Military was designed for media consumption and on analysis was mostly devoid of "facts". A series of debris charts released by the BEA and showing where and when various (but undisclosed as to what component) items were recovered, also shows positions for the bodies. It should be pointed out that due to the 36g force they suffered on impact, and other events that happen in the sea, most of those bodies will not have behaved as one would expect.
I have no further information to identify specific items of debris, other than that provided graphically by the BEA for the V/S, and for the Port Outer Spoiler obtained from a very reliable source. The difficulty with back-tracking the various objects is determining how they actually behaved in different sea states and wind. This is why the phase 3 search area is still relatively large, ie. 887NM2.

Perhaps the scenario you are developing fits the following, though substitute the "mountain wave" for a severe mesoscale event:-
In AF447's case, ACARS was quite capable of providing some clues to any of those events, but it didn't, and may be because they didn't happen.

mm43

Bearfoil, one correction: I believe I was the one proposing the possible turn based on mm43's data. I didn't mean to impute something to mm43 he might not have said.

And my understanding is that once the speed indications differ the computers go off-line suddenly while the plane is likely in very heavy turbulence.

Something else came to mind. I'm not a pilot so this needs feedback from a real pilot. If something caused an engine stall, which could account for loss of ACARS transmissions, the pilots would not be concerned about compass heading so much as aligning the plane nose down to gain speed to restart the engines. This could have lead to the mysterious heading change. Then the desperate attempt to pull out as the ocean came into view might finish the scenario, engines started or not.

{^_^}

I think our crew are well challenged w/o loss of an engine. It hasn't been discussed much, but it did appear. Crap airdata is certainly enough, we're starting to sound like a sim instructor throwing the sink at a pilot who's dating his wife.

We could disregard all the initial buzz about "breaking up in the air," "autopsies prove plane broke up". "no water in lungs...." etc.

If the accel value is said to be 36 g, well, the belts are stressed to forty, and w/o harness, not survivable.....just. Some victims would have water in their lungs, yet none did. Turbulence isn't a conclusion, it could have been as simple as a pint glass full of crystalline water ice. Not enough for two margaritas. God Bless them all.

mm43, I was just riffing in email with SallyAnne on my idea of sending delta positions as part of every ACARS message. If I remember correctly there is a full position report every 10 minutes. Planes seldom cover more than 50 miles from their last position report until the next one. Figure that as one BYTE of information each for latitude and longitude delta. At 0.2 miles resolution that's about a four orders of magnitude reduction in position possibilities in 10 minutes. Imagine the affect this would have on the search operations. It's a change to ACARS messages that would probably pay for itself in savings from one over the ocean disaster. Even the recent event West of Lebanon would have been easier for recovery.

(You's even be able to get a useful improvement in a pair of 64 bit printable characters using "Base64" style encoding and working with deltas from last delta or last position report extrapolated with its velocity vector.)

Relative to new fancier recorders or full time data streams this would be a really cheap solution with a large potential payback.

{^_^}

{mumble}{mumble}

Just when did this engine break away, bearfoil? And where does word of this mildly dramatic event appear in the ACARS reports? I'd even hazard a guess that something as dramatic as a VS separation would also be quite evident in the ACARS messages if it happened at altitude.

It takes a minute or to for something plane shaped to make a 35,000' altitude change unless it's in a vertical dive. And that would chop off ACARS messages. (A dive more than maybe 30 degrees in the right direction would block ACARS. In the likely direction it'd take closer to 45 degrees, I suspect. The ACARS antenna has a rather broad beam width judging from its specified gain.)

So it appears ACARS was unaware of really dramatic events such as significant pieces leaving the plane. (And if the plane was at altitude for that last report, belied by cabin pressure warnings, the debris was in the wrong place.)

{^_^}

This makes very little sense to me, unless I totally misunderstand what you're talking about.

One, transmitting a delta assumes every previous delta has not only been received, but also validated as being valid relative to a valid starting point.

Two, by the time you have to transmit an ident, a time stamp, and some other sync info to get the message across in the first place (not to mention a few bytes of checksum data), skimping on the actual position data to me sounds illogical.

CJ

Belgique,

You wrote: "...they are unlikely to ever recover the DFDR (or CVR). The effort this month is in reality a nominal and token, yet enforced, one. It has only a very slim chance of any success."

