By Morag MacKinnon
PERTH, Australia, April 26 (Reuters) - The undersea search for missing Malaysia Airlines Flight MH370 is to be extended beyond the small area identified as its most likely resting place as the quest for any sign of the missing plane enters its 50th day on Saturday.
The submarine drone Bluefin 21 has so far searched about 95 percent of a 10 square km area of the Indian Ocean seabed, pinpointed after the detection of acoustic pings believed to be from the plane's black box flight recorders.
Bluefin 21 had to abort the search on Friday and resurface due to a software malfunction. Technicians fixed the drone overnight and its 14th, 16 hour trip to the sea floor at depths of more than 4.5 km (2.8 miles) was underway on Saturday.
"If no contacts of interest are made, Bluefin-21 will continue to examine the areas adjacent to the 10km radius," Australia's Joint Agency Coordination Centre (JACC) in in charge of the search said in a statement.
Flight MH370 disappeared without a trace on March 8 flying from Kuala Lumpur to Beijing with 239 people on board.
The search for MH370 is the longest and most expensive in aviation history, with ships and aircraft from some two dozen nations taking part. The air and sea search continued on Saturday with up to 8 military aircraft and 11 ships.
A U.S. defence official told Reuters on Friday that the sea search is likely to drag on for years as it enters the much more difficult phase of scouring broader areas of the ocean near where the plane is believed to have crashed.
Speaking under condition of anonymity because he was not authorised to comment on the search effort, the official said Malaysia would have to decide how to proceed with the search, including whether to bring in more underwater drones.
The Australian and Malaysian governments are under pressure to show what lengths they are prepared to go to in order to give closure to the grieving families of those on board flight MH370.
Malaysia is also under growing pressure to improve its disclosure about its investigation. Prime Minister Najib Razak told CNN on Thursday his government would make public a preliminary report into the plane's disappearance next week.
(Writing by Morag MacKinnon, with reporting by Matt Siegel in Sydney; Editing by Michael Perry)