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AF 447 Search to resume

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AF 447 Search to resume

Old 10th Apr 2011, 05:06
  #3241 (permalink)  
 
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Originally Posted by takata
On the other hand, the fact that such incident happened only twice in the very same aircraft, as well as during the same flight, and that hundreds of other A330 flew safely many millions hours without ever experiencing it would give all the statistical depth necessary to conclude that this incident was obviously related to this particular aircraft and/or flight.
Actually according to the ATSB another QF A330 has developed a similar pattern of fault messages. the crew completed the relevant procedures (introduced since the QF72 event) Did it allow to prevent a possible upset ? We don't know. Interesting to note that this special procedure, still in force to this day, does not guaranty to eliminate the risk but just to minimize the exposure time during which an eventual upset could develop.
Does it make the 330 an unsafe aircraft ? Absolutely not I do agree.

Then, specific Air France procedure for A330 would ask for a speed reduced to M 0.80 and A/THR disconnected if an expected turbulence zone would be crossed. I don't think that they are different from Airbus ones in that respect.
As stated in QRH 5.01, unless thrust changes become excessive, it is not an Airbus procedure to disconnect A/THR when going through turbulence.
It would be interesting if airfrance has decided not to follow Airbus on this one ... Would you have a reference ?

There is plenty of books published about the sociology of the rumor spreadings. Maybe you should try to read one and avoid to make a fool of yourself.
I'm OK with it.
Investigate building 7
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Old 10th Apr 2011, 05:12
  #3242 (permalink)  
 
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jcjeant, methinks hydraulics failure would be a priority message. That strongly suggests that the VS was still attached up to one message time plus some Kentucky windage before the transmissions ended.

We have no real idea where the plane was at that time. The simplest suggestion is that transmissions ceased at the same time the plane ditched. The second simplest is a flameout for all engines, which, I believe, shuts down ACARS. So the plane could have still been a modest distance from its ditching location.

That aside, there is no compelling evidence that the VS was not attached at the time the plane met the ocean's surface and shattered. If someone postulates that a rudder setting somehow caused the VS to shear off they'd best be prepared to describe what the mount points, the clevis joints, that held the VS to the tail would look like in that case and show that they'd look like the damage we saw to the VS and the pieces of joint still attached.

The damage is particularly well suited to explanation via mm43's ditching diagram for the plane. The tail assembly hits the water with its nice wide flat surfaces and gets pushed upwards breaking at the bottom of the fuselage first. That leads to damage to the back end of the VS and rudder as well as a bunged nose on the leading edge where it was against the fuselage. The middle joints broke first then the others followed.

I cannot put together in my mind a scenario that has the VS mounting points come out looking the way we saw them in the pictures posted and in the BEA reports.

VS comes off in flight is not a scenario I can put together with the pictures and come out as a coherent picture.
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Old 10th Apr 2011, 07:12
  #3243 (permalink)  
 
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All bodies will be transported to France, where DNA examinations will occur.
Hopefully the bodies themselves that are still inside the fuselage (as mentioned in the press) will yield vital clues as has happened in the past.

Would be nice to see more info about the search & recovery instead of 50 pages of vertical stabiliser nonsense
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Old 10th Apr 2011, 10:03
  #3244 (permalink)  
 
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Originally Posted by ventus45
my scenario has the VS separating effectively only a handfull of seconds prior to impact
In that case, what significance does it have in the accident sequence?

considering the possible effects of resonant and flutter forces ?
And no damage anywhere else on fin, rudder and hinges?

Last edited by HazelNuts39; 10th Apr 2011 at 10:18.
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Old 10th Apr 2011, 10:29
  #3245 (permalink)  
 
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Originally posted by ventus45 ...
... the pilots, if still functioning on descent passing FL100, would, by that stage, have been open to trying "anything" to recover, including, full rudder inputs.
But you have forgotten one thing, the RTLU ... it was found to be set at 7.9° +/- 0.1°, which is the limit in Normal Law at Mach 0.8 and FL350.... (272+/-2 KCAS).

2:11:21WRN/WN0906010210 272302006F/CTL RUD TRV LIM FAULT

Sorry, but I can't see sufficient loading from +/- 7.9° to achieve what you are suggesting, when the uninhibited maximum is +/-31.6°.
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Old 10th Apr 2011, 10:46
  #3246 (permalink)  
 
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Originally Posted by ventus
Loss of the VS is a lunatic theory
No, I do not see it as lunatic. I see it as unproductive to pursue because of its low probability and in your case relative unimportance.
I seem to have upset a few people.
No, you and many others replowing ground that is already quite well furrowed. We're not singling you out, even though I am not quite fisking your article. It just gets boring. Although I will admit that most people presume the VS departed the plane which started the whole mess.

