30 percent of initial search area covered, but nothing is found

The autonomous underwater device Bluefin-21, which was deployed on Monday for its first search mission for MH370, faced unexpected depths and ended its mission prematurely, US navy Captain Mark Matthews said on Tuesday.

Matthews said the Bluefin was launched at 5:20 pm (0920 GMT) and was recovered at 1 am (1700 GMT) on Tuesday, Xinhua News Agency quoted him as saying.

Of the 40 square kilometers of search area initially planned for its first mission, 30 percent had been covered. But no discovery related to the Malaysian flight was made, said Matthews.

MH370, carrying 239 passengers and crew members, including 154 Chinese people, vanished en route from Kuala Lumpur to Beijing on March 8. The multinational search led by Australia has since focused on the plane’s black box data recorders.

"The area where the Bluefin was programmed for searching ranges from a depth of 4,200 to 4,400 meters, according to the chart. How the Bluefin was programmed to maintain an altitude over the sea floor of 30 meters. Unexpectedly, we encountered an area that was deeper than 4,500 meters, and if the Bluefin would have followed its directions, it would have exceeded its maximum operating depth," Matthews said.

The Joint Agency Coordination Center in Perth, which is guiding the search, said on Tuesday that after completing about six hours of its mission, Bluefin-21 exceeded its operating depth limit of 4,500 meters and its built-in safety feature returned it to the surface.

Matthews said the device has been reprogrammed with better instructions to prevent a similar mission abort and to keep it operating within its operating limits.

It was set for a second sweep of the seabed on Tuesday.

From the data gathered by Bluefin, searchers had been made aware that the conditions of the sea floor are "relatively barren" with only a few rocks.

Matthews emphasized that this is a normal operating condition and the operators had worked with such an environment before.

Bluefin-21 could take up to two months to scour a 600-sq-km area where MH370 is believed to have ended up, Reuters quoted US search authorities as saying on Tuesday.

Xinhua and Reuters contributed to this story.