Wanna bet? I'd be happy to take a case of Belgian beer off your hands when they are recovered.

Grizz

Grizz - and I'll bet they will be readable. I think this accident will be solved.

JD-EE

The following was in a post I made to a different thread sometime ago:-
I wouldn't get too concerned with the order of accuracy of any given position. There is a reason for that, e.g. an a/c over the equator reports with an accuracy of 0.01° or +/- 555.6 meters (1,824ft) in both the Lat and Long coordinates, and progression towards either pole increases the accuracy of the Longitude to say at 30°N by 1/secant 30° = 555.6*0.866 or to +/- 481 meters, and at 60°N to +/- 278 meters. The Latitude accuracy essentially remains the same - small changes on account of the oblate spheroid shape being ignored.

The BEA Flight Data Recovery Working Group Report - http://www.bea.aero/en/enquetes/flig...nal.report.pd has already indicated that "Regular transmission of basic aircraft parameters (via ACARS for example)" is the third preferred item on its "to do" list. As CJ has indicated, a few bytes saved here or there is not really the issue, and progressive Deltas might come unstuck when things get sticky. I expect that any consensus on common flight data parameters to be sent regularly by ACARS is still a long way off.

mm43

ChristiaanJ
I am proposing a delta from last full position transmission, which I believe is once every 10 minutes. If one of them is missed you get two small circles in which to search. That is still an improvement.

{^_^}

mm43, GPS is 100 meters accuracy "guaranteed" for the C/A channel. Generally you can do much better if your dynamics are not too large. If every transmission sends say 500 meters resolution position data how closely could they plot the plane's impact point, or at least the last point at which it is known to have missed a transmission?

If you send difference from last full report then you have pretty decent resolution within two BYTEs. A third BYTE with altitude might be nice for reconstructing the blow by blow of the accident. But it's probably not as big as win as the N/S and E/W BYTES.

You could get better position resolution with fancier coding - delta from straight line projection of the last two points, for example. But there is a point at which it all gets silly. A 0.8 km diameter circle is a whole lot better for searching than any 900 square miles search area. And that should be possible using only the printable ASCII character set.

(And it appears I must have left "full" out of "delta from last full position report." I figured they were the position reports. The deltas were delta reports. And as pointed out deltas on deltas isn't good. That was so obvious to me I forgot it would not be to many other people, I guess.)

{^_^}

JD-EE / Deltas
 

You are right, delta's are used succesfully in many other applications. I would just like to point out that the delta of two positions paired with time stamps is nothing else than ......
..... a groudspeed vector! Any GPS chip talking NMEA protocol provides this information free of charge, and one byte for course and one for speed every minute would be perfectly good enough for locating purposes. One additional byte for ROD or ROC would be luxury.

JD-EE

The slung engine(s) to which I refer belonged to AA587, there is a video, even. Re: VS and ACARS. I leave that one to your judgment, you are the Ee. AB300, not 330, different a/c type. I believe the engine broke away after the VS was torn off, I could be wrong. I use this example for a general understanding of the inertial and aerodynamic forces in play at <250 knots, the animation of the 587 crash a/c shows the effects of "Over-Ruddering" and excess Yaw in an a/c of substantial size. It also reiterates my position that the Rudder should be less robust than The Vertical Stabiliser, for obvious resons.

rgds. bear

Not to start a bunch of hoop to hoop replies, but since this is a subject of resuming the search, has anything recently been published about any results of the current effort. Thanks
ww

The search is to resume in about 2 weeks. The vessels involved, "Seabed Worker" and "Anne Candies" are to load necessary equipment, stores, fuel and personnel at Recife before proceeding to the search site - about 3 days sailing. Providing the weather is kind, and equipment is functioning correctly, it is anticipated that around 100km2/day will be covered using side-scan sonar.

