Santoso Sayogo, an investigator at the National Transportation Safety Committee, told Reuters that the pings were not detected in the wreckage of the tail, where the Airbus A320 would have carried the so-called black boxes during the flight.
"We have our fingers crossed it is the black box," Sayogo said. "Divers need to confirm. Unfortunately it seems it's off from the tail. But the divers need to confirm the position."
The cockpit voice and flight data recorders are designed to survive a crash and prolonged submersion in water. They contain underwater locater beacons which can emit electronic signals, or "pings", for up to 30 days.
The tail was located on Wednesday, partially buried in the sand of the Java Sea's shallow waters. However, searchers have been prevented from getting a closer look at the wreckage by the region's seasonal monsoon rains, which have caused big waves and murky runoff from rivers that have hampered divers, helicopters, and equipment.
On Friday, Indonesian search teams loaded lifting ballons onto helicopters ahead of a planned operation to raise the tail from the seabed. Fransiskus Bambang Soelistyo told reporters that the operation was proceeding on the assumption that the recorders were still in the tail.
"The divers are tying the tail with straps and then we will try [to lift the tail] two ways - floating balloons combined with cranes, so that the tail sector wouldn't be damaged," he said. "Because we assume the black box is in the tail sector."
The aircraft vanished on the morning of Dec. 28, about halfway into a scheduled two-hour fight to Singapore from Surabaya, Indonesia with 162 people on board. The last contact the pilots had with air traffic control indicated they were entering stormy weather. They asked to climb to 38,000 feet to avoid threatening clouds, but were denied permission because of heavy air traffic above them. Four minutes later, the plane dropped off the radar.
So far, bodies of 48 passengers and crew on the plane have been recovered, with four more victims discovered Friday. A few have been found floating while still strapped to their seats, but officials say many of those still missing are likely entombed in the fuselage. The bodies are sent to Surabaya for identification and handed over to their families for burial, but the process is becoming more difficult due to decomposition.
Relatives of the victims have urged officials to make the recovery of victims the main priority ahead of locating the black boxes.
The Associated Press contributed to this report.