Couple years ago most Low Cost carriers moved their operation from the Suvarnabhumi International airport (BKK) to Don Muang international airport. It is not uncommon for travelers to arrive using one of the main international carriers that lands in the main airport and then take advantage of the great prices that Low Cost airlines offer to national and international destinations.
Those connecting to international destinations and who in normal conditions need a tourist visa frequently find themselves wondering if they can take advantage of the good prices without having to obtain such a visa. There are some very important points to keep in mind.
If one has a connecting flight in the main international Airport BKK and one is not leaving the international area it is possible to transit without visa. It is important to be sure that bags have been ticketed to the final destination.
Suvarnabhumi International Airport and Don Mueang International airport are two completely separate airports not only in operation but in the geographical location. They are in opposite sides of the city. If one is arriving to one of the airports and flying out from the other the same rules for tourist visa that applies for an extended visit will apply here. There are some nationalities that are exempt of tourist visas, others can get it on arrival and others need to obtain a visa in the consulate. There is an article we posted it in our page about who needs a visa to enter Thailand and how to get it, but it is always better to reconfirm the information with the local Thai consulate.
Once one has cleared immigration, there are different ways to go from one to the another airport. Some people use cabs, other public transportation, but probably the most popular way is the free shuttle.
Finally if one needs a tourist visa to enter Thailand, and one plans to do that connection between airports two times (typically of a roundtrip flight) it is necessary to get a multiple entry visa.
Most airlines flying from and to Don Mueang International Airport are Low Cost carriers and as such many do not offer flight connections, so one will have to arrive and then clear immigration, pick up bags and check in again for the next flight and that will require a tourist visa. We know that Air Asia actually offers these kind of connections and one can fly through this airport without a visa in international to international connections.