Two dozen ships and planes spent another day searching the Indian Ocean from above amid growing confidence about what lies below -- Malaysia Airlines Flight 370, the Beijing-bound plane that vanished March 8 with 239 people on board.
"We have very much narrowed down the search area and we are very confident that the signals that we are detecting are from the black box on MH370," said Tony Abbott, the prime minister of Australia, during a visit to China today.
But those signals have not been heard since Tuesday and without them, there is no way to home in on the box, which officials are hoping contains data that will help solve the mystery of what happened to the plane. Teams plan to soon turn to a sonar scanner to begin looking for wrecking. The process is slow-going.
"It's probably a month and a half to two months of effort," said Capt. Mark Matthews of the US Navy.
The seafloor in the area is remote, a pitch-black, alien landscape of plains and 12,000-feet-high mountains under 15,000 crushing feet of water.
"There's a lot of silt down there," said Angus Houston, the retired Australian air chief marshal heading the search operation far off Australia's west coast. "That could complicate the search because the silt on the bottom of the ocean can be very thick."
When or if the plane's black boxes are finally located, a remotely operated submarine will bring them up.
"The ROV will go down and it will actually comb through the debris field and the black boxes and any other items the investigators need to help identify the cause of the crash," said Paul Nelson, the project manager of Phoenix International, a salvage company.
Time is running out to find the devices, whose locator beacons have a battery life of about a month. Earlier in the week marked exactly one month since the plane vanished.
"We're getting into the stage where the signal from what we are very confident is the black box is starting to fade," Abbott said today. "We are hoping to get as much information as we can before the signal finally expires."
ABC News' Clayton Sandell and The Associated Press contributed to this story.