mm43

Thank you. Wish them luck.
ww

mm43

Permit me a question. I am quite late to this thread it seems. I have missed how it is that some would require the VS separation to have been reported by ACARS, I suppose because it is thought that a/c disintegration must have happened before final ACARS transmission? That is counterintuitive. I realize comm from the flight is considered out of the ordinary for dropped, lost or untransmitted mxs. Bear with me. If the beginning of trouble was ADIRU and unreliable a/s, wouldn't the aircrew have almost instantly turned for land? Though airborne for 3:20, Brazil was not far, and ahead was bunk Wx and alot of Ocean. Why is it not possible for the a/c and crew to be flying during ACARS, but in consonance with a reasonable turn to land? The problem of duff a/s was well known, and I believe first thought would be to land asap. Why is it thought that the last transmission from ACARS was at impact? Is it? Why is it thought that the a/c instantly started descending at first ACARS and took those 4 minutes to crash? Last ACARS was disturbing, is it not thought that this could have signalled the beginning of uncontrolled descent? PRIM/SEC FAIL seems about as bad as it can get and still have some influence on controls. I still believe the VS separated quickly, as it is missing skin fracture, dimpling, folding, and penetration by other debris. Virtually all of the debris was diminutive, save galley and V/S Rudder. Most all of it also displays abrasion, ripping, penetration, and twisting.

Can you be of some help in a clear chronology? I am confused by the "4 minutes to impact". Aside. If I'm to turn, and I'm flying, I like the turn with the best view, so if the relief Pilot was flying LHS, I'd assume left turn. If the F/O is RHS, and he's flying, right turn. Left also seems away from Wx, I'm assuming a left turn.

bear

I'm not necessarily agreeing with that concept, but am guided by the very detailed analysis the BEA (obviously assisted by Airbus) have made and detailed of the debris recovered to date. Reference to the Interim Reports #1 & 2 will provide you with reasoning deduced for every one of the ACARS messages, and their sequencing.

The loss of signal from the a/c by the satellite in the period from 2:13:14z until a message sent at 2:13:45z has been explained by the BEA as either an a/c attitude event that caused antenna blanking or the total loss of both power sources. It is possible that the uncontrolled descent commenced during this period.

The Cabin Vertical Speed advisory has provided some indication of the FL passing through, when it was triggered. The actual time of this advisory (nominal timestamp 0214z) can only be guessed, but it was the last message sent/received by the aircraft. One fault message was effectively due to be sent at 02:15:14z, and though it was not received by the satellite due to "loss of signal" from the a/c at 02:14:28z, it is assumed that the aircraft's flight ended between 02:14:28z and 02:15:14z.

The BEA have carefully detailed the relationships between CAS, TAT and Mach, and also the upper/ lower boundaries at which disagreement will trigger PRIM/SEC faults. It is anyone's guess as to whether a mach critical or a low speed stall were the onset that lead to the end.

I don't believe there is anything further to be gained in this discussion until the evidence in the form of the DFDR/CVR is/are recovered and analyzed.

mm43

bearfoil, mm43, JD-EE, fascinating discussion; thank you for taking the time to place your arguments thoughtfully and clearly for non-engineers such as myself.
No. Such a decision is not made "instantly".

First, training and cockpit discipline prevent hasty decision-making in emergencies and abnormalities.

The kinds of circumstances and possibilities which a crew may encounter cannot be listed but establishing control of the aircraft, executing drills, securing the remaining systems and then, if stablized, tending to the navigation of the aircraft, resolving between all crew members that the situation was stable and then communicating with ATC, then company, all mitigate any tendency towards sudden, hasty action. The order will vary slightly because no emergency is the same as another, but this is the general nature of any response.

Unless the obvious requires it, (TCAS, EGPWS, actual stall), one does not normally make changes in configuration, change aircraft configuration or start any other maneuver with an unstable or questionable airplane while an abnormality is being handled, especially without crew consulation and especially not without the captain on deck.

This may seem at odds with what many consider to have been a dire emergency but I don't think that it initially was such an emergency, but a gradually degrading series of circumstances which, by paths we do not know yet, ultimately led to loss of control of the aircraft.

We know from past incidents on the A330 (discussed earlier) that loss of airspeed information in and of itself does not and should not lead to loss of the aircraft. Clearly something else intervened and we have posited these circumstances many times now.

The discussion is indeed fascinating and not at all "academic", but not far from our minds, I know, will be the question about why the loss of control occurred in the first place.

It may very well be that loss of control only occurred after the airframe was somehow compromised but there are problems with that scenario including wreckage/body distribution, size of the recovered pieces and telltale signs of high, uniform vertical 'g' loading on parts from widely separated locations on the aircraft. I know you all will have read the reports thoroughly so you will have solid reasons for alternate views, which again, make fascinating reading.

