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Old 28th Sep 2009, 20:25
  #4481 (permalink)  
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Thanks for your comments.
(1) WX radar faulty or crew didn't detect Cb cell(s). Probably former.
The fact that no ACARS messages were received regarding WX radar faults doesn't necessarily rule out some insidious problem that failed to trigger a fault warning. With regard to the above quote, I agree totally that we know nothing about what went on in the cockpit, but at this juncture I chose to give the crew the benefit of any doubt.

Suffice to say that if penetration of an active mesoscale system took place, then all bets are off and the events I described may or may not bear any resemblance to the truth. In fact, the only thing we do know is that the a/c sent a raft of ACARS messages and finished up in the Atlantic in a wings level, nose up attitude, with little forward velocity, tail yawing to port and a high sink rate. We don't even know where with any degree of certainty.

Presumably communication about that deviation between LH507 and ATLANTICO should have been overheard by AF447, as AF447 should have been on ATLANTICO's frequency from 0133 until 0220 hours.
Once the SELCAL had checked at 0135 it appears the crew selected SELCAL watch as ATLANTICO's attempts to contact them a few seconds later went unanswered. Why ATLANTICO failed to SELCAL them is another matter. We don't even know if AF447 had selected 123.45, but no one has reported hearing them on either HF or VHF after 0135. A failed ADS-C connection at 0201 with DAKAR OCEANIC is the only evidence of cockpit activity.

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Old 28th Sep 2009, 22:30
  #4482 (permalink)  
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Thanks for your response. While no messages from a failing radar would be highly unusual especially given the pattern of other messages, you are right in that "nothing issued" does not prove nothing happened, nor does it substantiate failure. As a safety specialist, I choose neither to give the crew the benefit of the doubt or look to them for answers but await where whatever evidence can be mustered, leads us. In the absence of the recorders (and even with them) we must stick with open questions in all areas, even the more difficult-to-accept ones such as crew performance until, somehow, they can be eliminated one by one towards a probable scenario, but I strongly suspect you already know and appreciate this necessity.

I am curious if the search continues either under the auspices of Airbus etc or informally and if so, are they using any of your information. I know that is speculative but for me it seems wholly reasonable. Perhaps they are already thinking along the same lines but I am a believer in "what, not who" and if good data or thinking can be had, the source is less critical than the use of same.

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Old 29th Sep 2009, 04:26
  #4483 (permalink)  
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I have previously raised doubts about some of the surface current data produced by NOAA/OSCAR and hope that SHOM specialists onboard the "Pourquoi pas?" during its recent two prolonged periods in the search area have gathered as much surface current data as possible. If they have done that, they surely will be able to analyze the actuals against those produced by the OSCAR project and ultimately be able to produce more factual vectors and speeds for the first 7 days of June.

The "Pourquoi pas?" is currently berthed at Horta, Azores and is engaged in its programed research - tectonic plate movements. I understand it sails for Brest on 30 September. Enter 38.53283333, -28.62133333 into Google Earth will take you to Horta.

The vessel's position is updated by satellite each hour at H+30 and is plotted at:-
Localisation des navires océanographiques de l'IFREMER


Last edited by mm43; 30th Sep 2009 at 21:51. Reason: update Pourquoi pas? position
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Old 29th Sep 2009, 13:03
  #4484 (permalink)  
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Where is BEA's second interim report ?

Where is the second interim report which the (still*) BEA director Arslanian announced on 1 September "within the next weeks" ? (* Arslanian's retirement seems imminent)

France Info reported on 24 September that according to the previsions of BEA, the effective search for the black boxes should recommence at the very beginning of next year ("Et selon les prévisions du BEA, la recherche effective des boîtes noires devrait reprendre en tout début d’année prochaine.").
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Old 29th Sep 2009, 13:07
  #4485 (permalink)  
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mm43, thanks for your reply.

If they were in SELCAL watch mode, learning after the fact what they might have heard had they been listening on the HF really matters for naught at this point.

It does raise retrospectively whether switching to SELCAL watch was the prudent choice in the circumstance that AF447 found itself that night, when crossing the ITCZ in an area of SIGMETs and having received an ACARS message from dispatch at 0031 hours, saying "PHOTO SAT DE 0000Z : CONVECTION ZCIT SALPU/TASIL". The transcript of the brief communications between AF447 and ATLANTICO around 0133 hours reveals no concern about the enroute weather.
As best as I can interpret the times and positions from the BEA report.

LH507 is at ORARO at 0140 and chooses then to deviate west by 10 NM because of what its radar is showing.