The loss of the VS is a lunatic theory is it. So your collective assertion is that the VS on AF447 could not have separated in flight, and could only have separated at impact ?
I repeat, it is not lunatic. It is simply low probability given other facts as presented by BEA so far.

With all due respect to all of you, perhaps you have a different theory to the NTSB for AA587 ?
No. That is an entirely different event.
Note: - from the NTSB report:-
page 159
3. Conclusions
3.1 Findings
6. Flight 587’s vertical stabilizer performed in a manner that was consistent with its design and certification. The vertical stabilizer fractured from the fuselage in overstress, starting with the right rear lug while the vertical stabilizer was exposed to aerodynamic loads that were about twice the certified limit load design envelope and were more than the certified ultimate load design envelope.
Note the bolded text above. The shear from that event presented itself differently on the mounts than the AF447 damage we see in pictures. Just because the VS came off in both events does not mean they came off for the same reason. One must examine the damage to further diagnose the obvious fact that the VS and plane parted company.

Reference Document.
In-Flight Separation of Vertical Stabilizer American Airlines Flight 587
Airbus Industrie A300-605R, N14053
Belle Harbor, New York
November 12, 2001
Aircraft Accident Report: NTSB/AAR-04/04 PB2004-910404 Notation 7439B
http://www3.ntsb.gov/publictn/2004/AAR0404.pdf
Content References:
pages 31 to 42 inclusive.
pages 50 to 52 inclusive.
pages 55 to 60 inclusive.
page 159
3. Conclusions
3.1 Findings
6. Flight 587’s vertical stabilizer performed in a manner that was consistent with its design and certification. The vertical stabilizer fractured from the fuselage in overstress, starting with the right rear lug while the vertical stabilizer was exposed to aerodynamic loads that were about twice the certified limit load design envelope and were more than the certified ultimate load design envelope.
Did you intend this apparent repetition. It still contains the significant sentence fragment.

Now, I re-emphasise:-

"The vertical stabilizer fractured from the fuselage in overstress, starting with the right rear lug while the vertical stabilizer was exposed to aerodynamic loads that were about twice the certified limit load design envelope and were more than the certified ultimate load design envelope."
(sigh) Three times does not make it true, Lewis Carroll notwithstanding.
I did not say, and I am surprised that many of you have apparently assumed, that I meant, or was implying, that the VS separated at initial upset. I did not, and I do not.
OK, on that much we do agree.
I actually think the VS came off somewhere between 5,000 feet and 0 feet, but probably closer to 5,000 than zero.
You are free to think this. I depart from agreement here. It is not the simplest scenario.

At the risk of repeating myself from a prior message the evidence in hand strongly suggests that the VS was still attached until the last 15 seconds or so of ACARS transmissions. It MAY have come off at the time the last message was being transmitted.

It is also fairly apparent that the plane was below about 6k to 8k' at the time. That leaves room for your scenario. It would be incumbent upon you to describe what might have happened between 0 and 5k', picking your numbers, that would be significantly different as far as the VS is concerned than what happened at higher altitudes. Furthermore you should be prepared to describe how the VS assembly took on an appearance that it had been pushed forwards rather than sideways given the visible clevis joint related fractures.

It also strongly suggests the plane was out of control and falling out of the sky at the time. It less strongly suggests that flight control recovery had been effected and pull out proved to be impossible and in fact the plane died in the middle of a frantic pullout attempt. I happen to like that scenario as it explains a few things. But it's too thoroughly based on coincidence to make me happy.
My thinking is that there are many plausible ways that AF447's VS could be (and I think were) "exposed to aerodynamic loads that were about twice the certified limit load" (if you will - and more) when the aircraft entered the "denser air" at lower levels.
That is part of an explanation. What loads? What was the plane doing at the time that created huge loads?

To begin at TOD.

For various reasons, I belieive that the initial upset was an underspeed stall upset, which resulted in the aircraft entering a fully stalled descent, with a flight path angle about 30 degrees off vertical (60 degree dive) but in a fully stalled condition, basically in a slow flat spin, slowly yawing (my theory is happy either way, but, lets say to the right if we assume that the BEA is correct with their "tail was moving to the left at impact" idea).
That is a fairly likely scenario. But if they are only 10 miles away from LKP was it God's hand that appeared in front of the plane and slowed it fairly rapidly and then let it fall in a stall? Facetiousness aside, what slowed the plane down so suddenly? It wants to fly and in four minutes it was in the water from 35000'. Where did all the plane's energy go? And more importantly, why?

The tail was moving to the left idea comes from the way the pairs of clevis joints tore off the plane. Study the pictures of the recovered VS REALLY closely. Then play with holes punched in paper with a fitted dowel through the holes. Pull it off different ways and see what form the tears in the paper take. It's only a rough equivalence. But you should quickly see a pattern. You have to get the tail or at least part of the tail moving forward up over the fuselage in order to break it that way. And I agree, how in heaven's name did it avoid getting bunged up by other parts of the plane?

