A pinger locator in the Indian Ocean has detected signals consistent with those sent by a flight data recorder and a cockpit voice recorder, said the head of the Australian agency coordinating search operations. The signals were picked up Sunday by the Ocean Shield, an Australian navy ship that's towing a sophisticated U.S. pinger locator through an area about 1,750 kilometers (1,100 miles) northwest of Perth. The first detection lasted for more than two hours; a second lasted for about 13 minutes.
More pings raise more questions about missing plane
By Tom Cohen
(CNN) -- Almost a month after Malaysia Airlines Flight 370 disappeared, searchers say pulse signals detected in the Indian Ocean provide the best hope so far for finding it.
However, those same officials warn it will take time to confirm if the sonar pings come from the missing plane, meaning nothing is certain yet.
The new information raises more questions about what the pulse signals mean and what happens now.
Is this it?
An Australian ship using high-tech equipment has twice detected signals along the suspected flight path of the airliner off its country's western coast.
Angus Houston, who heads the rescue effort, told reporters that a device called a towed pinger locator on the vessel Ocean Shield received signals similar to the kind that the aircraft's on board data and cockpit voice recorders would emit.
The first detection, which occurred over the weekend, lasted more than two hours before the ship lost contact, Houston said. A second detection several hours later lasted 13 minutes, and more importantly, included two separate signals audible to the locator device, he said.
Two signals could mean they came from the so-called black boxes, as expected.
"It's probably the best information that we have had," Houston said before immediately noting that "we haven't found the aircraft yet; we need further confirmation."
Why this may be it
The signals reported were near the 37.5 kHz "standard beacon frequency" of the recorders, officials say. That frequency was chosen for use to avoid interference from other ocean noises as much as possible.
In addition, the two pulse signals detected at the same time would be consistent with the two emitters on the plane.
Also, the location where the signals were detected is along the missing plane's probable flight path, according to the latest analysis of its known direction and fuel capacity. Houston said the new information on the likely flight path helped narrow the search area.
"With the acoustic events that we're getting in the area, we are encouraged that we're very close to where we need to be," Houston said, later adding: This is quite an extraordinary set of circumstances that we're now in a very well-defined search area which hopefully will eventually yield the information that we need to say MH370 might have entered the water just here."
On Saturday, a Chinese ship detected a single pulse signal more than 300 miles further south, also near the most recently projected flight path. Houston said the distance made it "unlikely" the Chinese ship and Australian vessel detected the same signal, but added "in deep water, funny things happen with acoustic signals."
Why this may not be it
From the beginning, search officials have stressed the long odds against figuring out where the plane might be without visible evidence such as wreckage.
For now, all we have are some pulse signals, Houston said, and in the ocean, those could be from a number of things.
"This has been done without finding any wreckage thus far, and I think it's quite extraordinary and what I'd like to see now is us find some wreckage because that will basically help solve the mystery," Houston explained, adding that "without wreckage, we can't say it's definitely here."
Oceanographers note that the ocean is full of sonar sounds, including whale calls and signals emitted by research equipment left on the bottom to help find it later. While the frequency of the black box signals are intended to be unique, other sounds can cause confusion, they note.
"Unlike in air where sound travels in a straight line, acoustic energy -- sound through the water -- is greatly affected by temperature, pressure and salinity," explained Peter Leavy, commander of the military task force conducting the search.
"And that has the effect of attenuating, bending -- sometimes through 90 degrees -- sound waves. So it is quite possible and very hard to predict -- it's quite possible for sound to travel great distances laterally but be very difficult to hear near the surface of the ocean, for instance."
The Ocean Shield and its towed pinger locator continued to search the area it detected the signals to try to hear them again. If they do, searchers would send out a Bluefin-21 Autonomous Underwater Vehicle with a more accurate sonar and possibly a camera for mapping and studying the the ocean floor, Leavy said.
"At the moment that's not deployed," he told reporters. "The focus is on trying to reacquire the acoustic signal that they had" by the end of Tuesday.
A major question is how long the batteries in the recorders will last. They have a 30-day expectancy when activated, and the plane disappeared on March 8, which was 31 days ago.
"We're already one day past the advertised shelf life," Houston said. "We hope that it keeps going for a little bit longer."
Confirmation that the signal comes from the Boeing 777 would mean "the possibility of recovering the plane -- or at least the black boxes -- goes from being one in a million to almost certain," said Simon Boxall, a lecturer in ocean and earth science at the University of Southampton.
Houston, a retired Australian Air chief marshal who is chief coordinator of Joint Agency Coordination Centre, warned against expecting a quick resolution.
"It could take some days before the information is available to establish whether these detections can be confirmed as being from MH370," he said. "In very deep oceanic water, nothing happens fast."
CNN's Jethro Mullen, Holly Yan, Catherine Shoichet, Judy Kwon, Ed Payne and Mitra Mobasherat and journalist Ivy Sam contributed to this report.Malaysia
Flight 370: New signal sounds 'just like' one from a plane's beacon
By Holly Yan, Jethro Mullen and Catherine E. Shoichet
(CNN) -- After weeks of searching vast swaths of ocean, investigators now have their "most promising" lead yet in efforts to find Malaysia Airlines Flight 370.
