Indonesia AirAsia Flight QZ8501 vanished from radar screens on Dec. 28, less than half way into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore. There were no survivors.
The Airbus A320-200 carries the black box cockpit voice and flight data recorders near the tail section. Officials had warned, however, that they could have become separated from the tail.
Santoso Sayogo, an investigator at the National Transportation Safety Committee, said it appeared that the black box was no longer in the tail.
"We received an update from the field that the pinger locator already detected pings," he told Reuters.
"We have our fingers crossed it is the black box. Divers need to confirm. Unfortunately it seems it's off from the tail. But the divers need to confirm the position."
The tail was found on Wednesday, upturned on the sea bed about 30 km (20 miles) from the plane's last known location at a depth of around 30 metres.
Indonesian search teams loaded lifting balloons on to helicopters on Friday ahead of an operation to raise the tail.
Relatives of the victims have urged authorities to make finding the remains of their loved ones the priority.
Forty-six bodies and debris from the plane have been plucked from the surface of the waters off Borneo, but strong winds and high waves have hampered efforts to reach larger pieces of suspected wreckage detected by sonar on the sea floor.
Indonesia AirAsia, 49 percent owned by the Malaysia-based AirAsia budget group, has come under pressure from the authorities in Jakarta since the crash.
The transport ministry has suspended the carrier's Surabaya-Singapore licence, saying it only had permission to fly the route on Mondays, Tuesdays, Thursdays and Saturdays.
Flight QZ8501 took off on a Sunday, though the ministry said this had no bearing on the accident.
While the cause of the crash is not known, the national weather bureau has said seasonal tropical storms common in the area were likely to be a factor.