rgbrock, the second phase, the sonar scan, is to take 4-6 weeks and cover 16,000 sq km. The area west of the track is very mountainous, with some peaks that appear to be 2,000 to 3,000 meters high. Large pieces of wreckage that are resting on a steep slope or are in a crevasse would probably present with a smaller vertical profile to a scan, if not altogether hidden entirely.
This may be a very formidable task.