Specifically for a moment, I disagree that the spoiler broke off in flight. Such devices are certified through dive speeds and don't break off from forward slipstream exposure. The FCOM does not state whether they are designed to blow back but I suspect they are. There is an MLA - Maneuver Load Alleviation system and a Turbulence Damping system which affects the flight controls in terms of reducing airframe (wing) loads. The system is active above 250kts and at about 2g. These systems will have been taken into consideration, I'm sure.

PJ2

PJ2

Thanks. Whatever the fallout, it is extremely important to keep this accident in front of the people who fly. It should be obvious to anyone that "Spin" can be used in other ways than aerodynamically; I have seen too many investigations of all types pass into the mist of the past without proper attribution of responsibility.

With an activation speed of 250 knots, is the limit/blow back system dependent on indicated air speed? likewise, is the 2g threshold reliant on equipment that may have been reporting falsely, as other sensors were?

It is not difficult to envision the impact as BEA reports it. What they describe is a hydraulic "Flat Plate", similar to an actual airborne maneuver, though executed in smaller and more robust airframe. May as well get some of the more impossible things out of the way, can a wide body "Flat-Plate" at altitude? My question is prompted by how minimal the damage of Galley and crew rest was. Doesn't look at all like a flat impact on what may as well have been concrete. Bear in mind these are modular installations, and have little "critical" strength engineered into them.

The pressure of the cabin as the a/c hit "flat" must have been quite high, assuming the hull was intact, as maintained by BEA. Would this explain some of the materials' failure relative to delamination (crew rest module), and some of the tearing and shredding of other thin materials, cabin liner, carpeting, seats, etc. The MedPak was quite unblemished, as other materials were, VS, laptop, FA seats, etc. I've not seen any crash scene of land impacts that show any relics 'undamaged', as here.

The crack in the Pin/Sleeve of the Rudder attachment, as well as the missing piece of "vertical arm" suggest a serious overload of the Rudder loading/attenuation system, but in its normally operating 'plane' of stress. This in itself doesn't mean the VS couldn't have been attached at impact, neither does it exonerate that conclusion. With the VS' condition relative to most of the other recovered aerodynamic surfaces, there is at least some doubt about the attachment at impact.

There is, of course, a popular thought that one needs to wait to be told what occurred. In my experience, that is reasonable. However, please understand that the ones who own the evidence own the conclusion, and truth be told, if one has a bias, it is humanly impossible to be objective.


So none of this should be taken as gospel. Similarly, there is no moral judgment here, but let me say that I have caught myself building a case one way, without knowing I was. There is a bias here, it is not mine.

It's human nature.

bear

How it hit, assuming a long time to fall, is a lot less important than what precipitated the fall.

The discussions need to always reflect back to the initation, else we are using up an awful lot of bandwidth to no avail.

To be fair, in what state it hit, could be very important in determining what precipitated, or at least in eliminating some possibilities.

Specifically, if the fall was precipitated by VS detatching due to aerodynamic loads at cruise, then the VS clearly wouldn't be attached at impact. So determining whether or not it was attached at impact becomes rather important... and therein lies the debate.

You have raised something that has bothered me for some time, i.e. the photographs that have been supplied in both interim reports, have been taken very early on in the investigation. One taken of the V/S attachments was clearly taken onboard the Brazilian warship "Constitucion" - the polypropylene rope used as a lashing is clearly visible. Likewise, the "vertical arm" shot has been taken once the skin panel has been removed. I would have hoped that some evidence of forensic metallurgy would have been presented, e.g. crack detection/bluing, ultra-sound, x-rays. Hopefully it has been done, and will be presented eventually.

Though the acceleration forces present on impact were high (36g), deformation has mostly been upwards from the bottom. This means in the case of the hull, that each frame was deformed through the same axis at which it had its greatest strength. Longitudinal framing and outer skin etc.. deforming equally like a you would expect to see a tennis ball do when being hit or striking a wall. The cabin pressure would have been low, but an implosion resulting from that was probably canceled out by the volume displaced as the frames deformed from the bottom. Hardly science, but you'll get the general idea.

mm43

lomapaseo;
Precisely.

Unless the aircraft was under control or recovering until a mid-air breakup occurred, what happened after the loss of control is not essential to understanding the causal pathway(s) to this accident.

bearfoil;
Re 'bias', having spent considerable time presenting flight data to those with the authority and responsibility to make changes and observing denial, explaining-away and normalization behaviours which set aside data in favour of opinion at work first-hand, I am familiar with the power of latent bias and the difficulty in breaking through a strongly-held world view which is not in accord with facts derived from non-empirical sources, (actual flight data as opposed to impressions of what the flight data 'says').

