Originally Posted by
TOM57
BEA says that the area where the plane was found had been researched in the early phases by sonar. Nothing was detected then, and that is why they had privileged other sectors in later searches.
While this isn't directly pertinent to the subject, I've got to say that there's major irony there. When the joint French/US team went looking for the Titanic in 1985, their starting point was the last sonar return not explored by Jack Grimm's expedition. As soon as the sonar scan started, the returns were so wild that they figured it must be a technical malfunction and brought the sonar device back up for recalibration. They then proceeded to spend weeks scanning the rest of the search area, finding nothing. It later transpired that while the sonar readings were fluctuating wildly at the beginning of the mission, some of the returns were true and they were in fact practically on top of the wreck site. Every pass they made in the following weeks took them further and further away from the target.
The US half of the team (having been away on what turned out to be a clandestine mission to film the USS Thresher and Scorpion) then put all their chips on sending the video cameras down at the starting point and found the wreck site with barely a couple of days to spare.
Deep-ocean exploration and salvage - possibly one of the hardest things in the world to get right!