Search crews have failed to once again pick up pulse signals heard deep in the Indian Ocean, possibly from the missing jetliner's black boxes. Angus Houston, the director of the Australian Joint Agency Coordination Center, said sound locating equipment on board Australia's Ocean Shield has picked up no trace of the signals since they were first heard late Saturday and early Sunday.

Meanwhile, the search for traces of the plane on the ocean's surface continued on Tuesday. Up to 14 planes and 14 ships were focusing on a search area covering over 77-thousand square kilometers. Meanwhile the race against time to locate the plane's black boxes continues.

Ocean Shield is conducting an underwater search at the northern end of the defined search area, while China's Haixun 01 and British HMS Echo are at the southern end. The battery life of a black box lasts only about a month. Once the beacons blink off, locating the black boxes in such deep waters would become an immensely difficult task.

Chinese Foreign Ministry Spokesman Hong Lei said on Tuesday that China will further coordinate with other countries to strenthen the search efforts, especially the underwater search.