Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 21:25 and arrives at Delhi Indira Gandhi International Airport at 00:25.
The flighttime is about 4h 30m. The distance travelled ("as the bird flies"): 2606 Km. So the average speed is roughly 579 Km.
There is an 1.5 hour time difference between Bangkok and Delhi
