AF 447 Search to resume

[ChristiaanJ]

Originally Posted by JD-EE

Figure that as one BYTE of information each for latitude and longitude delta.

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

[grizzled]

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

[PJ2]

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

[mm43]

JD-EE

The following was in a post I made to a different thread sometime ago:-

If AF447 had been sending its position via SATCOM every minute instead of the 10 min interval initiated by AF Operations/Maintenance, the search area would have been reduced to a maximum of 8NM radius. That's assuming it crashed in the 59th second, which gives an area of 201 square NM (690km^2). We do know that it was still airborne 4 minutes later, and the BEA are using 0215z as their crash time. This represents the 8 x 5 = 40NM radius they are ostensibly confining their search to, i.e 5026 sq. nautical miles (17,240km^2).

This boils down to one simple fact, i.e. the search area increases by the square of the time between position reports.

Just phoning home at smaller intervals increases the SATCOM costs proportionately, but reduces a search area by the square root of the changed interval. The costs of one versus the other are too large to even contemplate.

In meantime, implementing the above is the cheapest thing that AF or any other carrier operating Oceanic routes outside of SSR coverage could do right now.

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

[JD-EE]

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.

{^_^}

[JD-EE]

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.)

{^_^}

[clearedtocross]

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.

[bearfoil]

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

[wes_wall]

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

[mm43]

wes_wall ...
.... has anything recently been published about any results of the current effort

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

[wes_wall]

Thank you. Wish them luck.
ww

[bearfoil]

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

[mm43]

Bearfoil ...
Why is it thought that the a/c instantly started descending at first ACARS and took those 4 minutes to crash?

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

[PJ2]

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.

Originally Posted by bearfoil

wouldn't the aircrew have almost instantly turned for land?

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

[bearfoil]

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

[lomapaseo]

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.

[infrequentflyer789]

Originally Posted by lomapaseo

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

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.

[mm43]

Bearfoil ...
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.

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

[PJ2]

lomapaseo;

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

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.

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?

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;

So determining whether or not it was attached at impact becomes rather important... and therein lies the debate.

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

[CONF iture]

Originally Posted by PJ2

From the satellite imagery available in another thread and on the web and given 447's assumed path, (no deviation for weather)

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