No further signs have been confirmed from the pinger locator pulled by vessel Ocean Shield since four signals were heard between April 5 and 8. Australian officials said today they are deploying planes to scour about 47,644 square kilometres of water, down from 57,506 yesterday.

The search teams are listening from both ships and planes in an effort to re-locate the signals. The black boxes are key to hopes of learning why the Malaysian Airline System Bhd. plane disappeared March 8 en route to Beijing from Kuala Lumpur, reversing course and flying into some of the world’s most-remote ocean waters. The pingers’ batteries are now a week beyond their 30-day projected life at full power.

“It is a massive task and it is going to take some time,” said Hamish McLean, a lecturer in crises management at Griffith University’s School of Humanities in Brisbane. What searchers and authorities “need to do is look at the big picture, set realistic expectations, treat every bit of information nugget very carefully.”

The centre of today’s search areas is 2,200 kilometres (1,367 miles) northwest of Perth, with as many as 12 aircraft and 15 ships taking part, Australia’s Joint Agency Coordination Centre said. No confirmed acoustic detections had been made over the past 24 hours, the centre said, repeating a statement it also made yesterday and the day before.

Submersible vehicle

Investigators are in a race against time to detect more pulses and map the ideal launch zone for Ocean Shield’s Bluefin-21 submersible vehicle, which moves slowly and relies on sonar to spot wreckage in pitch-black waters thousands of metres deep.

JACC Chief Coordinator Angus Houston said April 11 a decision on when to deploy the sub “could be some days away.”

The Ocean Shield detected two signals on April 5 and two more on April 8, which authorities have linked to the beacons on the Boeing Co. 777-200ER’s black-box recorders. That gave hopes in the search that has failed to produce any physical evidence. That was damped on April 11 when JACC said that an initial assessment of a fifth potential transmission wasn’t related to an aircraft black box. — Bloomberg