Possibly there was considerable surface winds and they picked up the tail as it broke lose and moved it the critical distance.

This mode of descent would be obviously unstable, but it would also have been unrecoverable, due to total stall of both mainplane and HS, and aft-ish CG. So it was probably oscillating slightly in all axis on the way down, ie, probably oscillating in pitch from about level to perhaps 20+ degrees up, in roll a bit, and in yaw rate a bit, but with yaw always positive. In other words, sort of like a fully stalled spiral descent to the right with a bit of Dutch Roll-ish type motion happening.

Now, air loads are a function of dynamic pressure, and I am damn sure that the pilots, if still functioning on descent passing FL100, would, by that stage, have been open to trying "anything" to recover, including, full rudder inputs. But before you jump to the false conclusion that I am saying "AA587 First Officer", I am not.
If the plane was making very low headway at the time it was within 5k' of the water AND rudder travel was limited to in flight high altitude deflection limits, how would full rudder provide enough force? It was going forward too slowly to remain airborne. So full rudder deflection would not be quite as exciting as it would near 300MPH at 35000'.

I am actually thinking more along the lines of turbulent eddies shedding off the fully stalled HS imparting latterally asymetric cyclic loads on the VS, (sort of like the FA18 LEX vortex busting on the fins idea - if it helps your mind's eye) such that, at some point, both the forces and the frequency were sufficient to either break outright, and or generate a resonant flutter like condition, that snapped it off at the base. The latterally asymetric cyclic loads would be generated by the varying wake fields from the port and starboard HS's due to the oscillating yaw rate. If you think it's out of left field, fine. I don't. Read the DSTO reports on the LEX vortex busts. Interesting stuff.
Perhaps. And maybe the recorders MIGHT be able to sort that event out from the impact. It seems to be a huge stretch with coincidences.

And, as someone else observed, why is it important? The important information is that information which leads to learning why this whole sequence happened in the first place.

Additional forces, either in or out of phase, could be generated by pilot rudder input. The combination of both, as dynamic pressures increased with decreasing altitude, may well have been "more than enough".

For those who assert that the rudder arm needed 36g to break is proof of impact forces, is it worth considering the possible effects of resonant and flutter forces ?

I think the posts asserting that there were no ACARS messages indicating hydraulic failures, "thus the VS was definately present at impact" is also flawed logic.
It does prove that the VS was still attached down to a small fraction of AF447's reported flight level. It was provably still on until at least a few milliseconds before the start of the last transmission. Otherwise the word that it had come off would have preempted other messages, I believe.

That does leave room for double flame out and a short glide from under the altitude at which the pressure warning would be issued. And it cannot be issued if the plane is gliding. That's a "falling" rapidly sort of message.

First, the ACARS stream ended well before impact (some seconds at least) did it not ?
We do not know. And the simplest presumption is that it ended coincident with impact. There was a hiatus in the transmissions that is suggestive of the plane going through some interesting gyrations. (Or perhaps had turned 180 degrees from its flight heading so the antenna was aimed as far away from the satellite as possible. I believe the antenna lobe is large enough that a bank would be required to take it off the satellite. I wish I knew the dynamics of the antenna aiming algorithms. I suspect they are fast enough to track through a tight turn. So that loss could mean a very severe bank.)

Second, even if they did only end at impact, and since my scenario has the VS separating effectively only a handfull of seconds prior to impact, would any hydraulic messages have been generated, prioritised, and injected into the ACARS transmit stream in time to have been actually transmitted in those couple of seconds ?
Please see above. It would take milliseconds for the message to be reformatted to note the massive hydraulics failure. So until a very short time before that last message started transmission the VS was there. We don't quite know where "there" was.

It could be that the VS was attached at impact, but I think those who assert with a passion that it definitely had to be, and was, are being a bit closed mind-ish.
It would be nice to know one way or another. But, the really important thing is "what started the avalanche?"
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Old 10th Apr 2011, 11:35
  #3247 (permalink)  
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I'm now getting even more confused. I seem to recall that thousands of posts ago, in a universe somewhere like ours, there was a finding that '36g' referred to part number? Anyone recall?

If we must discuss VS separation, I am firmly in the camp that says 'no way' would a swept-wing a/c be able to remain in some state of yaw control without it, and I believe we are told it was travelling more or less 'normally' (in 'line of flight') at impact'.

As an aside, regarding potential loss of hyd fluid, are there no fuses built into the system?
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Old 10th Apr 2011, 11:54
  #3248 (permalink)  
 
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@mm43

BJ-ENG;

Here is the Impact Graphic post, and you will also find related information a page or two before and after.
Many thanks, much appreciated.

