Some planes and ships searching for a missing Malaysia Airlines jetliner 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 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.