ACCIDENT D'AVION RIO-PARIS(SUITE)

Publié le par ELMIR

ACCIDENT D’AVION RIO-PARIS(SUITE)

COMMENT « NOYER LE POISSON » AVEC LES SONDES DE VITESSE ?

 

En ce moment de deuil, il n’est nullement question d’entretenir la polémique sur la ou les causes du crash Rio-Paris dans la nuit du 31 mai au 1er juin. Dans mon précédent article, j’ai essayé d’imaginer des hommes en situation et des enchaînements « logiques » à partir d’informations diffusées par les médias. Mon intention n’était nullement de démontrer une hypothèse et de proférer des certitudes et des vérités universelles. Comme tout être humain, le crash de l’Airbus d’Air France m’a profondément choqué. J’ai imaginé cette scène horrible ou en quelques minutes des centaines d’hommes, de femmes et d’enfants ont perdu la vie dans des conditions atroces. C’est ce traumatisme psychologique qui m’a amené à m’interroger sur les raisons du drame.   

 

Dans mon précédent article, J’ai certes parlé d’AIR France comme entreprise capitaliste, mais soyons clairs, il n’y a pas qu’AIR France qui est soumise à l’implacable logique mercantile. Il se trouve que le crash survient sur AIR France mais il aurait pu avoir lieu sur une toute autre compagnie aérienne qu’Air France. Je dirai même, et personne ne peut me reprocher un quelconque chauvinisme vu mon nom de métèque, que la compagnie d’AIR France est réputée pour être parmi les compagnies aériennes les plus sûres au monde, qu’elle se taille la réputation d’un transporteur aérien fiable et que son personnel de maintenance est connu et reconnu dans le monde entier pour sa compétence technique. Mais aujourd’hui personne ne peut nier le fait que nous vivons dans un système capitaliste où il existe une seule loi qui gouverne nos sociétés, celle du profit. Une entreprise capitaliste n’est pas une association de charité ou de philanthropie, ni EMMAUS ni les RESTOS DU COEUR. La raison d’être d’une entreprise capitaliste, c’est l’exploitation des hommes et des machines pour faire du profit et rien que du profit. Dire ou penser le contraire, c’est se voiler la face pour ne pas voir la logique absurde d’un système dans laquelle nous sommes tous pris et dont nous sommes tous à un degré ou à un autre les victimes consentantes. Air France reste donc une entreprise capitaliste ou ses salariés figurent sous la rubrique Charges de sa comptabilité et que comme toute entreprise capitaliste se doit de diminuer ses charges pour faire plus en de profits sous peine de mettre la clé sous la porte comme Air Liberté ou d’autres compagnies aériennes. Ses lignes nationales et internationales doivent être rentables coûte que coûte et pour qu’elles le soient et pour atteindre des objectifs purement mercantiles., il est sans cesse demandé aux hommes et aux machines de fournir plus de sacrifices et plus d’efforts. En Europe, le mot profit est un tabou alors qu’en écoutant CNN par exemple ou les medias anglo-saxons en général, la performance d’une entreprise est mesurée par les profits qu’elles génère et non pas par le chiffre d’affaires. Nous vivons dans un système qui fonctionne selon sa propre cohérence interne et une entreprise capitaliste fait tout pour diminuer ses charges dans le but d’augmenter ses profits. Le secteur des transports aériens en général et AIR France en particulier n’échappent pas à l’implacable et sinistre logique mercantile et à la marchandisation des rapports sociaux. L’actionnaire d’Air France investit de l’argent et veut récupérer sa mise, il n’a que faire de la sécurité et des vies humaines qui ne sont pas vraiment les premières de ses préoccupations. Soumis à la dictature du profit et à la course effrénée aux rendements, les hommes sont broyés par un système qui les dépasse et qui leur fait perdre leurs moyens intellectuels en devenant ainsi des simples machines et des simples robots. C’est parce qu’ils deviennent des machines et des robots que les hommes deviennent dangereux pour leurs semblables car ils ont perdu toute faculté de discernement entre ce qui relève du domaine de l’humain et ce qui appartient au monde technique.  

