The search for the missing Malaysian jetliner was further complicated Tuesday, after the search area in the southern Indian Ocean proved too deep for a miniature, robotic submarine.
Australian officials said Tuesday the Bluefin-21 "exceeded its operating depth limit of 4,500 meters and its built-in safety feature returned it to the surface" following a brief, six-hour mission.
The Joint Agency Coordination Center said authorities are now extracting and analyzing the data gathered by the underwater vehicle, which they plan to redeploy if weather conditions improve later Tuesday.
The submarine was sent down Monday - nearly a week after sound locating equipment last heard signals that are believed to be from the missing jet's black boxes.
Locator beacons on the plane's flight recorder boxes emit signals so they can be more easily found, but their batteries only last about a month. It has been nearly 40 days since the jet went missing.
Without locating more signals, it is difficult to further narrow the possibilities of where the plane may have crashed. On Tuesday, the JACC said the visual search area was over 62,000 kilometers.
Search crews also are investigating an oil slick found in the search area. Crews have collected samples that have been sent for testing.
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, 1,000 kilometers from land, is a huge task that will not likely end anytime soon.
The small robotic sub is using sonar to chart any debris in the search for the plane's flight recorders on the sea floor. Officials say it will take 24 hours to complete each mission in which the sub will chart approximately 40 square kilometers.
The sub is not able to transmit live data as it searches the floor, so officials must bring it to the surface and analyze the data following each mission.
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 cellphone call after the jetliner deviated from its original course.
The 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 whom 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.