Thailand is a big country, and although there are many bus routes and trains in Thailand, airplanes are the easiest ways to travel long distance. Besides, flying is cheap, and there are many daily departures to the popular destinations. Below, you will find a list of airlines with domestic routes and a short description of them.
Please note that Bangkok has two airports, Suvarnabhumi International Airport and Don Muang Airport. Don Muang is the old international airport, and it closed when Suvarnabhumi opened in 2006. However, in 2007, Don Muang reopened and today the airport is the base for a number of domestic routes and a few international routes, typically from low-cost airlines.
In the description of the airlines below, you can see which airport they use.
If you arrive in Thailand at Suvarnabhumi International Airport and you want to continue to your final destination, it will, of course, be easiest to continue from Suvarnabhumi. However, if you stay in Bangkok a few days before continuing to your final destination, Don Muang may be a good choice. Typically, the routes from Don Mueang are cheaper; besides, the airport is smaller and has less traffic, making it faster and easier to use.
There is a free shuttle bus between the two airports; it takes 45-75 minutes depending on the traffic. A taxi may be faster, 30-60 minutes depending on the traffic; however, you also have to take the queue at the taxi stand into account. A taxi between the two airports will cost between 400-500 baht including airport "tax" and toll roads.
If you plan to continue from the other airport, please allow time for transportation; in addition, if you arrive on an international flight, please allow up to 90 minutes getting through immigration. Sometimes getting through immigration only takes 5 minutes, but sometimes it takes a lot longer than that.
Thai Airways is probably the best-known airline among Europeans because it is the only Thai airline that serves European countries. If you arrive in Thailand with Thai Airways, you may prefer to continue to your final destination with Thai Airways, as you do not have to deal with your checked in baggage at the Bangkok stopover.
Thai Airways is a member of Star Alliance; thus, if you are a member of a reward program in any of the 27 airlines in Star Alliance, you can earn bonus points when using Thai Airways.
Thai Smile is a subsidiary of Thai Airways. It is meant to be a semi-low-cost carrier offering tickets for prices between low-cost airlines and full-service airlines such as Thai Airways.
However, when I have searched for tickets at Thai Smile, I have not found any tickets cheaper than those offered by Thai Airways. All the flights I have checked have been more expensive. And much more expensive than the low-cost airlines! But, of course, I can have been unlucky in my searches.
In Bangkok, Thai Smile is using Suvarnabhumi International Airport.
Air Asia is an Asian low-cost airline that flies domestically in Thailand as wells as to other destinations in Asia. In Bangkok, they use Don Mueang Airport.
The prices look very reasonable when you start booking; however, you will find that the price changes in the process. For example, you will have to pay extra for checked in baggage.
Please take note of the first price offered; if the price changes in the process, it is because they add meals, insurance or baggage which you can then opt out of if you do not want it.
Thai Vietjet Air
Thai Vietjet Air is a sister company of the Vietnamese low-cost airline Vietjet Air. As one of the few low-cost airlines, it is flying from Suvarnabhumi International Airport in Bangkok instead of using Don Mueang Airport.
The airline started its first route between Bangkok and Phuket in 2015, and now (2018) it has routes between Bangkok and Chiang Mai, Chiang Rai, and Krabi. It is possible to find some very cheap flights at Thai Vietjet Air; however, with a fleet of only four aircraft, there are not many departures to choose.
Thai Vietjet Air does not have its own website; you book the flights at Vietjet Air's website. Please note that the first shown price is without airport taxes and charges; thus, the final price will be somewhat higher.
Thai Lion Air
Thai Lion Air is a sister company of Indonesian Lion Air. The airline opened its first route in December 2013 between Bangkok and Chiang Mai, and since then it has expanded dramatically.
Today, Thai Lion Air has a fleet of 30 aircraft serving a large number of Thai cities. In Bangkok, they use Don Mueang Airport. Unlike many other low-cost airlines, there is no extra fee for checked in baggage. You can have 10-20 kg depending on the ticket purchased.
Nok Air is a low-cost airline with Thai Airways as a majority shareholder. Having more than 100 domestic routes, it is by far the airline with most routes in Thailand. While many of the other airlines fly mainly to and from Bangkok, Nok Air has many routes directly between the smaller cities. In Bangkok, they use Don Mueang Airport.
Nok Air uses some extremely colourful planes, painted to look like birds. That is not only because they fly like birds, "nok" means "bird".
In addition to the many direct routes, Nok Air offers mixed transport to some destinations. For example, Nok Air does not have a direct flight to Samui; instead, they offer a flight to Surat Thani and a ferry from Surat Thani to Samui.
Nok Air offers free seat selection.
Bangkok Airways is not only an airline; they also own and operate several airports, including Samui Airport. Owing an airport gives them certain advantages, for instance, there are not any low-cost airlines serving Samui Airport; thus, a flight to Samui is much more expensive than flights to other tourist destinations in Thailand.
In Bangkok, they use Suvarnabhumi International Airport.