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PERTH, Australia — After four strong underwater signals in the past week, all has gone quiet in the hunt for the missing Malaysian airline, meaning the batteries on the all-important black boxes may have finally died.

Despite having no new signals to go on, crews are continuing their search Sunday for debris and any sounds that could still be emanating. Investigators are desperately trying to pinpoint where the Boeing 777 could be amid an enormous patch of deep ocean.

No new electronic pings have been heard since April 8, and the batteries powering the locator beacons on the jet’s black box recorders may already be dead. They only last about a month, and that window has passed.

Once officials are confident no more sounds will be heard, a robotic submersible will be sent down.

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