Indonesian investigators say they have found no evidence so far that terrorism played a part in the crash of an AirAsia passenger jet last month that killed all 162 people on board.

Andreas Hananto said his team of 10 investigators at the National Transportation Safety Committee (NTSC) found “no threats” in the cockpit voice recordings to indicate foul play during Flight QZ8501.

• Singapore navy locates AirAsia fuselage
• Weather and ice ‘triggering factor’ in AirAsia QZ8501 crash

The Airbus A320-200 vanished from radar screens on December 28, less than halfway into a two-hour flight from Indonesia’s second-biggest city of Surabaya to Singapore. There were no survivors.

When asked if there was any evidence from the recording that terrorism was involved, Hananto said: “No. Because if there were terrorism, there would have been a threat of some kind.”

“In that critical situation, the recording indicates that the pilot was busy with the handling of the plane.”

Investigators said they had listened to the whole of the recording but transcribed only about half.

“We didn’t hear any voice of other persons other than the pilots,” Nurcahyo Utomo, another investigator, said.

The recovered flight recorder. Photo: AAP

“We didn’t hear any sounds of gunfire or explosions. For the time being, based on that, we can eliminate the possibility of terrorism.”

Explosion also ‘unlikely’, says investigator

Mr Utomo said investigators could hear “almost everything” on the recording contained in one of the flight’s two black boxes.

The other is the flight data recorder, and both have been recovered from the wreckage at the bottom of the Java Sea.

He declined to give details about what was said during the doomed flight’s final moments, citing Indonesian law.

Indonesian authorities have said bad weather was likely to have played a part in the disaster.

According to Mr Hananto, evidence also showed an explosion was unlikely before the plane crashed, disputing a theory suggested by an official from the National Search and Rescue Agency last week.

“From the (flight data recordings) so far, it’s unlikely there was an explosion,” Mr Hananto said.

“If there was, we would definitely know because certain parameters would show it. There are something like 1,200 parameters.”

The final minutes of the AirAsia flight were full of “sounds of machines and sounds of warnings” that must be filtered out to get a complete transcript of what was said in the cockpit, said Mr Hananto, who has been an air safety investigator since 2009.

The first half of the two-hour long cockpit voice recording has been transcribed. That includes audio from the previous flight and the beginning of Flight QZ8501, which crashed around 40 minutes after takeoff.

The team, which is working with French, Singaporean and Chinese air safety investigators, hopes to finish transcribing the recording this week, Mr Hananto said.

Analysis of the flight data recorder would take longer because investigators were examining all 72 previous flights flown by the aircraft.

Investigators hope to finish a preliminary report on the crash early next week. The full report could take up to a year, but will not include the entire cockpit voice transcript.

“In Indonesia it remains undisclosed,” said Tatang Kurniadi, chief of the NTSC.

“Just some important highlights will be included in the report.”