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AF 447 Search to resume

Old 11th Apr 2011, 16:20
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Cabin V/S message

Quote from HN39:
"...if it [the negative relief valve] did not open, then please come up with a mode of the CPC that would command the cabin to climb or descend at a rate greater than 1800 fpm. I believe that to be so improbable that it does not merit discussion on this thread."

takata and I have argued about this before, but I think there is one very remote possibility.

If at 0214z the aeroplane was still at medium-to-high altitude, a failure of both packs (or a double engine-failure) would cause a positive cabin VS (loss of cabin pressure) until the outflow valves had a chance to close. This might exceed +1800ft/min, falling (hopefully) to +500ft/min or less with the outflow valves closed (depending on the state of the door seals). Outflow valves closure might be automatic by a serviceable CPC, or by crew action if not (see the drill on takata's post).

However, I would have expected double pack failure and double engine-failure both to be ahead of cabin VS in the ACARS message hierarchy - they would be in ECAM hierarchy.
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Old 11th Apr 2011, 16:35
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Maybe I should elaborate on my earlier post on ACARS.

"MAINTENANCE STATUS ADR2" was transmitted at 2:14:14.

This should have been followed up by a Class 2 fault message between 2:15:00 and 2:15:14 (referring to BEA interim report). That Class 2 Fault message was not received. Since the Aircraft's orientation should have permitted sattellite communication prior to impact - that makes it likely that impact was within a minute post 2:14:14 - making it unlikely that the aircraft was at "medium/high" altitude at 2:14:14.
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Old 11th Apr 2011, 16:49
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Originally Posted by HazelNuts39
we discussed this at length some time ago. The options are:
- if the negative relief valve opened, it is irrelevant what the cabin pressure control was doing.
- if it did not open, then please come up with a mode of the CPC that would command the cabin to climb or descend at a rate greater than 1800 fpm. I believe that to be so improbable that it does not merit discussion on this thread.
PS:: In the earlier discussion you mentioned that the ATA code of the message points to the CPC. I believe the reason for that to be that the cabin pressure sensor is located in the CPC.
Salute,
If, if, if, hourah !
:-)
My point is that everything unproved by BEA analysis is worth mentioning. And so far, no analysis of this Cabin V/S adivisory will point at: there is only one explanation to this ACARS: the aircraft altitude had catched the cabin altitude at 0214:26 (less transmission protocole, less 5 seconds).

a) When the CPC is working in auto mode, some FMGC and ADIRUs imputs are needed (in this case, there is none and an upset would switch it to descent mode without any recovery altitude entered). Then, it is left in semi-auto mode (no FMGC/ADIRUs imput). Then, up to what speed may work the CPC in case of brutal and massive loss of altitude? (those working limits are for the full-auto mode).

b) In case of CPC problem (I'm mostly thinking about power supply due to on-going engine flameout issue); the CPC should switch to manual mode and use its built-in backup sensor (the one that you are refering at). In this case, the difference in sensitivity alone could produce an immediate altitude difference in cabin altitude of +/- 1,000 ft. While 5 seconds is enough to trigger such an advisory (+/- 150 ft difference = 30 ft/sec = 1,800 ft/mn).

So, I'm not as sure as you about its meaning, considering also that it is the last in the sequence and much more could have followed if more ACARS could be sent after this point in case, of course, that some power supply was still available for the SATCOM (or that the aircraft was not crashed).
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Old 11th Apr 2011, 16:57
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high sink rate

That's probably true for the initial pitch down when you intentionally let the speed to increase to VMO with idle thrust but soon the ROD will decrease and you certainly won't lose 36000 in 6 minutes that way.
On what ground are experts still thinking in terms of a normal descent from 36.000 feet down to the ocean?

There must have been a upset scenario pretty much from the beginning to loose that amount of height in the probable time frame. In itself its nothing more then loosing the potential energy. It´s traded for speed and or distance in the normal flight regime, and its used up by a lot of drag and loss of altitude in a deep stall scenario nd airspeed below flying speed.

To regain the speed, the drag has to be reduced by flight control input, normaly the stabilator to reduce the AOA. For that you need a favorable CG and full stabilator effectiveness (no out of trim situation like full nose up trim).
That simplified basic probably applies to most aircraft designs. Can´t think of AB being totally different when it comes back to basic aerodynamics.