BJ-ENG
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Old 10th Apr 2011, 13:37
  #3249 (permalink)  
 
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Some of the more recent posts have raised a few things that I thought had been settled by the two BEA reports. Looking back over the reports, nine points stuck out and I thought it was worth raising them in light of the most recent information we've got. Sorry for the monster post…

First, the problems started *before* the last known position: the first ACARS error (AP off) was received at 2:10:10 and time coded by the aircraft at 02:10. It and all of the next 14 messages are time coded 0210.

The about 6 sec between each reflects transmission time: as BEA wrote "[t]he messages were at least five or six seconds apart, which can be explained by the limited rate of communication by satellite." I assume that a period of unbroken contact of 6 secs is needed to transmit. This may be wrong -- eg it could be that a message can be sent if there is intermittent or poorer quality contact over a longer period. I also assume clocks roughly synchronized. I'm sure someone can correct if I'm wrong. If that's the case, what follows below is affected in specifics, but probably not generality.

Note that the message recording LKP (an AOC message) was received at 2:10:34 "between two maintenance messages. This can be explained by the fact that AOC messages take priority over maintenance messages.". I've assumed that it was generated while the previous message was in the process of being sent, then inserted into the queue and sent after it was finished. (I assume that if the AOC message had been generated during an even earlier transmission, it would have immediately followed that transmission, not the one it in fact followed -- stand to be corrected if wrong.)

The LKP message was received at 2:10:34 ("#0210/+2.98-30.59"). If the earlier postulate is right, it was generated at a time between 2:10:23 and 2:10:29, while the previous message was being sent, which was about 20 sec after AP off.

Second, BEA concludes likely significant orientation problems between 2:13:14 and 2:13:45, based on non-receipt of ACARS messages ("due, at least in part, to a temporary interruption in the communication link between the aircraft and the satellite"). That is a 31 second difference, but is a "gap" of 25 seconds, since the final 6 seconds or so was the time taken to transmit the message received at 2:13:45.

Now, JD-EE has recently written: http://www.pprune.org/tech-log/39510...ml#post6354796

"A spinning condition would not necessarily stop ACARS. They were in a position for a very high angle view of the satellite. The ACARS antenna has a very big "main lobe". So a mere spin should not take the satellite out of the main lobe of the antenna. It would, perhaps, show up in satellite logs as degraded signal to noise ratios (technically speaking Eb/N0 - energy per bit divided by noise energy.)"
Postulate: between 2:13:14 and 2:13:39, although the main lobe was not pointing at the satellite sufficiently, the aircraft was likely *not* in a flat spin.

Third, there are also two earlier periods that look unusually long: 2:12:16-2:12:51 (35 sec, = 29 sec gap + 6 sec of message transfer) and 2:12:51-2:13:08: (17 sec = 11 second gap + 6 second transfer). After these periods, there are still messages coming in with time stamps of 0211 and 0212. BEA wrote: "There are two possible reasons for the longer gaps: either the aircraft did not have any messages to transmit, or it no longer had the means for doing so (loss of satellite communication performance, for example)." The fact that there were queued messages (with 2:11 and 2:12 stamps) suggests the former was not the case.

Although BEA did not positively suggest that these two gaps were also caused by orientation problems, let's mark them as possibles. An interesting pattern will emerge - see below.

Fourth, there were also some more long gaps directly after the 31 sec gap that were also not commented on by BEA. Following the message received at 2:13:45, there was the usual 6 sec difference for the next message (received at 2:13:51), but the following one was received at 2:14:14 -- 23 sec difference = a 17 second gap + 6 seconds for the message transmission. There is again a 6 second difference until the next (penultimate) message received at 2:14:20, and again for the final message received at 2:14:26.

Note that the penultimate message received was time coded 0213, but received at 02:14:20, again suggesting that there was some delay between when it was generated and when it could be sent.

Fifth, go back to the "speed or mach function" message received at 2:13:08. It is time coded 0211 but was received *after* the ADR disagree message (which was received 2:12:51 but time coded 2:12). So it was generated *before* the ADR message, but was held up.

This message *might* have a clue to altitude: BEA (report 2) says:

"The only cases of excursion outside the validity envelopes compatible with the CFR are: a CAS higher than 530 kt without the Mach value exceeding 1. This condition implies that the aircraft was at an altitude comprised between about 4,000 and 14,000 ft" or "a CAS such as the difference between the total and static pressures being lower than a given threshold. This case implies notably that the static pressure is higher than the total pressure. ... the “HARD” nature of the message indicates that the problem lasted longer than 2 seconds."
The second cause suggests bad pitots. The first cause requires consideration of speed and altitude - let's return to this below.

Sixth, the cabin advisory message received at 2:14:26 is time coded 0214. So it was likely no more than 20 secs old. It indicates "cabin altitude variation greater, as an absolute value, than 1,800 ft/min for five seconds."

