Some planes and ships searching for a missing Malaysia Airlines Flight MH370 in the Indian Ocean moved on Monday toward waters where a Chinese vessel had picked up "ping" signals at the weekend, raising hopes of finding the airliner's black-box recorders.
The black boxes, thought be to lying on the ocean floor, are equipped with locator beacons that send pings on the same frequency as those detected by the Chinese naval ship, but the beacons' batteries are thought to be running out by now, a month after Malaysia Airlines Flight MH370:disappeared.
"We are running out of time in terms of terms of the battery life," Retired Air Chief Marshal Angus Houston, head of the Australian agency coordinating the operation, told a news conference in Perth on Sunday.
The black boxes record cockpit data and may provide answers about what happened to the plane, which was carrying 227 passengers and 12 crew when it vanished off radar on March 8 and flew thousands of km off its Kuala Lumpur-to-Beijing route.
Chinese patrol ship Haixun 01 reported receiving a pulse signal with a frequency of 37.5 kHz, consistent with the signal emitted by flight recorders, on Friday and again on Saturday.
"The 37.5kHz is the specific frequency that these locator pingers operate on," said Anish Patel, president of Sarasota, Florida-based Dukane Seacom, which made the black box locator.
"It's a very unique frequency, typically not found in background ocean noise," such as whales or other marine mammals, he told Reuters.
The pulses were detected within two km (1.2 miles) of each other but were hundreds of nautical miles outside the main search zone in the southern Indian Ocean which has been scoured by planes and aircraft for more than a week.
Britain's HMS Echo, which is equipped with underwater sonar equipment, is due to reach the area, where the water is around 4,500 metres (14,764 ft) deep, later on Monday.
"The fact we've had two acoustic events in that location provides some promise, which requires a full investigation of the location," Houston said, but he stressed there was no conclusive evidence linking it to the Boeing 777.
Houston also noted that Australia's HMAS Ocean Shield, which is towing a U.S. navy "pinger locator" was the best-equipped ship to pinpoint the flight recorders.
The Ocean Shield will continue to investigate a separate "acoustic event" some 300 nautical miles away in the original search zone 2,000 km (1,243 miles) northwest of Perth. A decision on