Painstaking underwater search for MH370 black box

Perth: Two vessels were searching underwater for missing Malaysia Airlines Flight MH370 on Saturday, as air and sea missions failed to find any sign of the plane and the clock ticked on the signal from its black box.

Up to 10 military planes, three civilian jets and 11 ships were set to take part in the protracted search in the southern Indian Ocean for the Boeing 777 which disappeared on March 8 with 239 people onboard.

"Today Australian Defence Vessel Ocean Shield and (Britain's) HMS Echo continue underwater search operations," the Joint Agency Coordination Centre said.

The vessels are hoping to pick up a battery-powered signal from the plane's black box recorder but this sound is only emitted for roughly 30 days and could soon expire.

Angus Houston, Australia's former military chief and now coordinator of the eight-nation search, admitted Friday "we're now getting pretty close to the time when it might expire".

Australia is leading the hunt for the plane which Saturday was concentrating on about 217,000 square kilometres of the Indian Ocean some 1,700 kilometres (1,054 miles) north west of Perth.

"Today's search area will focus on three areas within the same vicinity," the JACC said, adding that the forecast was for fair weather with possible showers in the remote ocean region.

No debris of Flight MH370 had yet been found but it is thought to have crashed into the southern Indian Ocean after veering dramatically off course during a flight from Kuala Lumpur to Beijing.

Malaysian authorities believe satellite data indicates MH370 crashed in the Indian Ocean, far off Australia's western coastline.

Slow progress

Australian officials have pointed out that the search location and conditions are extraordinarily tough with Prime Minister Tony Abbott describing the search as "the most difficult in human history".

But he has refused to put a time frame on the mission, saying Australia owed it to the families and friends of all onboard to do everything it could to solve the mystery.

Australian officials are still trying to pinpoint the crash site.

"The Australian Transport Safety Bureau continues to refine the area where the aircraft entered the water based on continuing ground-breaking and multi-disciplinary technical analysis of satellite communication and aircraft performance," JACC said.

The centre revealed late on Friday that there had again been sightings of objects reported by ships in the search area, but as of late Friday "none were associated with MH370".

Since the plane disappeared nearly a month ago, eight nations, many of whom do not normally work together, have rallied to help track down clues to one of the world's greatest ever aviation mysteries.

Authorities still have no idea how or why the plane vanished, and warn that unless the black box is found, the mystery may never be solved.

The Ocean Shield, which is carrying a US Navy "black box" detector, and HMS Echo which has a similar capability are searching a single, converging, 240-kilometre track in hopes of finding the recorder.

However, progress is painstaking as the equipment which searches at depths of 3,000 metres or more only works when the vessels move slowly at about three knots.

"The search using sub-surface equipment needs to be methodical and carefully executed in order to effectively detect the faint signal of the pinger," Commodore Peter Leavy said.