This ground has been covered before. We assume that the cabin pressure was originally 8,000 feet. From report #2:

"The containers recovered closed showed that the passenger oxygen masks had not been released. There had been no cabin depressurisation. Note: Depressurisation means pressure inside the cabin corresponding to an altitude of more than 14,000 ft."
Hence, cabin was intact until at least 14,000 feet. There is no reason to think that the cabin didn't remain intact until impact, and BEA states: "The aircraft was probably intact on impact."

There has been an attempt to calculate numeric data from the message here: The AF 447 Cabin Vertical Speed Advisory « Dark Matter I won't go into it here though; I trust mm43's post more http://www.pprune.org/tech-log/39510...ml#post5870418. It does suggest altitude below 8000 feet.

Seventh, "[T]he last message was transmitted to the aircraft at 2 h 14 min 28 s and was effectively received". This was just after the "ADVISORY CABIN VERTICAL SPEED" message received at "2:14:26" with time code 02:14.

However, the "MAINTENANCE STATUS ADR2" message received at 2:14:14 should have been followed, one minute later, by the transmission of a class 2 fault message. This should have been received between 2 h 15 min 00 and 2 h 15 min 14. The aircraft therefore had, at 2 h 15 min 14 at the latest, one message to be transmitted. It was not received.

Report #2 notes that orientation was not the reason for this failure, based on the orientation at impact: "[t]he aircraft would therefore have been able, in the last seconds at least, to transmit an ACARS message." We know (p32) that the aircraft struck the surface of the water with a positive orientation, a low bank and a high rate of descent, and little sideslip on impact. The deformations of the fuselage frames at the root of the vertical stabiliser were not consistent with an aircraft nose-down orientation at the moment of impact. The aircraft was "in a straight line" (1.12.4).

The conclusion is end of flight between "2h 14min 26 and 2h 15 min 14". (I would have thought it should be after 2h 14min 28 sec, since that was when a message was successfully received by the aircraft.)

Eighth, contrary to recent speculation here (and the reason I went back to the reports), the vertical stabiliser was attached on impact:

"The damage due to separation from the fuselage was essentially located at the root of the vertical stabiliser". It "separated from the fuselage at the level of the three attachments". "Rib 2 was bent upwards with a right-left symmetry. The front of the fin showed signs of symmetrical compression damage … " "The vertical load pick-up arm in the rudder’s hinge axis (arm 36 g) broke at the level of the attachment lug on the rudder side. The size of this arm is calculated to withstand a maximum load of 120,000 N, corresponding to a relative acceleration of 36 g of the rudder in relation to the vertical stabilizer. … Shear cracks, along a top-down axis, can also be seen on the rudder hinge arm attachment fittings close to arm 36 g. These observations indicate that the vertical stabiliser was subjected to a load greater than 120,000 N in the rudder’s hinge axis."
36g and 120,000 N is impact damage, not free-fall damage.

At least some of the control surfaces were also attached:

"On the right-hand half elevator, four of the seven fittings attaching the elevator to the trimmable horizontal stabiliser were present. They had bottom-upwards deformations."
and
"Several parts of the flap extension mechanism fairing were found. There were marks on two of them (positioned at the level of flap track No. 3), made by the flap extension track on impact. Analysis of these marks (morphological and dimensional examinations) and comparison with an identical aircraft made it possible to determine that the flaps were in the “retracted” position at the time of impact with the water … "
Ninth, now let's look at the altitude data in the above:
  • 2:10: No reason to think that altitude at 2:10 was other than 35,000 ft
  • 2:11: the speed or mach message *might* have indicated altitude between 14,000 and 4,000 **OR** difference between the total and static pressures being lower than a given threshold. If the former is the cause, then the minimum average vertical velocity at this point would occur on a drop from FL350 to FL140 (assuming the aircraft is at the highest altitude in the band, ie shortest possible distance fallen) from 2:10:00 to 2:11:59 (which is the longest possible time for the message to have been generated and still have a 0211 stamp) = 10588 ft/min = 176 ft/sec. If it has dropped further, average velocity will have been much higher.

    If it is the latter cause, then presumably no altitude hints from this message -- just an indication that pitots are still non functional.
  • 2:15:14: latest time for impact.

If we disregard the 2:11 message for a moment, and focus on the first and last, then the smallest *average* rate of descent would be from 35,000 ft at 2:10:00 to 0 feet at 2:15:14, being 111 ft/sec. The 2:11 time is thus well above the ballpark for the calculation if it is speed, not pitot, related. Assume therefore that it is more likely to be pitot related, and gives no altitude or speed hints -- just that static was measured as higher than total pressure (still frozen up?).

