Originally Posted by
jcjeant
Pretty good ? my post tell me the contrary (they were involved in the researches)
And it's not their area of expertise, so I think holding the BEA largely responsible for the time it took to locate the thing is a little unfair.
For an idea of just how difficult it is to perform that kind of work, I'd recommend doing a little research on the 1985 WHOI/IFREMER expedtion to find the last resting place of the Titanic (among other things, now that info has been declassified).
Despite their best efforts, they only found it in the last two days of a mission that lasted several weeks (they'd have found it right at the start if not for a major blunder), and that was a 900ft iron ship in two major sections on a flat abyssal plain. The AF447 recovery expedition was trying to find pulverised scraps of aluminium from an approximately 200x200ft airliner in underwater mountains, which is an order of magnitude more difficult even with the advances in technology over the last 25 years.
For those that are interested, part of the classified mission involved the US half of the team going off to search for two sunken USN nuclear subs, which were easier to find due to exact satellite positioning at the time they sank. But what the US team discovered was that far larger and more widespread than the main pieces of wreckage was a debris trail of smaller, lighter items that trailed the larger wreckage as it sank. Pick up the debris trail, went the theory - and it would lead you straight to the wreckage.
Of course, all of the debris and wreckage in these cases came to rest on a more-or-less flat plain, so the trail was much easier to find and follow than it would be on the mountainous terrain in which AF447's wreckage was thought to be. The other major problem with mountainous terrain would be the fact that even if the flight recorder pingers were working, the sonar signals could bounce off the surrounding terrain, making following the trail even *more* difficult.