AF447 is at ORARO at 0200

IB6024 is at ORARO at 0212, encounters turbulence and cumulonimbus buildups, deviates east by 30NM when about 30(?) NM south of TASIL and then rejoins the airway in clear air close to TASIL

AF459 is at "the level" of ORARO at 0237, earlier (some time after 0200) this flight had deviated to the west by 20NM to avoid an area of radar echoes. During the deviation, the radar, while on max gain, reveals an extensive squall line ahead. AF459 then deviates east of the airway by 70-80 NM. and rejoins the airway north of TASIL at the ASEBA waypoint.
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Old 29th Sep 2009, 20:51
  #4486 (permalink)  
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AF459 is at "the level" of ORARO at 0237, earlier (some time after 0200) this flight had deviated to the west by 20NM to avoid an area of radar echoes. During the deviation, the radar, while on max gain, reveals an extensive squall line ahead. AF459 then deviates east of the airway by 70-80 NM. and rejoins the airway north of TASIL at the ASEBA waypoint.
I note that the above is a repeat of your 10 July posting. The problem I have is that the original interview with the AF459 F/O seems to have lost something in translation. So much so that its difficult to determine where and when they actually made their deviations. The "at the level" of ORARO could mean either abeam or at the same latitude. Really need INTOL time and TASIL estimate plus time at ASEBA to make much sense of where they actually went or were.

I still sense that the AF447 crew were preoccupied with the ADS-C log on with DAKAR. They didn't know that DAKAR hadn't received their flight plan, nor were they aware that DAKAR had created a virtual flight plan after receiving details from ATLANTICO, and that the existence of only a VFP prevented their ADS-C log on. Notwithstanding, the aviate, navigate and communicate rule should have applied.

The CVR is a "must have".

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Old 2nd Oct 2009, 20:42
  #4487 (permalink)  
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A resumed search is indeed being looked at using more suitable technology given the anticipated water depth. I cant say any more for now however.
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Old 2nd Oct 2009, 22:20
  #4488 (permalink)  
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UA -- thanks for that. The French Authorities have been saying for a month now that a new phase of searching would certainly occur, but no one has been forthcoming with any details. Your post, though sparse, gives some hope at least . . .
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Old 2nd Oct 2009, 23:00
  #4489 (permalink)  
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Starboard Outer Spoiler

The starboard outer spoiler recovered according to the FAB from a position 415km Northwest of St Peter & St Paul rocks on 13 June by a merchant vessel, was in fact recovered from a position 005°T x 41NM from TASIL at about 1300z. I do have the actual position and time, but in the meantime those who are interested will be able to identify it from the BEA's debris graphics in the preliminary report.

I am currently analyzing OSCAR surface current data in relation to the spoilers identified position, and as I had already suspected, the published current velocities need to be increased by about 40%. The possible impact position shown on graphics in post #4476 on page 224 is still valid.

Positional data supplied by the FAB was IMHO designed for media consumption and to be deliberately misleading for any other use.


Last edited by mm43; 3rd Oct 2009 at 00:15.
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Old 3rd Oct 2009, 00:04
  #4490 (permalink)  
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mm43 -- surely you're not suggesting that the FAB, or Airbus, were/are concerned that someone else might find things before they do? As in Bob Ballard?
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Old 3rd Oct 2009, 00:20
  #4491 (permalink)  
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grizzled -- "Keep y'r cott'n pick'n fingers off" is pretty close to the mark.
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Old 3rd Oct 2009, 01:47
  #4492 (permalink)  
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Diff gps accuracy

It's deeply embarrassing to be disagreeing with somebody who obviously knows more about GPS and aircraft than I do, especially as we seem to be totally at cross purposes.

read message 4463 - what you're talking about is phase tracking...

In 4463 you said ...
The phase-tracking used in attitude detection is a different animal. The wavelength at GPS frequencies is roughly (very) 25cm, so the theory predicts that one receiver moving vertically (e.g.) relative to a second one, toward or away from the satellite(s), would experience a detectable phase difference in the order of centimeters. Needs superfast processor and GPS chips, but it works....

I'm talking about taking the difference in readings between two bog-standard GPS receivers at the wing-tips. Bog-standard, without superfast processor and GPS chips. So how can I be talking about the phase tracking you refer to?

I was trying to make a simple observation. Which I still feel is correct, and is supported by the maths at the end of message 4472 ...
If you take the difference of the positions reported by two bog-standard GPS receivers on your plane, then the accuracy you achieve is the same as you would have achieved using two civilian differential-GPS receivers [and a nearby base station].

If you have an argument directed against this observation, I'm really interested. Perhaps offline as we're taking bandwidth.

Regards, Peter
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Old 3rd Oct 2009, 14:32
  #4493 (permalink)  
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A bit about GPS and GPS attitude

Differential GPS: This requires an accurately surveyed site to broadcast correction data – typically it needs to be within 100km of the user to be effective. It is therefore mostly used for maritime navigation close to land. A more useful variant is to the link the correction data from a host of accurately surveyed sites across a landmass to a central site and then generate a contour map of errors, a bit like pressure isobars. This map is unlinked to a satellite and rebroadcast on one of the spare GPS channels for use in the GPS receiver to give significantly improved accuracy. This is known as a Satellite Based Augmentation System (SBAS) but has only limited landmass coverage (WAAS in the USA, EGNOS in Europe and MSAS in Japan). These are intended for aviation use including Category I approaches. For obvious reasons it will not be available over large oceans, but then it is not necessary to know your location that accurately in cruise.
GPS Attitude: This does not require accurate GPS location information (e.g. Differential GPS or SBAS) but relies on the phase differential of the received carrier as seen by a number of closely spaced antenna. For an example of equipment capable of generating GPS attitude data refer (opens as .pdf):-

It should be noted that GPS attitude measurement requires a number of antenna on the aircraft whose 3D location geometry is accurately known. The further apart the antenna are the better, but any unintended variation in their relative position will result in attitude calculation errors, so mounting them on wing tips is not ideal due to flexing. I have heard engineers talking of errors resulting from flexing of the fuselage in flight and these variations may be difficult to characterise and thus correct. However, attitude accuracies of about 0.2 degrees can be achieved with a separation of only about 2m and adequate structural stability at this distance should be readily achievable.

