A submarine scouring the floor of the Indian Ocean for the missing Malaysian jet had to abort its maiden voyage after descending too deep, providing investigators with less than half the data the equipment was meant to capture.

The Bluefin-21 vessel was forced back to the surface by a built-in safety feature after dropping below its limit of 4,500 meters (14,800 feet), Australia’s Joint Agency Coordination Center said in an e-mailed statement. The six hours of data it captured is “being extracted and analyzed,” the agency said.

The submarine will continue its hunt later today when weather conditions permit, JACC said. As many as 11 aircraft and 11 ships will comb about 62,063 square kilometers (23,943 square miles) of ocean today for signs of debris from the jet. Investigators are relying on the submersible after stopping the use of a towed pinger locator to find the plane’s black boxes.

“That’s not good news,” Robin Beaman, a marine geologist at James Cook University in Cairns, Australia, said by phone. “The critical thing is it needs to be down close to the seafloor.”

The use of the submarine is the latest phase of an international search for Flight 370, which disappeared March 8 with 239 people on board. At 39 days, it’s now the longest search for a missing passenger jet in modern aviation history. No audio signals have been detected since April 8, suggesting the aircraft’s black boxes have run out of power.

The Bluefin-21, equipped with side-scan sonar, is supposed to be deployed for 24 hours at a time. It is intended to spend two hours descending, 16 hours on the ocean bottom, two hours returning to the surface, and four hours having its data downloaded, Angus Houston, who heads the JACC, told reporters yesterday. It was to search an area of about 40 square kilometers to produce a high-resolution, three-dimensional sonar map of the seabed, he said.

Side-scan sonar need to operate about 50 meters off the sea floor as they work by casting acoustic shadows to the sides of the sensors, Beaman said. That means it works better if the sensor is low down, like the evening sun, rather than high up and casting smaller shadows like those around midday.

“The Bluefin is a very capable machine, but at 4.5 kilometers down, things implode,” Beaman said. “They run the risk of losing it entirely,” he said, adding there are other systems that are rated to dive deeper than the Bluefin-21.

The underwater sonar search could take up to two months, the U.S. Navy’s Seventh Fleet said in an e-mailed statement yesterday.

The black boxes are key to determining why the Malaysian Airline System Bhd. plane disappeared 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.

Australia’s Ocean Shield ship, using the towed pinger locator, 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 raised optimism in the search. Hopes faded on April 11 when the JACC said an initial assessment of a fifth potential transmission wasn’t related to an aircraft black box.

Scouring the ocean surface for debris with planes and ships will be called off in two to three days as the chance of any floating material being recovered has “greatly diminished,” Houston said at a press conference in Perth yesterday. An oil slick has also been found in the same area and will be analyzed.