I think it is pretty sure that an upset occurred leading to low speed, high sink rate and that continued to prevail until the final end. Aircraft had been lost before for that reason and a descent rate of 6.000 feet / minute does nor look unbelievable in such a situation.

Do we know anything about the position of stabilator trim and the position of the CG? Could´nt find it in the amount of posts.
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Old 11th Apr 2011, 17:11
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ACARS

Originally Posted by sd666
Maybe I should elaborate on my earlier post on ACARS.
Originally Posted by sd666
"MAINTENANCE STATUS ADR2" was transmitted at 2:14:14.
This should have been followed up by a Class 2 fault message between 2:15:00 and 2:15:14 (referring to BEA interim report). That Class 2 Fault message was not received. Since the Aircraft's orientation should have permitted sattellite communication prior to impact - that makes it likely that impact was within a minute post 2:14:14 - making it unlikely that the aircraft was at "medium/high" altitude at 2:14:14.


Salute,

Two other ACARS were "in the pipe" after PRIM1 & SEC1 faults which should have triggered something also before 0215.

But look at the BEA explanation for the end of ACARS:
a) the aircraft crashed. (possible)
b) the ACARS system was inoperative (possible)
c) the was no other ACARS to be transmitted. (false)

b) A power supply failure after 0214:28 could have stopped the ACARS transmission. Consequently, the crash time canot be acertained from the end of ACARS alone.

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Old 11th Apr 2011, 17:30
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Originally Posted by takata
the CPC should switch to manual mode and use its built-in backup sensor (the one that you are refering at)
Hi Olivier,

Thanks for your informed and elaborate reply. I've just one question. As far as I could find in the available documentation, the CPC has only one source for cabin pressure, i.e. its built-in sensor. Am I missing something?
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Old 11th Apr 2011, 18:02
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Originally Posted by HazelNuts39
Thanks for your informed and elaborate reply. I've just one question. As far as I could find in the available documentation, the CPC has only one source for cabin pressure, i.e. its built-in sensor. Am I missing something?
The system diagrams are also quite obscure to me but look at the FCOM note "Control indicators":
Note:
The pilot may notice a variation (up +/- 1000 feet) in CAB ALT indication on the ECAM PRESS page, when the system switches from the cabin pressure control AUTO mode to MAN mode, due to the reduced resolution of the backup pressure sensor.

Obviously, the pressure sensors in AUTO and MAN modes are definitively different ones.
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Old 11th Apr 2011, 18:06
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HN39;

Just digging around while we anticipate further once the Ile de Sein arrives and begins work.

The following is some more information about the cabin pressure and the advisory message. Just trying to get information out there to think with:

The negative pressure relief valve (located between STA 24 & STA 25 on the port side of the fuselage), is rectangular, has 4 spring rods which force it closed until a pressure differential opens it. From what I can determine, the test equipment "vacuum" pressure for a test of the relief system is about 0.3psi. There is also a physical test...push the valve inwards for freedom of motion and re-seating after returning to the closed position. I don't know the valve's dimensions.

We know that the ADVISORY CABIN VERTICAL SPEED message was sent at 0214+.

Regarding system parameters monitoring and the ADVISORY function....Some system parameters are monitored throughout the whole flight and automatically displayed on the relevant system page when their value drifts out of normal range but well before the warning level is reached.

This is performed by the ADVISORY function of the EIS. In this case, the related key system light comes on on the ECAM control panel. The relevant page is displayed as long as the advisory is present and no other system page is called (manually or automatically).

On the right part of the lower ECAM (STS section) are displayed (in priority order):
- inoperative systems.
- maintenance items (class 2 maintenance status).

NOTE : The class 2 maintenance statuses are not displayed in flight but they are sent in real time to the CMC and they can be transmitted to ground via the ACARS when installed.

I don't think the Advisory message is a Class 2 maintenance message - as described, an advisory is an indication of a parameter exceedence and is not advice of a failure which requires maintenance action at the destination station. But the fact that Class 2 messages are sent in real time to the Central Monitoring Computer is interesting.

