I am a Sri Lankan travelling to SGN via Bangkok.
I am travelling on UL flight to Bangkok Suvarnabhumi Airport and my connecting flight to SGN is from Don Mueang Airport.
Do I need a transit visa to enter Bangkok to go to Don Mueang Airport?
Visa required, except for Passengers transiting through Bangkok (DMK) arriving on Thai AirAsia (FD) or Thai AirAsia X (XJ) with a confirmed onward ticket for a flight on Thai AirAsia (FD) or Thai AirAsia X (XJ) to a third country within 12 hours. The connecting flight must be booked on the same ticket. They must stay in the international transit area of the airport and have documents required for the next destination.
As you leave the transit area to switch airport you will need a visa.