PANGKALAN BUN, Indonesia — Strong currents and blinding silt thwarted an attempt by divers 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 for determining 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, Soelistyo said.