 

En sortant de son chapeau l’histoire des sondes de vitesse, Air France et le Bureau Enquête et Accident(BEA) cherchent à noyer le poisson en insinuant que la cause de l’accident Rio-Paris serait due à une simple défaillance technique. Pour parler vulgairement, l’histoire de sondes de vitesse est une « histoire à toto » que l’on raconte aux enfants avant de dormir. L’enquête officielle privilégie l’hypothèse d’une simple défaillance technique due au mauvais fonctionnement des capteurs de vitesse ou sondes Pilot, à laquelle AIR France tente de remédier en équipant ses avions A 330 et A 340. Cette hypothèse ne résiste pas à l’examen pour deux raisons principales. D’abord l’Airbus Rio-Paris subit une révision à mi avril et s’il y avait un problème de capteurs ou de sonde de vitesse, le personnel de la maintenance aurait détecté l’anomalie. Ensuite, une note interne d’Air France datant de novembre 2008, fait état d’un « nombre significatif d’incidents liés aux calculateurs de vitesse sur des A330 -340 ». Puisque la compagnie était au courant de l’existence de problèmes de calculateurs de vitesse, pourquoi ne s’est-elle pas employée à y remédier très rapidement avant que ne survienne le crash du vol Rio-Paris ? Logiquement, cette note interne aurait dû alerter la compagnie pour prendre les mesures nécessaires qui s’imposent et pour éviter un tel drame, pourquoi ne l’a-t-elle pas fait ?

 

Malheureusement, à ce jour, c’est l’hypothèse des conditions météorologiques qui est la plus probable. Quand j’ai émis dans un précédent article que ce sont les conditions météorologiques qui pourraient être à l’origine de l’accident de l’Airbus d’Air France, d’une zone de perturbation tempétueuse sur la trajectoire du vol je n’avais pas pris connaissance des analyses et des conclusions d’un spécialiste en météorologie qui s’est penché sur les conditions météorologiques de la zone traversée par l’avion d’Air France. L’auteur de cet article, Tim Vasquez, a conclu, cartes et images de satellite à l’appui, à l’hypothèse d’une violente tempête tropicale qui pourrait être à l’origine du crash de l’Airbus d’Air France. En effet, les conclusions de l’auteur font apparaître que le vol AF 447 se serait engouffré dans une zone de turbulence tempétueuse tropicale et qu’il aurait subi de fortes turbulences sur 125 km (75 miles). Ce sont ces violentes turbulences qui auraient entraîné une série de défaillances techniques en commençant par une panne radio puis la désintégration progressive, morceau après morceau, de la carlingue de l’avion.

 

FAOUZI ELMIR

 

 

Annexe

 

J’avais l’intention de traduire en français les analyses de Tim Vasquez sur les conditions météorologiques de la zone où se trouvait l’Airbus d’Air France. Mais faute de temps et vu l’ampleur du travail, j’ai dû me contenter de la reproduction du texte original en anglais.

 

 

Air France Flight 447: A detailed meteorological analysis

3 06 2009

by Tim Vasquez

Air France flight 447 (AF447), an Airbus A330 widebody jet, was reported missing in the equatorial Atlantic Ocean in the early morning hours of June 1, 2009. The plane was enroute from Rio de Janeiro (SBGL) to Paris (LFPG). Speculation suggested that the plane may have flown into a thunderstorm. The objective of this study was to isolate the aircraft’s location against high-resolution satellite images from GOES-10 to identify any association with thunderstorm activity. Breakup of a plane at higher altitudes in a thunderstorm is not unprecedented; Northwest Flight 705 in 1963 and more recently Pulkovo Aviation Flight 612 in 2006 are clear examples.

Back in the 1990s I did flight route forecasting for the Air Force. One of my assignments in summer 1994 was forecasting was the sector between Mombasa, Kenya and Cairo, Egypt for C-5 and C-141 aircraft. The Sudan region had tropical MCS activity similar to this with little in the way of sensor data, so this incident holds some special interest for me as one of our C-5s could easily have followed a very similar fate. Using what’s available to me I decided to do a little analysis and see if I could determine anything about the fate of AF447 and maybe through some circuitous, indirect means help give authorities some clues on where to look.

