Three distinct but brief signals from the Indian Ocean revived hope for investigators in the search for missing Malaysia Airlines Flight 370 on Sunday, as authorities rush to determine the origin of the signals before the batteries of the plane's black box run out.
Australian authorities confirmed on Sunday that a Chinese patrol vessel, the Haixun 01, had picked up a fleeting "ping" signal twice on Friday and Saturday in waters west of Perth, near where investigators believe Malaysia Airlines Flight MH370 went down on March 8. As a consequence, more planes and ships were being sent to assist in that area.
Meanwhile, on Sunday, an Australian ship carrying sophisticated deep-sea sound equipment picked up a third signal in a different part of the massive search area, some 300 nautical miles away.
After weeks of fruitless looking, the multinational search team is racing against time to find the sound-emitting beacons and cockpit voice recorders that could help unravel the mystery of the plane. The beacons in the black boxes emit "pings" so they can be more easily found, but the batteries last for only about a month.
"This is an important and encouraging lead, but one which I urge you to treat carefully," retired Australian Air Chief Marshall Angus Houston, who is coordinating the search, told reporters in Perth.
Houston stressed that the signals had not been verified as being linked to Flight 370, which was traveling from Kuala Lumpur, Malaysia, to Beijing when it disappeared March 8 with 239 people on board. Experts, meanwhile, expressed doubt that the equipment aboard the Chinese ship was capable of picking up signals from the black boxes.
"We have an acoustic event. The job now is to determine the significance of that event. It does not confirm or deny the presence of the aircraft locator on the bottom of the ocean," Houston said, referring to each of the three transmissions.
"We are dealing with very deep water, we are dealing with an environment where sometimes you can get false indications," he said. "There are lots of noises in the ocean, and sometimes the acoustic equipment can rebound, echo if you like."
China's official Xinhua News Agency reported Saturday that the patrol vessel detected a "pulse signal" Friday in the southern Indian Ocean at 37.5 kilohertz -- the same frequency emitted by the flight data recorders aboard the missing plane.
Australian authorities said such a signal would be consistent with a black box, but both they and Xinhua stressed there was no conclusive evidence linking it to the Boeing 777.
Houston confirmed the report, and said the Haixun 01 detected a signal again on Saturday within 1.4 miles of the original signal, for 90 seconds. He said China also reported seeing white objects floating in the sea in the area.
The British navy ship HMS Echo, which is fitted with sophisticated sound-locating equipment, is moving to the area where the signals were picked up and will probably get there early Monday, Houston said.
The Australian navy's Ocean Shield, which is carrying high-tech sound detectors from the U.S. Navy, will also head there, but will first investigate the sound it picked up in its current region.
Australian air force assets are also being deployed into the Haixun 01's area to try to confirm or discount the signals' relevance to the search, Houston said.
In Kuala Lumpur, families of passengers aboard the missing plane attended a prayer service on Sunday that also drew thousands of Malaysian sympathizers.
"This is not a prayer for the dead because we have not found bodies. This is a prayer for blessings and that the plane will be found," said Liow Tiong Lai, the president of the government coalition party that organized the two-hour session.
Two Chinese women were in tears and hugged by their caregivers after the rally. Many others looked somber, and several wore white T-shirts emblazoned with the words "Pray for MH370."
Two-thirds of the passengers aboard Flight 370 were Chinese, and a group of relatives has been in Kuala Lumpur for most of the past month to follow the investigation. Liow said some of them were planning to go home on Sunday.
Investigators believe Flight 370 veered way off-course and came down somewhere in the southern Indian Ocean, though they have not been able to explain why it did so.
The crew of the Chinese ship reportedly picked up the signals using a hand-held sonar device called a hydrophone dangled over the side of a small runabout -- something experts said was technically possible but extremely unlikely.
The equipment aboard the Ocean Shield and the HMS Echo are dragged slowly behind each ship over long distances and are considered far more sophisticated than those the Chinese crew was using.
Footage aired on China's state-run CCTV showed crew members in the small boat with a device shaped like a large soup can attached to a pole. It was hooked up by cords to electronic equipment in a padded suitcase as they poked the device into the water.
"If the Chinese have discovered this, they have found a new way of finding a needle in a haystack," said aviation expert Geoffrey Thomas, editor-in-chief of AirlineRatings.com. "Because this is amazing. And if it proves to be correct, it's an extraordinarily lucky break."
There are many clicks, buzzes and other sounds in the ocean from animals, but the 37.5 kilohertz pulse was selected for underwater locator beacons because there is nothing else in the sea that would naturally make that sound, said William Waldock, an expert on search and rescue who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Arizona.
"They picked that (frequency) so there wouldn't be false alarms from other things in the ocean," he said.
But after weeks of false alarms, officials were careful Sunday not to overplay the development.
Australian Prime Minister Tony Abbott said he was "hopeful but by no means certain" that the reported pulse signals were related to MH370.
"This is the most difficult search in human history. We are searching for an aircraft which is at the bottom of a very deep ocean and it is a very, very wide search area," Abbott told reporters in Tokyo, where he is on a visit.
The search area has evolved as experts analyzed Flight 370's limited radar and satellite data, moving from the seas off Vietnam, to the waters west of Malaysia and Indonesia, and then to several areas west of Australia.
A senior Malaysian government official said Sunday that investigators have determined that the plane skirted Indonesian airspace as it flew from Peninsular Malaysia to the southern Indian Ocean.
The official, who declined to be named because he isn't authorized to speak to the media, said Indonesian authorities have confirmed that the plane did not show up on their military radar. The plane could have deliberately flown around Indonesian airspace to avoid radar detection, or may have coincidentally traveled out of radar range, he said.
Houston, the search coordinator, conceded that his organization first heard about the initial signal China had detected when it was reported by a Chinese journalist aboard the Haixun 01. He said that at "almost the same time" he was informed of the development by the Chinese government.
The agency was formally told about the second Chinese detection on Saturday "in absolutely the normal way," he said.
"China is sharing everything that is relevant to this search. Everything," Houston said.
Still, the search agency will be adding a Chinese-speaking liaison officer "to make sure nothing falls through the cracks," he said.
Houston also said there had been a correction to satellite data that investigators have been using to calculate Flight 370's likely flight pattern. As a result, starting on Monday, the southern section of the current search zone will be given higher priority than the northern part.
The signals detected by the Chinese ship were in the southern high priority zone, Houston said.
Up to 12 military and civilian planes and 13 ships took part in the search Sunday of three areas totaling about 83,400 square miles. The areas are about 1,200 miles northwest of the Australian west coast city of Perth.
The Associated Press contributed to this report.