Deep waters in the Indian Ocean have been hampering the search for the missing Malaysia Airlines flight 370.

The autonomous underwater vehicle "Bluefin 21", which was submerged into the search area on Monday to scan the waterbed, had to be pulled out prematurely as it is designed for depths of up to 4,500 meters, CBC News reported.

"Maybe some areas where they are doing the survey are a little bit deeper than they are expecting. They may not have very reliable prior data for the area, so they have a general idea. But there may be some variability on the sea floor that they also can't see from the surface", marine robotics professor Stefan Williams commented.

Meanwhile, an oil spill 5.5km from where the last underwater sounds were detected is being analyzed by the Australian authorities.

No further signals resembling the aircraft black box have been picked up over the past days. Experts say this is due to the fact that batteries in these devices usually last up to a month, whereas the search is now in its 38th day.

The Malaysia Airlines flight from Kuala Lumpur to Beijing disappeared on March 8, with 239 people on board. It is believed to have gone down in the Indian Ocean, some 1,700 km off the Western Australian coast.

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