Indonesian investigators said they were homing in on the black box from a crashed jetliner after locating its "pings" yesterday, two days after the jet crashed shortly after take-off with 189 people on board.
Retrieving the black box will be key to unlocking why the Boeing 737-MAX, one of the world's newest and most advanced commercial passenger jets, nosedived into the Java Sea so soon after leaving Jakarta.
Authorities said they believed they were closing in on the main wreckage and had picked up the box's signals some 30-40 meters (100-130 feet) below the surface of the water off Indonesia's north coast, where the plane crashed Monday.
"We've detected the black box signal," Muhammad Syaugi, head of Indonesian search and rescue agency, told reporters in Jakarta.
The black box contains flight data that shows the speed, altitude and direction of the plane, while the cockpit voice recorder keeps track of conversations and other sounds in the cockpit.
Dozens of divers were taking part in the 1,000-strong personnel recovery effort along with helicopters and ships, but authorities have all but ruled out finding any survivors.
The development comes as Boeing officials were due to meet with Lion Air yesterday, after Indonesia ordered an inspection of the US plane maker's 737-MAX jets.
Indonesia's transport minister Budi Karya Sumadi took the unusual step of ordering the temporary removal of Lion Air's technical director and several other staff who cleared the flight, citing government authority over the aviation sector.
Aviation experts say it is too early to determine what caused the accident. But Lion's admission that the plane had an unspecified technical issue on a previous have raised questions about whether it had any faults specific to the newly released model, including a speed-and-altitude system malfunction.