The last message received was the Cabin Advisory message. We know that such an advisory indicates a system parameter exceedence, in this case, >1800fpm or <1800fpm cabin vertical rate. (The size of the negative pressure relief valve opening could be used to determine flow rates and therefore rates of descent of the cabin but the exercise may not be worth the trouble).

As discussed and posited, we have concluded that cabin pressurization would become negative below the cabin altitude, whatever that was, and we have assumed around 7500 to 8000 ft barometric altitude, perhaps slightly lower depending upon data available to the CPC, (ie, flight phase will not have changed from CRUISE to DESCENT because the FMGEC and therefore the CPC will not have been in the descent mode and may not have begun depressurizing the cabin as per the usual schedule).

Then we have this information:

Low Delta P/High Descent
This shows that the aircraft will have a negative differential pressure if the descent rate is continued and that a negative pressure relief will occur. The signal is sent from the automatic part of the cabin pressure controller 1.5 minutes before the external pressure is the same as the pressure in the fuselage.

and,

Low Differential Pressure
If the cabin pressure controllers detect that a negative differential pressure situation may occur in 1.5 minutes: - a single chime is heard, - the amber MASTER CAUT lights come on, - on the EWD of the EIS, CAB PR LO DIFF PR and the necessary steps are shown.

Pondering the question...depending upon altitude, descent rate and the incoming data to the CPC, we might have expected this caution to trigger if the conditions which triggered the CAB VERT SPD Advisory were as we are assuming, (essentially, high aircraft descent rate "caught the cabin", as we say) a high descent rate passing through 8000', approximately. But the CAB PR LO DIFF PR, which, (now theorizing), according to the above description would have occurred either before (a minute and a half to be exact) or simultaneously with the Advisory, is not in the ACARS listing. We don't know if the message depends on the flight phase, (some warnings and cautions are inhibited in various flight modes).

The risk is always in over-thinking something but "obvious" is only available afterwards! These are some random thoughts which may or may not be useful in others' thinking.
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Old 11th Apr 2011, 18:42
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A chilling conversation

Our discussion on the choice of initial, and subsequent, search area has been made with the assumption that the pilots on the flight deck were behaving as rational actors in most respects. From this, we attempt to solve the mystery regarding how far and for what amount of time they remained "on original track." This leads to the perplexing question of

"How can they not have been further than position "X" based on time, distance, velocity, and eventual arrival at the ocean after descent at "Y" rate?"

There's a chilling possiblity that had not occurred to me until I spoke with some old colleagues (we had a twenty-five year reunion from our old squadron) all of whom are now in either the Passenger Carrying or Freight Carrying profession with such companies as AA / Delta / Southwest or Fedex / UPS.

That possibility: a delayed course change (to evade towering cells) that was in progress at the time of the upset, the course change delayed due to physical fatigue. I asked a few of the guys if they'd been watching this investigation (after we'd had a chat on the Cargo Crash in UAE), and Capt "H" very quickly opined the following:

"I think you'll find out the crew were asleep when they find the CVR."

I wasn't prepared to consider that.

I asked how the heck he knows that?

I pointed out that I understood the Captain to be in rest, per a typical long haul practice in many airlines, with two FOs alive and well on the flight deck.

Capt "H" nodded, and said quite simply that he finds the Occam's Razor explanation to be that the two on the flight deck nodded off. He'd had it happen to himself more than once when he was an FO. Typical happening was the Captain on a long haul would advise him "I'll be getting 40 winks, make sure I am awake in an hour" and before an hour is up, "H" with all great intention to stay awake, nodded off himself, to be awakened by said Captain a bit later ... but nothing bad happened in any of those cases ...

He then helped me understand what could happen.

NOTE: this is a bit of reasoning not intended to injure the rep of the gents on the flight deck that evening, but a way to address

"How did they not go further down intended track based on what is available to know from Wx and ACARS to date?"
(Idea being that they should have been farther down track from LKP).

With a scheduling variation that doesn't allow both of the co-pilots to quite adjust their circadian rhythms, they are by rule "crew rested" but in mid-cycle (circadian rhythms) on the day of this event.

