How to find plane wreckage in the ocean

Inside Science News : Search crews found debris fields Tuesday in the area where Air France flight 447 apparently crashed into the Atlantic Ocean.Recovering parts of the aircraft on the seabed however, will be difficult."The water is deep in that region,” says John Perry Fish , CEO of American Underwater Search and Survey , “some 7000 meters deep in the deepest parts, but averaging about 4000 meters. It is near the mid-Atlantic ridge , [an undersea mountain range] which runs from Iceland to the south Atlantic."The first problem in finding the debris and black boxes from the plane, he said, is that the aircraft was not being tracked on radar when it disappeared, “so you don’t know exactly where to start. If you have a radar track, you can plot an area of a couple miles out from that point and start searching.” Without the radar, he said, the task is to find the floating debris and do “hindcasting,” which traces the path of debris backwards as it floats on the ocean currents. Chris German , the chief scientist for the deep submergence group at the Woods Hole Oceanographic Institute on Cape Cod, Massachusetts, says that even with two debris fields located miles apart, the backtracking can be done. “You look at the ocean currents and wind and determine where the debris was 10 hours before, then 10 hours before that. You do that all the way back to when you think the crash occurred.” Fish said that the hindcasting could trace out the path up to 30 days back in time.Unmanned sonar-mapping submersibles can then be used to look for wreckage on the seabed, particularly the blackbox &which contains data about the final minutes of the flight—that emits an ultrasonic acoustic ping to help guide rescuers to its location.The conditions however are at the limit of current technology, making any sort of recovery operation extremely difficult.