Use of standard GPS for attitude determination: The concept proposed by Peter H should work in theory, but two matched GPS receivers will not produce identical results. A long baseline (separation) would be required e.g. wing tips, and with residual GPS errors and wing flexing I would expect a roll error of typically 1 to 5 degrees. Differential carrier phase measurement technology would improve on this by at least an order of magnitude.
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Old 4th Oct 2009, 10:25
  #4494 (permalink)  
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GPS accuracy of two nearby units

I have started a separate thread on GPS accuracy and two GPS readings, if the mods let it stand. I have a separate question, as well as being interested in the one posed by Peter H, and my interest is nothing to do with AF447.

Chris N.

[edit: posted before I was able to see EmBee’s helpful answer to the question, above. I still have another question, on the other thread.]

Last edited by chrisN; 4th Oct 2009 at 11:03.
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Old 4th Oct 2009, 12:03
  #4495 (permalink)  
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Embee, let's review the goals with regards to attitude determination in an airplane absent conventional instrumentation or observation. Working and highly visible bog standard artificial horizon equipment may be the best way. But if somebody insists it is not there then GPS can provide some answers with a degree of roughness that depends on dynamics of the aircraft and expense you're willing to undergo.

Basically you need to know the relative positions of the two wing tips and the nose or tail to sufficient precision to determine an accurate attitude. GPS is one way to do it. Both differential GPS and phase tracking have been mentioned. A third method exists that might be called differential phase tracking, which can apply and will likely be cheaper to implement.

If we review differential GPS the conventional use requires, as you stated a precisely surveyed reference. Conventionally you need to know your position relative to physical features of the Earth. Thus the well surveyed reference position. Suppose a plane is flying near the surveyed site and you measure distances to both wing tipss and the nose. To get the attitude you play with the geometry of those three positions. The simple way is to note that the left wing tip is at some distance from the surface while the right wing tip is at some other distance. That gives you some attitude data. But it doesn't account for lateral distances along the surface of the Earth. Geometry gets messy.

Now presume the left wing tip is your "precisely determined position". Certainly it is, relative to the plane. And what you want is information about where the rest of the plane is relative to that wing tip. Once you know this you can shift the "reference" to the CG of the aircraft if that makes instrumentation read easier. What you need to know is all differences of position. If the left wing is higher than the right wing your plane is banked. You could care less if this is at FL 100 or FL 350. You know you are banked and can estimate how much. Instantaneous measurement precision for the GPS track for all three receivers limits your notion of how severely banked your plane is.

Phase tracking has a similar feature. It just gives more precise "where I am" information. If you simply measure relative carrier phases, which requires relatively little additional computer power you can get pretty accurate notions of position. (If you lose track you're more or less sunk, however. You have an ambiguity of 20 cm (roughly) to resolve. In turbulence it's fairly easy to have the dynamics kick the GPS
receiver out of lock. The loop time constants are large enough that the plane could move out of its established track by several times 20 cm quite easily.

So you're generally stuck with conventional differential GPS unless you have really good inertial measurement units to aid the GPS receivers in a military manner. (Or you can presume in designing the receiver that the loop time constants can be made much shorter to allow high dynamics tracking by sacrificing some of the GPS signals fairly dramatic anti-jamming margin. But I've already gotten too technical for this group, I suspect.)

GPS can be used. I'd need to see some analysis to show me it's usefulness for a differential GPS application before I'd endorse it for the application. It has promise. But the cost would probably make the artificial horizon gyroscopic approach sound exceptionally attractive.

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Old 4th Oct 2009, 17:16
  #4496 (permalink)  
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I thought I posted a note saying that I saw a French newspaper this morning blaming the pilots.

I can only assume it was deleted cos someone has PPRuNe by the short and curlies.

Tell me it in't so.
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Old 4th Oct 2009, 17:33
  #4497 (permalink)  
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Who knows? What I see is SPAF (the union) seeking to absolve the crew of blame. Le Journal du Dimanche article (Google translation into English [acknowledgements naturellement]) explains
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Old 4th Oct 2009, 18:22
  #4498 (permalink)  
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Seems to be picked up by many news media without any background about where this "report" is coming from
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Old 4th Oct 2009, 18:30
  #4499 (permalink)  
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SPAF? Le Journal du Dimanche article?
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Old 4th Oct 2009, 18:39
  #4500 (permalink)  
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Thread was deleted because frankly it didn't have any 'meat'. Maybe if there'd been a link to an article? Some basis? Something.............?

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