Finally, where all the above comes together is putting the above into a timeline:
  • 2:10:04-2:12:16 - cascade of faults generated but ACARS still able to be sent - 17 received.
  • (in this period sometime between 2:12:00 - 2:12:45: ADR disagree message generated, it is received at 2:12:51)
  • 2:12:16-2:12:45: (29 sec gap) possibly, orientation means no ACARS
  • 2:12:45-2:13:14: (29 sec gap) orientation OK to send ACARS. 3 received. First started transmitting at 2:12:45 and was received at 2:12:51. Next two received at 2:13:08 and 2:13:14)
  • 2:13:14-2:13:39: (25 sec gap) orientation problems significant enough to stop ACARS.
  • 2:13:39-2:13:51: (12 sec gap) orientation OK to send ACARS. 2 received. First started transmitting at 2:13:39, received at 2:13:45. Second received 2:13:51.
  • 2:13:51-2:14:08: (17 sec gap) possibly, orientation means no ACARS
  • 2:14:08-2:14:26: (18 sec gap) orientation OK to send ACARS. 3 received. First started transmitting at 2:14:08, received at 2:14:14. Next two at 2:14:20 and 2:14:26.
  • (in this period, possibly 2:14:20, the cabin advisory message is generated)
  • 2:15:14: latest time for impact for followup ACARS fault message not to be received.

If these additional ACARS window outages are right, does this not suggest two distinct phases:

1. initially, upset -- eg pitot related -- then high vertical sink, but orientation within normal bounds that still allows ACARS. About 2 mins 12 sec in duration. (Could be a flat spin or a deep stall?)

2. then a 2min 10 sec period in which orientation varies sufficiently that ACARS is interrupted: can't send (29 sec), then can (29 sec), then can't (31 sec), then can (16 sec), then can't (17 sec), then can (12 sec). Note that the periods are roughly equivalent, but shortening. Then some unknown time, max 54 sec, to impact, but effectively flat and able to send ACARS.

At some point, either before (within about 16 sec), at the time of, or during the first attitudinal upset sufficient to cause loss of ACARS, there is the ADR disagree, followed by PRIM 1 and SEC 1 fault - either command or a failure. (Crew trying to reset? Or everything goes down?) There seems to be a correlation between it and attitudinal upset -- is there any likely causation?

The new key piece of information is that we now know that the aircraft didn't travel very far horizontally -- perhaps 10 nm(?) (I recall that figure earlier this week). This suggests mostly vertical movement -- would there have been enough control to loop back?

More interestingly, if the above is right, what orientation would cause a cycling of available/unavailable ACARS window, if not a spin? I'm trained as a scientist, not a commercial pilot. I assume the most likely cause is pitch? More or less nose down, trying to recover from spin? Or a spiralling/barrel rolling descent mostly nose down, where the aircraft's back points towards, then away, then towards, then away from satellite? Since the aircraft strikes flat, have they finally pulled out of a dive/spiral, but have run out of sky?

(Loss of satellite contact caused by roll, while dropping vertically, doesn't sound as plausible, does it?)

(The above has borne in mind the BEA note: "message-timing by the CMC is accurate to within one minute" but "the order in which these messages are transmitted does not necessarily correspond to the associated sequence of events" and the time coded in the fault messages are with hour and minute only (p48).)
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Old 10th Apr 2011, 14:12
  #3250 (permalink)  
 
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Back to the TCAS

Maybe it's time to shed some topics, such as VS and TCAS, into separate threads. That said, I'll continue here.
-------------

Thanks to mm43 and HN39 for your responses on 8 April.

As a point of information, communication between avionics boxes is via a one way tertiary 32 bit data bus. Included in every word is a parity bit, and three validity states: Normal, No Computed Data, and Fail Warn.

From the report:
This message indicates that the TCAS is inoperative. Without an associated fault message, it could be the consequence of an electrical power supply problem or of an external failure. Amongst the possible external failures, only one is compatible with the CFR received. This is a monitoring process internal to the TCAS which applies to the standard altitude parameter. The latter is received from the active transponder (it can thus be the altitude elaborated from ADR 1 or 2) and is submitted to a “credibility” test. In actual fact the TCAS elaborates an altitude prediction that it compares permanently with the altitude received.
When these two parameters move too far apart, it stops operating and generates this ECAM message. Once the altitude becomes “credible” again, normal operation resumes and the message disappears.
This is illogical. Why would the TCAS have a credibility filter on altitude data from the transponder? It would be just as important for the transponder to have the same credibility filter, as it transmits own ship altitude to ATC and other aircraft. If there were such a filter, it should be in the ADIRU, or even the Air Data Module, whichever unit contains the correction factor for airspeed.

Again, when the ADM or ADIRU detects a fault, Fail Warn is transmitted on the data bus to the transponder. The transponder reverts to responding with Mode C, no altitude, which it also relays to the TCAS. The TCAS then stops, and annunciates OFF to the pilots. This is not a TCAS Fail.

Think about it: ACARS maintenance messages are transmitted to the destination. You don't want the mechanic to change a TCAS processor when it's a source that's faulted.

