Search crews in the Indian Ocean have reacquired the underwater signal they believe could belong to the flight data recorder of the missing Malaysian jetliner.
Australian search chief Angus Houston said a U.S. Navy towed pinger locator heard the transmission on two separate occasions Tuesday.
"Yesterday's signals will assist in better defining a reduced and much more manageable search area on the ocean floor. I believe we are searching in the right area but we need to visually identify aircraft wreckage before we can confirm with certainty that this is the final resting place of MH370," said Houston.
He said more signals need to be detected and the search area better refined before authorities can deploy a robot submarine to search the ocean floor.
Authorities are running out of time, as the battery on the plane's black box locator beacon that transmits the "pings" lasts only for about 30 days.
It has now been over a month since the Boeing 777 disappeared en route from Kuala Lumpur to Beijing, carrying 239 people.
The Australian Navy ship Ocean Shield, which is carrying the towed pinger locator, first picked up the signals on Saturday and Sunday, before losing them.
Houston said one "ping" was heard Tuesday afternoon for about five minutes. A second was picked up late Tuesday for about seven minutes.
He said the signals, at 33.331 kilohertz and at 1.106 intervals, were consistent with those expected to be transmitted by the black box's beacon.
The retired air chief marshal said search crews were "very fortunate" to have relocated the transmissions, since it had been 33 days since the plane disappeared.
If additional signals are detected, Houston said he hoped to find something "within a matter of days" that would confirm the plane's "final resting place."
Once the black box is retrieved, authorities will be able to determine what led to the crash, which 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.