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AF 447 Search to resume

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AF 447 Search to resume

Old 9th May 2010, 20:22
  #941 (permalink)  
 
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Gualala;

I note from the CMA-2102 specs that the beam switch speed is less than 50uSec and the nominal 12dBi gain should be good provided the aircraft does not get in the way. I wonder why the BEA decided that there was LOS in the times they mentioned. Perhaps one day they will correct that error.

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Old 9th May 2010, 20:52
  #942 (permalink)  
 
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snowfalcon2, the initial search was a long, narrow, rectangular box from the last reported position almost to Tasil, favoring the right of the expected track. A second search box was flown that day in a more square-shaped rectangle from the last known position to about half-way to Tasil.

Searches on the days following were made to the right of the track, and south of the last known position, even south of the St Peter & St Paul islands. Various sightings of possible debris led in part to searches in these areas. I believe no debris from AF 447 was actually found in the searches from June 1 through June 5.

Once a search was again done that covered the area that was left of the track, the first bodies were discovered on June 6, approximately halfway between the last reported position and Tasil. These bodies were left of the track. If the bodies had been in that location on June 1, I believe that they would have been within the boundaries of the two search boxes of June 1.

By being outside the boundaries of the initial search, they were missed.

Hindsight is always 20/20, but it is unfortunate that the search on subsequent days was devoted to areas to the right of the track. If the search boxes of day 2, which were run basically perpendicular to the right of the track (as if the aircraft had deviated right) had been mirrored by searches to the left of the track, its quite likely bodies and floating wreckage from AF447 would have been found on June 2nd or 3rd. That would have fixed the impact position a lot more precisely.

Having limited resources, a long distance to fly to the search region, the Brazilian military made the judgment of where, given the currents and meteorology, the impact was more likely to be, and focused their efforts there. In a more perfect world, they would have looked as earnestly at the area to the left of the track as they did on the right.
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Old 9th May 2010, 22:40
  #943 (permalink)  
 
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Update: "Seabed Worker" - position

Here are the latest available positions for the vessel:-

9 May 2010 11:59z Hdg 050.0 Spd 01.5 2°42'12"N 31°08'07"W
9 May 2010 09:50z Hdg 166.1 Spd 02.9 2°42'17"N 31°08'18"W



The ROV appears to be down, and hopefully the recovery of the DFDR and CVR is underway.

mm43

Last edited by mm43; 9th May 2010 at 23:01. Reason: update graphic
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Old 9th May 2010, 23:13
  #944 (permalink)  
 
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Sounds good, mm43. Bon courage à tous. May all our speculations soon face the moment of truth. In the meantime…

Quote from mm43:
“If the APU had been started, would the Cabin Pressure controller have been active? I haven't seen any data on this, and have assumed that should there be no electrical supply from the prime sources that the controller would operate below 8000/7350 feet to equalize the cabin pressure.”

Don’t have an A330 Tech Manual, and no doubt the Cabin Pressure controller employs data from many sources, including the Air Data elements of the ADIRUs. As I think HazelNuts39 has said somewhere above, however, aircraft cabins are not designed to withstand a negative differential pressure, i.e., a lower pressure inside than out. In an unusually rapid descent to sea level from normal cruising altitude, the controller will do its best to keep the cabin altitude below aircraft altitude, by increasing the cabin VS; but may eventually be unsuccessful. In a rapid descent, we call that “catching up with the cabin”, don’t we? That’s why there has to be an inward relief valve, which is purely mechanical.

As for the readings of cabin altitude, I don’t see why even (improbable) icing of the static ports, as postulated by takata, should invalidate cabin altitude (or VS). If I was a passenger on the aeroplane, and was carrying on my lap a good old-fashioned altimeter and similar VSI, their readings would be little different from those used by the Cabin Pressure controller. Cabin pressure is cabin pressure, and is measured somewhere inside the cabin or pressure hull; nothing to do with static ports.

Unless I’m missing something, the readings should be valid, and their interesting implications follow.

