The unmanned underwater vehicle searching for the missing Malaysia Airlines flight MH370 in the southern Indian Ocean is expected to analyse data from its third trip on Thursday morning.
After the first mission carried out by the Bluefin-21 was aborted earlier than expected after its deployment on Monday, changes were made in an attempt to ensure the vehicle would remain underwater for longer.
The mission had been aborted prematurely because the vehicle reached its maximum depth of 4.5 kilometres. The search lasted for about four hours.
A US military spokesman had said the Bluefin's search profile had been adjusted ''to account for inconsistencies with the sea floor'' to allow the sonar searches to last longer.
It was returned to the ocean on Tuesday night after nothing of interest was found on the data from the first underwater search.
However, on Wednesday it returned to the surface early because of technical issues.
The sonar device takes about two hours to descend and is capable of scanning parts of the search area for 16 hours before taking another two hours to return to the surface. This would allow a five-kilometre by eight-kilometre area to be searched.
Analysing data from the device can take up to four hours.
The centre of the search area on Wednesday was about 2087 kilometres north-west of Perth.
It has been 41 days since the flight, carrying 239 passengers disappeared.
