The eighth underwater drone mission to search for the missing Malaysia Airlines flight MH370 has failed to find any evidence of plane wreckage on the sea bed. The Bluefin-21 submarine employed for the task has so far screened over two-thirds of the narrowed search area. The underwater hunt is expected to finish within this week, Since its fourth mission, the submarine was reprogrammed to scour the seas 604 feet below its permissible limit of 14,800 feet. The part of the Indian Ocean narrowed down for the search is deeper than the previously estimated range at some places, "The [underwater drone]...