Chris
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Old 9th May 2010, 23:27
  #945 (permalink)  
 
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Thanks mm43,

So the sharp turn at 2:10:34 or so did NOT cause a communications blackout. That came later. Communications should have blocked out during the postulated 50 degree bank for the 135 degree turn. Apparently it didn't, which is strange. And then it did blank out when the plan was apparently straight and level.

This gets more puzzling each time we get a little more data.
{^_^}
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Old 9th May 2010, 23:35
  #946 (permalink)  
 
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Machinbird, the ACARS antenna is, apparently, a patch style antenna with no "gimbles" as such. It's electronically steered with a very wide beamwidth. (50 to 90 degrees) It can probably be steered to within 15 degrees to 20 degrees of the antenna's plane and, of course, all the way up to normal to the antenna's plane.

What I don't know is whether the antenna is operated open loop off aircraft navigation data or closed loop with a servo. Given the wide beamwidth I suspect the antenna is simply steered off basic aircraft navigation data and the (fairly well) known satellite position.

We discussed this back in the old thread. I don't remember enough of it off the top of my head to be sure on details. But I do believe a 50 degree bank would have put the aircraft between the antenna and the satellite which was off to the West of the aircraft by a significant amount. Digging back to the original discussion should dig out the details of the antenna. I remember a posting that pointed to the manufacturer's data sheet.

{^_^}
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Old 10th May 2010, 00:00
  #947 (permalink)  
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mm43;
If the APU had been started, would the Cabin Pressure controller have been active? I haven't seen any data on this, and have assumed that should there be no electrical supply from the prime sources that the controller would operate below 8000/7350 feet to equalize the cabin pressure.
The #1 CPC is powered by the DC ESSential bus, the #2 CPC is powered by the DC1 bus and CPC Manual Control is provided by the DC BATtery bus.

So yes, the control of cabin pressure would have been fully available with APU and even with with no APU with manual control from the DC BAT bus.

Chris Scott is correct regarding negative pressure relief; the single valve is installed aft of the L1 door.

Takata;

Just for info....it is not possible to say without very detailed examinations and perhaps simulator investigations, that the CPCs would be affected by loss of just the 3 ADRs due to iced pitots only. I wondered about this but cannot determine it from the FCOM.

Some data may still be provided to the CPCs or it may not - the FCOM is very simplified and geared towards the flight crew "need-to-know" level. It is not entirely possible to confirm the effects of loss of just the static ports either, without a similar investigation.
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Old 10th May 2010, 00:03
  #948 (permalink)  
 
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Chris Scott;

Thanks for answering the question. Reference to the Cabin Pressure Controller schematic shows that in Automatic Mode the barometric reference comes from the ADIRUs, but my take is that should that reference fail, then it selects Manual and the Safety and Relief valves will attempt to keep Cabin Pressure equal to the outside when descending below 8000/7350 feet. Here's the schematic for good measure -



mm43
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Old 10th May 2010, 03:05
  #949 (permalink)  
 
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Good to hear about the progress of the search.

What are the chances of larger fuselage pieces being found as well considering some bulky pieces were found in the initial search. Hope to hear more news soon.
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Old 10th May 2010, 03:27
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Just another theory.....

If the cabin v/s condition followed engine flameout, the corresponding ACARS message would not have been sent. In my opinion

flameout is a dispensable element in this chain of events.
and as HarryMann said:
There are many other ways the descent and the actual crash into the sea could have been connected together, without one continuous event, surely?
The satcom on aircraft is an electronically steerable phased array antenna with nominal gain 12dB (type CMA2102). The info in BEA report re a satcom drop out is, I am reliably informed, a misunderstanding by BEA and there is no conclusive evidence of a dropout.
Astute .... unless there were onboard electrical disruptions....

All logical and tends to point to a structural failure (i.e. a partial loss of fuselage integrity causing a pressurization loss) following the high altitude loss of control - an overstress event that would not be a surprising outcome of a high-speed loss of control and tightening spiral.