So, per usual, Captain does take off, and a bit later goes off to rest bunk to be sure he's fresh for approach and landing later on in Paris. Two perfectly good and reasonably rested pilots/FO's are on the flight deck, but due to their Circadian rhythm being a bit out of synch, are on a not-quite-settled rest cycle. (I ran into this problelm in the fleet years ago when we began a few weeks of midnight launches, after a few months of mostly day and evening ops. It takes a few days to reset the clock ... we had a number of close calls with eyelids on pilots, and in one case a crewman who made the "wake up" call in time ... )

One nods off, then the other ... and by bad luck, none of the FA's or other Cabin Crew had occasion to communicate with the flight deck for any of the usual reasons. When the big cells appear on Wx radar, neither cued the other to avoid storm (stay with me here) since neither saw the display.

At little bit later (perhaps an FA knocks on the door with coffee?) one of the two awakens much closer to the storm system, and with a peak at the radar realizes

"Whoa, must deviate/change course, too close to storm system."

Being human, and not wanting the Captain to be angry for getting behind the situation, he has awakened his mate and is in process of a course change (both being in the "must sort this out and not get the Captain mad at us" mind frame) when they encounter the severe weather's effects on the airplane. (Note, this sequence of events also points to flying as a priority, aviate navigate communicate, and thus they don't get the message out to the pax "strap in, rough weather ahead" nor to the FA's. Playing catch up, and all that goes with it. Evidence points to quite a few folks not being not strapped in ... )

With (5 or 10 or 15? degree) AoB of turn, you lower your stall margin, right? (At those altitudes, and at that mach number, per previous posts in this thread, it's pretty obvious that one handles any turn with care.)

That aerodynamic reality suggests that if this course change were in progress, the stall occurred in turning flight rather than in level flight ... with the idea that the stall was triggered by hitting unstable air with less stall margin than one normally carries.

This might explain the upset in the first place. (Reduced stall margin).

To compound that, pitot tubes all iced up won't help them after upset occurs, and they have bad to no airspeed information (at least initially) in their scan as they attempt to recover from the upset.

With this unexpected event confronting them, crew for one reason or another (many such reasons were discussed in massive depth in this thread for the past year and a half) were unable to recover.

While attempting to, they were not heading in the general direction of the original flight planned route, but in a turn (one way or the other) away from flight planned route. This changes/reduced the time and distance clicking away. This proposed scenario may resolve the puzzle over why they were this close to LKP.

The other chilling idea based on Capt "H" and his Occam's Razor -- nod off and just fly into the cells -- doesn't answer the problem of "so close to LKP" and isn't something to discuss in the context of

"How do you decide where to look and why, based on a datum of LKP and an estimate of upset based on ACARS?"

BEA had to make some assumptions on where to place datum and where to begin their search. If the assumption included "generally heading along original course from this flight plan" it could explain why they didn't look closer to LKP.

If I remember rightly, early on in the discussions here on PPRUNE forums, some folks had raised that idea of a nod off. It is not my intention to resurrect that zombie, but to apply that idea to the possible effects of track and thus location of the wreckage based on LKP.

Apologies if I was not clear about that earlier.

I am not sure if Capt "H" is right. His remark got me thinking that AF447 migh have been making a course correction/deviation around the cells when an upset occurred, with consequences that I had not yet seen in our lengthy discussion here.

EDIT: I had to revise this a bit to make it clearer.

Last edited by Lonewolf_50; 11th Apr 2011 at 19:10.
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Old 11th Apr 2011, 18:56
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Update on 2010/04/11 meeting between BEA and family representatives

Tour Hebdo - site officiel - Transport : AF 447 : les éléments de l'avion rapatriés mi-juin

Google translation:

AF 447: The elements of the aircraft returned mid-June

Posted on 04/11/2011 4:45:00 p.m. Secretary of State for Transport, and Jean-Paul Troadec, Director, Office of Investigations and Analysis (BEA) for the safety of civil aviation, today received the Information Committee Families of victims of Flight 447 from Rio to Paris, with representatives of the Gendarmerie Air Transport and the Institute of Criminal Research Gendarmerie Nationale.

