The head of the search for missing Malaysia Airlines Flight 370 said an Australian ship will deploy an unmanned mini-sub "as soon as possible" to determine if signals detected by sound-locating equipment were from the missing jet.
Angus Houston, who heads Australia's Joint Agency Coordination Center, said Monday that the Ocean Shield will stop towing a U.S. Navy ping locator and launch the underwater vehicle Bluefin 21 later in the day.
Houston told a news conference in Perth, "We haven't had a single detection in six days, so I guess it's time to go underwater."
The small sub will use sonar to chart any debris in the search for the plane's flight recorders on the floor of the Indian Ocean.
Houston also said an oil slick was found in the area Sunday evening, but it would be several days before the oil could be tested for its origin.
Authorities have warned that investigators will have lost their chief means of detection when the flight recorder transmitter batteries lose power. Those batteries are designed to operate for 30 days -- possibly a little longer. The plane disappeared 38 days ago.
Australian Prime Minister Tony Abbott continues to sound notes of caution, stressing that trying to find anything nearly five kilometers below the surface of the Indian Ocean a thousand kilometers from land is a huge task that will not likely end any time soon.
The Boeing 777 with 239 people on board disappeared March 8 during a scheduled flight from Kuala Lumpur to Beijing. Two-thirds of those on board were Chinese nationals.
A leading Malaysian newspaper has said investigators probing the plane's disappearance suspect the co-pilot attempted to make a cell-phone call after the jetliner deviated from its original course.
The pro-government New Straits Times has said investigators believe the call ended abruptly after the phone made contact with a communications tower, as the jetliner flew at low altitude northwest of the island of Penang. The newspaper said its sources declined to reveal who the caller was trying to reach.
Malaysian Defense Minister Hishammuddin Hussein has cast doubt on the report, telling reporters he would have been informed about such a call if it had taken place.