Divers are preparing to examine the wreckage of AirAsia Flight 8501 as the weather improves.

They hope to retrieve the rest of the bodies and find clues to what caused the plane to crash in stormy weather a week ago.

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The breakthrough in the hunt for the Airbus A320 came after sonar equipment aboard search ships detected four massive objects on the ocean floor in the Java Sea, and Indonesian officials said they were confident they belong to the plane.

Rescuers have identified two large fragments in the ocean. Photo: AAP

The biggest piece, measuring 18m long and 5.4m wide, appeared to be part of the jet’s body, said Henry Bambang Soelistyo, chief of the National Search and Rescue Agency.

Strong currents and big waves that had prevented divers from entering waters eased on Sunday.

About 90 divers from Indonesia and Russia were being deployed to recover more bodies that officials believe are still strapped in their seats, said National Search and Rescue deputy chief Tatang Zainudin.

“We hope lower waves will give us a better result today,” Zainudin said.

“We are racing with time and weather in running this mission.”

There were 162 people aboard the plane, but after a week of searching, only 30 bodies have been found floating in the choppy waters.

The plane crashed on December 28, halfway into a two-hour flight from Surabaya, Indonesia’s second-largest city, to Singapore.

Minutes before losing contact, the pilot told air traffic control that he was approaching threatening clouds, but was denied permission to climb to a higher altitude because of heavy air traffic.

It remains unclear what caused the plane to plunge into the sea.

Bad weather appears to have been a factor, according to a 14-page report released by Indonesia’s Meteorology, Climatology and Geophysics Agency.

“Flight 8501 appears to have been trapped in bad weather that would have been difficult to avoid,” the report said.

The plane’s black boxes – the flight data and cockpit voice recorders – have yet to be located.

Indonesian authorities announced the grounding of AirAsia flights from Surabaya to Singapore, with the Transport Ministry saying the airline did not have a permit to fly on Sundays.

However, Singapore’s Civil Aviation Authority said on Saturday that from its end, the airline had been approved to fly the route daily.

AirAsia, which began operations in 2001 and quickly became one of the region’s most popular low-cost carriers, said it was reviewing the suspension.