This meeting served to discuss with families the BEA and the organizing of the raising of the wreck, a week after its location. The ship Ile de Sein French group Alcatel Lucent, responsible for the wreckage recovery, from Cape Verde on April 21 without a representative of families on board, "so as not to affect the judicial process."

The return of the ship is scheduled for mid-June. Priority will be given to the technical investigation and, if found, the recovery of flight recorders. He also indicated that attempts to families will be conducted to trace the bodies of victims to meet the obligations of the judicial inquiry. If it is possible to go back, they will be identified in France and returned to their families faster.

"The timing of the operator today can be readjusted if the recovery operations require more time," said Thierry Mariani. At this meeting, the Secretary of State presented Philippe Vinogradoff new ambassador in charge of relations with families, appointed by the government to be the sole contact between the families of victims and the various authorities of each country.

Last edited by auv-ee; 11th Apr 2011 at 19:28. Reason: Restored the sentance about return in June, which was accidentally deleted.
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Old 11th Apr 2011, 19:44
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Ah the great french judicial system, the wreckage will probably spend another 2 years in a shed near paris waiting for a "justice" to decide whether or not to allow the BEA access to it.
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Old 11th Apr 2011, 19:47
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Ah the great french judicial system, the wreckage will probably spend another 2 years in a shed near paris waiting for a "justice" to decide whether or not to allow the BEA access to it.
And before this will start, the President himself, Mr. Sarkozy, will do a "test flight" on an A330 Simulator.
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Old 11th Apr 2011, 19:53
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More on 2010/04/11 BEA meeting

Nothing new on the recovery, but more insight into the relations between France and the families:

Frana nega representante de famlias no resgate do voo 447

Google translation (too long to paste):

Google Translate
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Old 11th Apr 2011, 20:09
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Cool

Hi,

And before this will start, the President himself, Mr. Sarkozy, will do a "test flight" on an A330 Simulator.
The president Sarkosy don't need a A330 simulator ... as the presidential plane "SARKO 1" is a A330 !
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Old 11th Apr 2011, 20:24
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CPC

PJ2;

Thank you for collecting and sharing so much fascinating information!

One question comes to mind. In order to generate the 1.5 minute advance warning, the CPC's need aircraft altitude (or static pressure). Would that information coming from the ADIRU's in ADR DISAGREE mode be considered valid by the CPC's?

Last edited by Jetdriver; 12th Apr 2011 at 04:58.
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Old 11th Apr 2011, 20:32
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Takata:

"b) A power supply failure after 0214:28 could have stopped the ACARS transmission."

What evidence is there of a power supply failure?

The only evidence is the absence of a Class 2 status message. This would require the loss of both power sources within a 60 second window. It's possible (so BEA rightfully list it) but unlikely - there's redundancy in the power supply.
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Old 11th Apr 2011, 20:47
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Hi SD666,

Quote:
What evidence is there of a power supply failure?

(I shall assume that is not a rhetorical question.) Definitely at the end of flight; otherwise it reqiures the roughly-simultaneous loss of all AC generation. Assuming the APU was not running, this would involve the loss of both engine-driven AC generators (one per engine). In each case, that could be caused by a failure of either the generator itself or the engine. As you could tell me: to prevent an ACARS message being sent for the first failure, the second failure has to be very soon after the first. By definition, therefore, there can be no ACARS evidence of such a failure sequence.

Thanks for your informative and well-argued posts.
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Old 11th Apr 2011, 21:22
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Bleeding speed fast

Gentlemen,

there is one possibility for a very fast deceleration from cruising speed to stall speed (low speed, high AOA stall), and that possibility was only brushed by a few people here : pulling back hard on the elevator controls.

I leave to your imagination why such an action would be taken. I have my own idea. And remember, the humans in the cockpit are not the only ones with access to flight controls. The aircraft itself usually has the final say over these controls.

Regards
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Old 11th Apr 2011, 21:29
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Chris:

Good point, though I'd still argue you've got auto re-light and RAT as protection layers. All-in, I think dual-flameout is not a high probability.
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Old 11th Apr 2011, 21:44
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sd666,

All agreed, with the proviso that RAT in itself would not, I think, restore enough AC power to enable ACARS messages.
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