Australian officials say they've located two signals that could be coming from the black box of missing Malaysia Flight 370.
"Clearly this is the most promising lead probably in the search so far," said Angus Houston, the air chief marshal who is leading the Australian search effort.
Navy specialists are now trying to determine the exact position of the signal they picked up. It was detected for nearly two and a half hours on Saturday and then again for 13 minutes on Sunday.
This new lead allows searchers to zero in on a very small area, but they want to hear a third ping to narrow it down even further.
"That will be the trigger at the moment to launch the autonomous underwater vehicle with a more accurate sonar and potentially a camera for mapping and visually looking at the ocean floor," Peter Leavy, commodore of the Royal Australian Navy, explained.
That deep sea search will take place about three miles below the surface.
Time is running out for teams to locate the black boxes. The batteries were only supposed to be at full strength through this past weekend, but the manufacturers say there could still be a few more days of solid signal.
Experts warn that it could still be days before authorities decide whether the signal is actually coming from the plane's cockpit voice and data recorders, and then it could be months before any wreckage is found.
Meanwhile, experts say it's difficult to come up with a full estimate for the cost of the ongoing search.
The United States has allocated nearly $8 million to the effort. And Australia is spending almost $1 million a day trying to locate the lost airliner.