I'm sure BEA is mistaken. There was another reason for the TCAS Fail.

There is a use for an altitude credibility filter in older aircraft which have only Gilham code air data source. Gillham code is a dozen discrete wires, with no parity or validity bits. This credibility filter, if it existed, would logically be in the Mode S transponder, not the TCAS. Early in TCAS history, a KAL 747-1 with Gillham code source, was reporting 7,000 feet when they were at 10,000, and had a near collision with a JAL 747.

GB
My credibility? I was heavily involved with Mode S transponder and TCAS certifications at OEMs and airlines for over a dozen years. I had access to the avionics OEM specialists.
Graybeard is offline  
Old 10th Apr 2011, 16:06
  #3251 (permalink)  
 
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Questions for the guys up front

I have been following all the AF447 threads since they started. I would like to thank all the pilots, engineers and other subject matter experts who have posted on these threads, not only for being generous with your expertise, but also for your infinite patience with the less knowledgeable among us.

I have learned huge amounts from you all. My respect for flight professionals, which was already considerable before all of this, is now immeasurably greater.

As a frequent airline passenger I have little to contribute, other than my own logical analysis based on the wealth of information posted here. Until now, I have not felt that my contribution would add anything to the discussion.

So with all that preamble out of the way, I now have some questions for the flight crews and/or aircraft engineers.

Since the beginning I have wondered if the original "upset" is not an extreme weather event, analogous for example to the rogue open-ocean waves that are large enough to swamp an oil tanker leaving no trace.

Is it plausible that extreme weather dynamics in a storm system could create opposing up/down currents violent enough to flip a commercial airliner on its back, notwithstanding its size? If this were to occur, how would the aircraft then behave in terms of vertical and forward motion? How would an attempted recovery play out?

Two reasons for asking this question now:
(1) it might explain the proximity of the wreckage to LKP;
(2) it might explain the apparent hiatus in ACARS transmissions (upside down antenna loses the satellite).

If this all comes across as another hare-brained theory, more suited to the Rumours thread, then feel free to admonish me accordingly. And if this has already been discussed, I apologize for having missed it.
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Old 10th Apr 2011, 16:19
  #3252 (permalink)  
 
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TCAS

Salute,

Originally Posted by Graybeard
This is illogical. Why would the TCAS have a credibility filter on altitude data from the transponder? It would be just as important for the transponder to have the same credibility filter, as it transmits own ship altitude to ATC and other aircraft. If there were such a filter, it should be in the ADIRU, or even the Air Data Module, whichever unit contains the correction factor for airspeed.
Well, considering that the purpose of a TCAS (Traffic Collision Avoidance System) is to predict a safe flight vector, it seems someway quite logical that its own "prediction" function would be compared to any computed air data received from any sensor source. What is obviously discussed, here by the BEA, is the way that this TCAS function will be shut down to inop, they are not discussing the relevance of the whole architecture of the air data computations in relation with other systems -transponder and/or ADIRU- failures.

Originally Posted by Graybeard
Again, when the ADM or ADIRU detects a fault, Fail Warn is transmitted on the data bus to the transponder. The transponder reverts to responding with Mode C, no altitude, which it also relays to the TCAS. The TCAS then stops, and annunciates OFF to the pilots. This is not a TCAS Fail.
Nowhere the BEA said that the TCAS "failed". In fact, the opposite is said: it is inoperative because of those "wrong data" from external sources (ADR1-2) were detected by its built in function.

Originally Posted by Graybeard
Think about it: ACARS maintenance messages are transmitted to the destination. You don't want the mechanic to change a TCAS processor when it's a source that's faulted.
But, be sure they won't change anything as the CFR (Code Failure Received) is pointing at an external source and there is only one possibility (external) for this message, as duly mentioned by the BEA.

Originally Posted by Graybeard
I'm sure BEA is mistaken. There was another reason for the TCAS Fail.
Sure, the BEA is always mistaken each time it doesn't fit with your own theories (vertical stab, systems, attitude, etc.)

S~
Olivier
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Old 10th Apr 2011, 16:51
  #3253 (permalink)  
 
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when I was a much younger man

there was a post, or sequence of posts, analysing the ACARS sequence by people who knew what they were talking about. Could a kind soul point me to where that is please, I have looked and become discouraged

One other thing, a few posts back there was a question about what objects #9 and #11 where in the debris field (as they sit above the presumed resting place). Was that answered and I missed it ?
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Old 10th Apr 2011, 16:51
  #3254 (permalink)  
 
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This message indicates that the TCAS is inoperative. Without an associated fault message, it could be the consequence of an electrical power supply problem or of an external failure...
Electrical power supply problem? Please explain what kind of power supply problem it could be, Olivier. Are the TCAS antennas in this case considered internal or external?
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Old 10th Apr 2011, 17:16
  #3255 (permalink)  
 
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Originally Posted by Greybeard
Electrical power supply problem? Please explain what kind of power supply problem it could be, Olivier. Are the TCAS antennas in this case considered internal or external?
IMO, it is too much reading and the wording may induce it.
The BEA is listing the two shut down cases due to "external" systems.
a) its electrical power supply => if not powered anymore, the TCAS become inop.
b) another external failure.