Neither would it be inconceivable that the FBW flight control's circuitry (i.e. vice designed "graceful" degradation) may have been affected physically by any loss of fuselage integrity or bus loss (==> loss of roll or pitch axis control). But partial/limited control might have been regained latterly, sufficient to enable an erect attitude at impact.That theory of two "follow-on" event scenarios, broken by a brief interlude of partial control, ties in with the loss and later regain of signal period for the ACARS data.

I tend to favour the theory that something beyond normally allowable RTL-limited rudder deflections were permitted during their unusual attitude recovery, following the airspeed anomaly and ADIRU compromise. Large unintended rudder deflections during a high-speed LoC event may have partly detached the vertical stabilizer from its mounts, or even locked the rudder at a significant deflection.

Following the LoC recovery, with a rudder stuck at a significant deflection, the yawing roll may have been able to be countered by aileron control to achieve a wings level attitude, but the overall drag, limited controllability and descending trajectory may have quickly forced a ditching solution, notwithstanding that some power may have been available. A higher speed ditching may have been predicated by the limited controllability.
.
.
Just another theory.....
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Old 10th May 2010, 05:21
  #951 (permalink)  
 
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Higher Speed Impact

Some time ago, I offered the opinion that the evidence presented by the recovered debris and reports of injuries to passengers indicated a low speed impact. BEA hasn't yet come out with much on the horizontal velocity of the aircraft on touchdown but indicated a high vertical velocity existed.
My accident scene experience is limited to tactical jet aircraft and may not apply strictly to much larger aircraft, however let me share some mental data points I used to form my initial assessment.
Situation 1. An aircraft flying into the sea in near level flight at 300 knots. Data point: A piece of a crewman's boot, specifically the heel, torn away, complete with insole, and sheared in half lengthwise leaving only the starboard side of the heel. The few pieces of wreckage recovered were generally in the 18" to 24" size range.
Situation 2. An aircraft, departed from controlled flight <250 kt, with very high sink rate impacting the earth on the leading edge of the stbd (swept) wing. Data point: Every element of the forward fuselage was shattered to small pieces and most washed out of the crater by the fuel load. The after quarter of the fuselage did not shatter and retained its characteristic shape.
Situation 3. An aircraft impacting the water at 550 kt, 50 degrees nose down. Data point: Pieces of the crew were extruded into the instruments, some instruments were shattered some just crushed. Engine shells were converted into bent pieces of sheet metal.
I cannot convince myself that an airliner sized aircraft, impacting the sea at 300 knots with a high sink rate (even if in a level attitude) would not result in damage comparable to situation 1. The large size of the recovered cabin components indicates a significantly slower touch down.
It will certainly be interesting to see what the aircraft actually did assuming the DFDR is found and contains data all the way to touchdown.
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Old 10th May 2010, 05:45
  #952 (permalink)  
 
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Hello everybody,
Originally Posted by PJ2
Takata;
Just for info....it is not possible to say without very detailed examinations and perhaps simulator investigations, that the CPCs would be affected by loss of just the 3 ADRs due to iced pitots only. I wondered about this but cannot determine it from the FCOM.
Some data may still be provided to the CPCs or it may not - the FCOM is very simplified and geared towards the flight crew "need-to-know" level. It is not entirely possible to confirm the effects of loss of just the static ports either, without a similar investigation.
I agree with that, and like many here, I don't have access to A330 simulator and can't say a lot more about it.

Nonetheless, as a recapitulation of my point: (1) cabin pressure controler need to be feeded by external data and those data are known corrupted by (at least) pitot probes freezing with a verified error range well above 1,800 ft per min. in absolute value = 30 ft per second. (2) ADIRUs 1, 2, 3 are used to feed the controler, and all three are supposed rejected. (3) this alert (at this point) is minor, only informing the crew that cabin pressure is to be controled manually.

