The Dutch co-pilot died later at the Prince of Songkhla University Hospital in Hat Yai.
The incident happened today on Flight SL 8537 from Hat Yai to Don Mueang airport on which 152 passengers and crew members were on board.
Twenty minutes after taking off from Hat Yai airport, the pilot noticed his co-pilot seated beside went unconsciously.
He immediately radioed the control tower at Hat Yai airport to prepare ambulance and seek emergency landing.
The plane landed safely and the Dutch co-pilot was rushed to hospital where he was pronounced dead afterwards.
It was immediately known the cause of his death.