AF 447 Search to resume

[takata]

Hi Chris,

Originally Posted by Chris Scott

Can you explain what “external pressure” has to do with cabin pressure (cabin altitude) and cabin VS? What am I overlooking?

Maybe the controller schematic. What ADIRU 1+2+3 are used for?

Originally Posted by Chris Scott

Alternatively, why would an ECAM warning of excessive cabin VS be spurious? The creation of the warning implies that cabin pressure data were still available. That being so, what would cause them to be corrupted?

It is not ECAM warning. It's an ADVISORY (controller to be set on manual).
S~
Olivier

[takata]

Originally Posted by bearfoil

Then again, Figaro tells me the Muslim "problem" is overblown

Well not really:
"Six mois après, la «Musulin mania» s'est essouflée"
read: mu -su- lin
It is someone's name (a money convoyer), and nothing to do with "Muslim problems".
But the beacon possible range of separation is 1.5 to 8 km, will certainly be the smaller range and might be simply due to area relief.

Originally Posted by savu

The uncertainty comes from : the sub's navigation uncertainty added to the bias on sound propoagation

Sub's undersea navigation is quite accurate and signal was picked during some time along this zone exploration. Signal propagation is certainly the main factor but as sub moved, it would be possible to make corrections.

[takata]

Using this false post to answer Savu post below:
Sub navigation (SNA) had to be precise at any time to cover assigned search area. This was a systematic search, controled by surface vessels and all military navigational systems.
Here are BEA maps from today presentation: SNA search zone assigned (until 10 July) is the left zone while TPL searched the right zone.

[savu]

Just like when we're flying, submarine inertial navigation accuracy depends on many factors such as the length of time since the sub had a positive fix on an external reference (whether visual - not easy in that place- or sattelite or radionav). However accurate inertail plant may be, there always comes a time when the estimated position has been drifting a bit. My guess is, would that sub have detected some signal, they would have soon fixed their position, but at that time, the inacurracy was not a big deal as long they had nothing to report.

[Hyperveloce]

Takata, do you mean that the pingers signal separation (1.5 to 4 NM) could be spurious and due to multipath (like echoes, delayed replicas) induced by the rough seafloor ?
Jeff

[takata]

Originally Posted by Jeff

Takata, do you mean that the pingers signal separation (1.5 to 4 NM) could be spurious and due to multipath (like echoes, delayed replicas) induced by the rough seafloor ?

This will give the incertitude range but it is not the only factor. Sinking down to 3,000-4,000 depth in mountainous terrain might give separations even if both were close in surface. One piece may sink and hit one sloped face of a mountain, roll down into one valley while another may sink and hit the other face and roll down into a different valley.

[mm43]

Update: "Seabed Worker" - positions

The "Seabed Worker" has been moved a little more to the east. Limited position information makes it difficult to judge what she is doing, but currently my guess is that she is still running her two Remus AUVs.

10 May 2010 12:14z Hdg 319.2 Spd 02.3 2°43'05"N 31°06'26"W
10 May 2010 10:22z Hdg 318.3 Spd 02.2 2°40'00"N 31°03'44"W
09 May 2010 23:50z Hdg 281.4 Spd 00.9 2°41'59"N 31°08'03"W
09 May 2010 22:06z Hdg 120.8 Spd 01.0 2°41'52"N 31°07'45"W

An updated bathymetric chart which includes an added colour spectrum scale along with a lat/long grid as a reference. Remember the spectrum colors are only a guide and that the contour relief of the bathymetry will change the saturation.


mm43

[Chris Scott]

Possible implications of CABIN VERTICAL SPEED ADVISORY (cont’d)

Bon soir takata,

Quote:
“Maybe the controller schematic. What ADIRU 1+2+3 are used for?”

To do its whole job, a CPC obviously needs to know the aircraft altitude (external static pressure), which it obtains from the AD part of the ADIRUs. It is also interested in the aircraft VS, and during aircraft climb and descent will adjust the cabin VS − for example if the aircraft VS is higher than expected − to keep the differential pressure at manageable values. These are the data it obtains from the ADIRUs. Their accuracy would be affected in the unlikely event of icing of one or more static ports.

Unfortunately, the schematic does not show where the CPC obtains the cabin altitude and cabin VS from. But these require, by definition, a sensor or sensors within the pressure hull. These presumably communicate data to the CPC and the FWC electronically. A loss of power could interrupt receipt, but received data should be valid.

Again unfortunately, I don’t have the exact criteria for the production of this advisory by the FWC, so am relying on other’s posts. These indicate that it is triggered by excessive cabin VS for at least 5 seconds, no other data being considered.

So I repeat my question: why do you dismiss this ECAM warning (sorry − advisory) as being spurious, or irrelevant?

