PERTH, Australia (AP) — The joint agency coordinating the search for Malaysia Airlines Flight 370 says there's been no sign of the plane yet as a robotic submarine searches the depths of a section of the Indian Ocean for a second day.

The Bluefin 21 sub surfaced early on its first day when waters it encountered got too deep.

And today, the sub experienced technical problems. It was sent back underwater after its data were downloaded.