1. Reports and evidence

Reports indicate AF447 reported INTOL (S01 21.7′,W32 49.9′ or -1.362,-32.832) at 0133Z and was to proceed to TASIL (N4 00.3′,W29 59.4′, or +4.005,-29.990) in 50 minutes (a true track of 28.1 deg) (source) indicating that it flew high altitude route UN873 (see below).


Enroute High Altitude Caribbean and South America H-4, 30 AUG 2007 (National Geospatial-Intelligence Agency)

Though the actual flight plan data was not accessible to me, this corresponds well with an actual flight plan found on the Internet for a Varig B767 from Rio de Janeiro to Frankfurt:

(FPL-VRG8744-IS -B763/H-SIRYW/S -SBGL0110 -N0485F290 PCX3 POKA UA314 NUQ/N0475F330 UA314 SVD UZ10 NTL/M080F320 UN873 FEMUR/M080F320 UN873 INTOL/M080F320 UN873 EPODE/N0476F340 UN873 ASEBA/N0475F340 UN873 SAGMA/M080F340 UN873 CVS/M080F360 UN873 LIMAL/N0463F360 UN873 GDV UN858 SUNID/N0454F380 UN858 DGO UN976 PPN/N0457F360 UN976 LATEK UN871 KUDES T163 PSA PSA2W -EDDF1129 LSZH EDDL -EET/SBRE0050 SBAO0309 ORARO0340 GOOO0355 GVSC0518 GCCC0618 GMMM0746 LPPC0836 LECM0848 LFFF0951 LSAS1042 EDUU1059 EDFF1111 RIF/PPN/N0456F390 UN857 BAN BAN2E LEMD RMK/ETOPS UNDER 120 MIN RULE ENROUTE ALTS SBNT GVAC)

I decided to project the flight forward from INTOL. An altitude of FL350 and speed of 520 mph was given. Presumably this is ground speed according to the ACARS specification. Compensating for a 10 kt headwind as given by the SBFN sounding this yields an airspeed of M.80, which correlates well with the A330’s typical early cruise profile. This yields the following aircraft coordinates:

Time

Coordinates

Description

0133Z

-1.362,-32.832

Reported INTOL

0145Z

-0.033,-32.125

Extrapolation

0200Z

+1.629,-31.242

Extrapolation

0215Z

+3.290,-30.357

Extrapolation

0223Z

+4.150,-29.876

Estimated TASIL

0230Z

+4.951,-29.469

Extrapolation

2. Meteorological analysis

Surface analysis showed the suspected crash region to be within the intertropical convergence zone (ITCZ), which at this time of year is usually found at about the 5-10N parallel. A region of strong trade winds covered most of the tropical North Atlantic and this kept the ITCZ in a somewhat southerly position. The linear convergence along the ITCZ and the unstable atmospheric conditions combined to produce scattered clusters of thunderstorms.


Surface analysis for 0000Z. (NCEP)

Using McIDAS I acquired satellite GOES-10 satellite data from UCAR and centered it over the region between INTOL and TASIL. I then plotted the waypoints using McIDAS’s built-in coordinate entry panel. Since the source satellite images are georeferenced NOAA/GINI datasets, the points shown here are very accurate and are NOT placed by hand but by lat/long coordinates to the nearest 0.001 deg (0.06 mile). In the image below, the stationary southerly point in blue is INTOL and the aircraft’s estimated location from the above table is marked with a cross. Graticule spacing is 5 degrees. For the orange temperature plots I used the NCL/3aw curve; the sharp gradient of the enhancement from dark to light occurs at 243K (-30 deg C), indicating a cloud top of FL310 assuming the satellite pixel is completely overcast with that layer (which is not always true).