Consequently, it is not possible at this point of the flight (02.13) to deduct anything from this ACAR about:
1) Flight altitude;
2) Rate of descent/climb;
3) Depressurization issue.
i.e. This alert may be related to purely sensor/ADIRUs errors; it may be related to a real aircraft descent rate above 1,800 ft/mn from whatever altitude (in case external pressure is still feeded to the controler by another circuit - but whilch one?); it may be related to crew actions during troubleshooting...

But it doesn't mean that the controler was trying to regulate the cabin pressure at 7,350 ft or below. It is alerting the crew that the controler would be unable to regulate it automatically..

S~
Olivier

Last edited by takata; 10th May 2010 at 05:59.
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Old 10th May 2010, 06:08
  #953 (permalink)  
 
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Pinger Range

DjerbaDevil:

"First, it is difficult to imagine that a highly sophisticated and modern nuclear submarine would miss 'hearing' the signals from the black boxes but much more so to accept, that while they were recording sound, they did not record their position relative to the sound recording. "

Actually, detecting these pingers under the conditions encountered in the search is not so simple. Judging from the typical characteristics of the pingers used: (see Dukane model DK120 and DK100 Underwater acoustic locating beacons), 37kHz and 30 day duration, they are most useful when a plane goes down in shallow water and/or close to shore. After all, most aircraft accidents occur in the takeoff or landing phase, and thus happen in the vicinity of airports. What is needed for deep water recovery are larger/heavier transducers at 9-15kHz (lower attenuation), and transponders (rather than pingers), which only ping when interrogated, so that they don't waste power when no one is listening. This is the usual weight/cost tradeoff that aircraft are so sensitive to.

In this case, the a/c went down in deep water far from shore. This affects the search in two ways: the mid-ocean location takes time to reach, using up part of the 30 days, and the deep water consumes much of the limited range afforded by a high frequency pinger (unless you can deploy a deep receiver).

Consider this calculation:

The source level of the pinger is 160db re 1uPascal @ 1meter.

The deep ocean ambient noise, in a calm sea-state 2-3 (4-10kt wind) at 37kHz is about 37db re 1uPa/sqrt(Hz). The pinger has a 10ms pulse length, giving it roughly a 100Hz bandwidth, so the noise is effectively summed over a 100Hz band: sqrt(100Hz) = 10 times = 20db; so, the total noise in-band is about 57db re 1uPa.

Thus the loss budget is 160-57 = 103db.

Spherical spreading from the source, in db, is 20*log10(R in meters) (because the source level is specified at 1m), and the attenuation loss at 37kHz is greater than 6db/km.

At 5km, the spreading loss is 20*log10(5000) = 74db, and the attenuation is 5km * 6db/km = 30db for a total of 104db. Thus at 5km, the signal power is about equal to the noise power. This ignores other sources of noise, such as higher sea-state, ship self-noise, receiver thermal noise, etc. Normally, a 20db signal-to-noise ratio is required for simple detection, resulting in the commonly quoted 2-3km detectable range.

Now the pingers may be at 4km depth, and the sub can only descend to some classified depth, but a published value for Emeraude of only 300m. That difference may (depending on actual pinger depth) consume over 3km of the detection range.

As for the ambiguity in location, I doubt that it is due to navigational uncertainty, but rather due to acoustic localization uncertainty. I have no idea what signal processing was done to actually extract the signal from the noise, but it would likely have involved integration over long periods of time: as long as the sub, traveling at, say, 3-6knts to minimize self-noise, would have been within a few of km of the pinger. After a long integration, one would only be able to guess the location with a resolution of roughly that integration "distance" (time, times the sensor transit speed), i.e a few km.
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Old 10th May 2010, 06:18
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Hi Denis,
Originally Posted by DenisG
Hi takata.
You mentioned 473 knots between position at 02.00h and LKP (last known position). I got a slightly different result, but mine was done on paper with a pen... I guess you have more accurate data?

