pax2908, the BEA did earlier lay out the grids for the sonar search, with a search radius based on last position, and which extended beyond the radius to cover areas north and west of the presumed track. Apparently, the sonar found nothing. This may be a consequence of the subsurface terrain which is very mountainous, and I suppose it is possible the wreckage fell into a crevasse, or is undetectable by sonar because rock features are blocking the signal.