In this case it isn't just "human nature", it is more specifically labelled, "cognitive dissonance". Accepting a state of affairs which is strongly in conflict with one's "understanding of affairs", especially when "perceived stakes" are high as is always the case in this business, is a significant challenge especially where "groupthink" may be latently at work. Official reports may be no more than the very best efforts of particular world views, although it's never that simple. If we switch the words "see" and "believe" around from the phrase we're all familiar with, the phrase, "I'll see it when I believe it" perhaps captures a sense of this.
I left this notion out partly because I knew you'd know this as a possibility but also because I don't know what such possibility's effects would, specifically, be.
I believe the system would be predicated on Indicated/Calibrated Airspeed as that is what the airframe is exposed to; I know the A320's 'g' sensing is very reliable (unlike the B777 'g' parameter, which sensor is located under the cockpit and can be, in flight data work, suspect) so I would tend to dismiss the possibility of any errant 'g' data.

Before permitting too much credence to any notion involving, "automatic deployment of spoilers in response to errant data", it should be understood that the system has limited authority and is designed to only momentarily reduce wing-bending moment. The Lockheed L1011 - decades ahead of its time, (not sure if it was just the -500, ...411A?) had the same system.

MLA authority is limited to the ailerons and to spoilers 4,5, & 6 and always symmetrically. MLA adds a maximum of 11deg up-aileron onto any roll demand and a maximum of 9deg deployment symmetrically on any roll demand. Eight degrees of aft sidestick movement, (a HUGE amount at cruise speeds and altitudes) activates the system, (for obvious reasons - it is load-relieving the wings). Deflection is proportional to the 'g'-loading in excess of 2g. The system functions in Normal and Alternate laws. My tendency would be to place this low on any layering of possibilities.

Some thoughts...
My own impression of the cockpit environment during is that it would be a very challenging set of circumstances in heavy turbulence. Maintaining a stead pitch attitude in manual flight is not difficult nor is maintaining engine thrust with manual thrust - one just brings the thrust levers back, out of the CLB (Climb) detent and sets the power that was being used before disconnection of the autothrust, (Leaving the thrust levers in the CLB position with the autothrust disengaged would request max climb power which is more, (but not much more) than would have been commanded for cruise power).

But doing so while in heavy turbulence and while handling ECAM messages, which would be a series of Master Cautions and a few Master Warnings (with associated auditory warnings) all being re-prioritized themselves on the Lower ECAM as the affected systems degraded as a result of the original loss of ADR data, would in-toto, be a very challenging environment for any crew no matter how disciplined, no matter how constituted, (captain absent, Relief Pilot in the Left Seat, etc). Cancelling warnings and assessing the next ECAM messages in a continuously re-prioritizing series of ECAM messages and drills would present a very busy and perhaps overwhelming number of "#1" tasks.

From the satellite imagery available in another thread and on the web and given 447's assumed path, (no deviation for weather), one may reasonably assume that turbulence would be increasing and the difficulty of handling the penetration of the line of TS may have been exacerbated by the unfolding degradation of some aircraft systems with associated warnings and demands for crew attention, as well as the difficulty in actually reading the PFD and ND displays (the ND has the radar presentation superimposed upon the navigation data) in turbulence.

Except for possible mid-air break-up, (which I had initially posited but through discussion with others, dismissed), these are the factors which I think are more critical to an understanding of this accident. Evidence for this view comes from the fact that other incidents of loss-of-ADR with similar patterns of ECAM/ACARS messages and which were discussed at great length in the original (replacement) AF447 thread now in Tech Log, have not resulted in loss of the aircraft.

infrequentflyer789;
I don't think so. A VS separation would result in a high forward speed impact with the sea rather than a low forward speed, high vertical velocity impact. The evidence just isn't there for any high forward speed impact. Fragmentation of interior cabin parts was not high in this accident. Large, relatively fragile structures survived, intact.

Neither do I think that there is much to learn that we don't know already from the Japan Air B747 which lost the VS through loss of the aft pressure bulkhead and AA 587, in terms of pilot handling.


I like Occam too.

PJ2

Somehow inconsistent with what the last coordinates recieved might suggest ...