The first of the signals was held for more than two hours, retired Air Chief Marshal Angus Houston, who is leading the multinational search, said Monday. On a return trip along the same path early on Sunday morning, two distinct “pinger” signals were detected and held for about 13 minutes.

“Significantly, this would be consistent with transmission from both the flight data recorder and the cockpit voice recorder,” Air Chief Marshal Houston said. “Clearly this is a most promising lead and probably in the search so far. The audible signal sounds to me just like an emergency locator beacon,” he added.

Searchers still need to fix on a precise location before sending an underwater vehicle to investigate the finding, in an area of ocean some 4,500 meters (14,764 feet) deep, he said. Those depths are at the absolute limit of the undersea vehicle aboard Ocean Shield, after which crews would have to turn to other submersibles or dropping cameras to the ocean floor.