Search crews have detected more underwater transmissions they believe could belong to the flight data recorder of the missing Malaysian jetliner.
Australian authorities said an Orion surveillance aircraft heard a "possible signal" Thursday in the southern Indian Ocean, near where ships heard similar sounds earlier this week.
Search chief Angus Houston said in a statement "the acoustic data will require further analysis overnight, but shows potential of being from a man-made source."
Houston, who is coordinating the search, on Wednesday said he hopes the developments mean authorities can find the missing Boeing 777 "in the not too distant future."
The pings have helped greatly narrow the search area. But on Thursday, planes and ships continued searching a region stretching 57,000 square kilometers.
Time is running out for authorities to locate the origin of the signals, since the batteries on the black box's locator beacon are set to run out after about 30 days.
The Malaysia Airlines jet, which was carrying 239 people, disappeared on March 8 while traveling from Kuala Lumpur to Beijing.
Malaysian authorities believe the plane was deliberately diverted and crashed into the sea. But without wreckage, many are skeptical.
In the Malaysian capital Thursday, salesman Wee Boon Seow said it is hard to be optimistic that search crews are narrowing in on the plane.
"I mean, as a Malaysian, we tend to take everything with a pinch of salt, because there is always this latest development, this latest news about how they discovered the 'pings' in the south Indian Ocean. But I don't know. I'm pretty pessimistic about the news."
A total of 14 planes and 13 ships are involved in Thursday's search for the plane, which extends from about 2,300 kilometers northwest of the Australian city of Perth.
If authorities can locate more pings, they plan to deploy a robot submarine to search the ocean floor.
Once the black box is retrieved, authorities will be able to determine what happened to the plane. Its fate has become one of the most puzzling mysteries in modern aviation.
The plane vanished without any distress calls, and authorities have refused to rule out any possibilities, including hijacking, sabotage or a mechanical malfunction.