The search for missing Malaysia Airlines Flight MH370 enters its sixth week with six days since the last pings from what are thought to be the aircraft's black box recorders.
"There have been no confirmed acoustic detections over the past 24 hours," the Joint Agency Coordination Centre said on Sunday, repeating its message from a day earlier.
A series of pings picked up by Australian naval vessel Ocean Shield last week had led authorities to believe they were closing in on the final resting place of the jet, which disappeared en route to Beijing from Kuala Lumpur on March 8.
But authorities confirmed the newest signal, picked up from a sonar buoy on Thursday, likely didn't come from the missing aircraft. The statement came as the authority widened its search zone yesterday.
Ships and aircraft have been working to refine the size of the possible underwater search area to allow the use of an autonomous underwater vehicle, which will more closely scour the sea floor to get visual images of any possible wreckage.
The visual search area will now cover an area of 57,506 sq km.
"Today's visual search area is a continuation of the systematic search for floating debris derived from the probable area determined by the international investigation team and the area of acoustic event detections," the authority said.
"The daily visual search areas will vary in size according to factors such as oceanic drift and weather information optimized for aircraft search operations."
Australian Prime Minister Tony Abbott on Saturday said there continues to be a "high degree" of confidence that signals detected this week are Flight 370, but added that the difficulty of the search meant it would go for "a long time to come."
Airline's future in doubt
Meanwhile, Japan’s Nikkei Weekly newspaper reports the mystery of missing Flight MH370 has cast an additional cloud over the already struggling Malaysian national airline.
“The carrier may have to turn to the government for relief once more, but indulging the company with public money will not likely solve the problems it has been facing for more than 10 years,” the report says.
“Even more damaging to the carrier's reputation than potential safety issues is its slow and often mishandled investigation into the matter, including unsympathetic treatment of grieving family members. The incident may deal a near-fatal blow to a management that has been heavily reliant on public money.
“Hostility toward the company and the Malaysian government is especially strong in China. Out of 239 passengers and crew on the missing flight, 153 were Chinese.
“On March 26, China Youth Travel Service, a leading travel agent in China, announced that it would suspend bookings with the airline and refund the full fares of those who have already made reservations.
“If the problem persists, it may hurt not only the carrier's ticket sales for international flights but Malaysia's tourism industry as a whole. In 2013, nearly 10% of tourists to the country were Chinese.
“The airline also carries the long-term risk of having to pay damages to the families of the missing passengers. Local papers estimate that compensation could total $110 million. However, the amount is subject to change, because the cause of the incident has yet to be determined. Damages may increase if any major negligence on the part of the airline is found.
“The biggest problem is that the company has no funds to absorb the increased costs, “ Nikkei says. “In the fiscal year through December 2013, it posted a net loss of 1.17 billion ringgit ($US356 million), although passenger numbers increased by almost 30% and sales grew by around 10% from the previous year.”