Finding the black boxes quickly is a matter of urgency because their locator beacons have a battery life of only about a month, and Tuesday marked exactly one month since the plane vanished on March 8 with 239 people on board.

If the beacons blink off before the black boxes' location can be determined, finding them in such deep water - about 4,500 meters, or 15,000 feet - would be an immensely difficult, if not impossible, task....