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Adek Berry, Pool, Associated Press
A national search and rescue helicopter flies over Indonesia's MGS Geosurvey ship where the team found the tail of AirAsia Flight 8501 on the Java Sea, Indonesia, Thursday, Jan. 8, 2015. Divers were hoping to zero in on the flight's black boxes Thursday, after search and recovery operations got a much-needed boost with the discovery of a chunk of the plane's tail - nearly two weeks after it plummeted into the sea, killing everyone onboard.

PANGKALAN BUN, Indonesia — Strong currents and blinding silt thwarted divers' attempt on Thursday to find AirAsia Flight 8501's black boxes, which are believed to still be in the recently discovered tail of the crashed plane.

The flight data and cockpit voice recorders are crucial to helping determine what caused the jet carrying 162 passengers and crew to vanish on Dec. 28, halfway into a two-hour flight between Surabaya, Indonesia, and Singapore.

Four bodies recovered Thursday raised the total to 44, Indonesian Search and Rescue Agency chief Henry Bambang Soelistyo said.

Days after sonar detected apparent wreckage, an unmanned underwater vehicle showed the plane's tail, lying upside down and partially buried in the ocean floor.

Divers looking for the black boxes on Thursday were unable to make it past currents and 1-meter (3-foot) visibility, said Soelistyo.

He said efforts will be intensified Friday to lift up the tail — either by using lifting balloon or crane.

Ping-emitting beacons in the black boxes still have about 20 days of battery life, but high waves had prevented the deployment of ping locators, which are dragged by ships.

Six ships with ping locators were in the search area in the Java Sea, said Nurcahyo Utomo, an investigator of the National Commission for Transportation Safety.

Based on pictures taken by divers, he believed that the black boxes were still attached to their original location in the plane's tail.

"Once detected, we will try to find and lift up the black boxes as soon as possible," he said.

Officials are hopeful many of the bodies not yet recovered are inside the fuselage, which is thought to be lying near the plane's tail. Divers reaching the tail Thursday said they did not see bodies trapped in the broken-off tail section.

It's not clear what caused the crash, but bad weather is believed to have been a factor. The pilot told air traffic control he was approaching threatening clouds, but he was denied permission to change altitude because other planes were nearby. The plane soon lost contact.

Associated Press writers Niniek Karmini and Ali Kotarumalos in Jakarta, Indonesia, contributed to this report.