PERTH, Australia -- An underwater robotic submarine is expected to finish searching a narrowed down area of the Indian Ocean seabed for the missing Malaysia Airlines plane within the next week, after completing six missions and so far coming up empty, the search coordination center said Saturday.
As the hunt for Flight 370 hit week six, the Bluefin 21 unmanned sub began its seventh trip into the depths off the coast off western Australia. Its search area forms a 6.2-mile circle around the location of an underwater signal that was believed to have come from the aircraft's black boxes before the batteries died. The sonar scan of the seafloor in that area is expected to be completed in five to seven days, the center said in an email to The Associated Press.
The U.S. Navy sub has covered around 51 square miles since it began diving into the depths March 14. The latest data are being analyzed, but nothing has yet been identified.
Malaysian Defense Minister Hishammuddin Hussein told reporters in Kuala Lumpur that there are no plans to give up once the Bluefin concludes its work. Instead, he said the scope of the search may be broadened or other assets may be used.
"The search will always continue," he said. "It is just a matter of approach. All efforts will be intensified for the next few days with regards to the underwater search."
Meanwhile on Saturday, up to 11 aircraft and 12 ships continued to scan the ocean surface for debris from the Boeing 777 that disappeared en route from Kuala Lumpur, Malaysia, to Beijing with 239 people on board.
Radar and satellite data show the plane mysteriously veered far off-course for unknown reasons and would have run out of fuel in the remote section of the southern Indian Ocean where the search has been focused. Not one piece of debris has been recovered since the massive search effort began.
The tiresome search that continues to raise more questions than answers has tormented the families whose loved ones never came home March 8. About two-thirds of the passengers were Chinese.
On Friday, around three dozen Chinese relatives in Beijing held a prayer meeting for their missing spouses. Many sobbed heavily as candles burned on a table in the shape of a heart with the letters MH370 in the middle. A banner behind them read in Chinese: "Husband, wife, come home soon."
There have been numerous leads throughout the painstaking hunt, but all have turned out to be false. The latest hope involved an oil slick found near the underwater search area, but analysis of a sample taken from the site found it was not connected to the plane.
The most promising development came when four underwater signals were detected April 5 and 8. The sounds were consistent with pings that would have been emanating from the flight data and cockpit recorders' beacons before their batteries died.
The underwater operation is being complicated by the depth of the largely unexplored silt-covered seafloor. The U.S. Navy's unmanned submarine has gone beyond its recommended limit of 15,000 feet, according to the U.S. 7th Fleet. That could risk the equipment, but it is being closely monitored.
The search coordination center has said the hunt for floating debris on the surface will continue at least into next week, even though head of the search effort Angus Houston had earlier said it was expected to end sooner.
On Saturday, the visual surface search was to cover an estimated 19,382 square miles of sea.