With vast area of Indian Ocean finally mapped, ships prepare to resume search ...

FILE - In this March 18, 2014 photo, a young Malaysian boy prays, at an event for the missing Malaysia Airline Flight 370, at a shopping mall, in Petaling Jaya, on the outskirts of Kuala Lumpur, Malaysia. After a four-month hiatus, the hunt for Malaysia Airlines Flight 370 is about to resume in a desolate stretch of the Indian Ocean, with searchers lowering new equipment deep beneath the waves in a bid to finally solve one of the world's most perplexing aviation mysteries. (AP Photo/Joshua Paul, File)

Associated Press

By KRISTEN GELINEAU, Associated Press

SYDNEY (AP) - After a four-month hiatus, the hunt for Malaysia Airlines Flight 370 is about to resume in a desolate stretch of the Indian Ocean, with searchers lowering new equipment deep beneath the waves in a bid to finally solve one of the world's most perplexing aviation mysteries.

The GO Phoenix, the first of three ships that will spend up to a year hunting for the wreckage far off Australia's west coast, is expected to arrive in the search zone Sunday, though weather could delay its progress. Crews will use sonar, video cameras and jet fuel sensors to scour the water for any trace of the Boeing 777, which disappeared March 8 during a flight from Kuala Lumpur to Beijing with 239 people on board.

The search has been on hold for months so crews could map the seabed in the search zone, about 1,800 kilometers (1,100 miles) west of Australia. The 60,000-square kilometer (23,000-square mile) search area lies along what is known as the 'seventh arc' - a stretch of ocean where investigators believe the aircraft ran out of fuel and crashed, based largely on an analysis of transmissions between the plane and a satellite.

Given that the hunt has already been peppered with false alarms - from underwater signals wrongly thought to be from the plane's black boxes to possible debris fields that turned out to be trash - officials are keen to temper expectations.

'We're cautiously optimistic; cautious because of all the technical and other challenges we've got, but optimistic because we're confident in the analysis,' said Martin Dolan, chief commissioner of the Australian Transport Safety Bureau, the agency leading the search. 'But it's just a very big area that we're looking at.'

That area was largely unknown to scientists before the mapping process began in May. Two ships have been surveying the seabed using on-board multibeam sonar devices, similar to a fish-finder. The equipment sends out a series of signals that determine the shape and hardness of the terrain below, allowing officials to create three-dimensional maps of the seabed.

Those maps are considered crucial to the search effort because the seafloor is riddled with deep crevasses, mountains and volcanoes, which could prove disastrous to the pricey, delicate search equipment that will be towed just 100 meters (330 feet) above the seabed. Two of the search ships will be using underwater search vessels worth around $1.5 million each.

'You can imagine if you're towing a device close to the seafloor, you want to know if you're about to run into a mountain,' said Stuart Minchin, chief of the environmental geoscience division at Geoscience Australia, which has been analyzing the mapping data.

The terrain isn't the only challenge. The area is prone to brutal weather, and is so remote that it takes vessels up to six days to get there from Australia. Water depths are also tricky: They range from 600 meters (2,000 feet) to 6.5 kilometers (4 miles). That's about the deepest the sonar equipment can go, Dolan said.

'In all sorts of ways we're operating towards the limits of the technology that is available,' Dolan said.

With the mapping nearly complete, the GO Phoenix, provided by Malaysia's government, will begin hunting in an area considered the likeliest crash site, based on an analysis of satellite data gleaned from the plane's jet engine transmitter and a series of unanswered phone calls officials on the ground made to the plane.

The other two vessels, the Equator and Discovery, provided by Dutch contractor Fugro, are expected to join the hunt later this month.

Malaysia and Australia are each contributing around $60 million to fund the search.