By Ed Payne and Catherine E. Shoichet
(CNN) — The pulses that an Australian navy ship detected over the weekend from a remote location in the Indian Ocean have not been picked up since, but authorities are not letting that deter their search for Malaysia Airlines Flight 370.
“We have at least several days of intense actions ahead of us,” Australian Defense Minister David Johnston told reporters Tuesday. “We’re throwing everything at this difficult, complex task.”
Investigators hope the signals were from locator beacons that were attached to the data and voice recorders that were stored in the tail of the Boeing 777-200ER when it disappeared from radar screens on March 8.
Buoyed by the hope that they’re closing in on the beacons, they reduced the search area Tuesday.
Their current focus is 30,000 square miles (more than 77,500 square kilometers) of the Indian Ocean, about 1,400 miles (2,250 kilometers) northwest of Perth. That’s about a third of the size of the previous search zone.
“Instead of looking at an area the size of Texas, we’re now looking in an area the size of Houston,” aviation expert Geoffrey Thomas told CNN.
Time, however, is looming as a factor.
The batteries powering the beacons, which are designed to emit signals when submerged in salt water, are certified to last 30 days.
Tuesday marks day 32.
Experts have said the batteries could last longer if they were fully charged when the plane disappeared while carrying 239 people on a flight from Kuala Lumpur, Malaysia, to Beijing.
“We need to continue … for several days right up to when the point at which there’s absolutely no doubt that the pinger batteries will have expired,” said retired Air Chief Marshal Angus Houston, the chief of the Australian agency coordinating the search.
Retired Royal Air Force Lt. Col. Michael Kay predicted the search for the pingers would continue for another week and a half.
“We know that the batteries can last up to 40 days,” Kay told CNN. “If I was Angus Houston, I would be putting the search out to at least 42, 43 (days) to make absolutely sure that the batteries had failed.”
The race against time is the “Number one challenge” searchers face, U.S. Navy Cmdr. William Marks told CNN.
“We haven’t quit since we initially heard these signals,” he said. “We’ve been going continuously around the clock and we haven’t been able to reacquire them.”
Searchers are still scouring the waters, but their optimism is “more cautious” now, he said. “As hours pass,” he said, “our optimism is fading away, ever so slightly.”
But the search area still presents major challenges.
The location is deep, and a cyclone that packed wind speeds of more than 160 mph churned through the area two weeks ago, when crews were focused elsewhere in the Indian Ocean. In doing so, it would have further spread any debris.
“This was an area that looked like a washing machine in the first place, but now we know it was even worse than that,” CNN meteorologist Chad Myers said.
But Tuesday’s weather was calm, with no major systems near where the pings were detected, said CNN meteorologist Sherri Pugh.
Cheers erupted Saturday when the team aboard Australia’s Ocean Shield first detected a possible signal from one of the plane’s recorders.
The Australian ship is equipped with two key pieces of U.S. equipment to scan the water for signs of the plane: a towed pinger locator and a Bluefin-21 underwater vehicle.
The first detection continued for more than two hours; the second for about 13 minutes.
The signals, detected about 1,750 kilometers (1,100 miles) northwest of Perth, Australia, were consistent with those sent by a flight data recorder and a cockpit voice recorder, Houston said. They were heard in seawater about 4,500 meters (14,800 feet) deep.
“The audible signal sounds to me just like an emergency locator beacon,” Houston said. “We are encouraged that we are very close to where we need to be.”
If the signals are heard again, searchers could deploy an underwater drone to take photos to determine whether they do indeed mean the discovery of the so-called black boxes. That process could take more than a week.
“Until we have stopped the pinger search, we will not deploy the submersible,” Houston said. “We will not deploy it unless we get another transmission in which we’ll probably have a better idea of what’s down there.”
Teams are also still investigating pulses detected Friday and Saturday by a Chinese ship about 600 kilometers (375 miles) southwest of where the Ocean Shield is searching.
The signals detected by the Chinese weren’t as sustained as those picked up by the Ocean Shield, and the Chinese vessel’s detection gear isn’t thought to be as advanced as the U.S. pinger locator.
Houston said Monday that they were probably separate events.
Some friends and relatives of passengers said they were keeping their hopes in check.
“Until they physically locate the bulk of the plane with the black box intact and passenger bodies, I won’t believe it,” said Sarah Bajc, the partner of American passenger Philip Wood.
At a candlelight vigil in Beijing on Monday night, some relatives sobbed and others bowed their heads.
“If the plane is there, it’s there. We can’t change it,” the husband of one passenger said. “But I am still hoping for a miracle to happen.”
CNN’s Tom Watkins, Jethro Mullen, Matthew Chance, David Molko, Will Ripley, Judy Kwon, Ed Payne and Mitra Mobasherat and journalist Ivy Sam also contributed to this report.
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