NOTE: If you have trouble seeing some of the large images, the source link is here -Anthony

Frame Controls

Satellite images

Loop Mode:

Adjust Speed:

Dwell First/Last:

Frame No:

Omit Frame:
1  2  3
4  5  6
7  8  9

(Hit reload if you don’t see the satellite images in the looper above)

Raw infrared images are also available here: 0145Z, 0200Z, 0215Z, 0230Z.

And finally this image shows a zoomed image at 0215Z when AF447 made its last transmission:

click for a larger image

About 90% of the cloud material seen on this image is actually multiple levels of convective debris fields from dying storms and activity that occurred previously during the day, with only scattered cirrus fields at flight level. The active thunderstorm areas are defined by small-scale mottled areas of cold cloud tops. Compare with this structural diagram below of a similar tropical MCS in the same area in 1977. It illustrates that planes inflight are clear of most dangerous weather throughout a tropical system except when directly above an active updraft area.


Schematic of a typical tropical MCS observed in the Atlantic southwest of Dakar on 4 Sep 1974. (Structure and Dynamics of a Tropical Squall-Line System, R. A. Houze Jr., Mon. Wea.
Rev., 105, 1540-1567)

It appears AF447 crossed through three key thunderstorm clusters: a small one around 0151Z, a new rapidly growing one at about 0159Z, and finally a large multicell convective system (MCS) around 0205-0216Z. Temperature trends suggested that the entire system was at peak intensity, developing rapidly around 2300-0100Z and finally dissipating around dawn. From a turbulence perspective, these cold spots would be the areas of highest concern as they signal the location of an active updraft producing new cloud material in the upper troposphere.

The last communication from the plane was at 0214Z (12:14 am local meridian time). This was an automated ACARS message reporting an electrical fault and pressurization problem. This would be about the time the plane was beginning to exit the cluster, but not before having flown for 75 miles of numerous updrafts. The exact aircraft location cannot be determined with certainty, however, since a 1-minute time error in position or reporting time translates to 9 miles of spatial error.

The Fernando de Noronha sounding is available here and shows typical tropical conditions with modest positive energy throughout the column from the surface up to 45,000 ft. There is what looks like anvil level material above 25,000 ft. The significant dry mid-level air is somewhat unusual and suggests the potential for enhanced evaporational cooling in the upper troposphere enhancing downdraft production, and any synoptic-scale lift (if present) enhancing instability through adiabatic cooling of the layer.

I modified this sounding (see below) using the prevailing temperature/dewpoint field across that part of the ocean and modifying for some cooling due to nighttime loss of heating. This is my best guess at the parcel profile that fed this storm. It yields a worst case instability of 1048 J/kg of CAPE, which is moderately strong but considered borderline for typical severe weather. Vertical velocity can be obtained by w=2*CAPE^0.5 yielding a maximum possible updraft speed contribution of 45.8 m/s or 102 mph, though in reality this is usually much less (on the order of half or less) due to precipitation loading and other factors.

3. Conclusions

The satellite imagery indicates that numerous cumulonimbus towers were rising to at least 51,000 ft, and were embedded in extensive stratiform anvils with tops of 35,000 to 45,000 ft. This kind of configuration is actually quite normal for equatorial storms due to the higher tropopause height, but it emphasizes that the aircraft was certainly within the bulk of an extensive cumulonimbus cloud field for a significant amount of time and that storms could indeed have been a contributing factor to the crash.

I’ve edited this section Monday night to cut down on the speculation about the accident chain, especially since I don’t know a whole lot about A330 systems. The airliners.net board and other sites cover the aircraft and CRM systems quite well. What I will try to do, however, is summarize what the aircraft probably encountered based on the data and my own experience.

* Turbulence — Turbulence is a definite candidate as a contributing factor. There is an isolated storm at (1.6,-31.5) that appears suddenly at 0200Z just as the A330 enters the main MCS cluster. From a turbulence perspective it is by far the most dangerous formation found on the loop. However it is 10-25 km to the left of UN873 and it is doubtful the crew would have been deviating at this time. Other cells like this one embedded within the main MCS may have caused severe turbulence. Young updrafts are particularly dangerous to flights because they contain significant rising motion yet precipitation fields have not yet fully developed and airborne radar signatures are weak, reducing the likelihood the crew will deviate around the cell. Another concern is the extensive upper-level dry air shown on the SBFN sounding (not counting the anvil debris at 350-300 mb), which may have contributed to enhanced evaporative cooling in and around the anvil and aggravated the turbulence experienced by the flight, especially around the margins of anvil clouds and towers. It is worth considering that cumulative periods of heavy turbulence crossing through the cluster may have caused minor internal damage that progressed in some way into an emergency.