(1) What is the distance between position at 02.00h and LKP?
(2) What is the distance between INTOL and LKP?
(3) Do we know when they passed INTOL? BEA (JUL-09,p.41) states 01.33h.
(4) What speed was reported at INTOL?
Sorry Denis, I missed your post. I cited the distance from memory without verifying it and from the BEA flightplan and positions (below), you are correct, speed between 0200-0210 was about 468 knots (not 473)

AF447 positions:
0210: 02°58'47"N 30°35'23"W (LKP)
0200: 01°48'00"N 31°08'59"W
0150: 00°38'23"N 31°45'36"W
0140: 00°29'23"S 32°22'11"W
0130: 01°38'59"S 32°58'47"W
0120: 02°49'11"S 33°36'35"W
0110: 04°01'11"S 34°14'24"W
0100: 05°12'35"S 34°52'11"W

So, you can make all your calculations from that.
S~
Olivier
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Old 10th May 2010, 06:54
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BEA press conference

BEA will hold a press conference today, Monday, at 14:00 Paris time.
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Old 10th May 2010, 06:57
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Originally Posted by mm43
Reference to the Cabin Pressure Controller schematic shows that in Automatic Mode the barometric reference comes from the ADIRUs, but my take is that should that reference fail, then it selects Manual and the Safety and Relief valves will attempt to keep Cabin Pressure equal to the outside when descending below 8000/7350 feet.
Good guess, but how would the controller know "outside" pressure without ADIRUs providing "oustide" pressure?
That's the bug and what might have caused this alert.
S~
Olivier
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Old 10th May 2010, 07:21
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@PJ2
Originally Posted by PJ2
The DFDR is powered by the AC2 bus which would be lost in the Emergency Electrical Configuration, (loss of both generators). I believe the CVR is similarly powered.
A320 CVR was recording Sully's cockpit conversation during their dual flameout and Hudson ditching. They were under APU, but there is no precision about FDR data. It should be the same for A330.
S~
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Old 10th May 2010, 07:29
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auv-ee;
Many thanks for the path loss calculations. I am in agreement with what you say, the only additional problem in deep water searches is the salinity inversion layers - one at 250 - 350m and if deep enough another near 4,500m.

I suspect, and it would appear to be the BEA's position, that the upper inversion layer was the barrier to the Emeraude recovering something useful above the S/N. Whatever technique has been used to to extract viable data, probably had to make use of some analogue techniques to mix something out of the noise. As I mentioned in a previous post, playing with digital analysis in a playpen of noise, is a bit of a no go area.

You might like to share your ideas on what form the Thales analysis probably took. On the otherhand, as the data was obtained by the military, we will probably never know what was actually done!

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Old 10th May 2010, 08:24
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From Seabed Worker positions provided by mm43, I retrieved the ocean depth searched between 6 May and 9 May and it doesn't look to be the best place as it is fairly rugged and deep near to -4,135 m at lowest point. I'm not sure that something has been already located as the zone is still about 8 x 8 NM:



06 May 2010 22:18 -3,028
06 May 2010 23:54 -3,746
07 May 2010 10:33 -3,362
07 May 2010 12:12 -3,362
07 May 2010 21:08 -3,726
07 May 2010 22:44 -3,800
08 May 2010 00:30 -3,575
08 May 2010 09:19 -3,827
08 May 2010 11:01 -4,003
08 May 2010 12:45 -3,839
08 May 2010 23:18 -3,571
09 May 2010 11:59 -2,769
09 May 2010 09:50 -2,816
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Old 10th May 2010, 08:37
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Cabin v/s advisory

takata;

as shown in the diagram produced by mm43 #946 (my thanks to mm43 for that) the negative relief valve is not controlled by the CPC. Intended as an 'emergency' backup, it is often no more than a simple mechanical device that requires no more than a negative pressure differential to open. As explained by Chris Scott, that happens when the aircraft overtakes (catches up with) the cabin, which is unlikely to occur above 7350 ft aircraft altitude.

HN39
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