The hunt for a missing Malaysian passenger jet entered a new phase as an international team abandoned its aerial search for debris and stepped up efforts to find wreckage on the floor of the Indian Ocean.

After 52 days, it’s “highly unlikely” that any debris will be found on the surface, Australian Prime Minister Tony Abbott told reporters in Canberra today. Malaysia and Australia will hire commercial companies to carry out an intensified underwater search that may take several months, he said.

The hunt for the Malaysian Airline System Bhd. jet, which vanished March 8 with 239 people, is already the longest for a missing passenger plane in modern aviation history. An unmanned submarine has failed to find any wreckage on the ocean floor after scouring 400 square kilometers and the underwater search area will be expanded.

“What we are looking to do is conduct as thorough an undersea search as is humanly possible, if necessary of the entire probable impact zone” measuring about 700 kilometers by 80 kilometers, Abbott said.

Aircraft have spent 3,000 hours searching 4.5 million square kilometers of ocean, with no debris found, he said.

Flight 370’s disappearance has baffled authorities because contact was lost less than an hour into a routine trip to Beijing from Kuala Lumpur. The widebody plane vanished from civilian radars while headed north over the Gulf of Thailand, then doubled back and flew over Peninsular Malaysia and on into some of the world’s most remote waters.

The jet’s data recorders, designed to emit regular pings, had a battery life of only about 30 days.

The Bluefin-21 submersible had focused on an area within a 10 kilometer radius of where acoustic pings were detected on April 8.

The search zone is about 1,600 kilometers (1,000 miles) northwest of Perth, Australia.

To contact the reporter on this story: Jason Scott in Canberra at To contact the editors responsible for this story: Rosalind Mathieson at 

Photo Credit: In this map provided on Thursday, April 24, 2014, by the Joint Agency Coordination Centre, details are presented in the search for the missing Malaysia Airlines Flight 370 in the southern Indian Ocean. Joint Agency Coordination Centre / Associated Press