Indonesian investigators said audio recordings from Air Asia Flight QZ8501 showed no evidence of any terrorist attack aboard the plane.
The aircraft’s cockpit voice recorder, which was recovered from the crash site in the Java Sea contained "no threats" National Transportation Safety Committee investigator Andreas Hananto said.
"The voice from the cockpit does not show any sign of a terrorist attack. It is only the pilot, sounding very busy," he said.
It is still unclear what caused the downing of Flight QZ8501 with 162 people on board last month, with bad weather, mechanical failure or human error suspected.
Crash investigators admitted they are focusing on possible human error as radar data showed the plane climbed at a speed that was higher than normal and probably stalled.
"In the final minutes, the plane climbed at a speed which was beyond normal," said Transport Minister Ignasius Jonan.
Divers have so far recovered 53 bodies and several attempts to get inside the fuselage have been hampered by high waves and strong currents.
Search and rescue teams said they may using giant balloons to lift the fuselage from the seabed to the surface, as they did successfully with the tail section earlier this month.
