The first of the two black boxes of the ill-fated AirAsia flight QZ8501 has been successfully retrieved from Java sea waters as speculations suggest the aircraft exploded in the air.
The recovered device is the Flight Data Recorder storing technical information about the flight. The investigators hope it will shed light on the causes of the tragedy that took place on 28 December halfway through a regular two-hour flight from Surabaya, Indonesia's second-biggest city, to Singapore.
The second black box, the cockpit voice recorder containing recordings of conversations between the plane’s pilots, has yet to be recovered but officials said they knew the position of the device.
"(The cockpit voice recorder) seems to be under a wing, which is quite heavy," said Suyadi Bambang Supriyadi, operations coordinator at Indonesia’s National Search and Rescue Agency. "So we will use airbags to lift it. This will be done tomorrow."
The cockpit voice recorder lies only about 20 metres from where the Flight Data Recorder was found.
According to Supriyadi, the state of the wreckage indicated the plane, an Airbus A320-200 with 162 people aboard, may have exploded before hitting the water surface.
He said the left side of the plane seemed to have disintegrated, pointing to a change in pressure that could have caused an explosion.
In support of this theory he mentioned testimonies of local fishermen who had reported hearing an explosion and seeing smoke above the ocean at the time of the accident.
However, National Transportation Safety Committee (NTSC) investigator Santoso Sayogo disputed the hypothesis. "There is no data to support that kind of theory," he said.
Investigators may need up to a month to extract data from the black box, despite the device being in a good condition. The analysis will be conducted by local experts in Jakarta.
"The download is easy, probably one day. But the reading is more difficult ... could take two weeks to one month," said NTSC's head investigator Mardjono Siswosuwarno.
The black box recovery came only days after pings from the recorders’ beacons had been intercepted.
According to sources familiar with the investigation, the aircraft’s transponders kept transmitting data as it ascended to an altitude of more than 11.5km probably to avoid major storms. From this altitude the aircraft started falling sharply to the Earth. At about a third of the descent, the transponders suddenly went silent. The jet only kept sending other data such as the speed of descent, which was the last parameter to be broadcast before it hit the water close to where the wreckage was subsequently found.
It is not yet clear whether the gap in altitude data below 22-24,000ft originated in the A320's systems or problems in transmission, underlining the importance of recovering complete evidence from the data recorder.
Separately, Airbus has begun talks with a European regulator on proposals to make ejectable flight recorders available on its two largest models, potentially making them the first commercial planes to use the technology.
Indonesia AirAsia, 49 per cent owned by the Malaysia-based AirAsia budget group, has come under pressure from authorities in Jakarta since the crash.
The transport ministry has suspended the carrier's Surabaya-Singapore licence for flying on a Sunday, for which it did not have permission. However, the ministry has said this had no bearing on the crash.
Only 48 bodies of victims of the disaster have so far been recovered much to the dismay of the passengers’ families. Searchers believe more bodies will be found inside the plane's fuselage.