Where Are the Pings? Searchers Report None in 24 Hours

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No signals that might be from the missing Malaysia Airlines jet have been heard in 24 hours, the agency coordinating the search said early Saturday.

The search zone was narrowed yet again to about 16,000 square miles, down from 22,000 on Thursday and double that the day before. At its largest, the search covered 2.96 million square miles, or 11 percent of the Indian Ocean.

The last report of an acoustic signal that might be emanating from the Boeing 777 was on Thursday, when an Australian navy aircraft picked up the signal in the same area a ship first heard sounds consistent with an aircraft's black boxes. The signal picked up by the plane was later determined not to be related to a locator beacon.

Teams are trying to zero in on the black boxes before their batteries run out.

Australia's prime minister has said authorities are confident that signals pulsing in the Indian Ocean are from the jet, missing since March 8.

But an air-disaster expert cautioned Friday that it could just be old oceanography equipment. Greg Feith, a former investigator for the National Transportation Safety Board and an NBC News analyst, said that not much equipment sends signals over the frequency 37.5 kilohertz.

Australia's Joint Agency Coordination Centre said Saturday that the ship Ocean Shield would continue sweeps with a pinger locator. P-3 Orions also would continue acoustic searches in an attempt to further narrow the area where the black boxes might be.

A towed pinger locator on the deck of the Australian ship Ocean Shield in the Indian Ocean west of Australia on March 31.Bradley Darvill / Australian Defence via EPA