A pinger locator in the Indian Ocean has detected signals consistent with those sent by a flight data recorder and a cockpit voice recorder, said the head of the Australian agency coordinating search operations.
The signals were picked up Sunday by the Ocean Shield, an Australian navy ship that's towing a sophisticated U.S. pinger locator through an area about 1,750 kilometers (1,100 miles) northwest of Perth. The first detection lasted for more than two hours; a second lasted for about 13 minutes.
The sounds were heard in a part of the ocean that's about 4,500 meters (about 14,800 feet) deep, retired Air Chief Marshal Angus Houston said Monday.
"We've got a visual indication on a screen, and we've also got an audible signal. And the audible signal sounds to me just like an emergency locator beacon," he said.
"We are encouraged that we are very close to where we need to be."
But it could take days before officials can confirm whether the signals came from the plane, which fell off radar on March 8 with 239 people on board.
"In very deep oceanic water, nothing happens fast," Houston said. "I would ask all of you to treat this information cautiously and responsibly. ... We haven't found the aircraft yet."
"We have a promising lead, but we have yet to get confirming evidence."
At least one investigator has described the search not as finding a needle in a haystack, but rather trying to find the haystack.
"It's very exciting, very exciting," forensic audio expert Paul Ginsberg said Monday. "I think we have finally found the haystack."
And Malaysian authorities are hopeful there will be a positive development in the next few days, if not hours, acting Transportation Minister Hishammuddin Hussein told reporters Monday.
But some friends and relatives of passengers said they're not putting too much stock in Monday's news.
"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.
Teams are also still investigating pings detected Friday and Saturday by a Chinese ship about 600 kilometers (375 miles) southwest of the area that the Ocean Shield is searching.
But time could be running out in tracing the sounds. In a few hours or days, the pingers aboard the plane could stop transmitting for good.
The batteries inside the beacons, which are designed to start sending signals when a plane crashes into water, last about 30 days after the devices are activated.
Monday marks the 31st day of the search.
New flight details
While searchers may be getting closer to the plane, a fresh mystery has emerged about what happened during the flight.
The jet skirted Indonesian airspace as it went off the grid and veered off course, a senior Malaysian government source told CNN on Sunday.
After reviewing radar track data from neighboring countries, officials concluded that the plane curved north of Indonesia before turning south toward the southern Indian Ocean, the Malaysian source said.
Whoever was flying the plane could have been trying to avoid radar detection, the source said.
Like most details in the case that's baffled investigators ever since the plane dropped off Malaysian military radar, it depends on whom you ask.
CNN law enforcement analyst Tom Fuentes cautioned against assuming a nefarious reason for steering the plane around Indonesia's airspace.
"I think the plane's being intentionally flown there, but I think it's still a mystery as to why. ... I think they would probably guess they're not avoiding anybody's radar, because there's a lot of radar in the area," he said. "I think they're avoiding getting shot down or colliding with another airplane."
CNN aviation analyst Miles O'Brien said the new route includes designated waypoints that pilots and air traffic controllers use.
"This particular route that is laid out happens to coincide with some of these named intersections," he said. "So what it shows is an experienced pilot somewhere in the mix on this."
Investigators haven't said who they think might have flown the plane off course or why.
But Hishammuddin, Malaysia's acting transportation minister, said Monday that Indonesian military authorities told the Malaysian defense force that they had "no sighting" of the plane the night it disappeared.
The possibility that the plane was hijacked by someone who knew how to fly a commercial jet is still on the table. Authorities have also been investigating the plane's captain and co-pilot. And they haven't ruled out mechanical problems as a possible cause of the plane's diversion.
So far, no physical evidence of the plane's eventual whereabouts has been found, leaving many relatives of those on board trapped in uncertainty.
The Ocean Shield, whose high-tech pinger locator was borrowed from the U.S. Navy, will continue to pursue the sound it heard. If that lead turns cold, it will move to another detection area, a journey that will take at least a day, officials said.
The HMS Echo, a British navy ship equipped with advanced detection gear, sailed into the area of the southern Indian Ocean on Monday morning (Sunday afternoon ET) where a Chinese crew had detected two audio signals.
The arrival of the Echo will be critical to the search for the missing Boeing 777. It has state-of-the-art sonar and is capable of mapping the ocean floor.
It should be able to help determine more confidently whether audio signals picked up Friday and Saturday by the Chinese patrol ship Haixun 01 came from the plane.
The Chinese said the electronic pulses -- detected only 2 kilometers (1.25 miles) apart -- were consistent with those emitted by pingers on an aircraft's "black boxes."
Houston, the head of the Australian agency coordinating the search, said sounds travel long distances underwater, making it difficult to find their sources. If detectors were near a pinger, they would pick up the signal for a more sustained period.
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. But officials say they can't discount anything at this point.
Houston said the pulses detected by the Chinese ship are particularly notable because they occurred in an area that fits with the latest expert calculation of roughly where the plane likely entered the water.
