Was the pilot of missing AirAsia plane flying too SLOW? Experts say jet carrying 162 people may have 'stalled' during storm... and search chief believes it is already 'at the bottom of the sea'

Missing AirAsia flight QZ8501 was flying 'about 160 km/h too slow' when it encountered bad weather conditions, according to aviation experts.

As the search resumes for the Airbus A320, which went missing at 6.17am local time on Sunday morning while travelling from Indonesia to Singapore with 162 people on board, speculation on what may have happened points to weather, speed and an older radar system.

On Monday, the head of Indonesia's National Search and Rescue Agency, Henry Bambang Sulistyo, said that the plane is most likely 'at the bottom of the sea'.

'Based on the coordinates given to us and evaluation that the estimated crash position is in the sea, the hypothesis is the plane is at the bottom of the sea,' Mr Sulistyo told a press conference.

'That's the preliminary suspicion and it can develop based on the evaluation of the result of our search.' 

Aviation expert Geoffrey Thomas spoke to several check captains and believes the pilot of the QZ8501 encountered difficult weather conditions but flew too slow in his efforts to avoid it.

'The QZ8501 was flying too slow, about 100 knots which is about 160 km/h too slow. At that altitude that's exceedingly dangerous,' Mr Thomas said.