* Icing — With a flight level temperature of -43 deg C suggested by the proximity sounding the A330 would have been flying mostly in rime ice and possibly some clear ice and graupel. At -43 deg C, water cannot exist even in supercooled form (see here for an explanation). The equivalent potential temperature throughout the profile is absolutely insufficient to bring warmer air with supercooled water to flight level. Without the supercooled water there is very little ice buildup on the airframe. My conclusion is that unless the plane descended below FL300 icing would not be the culprit.

* Lightning — Due to the high cloud tops and freezing level at 16,000 ft, there was extensive precipitation by cold rain process and it is likely the MCS was electrified. Lightning of course being considered with good reason since the A330 is one of the most computerized and automated airliners in service. I will say based on my 25 years of meteorology the storms were almost definitely producing lightning. As far what a strike would do to the A330, I have to leave that to to the avionics experts. Some answers might be found at http://www.airliners.net/aviation-forums/.

* Precipitation — A dual engine flameout due to precipitation or ice ingestion is a noteworthy possibility as has been discussed on other sites (specific to the A330 type too). The precipitable water content in any tropical weather system can run very high. However a rain-induced flameout is not possible because supercooled water cannot exist at the -43C cruise altitude and insufficient equivalent potential temperature exists, even in updraft cores, to bring warmer air beyond a few degrees change to the flight level. Therefore the plane at FL350 was completely within some mixture of rime ice, graupel, or small hail. But again, as the link indicates, even ice poses risks to the engine.

* Hail — I got a few comments about hail. I am not entirely convinced that structural hail damage is a factor, partly because I can’t recall hearing much about large damaging hail at altitude in my experience with equatorial flight operations. This would require strong instability, which I’m not yet sure we have, not only to grow the stones but to loft large hailstones from the embryo “nursery” at FL200-250 up to flight level. A value of 1000 J/kg CAPE is really on the fence but not out of the question. The other problem is the mounting body of evidence (see SPC studies) suggesting well-sheared storms (this profile is poorly sheared) are the ones conducive to structures that support hail growth. Finally, another issue is airborne radars are be highly sensitive to hail because of the very high backscatter values of ice, making evasive action likely, and the “young updrafts” I pointed out earlier as a threat would not have provided the residence times necessary yet to contain hailstones; their main threat would be severe turbulence. I am not sure about the hail hypothesis, but I believe there is a high probability of graupel, small ice pellets, or small hail at FL350 in the storm complex (see Icing above).


Overall what we know for sure is weather was a factor and the flight definitely crossed through a thunderstorm complex. There is a definite correlation of weather with the crash. However the analysis indicates that the weather is not anything particularly exceptional in terms of instability or storm structure. It’s my opinion that tropical storm complexes identical to this one have probably been crossed hundreds of times over the years by other flights without serious incident.

Still, in the main MCS alone, the A330 would have been flying through significant turbulence and thunderstorm activity for about 75 miles (125 km), lasting about 12 minutes of flight time. Of course anything so far is speculation until more evidence comes in, and for all we know the cause of the downing could have been anything from turbulence to coincidental problems like a cargo fire.

My own opinion of the crash cause, as of Monday night, based on the complete lack of a HF radio call and consideration of all of the above, suggests severe turbulence (see the BOAC 911 and BNF 250 tragedies) combining in some unlikely way with CRM/design/maintenance/procedural/other deficiencies to trigger a failure cascade. We can almost certainly count on some unexpected surprises once the CVR is recovered. Until then, all we can do is await the investigation and hope that the world’s flight operations stay safe until AFR447’s lessons are revealed.


 

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