Chris

[mm43]

Hyperveloce;

There is always the possibility that the 37.5kHz pinger bursts ducted between salinity inversion layers, and when detected by the sonar their source wasn't necessarily in the immediate vicinity. A reason why the BEA wants the ULB frequency lowered to a nominal 9kHz.

mm43

[mm43]

originally posted by takata ....
Good guess, but how would the controller know "outside" pressure without ADIRUs providing "oustide" pressure?

Further examination leads me to believe that should barometric data not be available from ADIRUs 1, 2 or 3, then the Captains static baro is supplied via the FMGC.

mm43

[Hyperveloce]

Cabin Vertical Speed Advisory

thinking to this last ACARS at 02:14Z, we can bear in mind that all the past Pitot freezing events duration was less than 4 mn (typically 3mn): even if the static ports were compromised during the cruise phase at high altitude at 02:10Z (during these past events, it induced a slight barometric altitude bias: a few 100ft), after more than 4 mn and probably, in the AF447 case, a large loss of altitude (external temp. increase), isn't it probable that the air data (ADR) had recovered/de-iced ? beside the BEA reports have raised the possibility that the PRIM were manually reset at 02:13Z (to explain ACARS that were not seen during the other past Pitot freezing events): if true, this could only have happened because the air data was back at 02:13, prompting the crew to try to regain the normal law, don't you think ?
Jeff

[Yiorgos]

Originally Posted by Takata:
One piece may sink and hit one sloped face of a mountain, roll down into one valley while another may sink and hit the other face and roll down into a different valley.

True, and let's not overlook that one piece may go straight down, while another may be attached to a structure with some buoyancy and therefore drift due to currents a considerate distance before it settles on the seabed.

Maybe someone who knows how the black box and CVR are attached to the airframe can shed some light on this possibility.

[HazelNuts39]

Cabin Vertical Speed Advisory

RE: hyperveloce #989

Hi hyperveloce;

your observations are correct and relevant. However the main contention seems to be whether the advisory was necessarily generated below 7350 ft aircraft altitude, or that it could have been generated at cruise altitude.
EDIT:: By the way, freezing level was at 16350 ft according to Tim Vasquez.

regards
HN39

[mm43]

The vessel is still working in the zone in which the SNA "Emeraude" is believed to have recorded very low level ULB pinger signals. The BEA have said that should debris not be located in this zone by 12 May, the search area will be extended. Should that occur, then the ducting theory will have been correct, but the path loss is such that the search zone would normally have taken that into account.

10 May 2010 22:40z Hdg 262.6 Spd 07.0 2°41'07"N 31°10'28"W
10 May 2010 20:54z Hdg 260.9 Spd 00.4 2°42'28"N 31°05'45"W

Weather is wind 090/5-10KT, swell 090/1.5m period 8/9 sec. with little change expected over next 3 days.

mm43

[auv-ee]

MM43 wrote:

The BEA have said that should debris not be located in this zone by 12 May, the search area will be extended. Should that occur, then the ducting theory will have been correct, but the path loss is such that the search zone would normally have taken that into account.

If the sound does become ducted, then from that point on, spherical spreading no longer applies, so the amplitude would not drop as much with increasing range. The closest model may be circular spreading (if the sound is trapped in planar layers), or some other depending on the boundary constraints. If this happens, the detection range, as measured along the ray path can be extended. The attenuation loss continues to apply, but is a function of temperature, salinity and pressure, and thus will be somewhat different for a near-surface path than for the deep ocean path. Within a duct, there are usually multi-paths, and these interfere in ways that can decrease or increase the sound level at various points in the duct. This scenario assumes the receiver is also in the duct or is at a point where previously ducted sound is escaping the duct.. I have no idea if any such duct existed at the place and depth that Emeraude recorded the signals. A local sound speed profile would shed light on that, but one likely does not exist close enough to place and time.

I'm not sure what conditions have to exist for sound from a deep water source to enter a duct. It seems like the angle of incidence would have to be far from vertical, which would increase the path length (slant range) making for an already weak signal at entry. I was assuming previously that useful ducting was unlikely on that basis, but who knows.

[mm43]

auv-ee wrote:-

I'm not sure what conditions have to exist for sound from a deep water source to enter a duct. It seems like the angle of incidence would have to be far from vertical, which would increase the path length (slant range) making for an already weak signal at entry. I was assuming previously that useful ducting was unlikely on that basis, but who knows.

My assumption was based on the angle of incidence having changed when transitioning a deepwater inversion (4,000m) and subsequently becoming entrapped on encountering another layer in the 300 - 500m range. If that was the case, it would explain the apparently low signal/noise levels that have been recorded.

