Flight Bandaranaike International Airport departs from Colombo Bandaranaike International Airport at 01:15 and arrives at Bangkok Suvarnabhumi Airport at 06:20.
The flighttime is about 3h 35m. The distance travelled ("as the bird flies"): 2317 Km. So the average speed is roughly 647 Km.
There is an 1.5 hour time difference between Colombo and Bangkok
