More of the retrieved bodies were transferred from Pangkalan Bun to Surabaya on Monday. Photo: AP

Transport safety committee investigator Andreas Hananto told the BBC that there were also indications that the plane encountered bad weather.

The plane is thought to have gone down on 28 December when it encountered difficulties from an approaching storm.

All 162 people onboard the flight from Surabaya to Singapore perished.

Two more bodies were recovered on Monday, bringing the total found so far to 53.

Mr Hananto told BBC Indonesian that investigators had listened to the entire two-hour recording, and found that there was "no threatening voice on board."

The recording appeared to indicate that the pilot was too busy attempting to regain control of the aircraft to send a distress signal, he said.

Some of the parameters retrieved from the flight data recorder seemed to indicate that the plane had encountered bad weather.

More analysis was needed from the rest of the 1,200 parameters to determine the exact weather conditions and the impact the weather had on the plane's engines, Mr Hananto added.

Investigators have only transcribed half of the cockpit voice recording and that would require more analysis as well.

Preliminary report due soon

Search teams managed to find the cockpit voice recorder and the flight data recorder last week.

The fuselage of the plane, believed to hold most of the bodies, has also been located and search teams are now working out how to retrieve it.

The authorities are expected to issue a preliminary report on the crash on 28 January.

The cause of the crash is not yet clear, though the plane was flying through bad weather at the time and the pilot's last communication with air traffic control was a request to fly higher to avoid a storm.

Since the plane disappeared a multi-national search has been under way involving aerial reconnaissance and more than 30 ships. However, strong currents, high waves and poor visibility have slowed operations.