This CFR from ACARS is pointing to b) wrong air data, altitude, ADRs. (and much more would be said by the maintenance computer after landing).
This is also consistant with no "Electrical power supply" failure detected.

All relevant parts of any system are of course part of it. Then, this mean that those "TCAS antennas" are included inside TCA system like those SATCOM antennas are part of the SATCOM system.
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Old 10th Apr 2011, 17:37
  #3256 (permalink)  
 
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Meanwhile back on AF447

Meanwhile back on board AF447..........I am so curious as to know what reasons are there for a very experienced flight crew to not have followed normal procedures. Some questions that drivers may be able to enlighten us on.
1. Twice Recife had to correct crew on confirmation of HF fequencies, minor errors they may be. Casual responses by crew, or distracted?
2 Crew did not respond to ACC-AO request for Tasil estimate. (One reason given in previous thread was that some crews switch to new frequency early)
3. and why did they fly into the Cbs in the first place? AF Inflight procedures state that radar watch is obligatory on all flights, except day time with good vis.
4. Providing the crew were not incapacitated,
a) can it be assumed that they were too complacent?
b) why did the Captain leave the FD for his nap (assuming he did) when the flight was heading for the ITCZ? Was it a case of 'okay guys I am obliged to take a rest now. Good luck at the ITCZ'? I would have thought he could have waited until after. But procedures have to be followed I suppose.
c) and how about this scenario. Did the remaining two crew have a visitor after the Captain had gone to the crew rest, say an FA? I know that happens some times. It is a long boring flight. While the Captain's away,the flight crew will play?
These were very experienced crew, especially the FO in the RH seat with 39 rotations on the SA sector. Very well aware of the ITCZ they were.
I am not making any accusations, unlike the French magistrate. Just getting things back in line with this thread.
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Old 10th Apr 2011, 17:59
  #3257 (permalink)  
 
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2. then a 2min 10 sec period in which orientation varies sufficiently that ACARS is interrupted: can't send (29 sec), then can (29 sec), then can't (31 sec), then can (16 sec), then can't (17 sec), then can (12 sec). Note that the periods are roughly equivalent, but shortening. Then some unknown time, max 54 sec, to impact, but effectively flat and able to send ACARS.
I was wondering a bit the same why BEA only considered one of those phases where there was a delay as a loss of signal.

If all these phases were due to loss of signal, that would indicate really severe movement of the aircraft.
As to what kind of attitude would fit to that:
Maybe a 'Falling Leaf'.
However I'm not sure if a swept wing airliner is susceptible to that. I'm not aware of any previous case of an airliner coming down in a genuine 'Falling Leaf' attitude.
A simple spin probably won't do.
On the other hand I'm a bit surprised that BEA doesn't know if it was due to weak signal. I would have assumed the SATCOM provider should be able to determine that.
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Old 10th Apr 2011, 19:25
  #3258 (permalink)  
 
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Originally posted by Graybeard ...
This credibility filter, if it existed, would logically be in the Mode S transponder, not the TCAS.
I wondered when I last posted on this, if the TCAS also inhibited the the Mode S Transponder at the same time, to avoid the potential for mayhem.
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Old 10th Apr 2011, 19:32
  #3259 (permalink)  
 
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From Auraflyers calculations,

  • 2:10:04-2:12:16 - cascade of faults generated but ACARS still able to be sent - 17 received.
  • (in this period, possibly 2:14:20, the cabin advisory message is generated)
  • 2:15:14: latest time for impact for followup ACARS fault message not to be received.
If the sequence started at 2:10:04 with cabin pressure advisory at 2:14:20 end of sequence 2:15:14, then from a starting altitude of 35000 and 6000 assumed at the pressure advisory, a linear calculation of height loss gives 113 fps 35000-6000, and a remarkably similar 111fps for the final 6000 feet. That would indicate a continuity in the vertical dynamics.

Incidentally, would engine power loss and switching the APU on generate an ACARS message ? Maybe loss of power and then restoration would have caused a gap in transmission.

Last edited by Mr Optimistic; 10th Apr 2011 at 19:49.
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Old 10th Apr 2011, 19:34
  #3260 (permalink)  
 
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Originally posted by auraflyer ...
Some of the more recent posts have raised a few things that I thought had been settled by the two BEA reports.
You are right, though there are some that believe that the BEA have got it wrong. Why? I don't know, as at the very least they have in their hands what has already been recovered and access to all relevant data.
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