Despite the new hints that the plane may be in the ocean, some relatives of passengers are still hoping for the best.
"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 Judy Kwon, Ed Payne and Mitra Mobasherat and journalist Ivy Sam also contributed to this report.
Navy specialists were urgently trying to pick up the signal again so they can triangulate its position and go to the next step of sending an unmanned miniature submarine into the depths to try to identify plane wreckage.
Confirmation that the signals picked up by the Australian navy ship Ocean Shield belong to Flight 370's black boxes could take days, but the discovery offers "a most promising lead" yet, said Angus Houston, the head of a joint agency coordinating the multinational search. They were stronger and lasted longer than faint signals a Chinese ship reported hearing farther south in the search zone in the remote Indian Ocean.
"Clearly this is a most promising lead, and probably in the search so far, it's probably the best information that we have had," Houston said at a news conference. "We've got a visual indication on a screen and we've also got an audible signal — and the audible signal sounds to me just like an emergency locator beacon."
After a monthlong search for answers filled with dead ends, Monday's news brought fresh hope given that the two black boxes, which contain flight data and cockpit voice recordings, are the key to unraveling exactly what happened to Flight 370 and why.
In Kuala Lumpur, Malaysian Defense Minister Hishammudin Hussein told reporters that in light of the new information, "We are cautiously hopeful that there will be a positive development in the next few days, if not hours."
Little time is left to locate the devices, which have beacons that emit "pings" so they can be more easily found. The beacons' batteries last only about a month — and Tuesday marks exactly one month since the plane disappeared during a flight from Kuala Lumpur to Beijing with 239 people on board.
The Ocean Shield, which is carrying high-tech sound detectors from the U.S. Navy, picked up two separate signals late Saturday night and early Sunday morning in seas far off the west Australian coast that search crews have been crisscrossing for weeks. The first signal lasted two hours and 20 minutes before it was lost. The ship then turned around and picked up a signal again — this time recording two distinct "pinger returns" that lasted 13 minutes, Houston said.
"Significantly, this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder," Houston said.
Still, Houston cautioned that it was too early to say the transmissions were coming from the missing jet.
"I would want more confirmation before we say this is it," he said. "Without wreckage, we can't say it's definitely here. We've got to go down and have a look."
The ping locator is pulled behind the ship at a depth of 3 kilometers (1.9 miles) and is designed to detect signals at a range of 1.8 kilometers (1.12 miles), meaning it would need to be almost on top of the black boxes to detect them if they were on the ocean floor, which is about 4.5 kilometers (2.8 miles) deep.
"It's like playing hot and cold when you're searching for something and someone's telling you you're getting warmer and warmer and warmer," U.S. Navy Capt. Mark Matthews said. "When you're right on top of it you get a good return."
The black boxes normally emit a frequency of 37.5 kilohertz, and the signals picked up by the Ocean Shield were both 33.3 kilohertz, he said. But the manufacturer indicated the frequency of black boxes can drift in older equipment.
The Ocean Shield was slowly canvassing a small area trying to find the signal again, though that could take another day, Matthews said.
If they pick up the signal again, the crew will launch an underwater vehicle to investigate, he said. The Bluefin 21 autonomous sub can create a sonar map of the area to chart where the debris may lie on the sea floor. If it maps out a debris field, the crew will replace the sonar system with a camera unit to photograph any wreckage.
That may prove tricky because the water depth is right at the limits of the sub's capability.
"It could take some days before the information is available to establish whether these detections can be confirmed as being from MH370," Houston said. "In very deep oceanic water, nothing happens fast."
Geoff Dell, discipline leader of accident investigation at Central Queensland University in Australia, said it would be "coincidental in the extreme" for the sounds to have come from anything other than an aircraft's black box.
"If they have a got a legitimate signal, and it's not from one of the other vessels or something, you would have to say they are within a bull's roar," he said. "There's still a chance that it's a spurious signal that's coming from somewhere else and they are chasing a ghost, but it certainly is encouraging that they've found something to suggest they are in the right spot."
Meanwhile, the British ship HMS Echo, was using sophisticated sound-locating equipment to try to determine whether two separate sounds heard by a Chinese ship about 555 kilometers (345 miles) away from the Ocean Shield were related to the plane. The patrol vessel Haixun 01 detected a brief "pulse signal" on Friday and a second signal on Saturday.
The crew of the Chinese ship reportedly picked up the signals using a sonar device called a hydrophone dangled over the side of a small boat — something experts said was technically possible but extremely unlikely. The equipment aboard the British and Australian ships is dragged slowly behind each vessel over long distances and is considered far more sophisticated.
The search effort continued on the ocean surface Monday. Twelve planes and 14 ships searched three designated zones, one of which overlaps with the Ocean Shield's underwater search. All of the previous surface searches have found only fishing equipment or other sea trash floating in the water.
Associated Press writers Eileen Ng in Kuala Lumpur, Malaysia, and Rohan Sullivan and Kristen Gelineau in Sydney contributed to this report.