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article imageAF447 disaster: Making sense of the evidence

By Michael Cosgrove     Jun 5, 2009 in World
It is becoming clear that the constant flood of statements concerning the crash, some correct, some erroneous, is clouding the issue for many observers. Here is a round-up of what is known, what is not, and where the investigation is heading.
What caused the accident is not known at this time, although theories abound. They are detailed below.
The only crash theory that has substantial and confirmed circumstantial evidence to support it right now it is that of the plane being brought down by a combination of violent weather conditions and systems breakdown. This evidence remains incomplete however, and thus cannot be said to constitute proof of the reason for the crash.
It is not being contested by investigating authorities (as opposed to pundits, ex-pilots and others) that storms violent enough to bring down an airliner do, and have, occurred in the crash area. These storms can reach a height of 50 000 feet, and their epicentre can be at the top of them or lower down. This is why planes sometimes fly under them or over them. In cases of very large turbulent zones, planes detour around them.
The crash area is in the middle of a zone where different equatorial convective air currents meet, which makes it a very volatile zone to cross at certain times. Violent conditions can develop very quickly.
The pilot of AF447 issued a manual message indicating the presence of violent weather ahead. This has been corroborated by the BEA, the French civil aviation crash investigating authorities, who have also confirmed that severe turbulence was present at the time.
Ten minutes later the plane automatically issued a series of messages indicating the successive breakdown of its electrical and computer systems and, finally, its depressurisation. Those messages lasted four minutes before stopping abruptly. They represent the last contact with the plane.
Those messages, instantly and automatically sent to Air France via satellite, and detailing cascading systems failure, have been corroborated by both Airbus and the BEA.
For more detailed descriptions of the messages, as well as how and why they are transmitted, please read this article.
That is what is known of the weather and plane itself, but, as the BEA points out, it is not concrete proof of the plane being brought down by weather, although it suggests it. This would be better cleared up with the recovery of the flight recorders, notably that containing the crew’s conversation and sounds in the cockpit.
Investigators have also contacted various airlines concerning around ten planes which crossed that area before and after the accident. They hope to find out more about weather conditions by interviewing crews and passengers.
Large hailstones big enough to puncture holes in a plane’s fuselage are known to have been experienced in that zone by aircraft in the past, but meteorologists tend to think that it is unlikely they were present in the weather on the night of the crash. Analysis of fuselage parts would help to establish if that was the case or not.
That a plane be brought down by lightning alone is theoretically possible but extremely unlikely. It is not being presented as the primary likely cause. Investigators will examine any fuselage fragments and other debris that may be found to check that.
The fact that debris has been found over a large area seems to indicate in-flight break-up, although the BEA says it is still studying the wind and sea currents that have been prevalent since the crash. Once known, it will be possible to determine if the debris was dispersed or not by the weather, and to what extent, and thus to establish or not that a mid-air break-up occurred.
Brazilian authorities announced the finding of more debris on Thursday, a statement they later retracted as erroneous when they found out that that debris could not have come from the plane.
Brazilian authorities had also announced that the plane probably hit the water intact and with no explosion taking place during its fall. They based this on their previous announcement that a large kerosene slick had been found. They had to go back on both of those statements too when it was discovered that the slick did not consist of kerosene but oil. Also, the amount of this liquid, oil or not, is said to be much greater than would have been contained in the plane.
The Brazilian press and authorities have been roundly criticised here in France for what are considered to be far too many overblown, sensationalist and erroneous announcements due to their being diffused without the information contained in them being correctly verified.
The BEA has announced that the plane was flying at 35 000 feet and not the 37 000 it had been asked to reach. This is being read as a possible attempt by the crew to fly under what has been confirmed by meteorologists to be the most violent part of the bad weather, which was at 37 000 to 38 000 feet.
In another extremely important and little-reported development which has been playing out over the last few days, the BEA stated that the plane’s speed varied to a substantial degree according to which instrument was showing it. There are several systems which transmit a plane’s speed and they were said not to show the same speed. The BEA spoke of “Incoherence in speed measurement.” No publicly-stated conclusions have yet been drawn from this evidence.
However, and very importantly, one of these measurements shows the plane flying at what would have been too low a speed to avoid possible stalling under certain adverse wind and turbulence conditions. Stalling in severe turbulence can be fatal to a plane because recovering control would be difficult due to the plane being buffeted around by the storm, and if control and direction are not quickly recovered using engine power in severe turbulence, break-up becomes a strong possibility.
Liberation then announced that Airbus was shortly to issue a pilot recommendation reminding them that “In difficult weather conditions pilots should keep engine thrust high and maintain pitch and roll to a minimum in order to maintain control of the plane.” The BEA at first refuted that such an announcement was being prepared.
But Airbus did in fact issue that recommendation, yesterday evening. In the recommendation, sent to operators of all its planes and not just the Airbus A320-200, it was stated that both Airbus and Air France confirmed that there was extreme turbulence in the crash area at the time of the disaster.
This is being interpreted here as a sign that weather is being seriously considered as a possible factor in the crash by both Air France and Airbus.
It has been suggested that a terrorist missile attack could have been responsible for the accident. There is no evidence for this and no witnesses have seen evidence of it. Moreover it is universally accepted that terrorists do not possess the extremely sophisticated high-technology missiles needed to reach a target flying at 30 000 feet. The SAM missiles they have generally have a range of only two to five kilometers.
There is no way of excluding a terrorist or hijacking attack at this time and this possibility is not, as has often been erroneously suggested, being excluded by authorities, who will examine all plane fragments found for physical and forensic evidence of explosives or an explosion.
Indeed, Hervé Morin, the French Defence Minister, answering questions put to him by representatives of the AJPAE, the Aeronautical and Space Journalists Press Association less than an hour before this article was published, confirmed that “There is no element or clue to corroborate (..terrorism..) but the ongoing investigation has never excluded it.”
There is little concrete circumstantial evidence in circulation to support terrorism at this time, particularly given that the plane is generally accepted as having lost its systems progressively and not as the result of a single and sudden incident such as a bomb explosion.
The fact that debris spread was extensive could theoretically indicate an explosive break up of the plane, but is not evidence of a bomb, as a plane breaking up due to structural stress or a fuel tank explosion, for example, would lead to much the same result.
In this regard, the Captain of Air Comet Flight 974, Lima-Madrid, whose plane was in the area at the time, reported seeing “An intense shining of white light which followed a downward trajectory and disappeared after about six seconds.”
This statement has not yet been corroborated by Air Comet, although they passed it on to Air France as a routine measure. The BEA announced that it would not suggest an explosion or disprove it either. Moreover, they point out that transmission, radar and other evidence seems to indicate that the Air Comet plane was too far away from AF447 to have seen its supposed disintegration in the prevailing murky flying conditions.
The DEA, the French authorities and all other organisations involved in the investigation are insisting on the fact that there are a lot of erroneous theories concerning the accident and they are pointing out, in a recent communiqé mentioning the Brazilian press and authorities, that coming to hasty conclusions about developing events is not in the best interests of the investigation or those of the victims’ families.
At 15:40pm Paris time there has been no news of debris being found so far today, and no official announcements with respect to information about AF447.
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