As you say, we don't know at what depth the sub was operating, though on examination of some bathymetry I believe she obtained, I'd make a guess and say in the 150 - 200m range.

mm43

[DjerbaDevil]

To auv-ee:

Thank you for your detailed and informative reply. Seems Thales worked a miracle to find ways to identify the pings from the background noise. Let's hope there's news of a find soon.

[grizzled]

While we wait (with the highest of hopes) for news, and in between mm43’s –and others – amazing and informative contributions, I would like to bring up a matter raised a few days ago by machinbird.
His post related to accident remains, and it got me thinking again about the issue of the autopsy reports. Sadly, like machinbird, I too have some experience with accident remains (meaning the aircraft and its contents). In that regard I agree with his comments about the nature of damage and injury in different scenarios. For that reason I find it amazing that it’s almost a year since the accident and yet the autopsy reports have not yet been shared with the BEA.
Though it’s of course not a pleasant subject, it must be said that much can (and would) be learned by the BEA from the autopsy information (assuming of course that the autopsies were professionally performed. I have seen nothing that casts doubt upon that notion.)
One small example: The information we do have (from the BEA) suggests that the bodies that were recovered were identifiable and intact. That in turn strongly suggests an impact that was not as catastrophic as some have surmised. Indeed, to me it suggests the possibility that some semblance of control may have been present until impact, or until shortly before impact. This scenario seems even more plausible as the now presumed location hints at the possibility of a longer flight time than was previously envisioned by some.
CAVEAT: I have gone to great pains to use terms such as “may have, possible, plausible, and suggest” extensively. I am NOT putting forth an explanation; I’m simply pondering.

grizz

[takata]

Hello mm43,
Thank you for keeping updated the Seabed Explorer positions.

Originally Posted by mm43

Further examination leads me to believe that should barometric data not be available from ADIRUs 1, 2 or 3, then the Captains static baro is supplied via the FMGC.

FMGC doesn't supply air data to the controller but only flight plan related data: altitude at departure, altitude at landing, altitude at cruise, etc. in order to calculate the various cabin altitude regulation adjusted in time with the flight plan. On the other hand, what is mentioned is that the controller will use Captain ADIRS (ADIRU 1). "Captains static baro" is displayed by ADIRU 1 which is either ON or OFF (no separation is made from the components of Air Data (AD) part of each ADIRU, only Inertial Reference (IR) part may be separated if AD part fails.

MAIN COMPONENTS
Cabin Pressure Controllers:
Two indentical, independent, automatic controller are used for cabin pressure control. They recieve signals from the Air Data Inertial Reference System (ADIRS), the Flight Management and Guidance Computer (FMGC), the Engine Interface Unit (EIU), the Landing Gear Control Interface Unit (LGCIU), the Proximity Switch Control Unit (PSCU), and the pack flow control valves. They perform the automatic cabin pressure control. They generate signals for the ECAM. In automatic mode, each controller had a backup section, which is powered by an independent power supply in the controller No.1 position. This selection also has a pressure sensor that generates the cabin altitude and pressure signal for the ECAM, when MAN mode is selected. The controllers communicate via a cross-channel link.

SYSTEM OPERATION
Automatic Pressure Control Mode:
- The controller normally uses the landing elevation and the QNH from the FMGC, and the pressure altitude from the ADIRS. If FMGC data are unavailable, the controller uses Captain Baro Reference from the ADIRS and the LDG ELEV selection.

[takata]

Hi,

Originally Posted by Hyperveloce

thinking to this last ACARS at 02:14Z, we can bear in mind that all the past Pitot freezing events duration was less than 4 mn (typically 3mn): even if the static ports were compromised during the cruise phase at high altitude at 02:10Z (during these past events, it induced a slight barometric altitude bias: a few 100ft), after more than 4 mn and probably, in the AF447 case, a large loss of altitude (external temp. increase), isn't it probable that the air data (ADR) had recovered/de-iced ? beside the BEA reports have raised the possibility that the PRIM were manually reset at 02:13Z (to explain ACARS that were not seen during the other past Pitot freezing events): if true, this could only have happened because the air data was back at 02:13, prompting the crew to try to regain the normal law, don't you think ?

Well, there is no rule saying that, because previous documented freezing events at such high altitude lasted from few seconds to 2 mn, this one would be over after 3 mn. Also, none of the previous events caused an aircraft to crash. Going lower may in fact add much more to the problem rather than resolving it as we might suppose that they were flying above thunderstorms. In fact, much more water particules would be encountered below AF447 actual cruise level before going out of the "freezing zone".
The only reason (beside other problems) why they would have to initiate a descent is that they couldn't climb above this level while turbulences would make their current flying altitude dangerous.

Furthermore, going back to "Normal Law" was certainly not an option as they would have to land first before it could be restored. Once ALT2 is triggered by such faults, they would be struck into this mode until landing and maintenance performed on the Air Data systems.

S~
Olivier