On January 31st, 1911, a farung brought an airplane to demonstrate in Siam for the first time at the Sa Pathum Racecourse or the current Royal Bangkok Sports Club.
(A Belgian aviator, Charles Van Den Born, and his Farman biplane on his show to Siamese for the first time in history)
Shortly thereafter, an aviation department was established and an airport was built there which was called Sa Pathumwan Airport. This first airport in the history of Siam/Thailand was officially opened on December 29th, 1913.
Not long after, the Ministry of Defense found the problem of this airport being too small and too close to the bustle of the city and moreover, it was from time to time flooded after hard rains.
Air Chief Marshal Praya Chalerm-akart therefore, searched for a new area to set up a new airport. The place chosen was an upland (??) area in Don Mueang Subdistrict, the northern part of Bangkok.
This area was originally called Don E-Yeaw (= hawk/falcon) because it was a place where large number of such birds gathered together. The new airport was constructed and when being done was named Don Mueang Airport.
Later in March, 1914, the Aviation Department was transferred to Don Mueang Airport, ending the old Sa Pathumwan Airport.
In the beginning, Don Mueang Airport was only in good condition for accommodating small and light planes. The runway surface was still covered with grass being adjusted.
On March 8th, 1914, a Nieuport and Breguet planes purchased by Siam government for official assignment touched down at Don Mueang airport for the first time.
(The Nieuport aircraft on the grass covered runway at Don Mueang Airport)
While having been developed steadily, in the first phase after being moved to Don Mueang, there were regularly government officials, merchants, and people visiting the aviation business.
In 1924, the Royal Dutch Airline (KLM) was the first commercial airline to land at Don Mueang Airport.
In 1955, the name Don Mueang Airport was officially changed to Bangkok Airport.
An appendix...
An English translation (by me) of a Thai advertisement, shown above, titled:
"Flying around Bangkok"
A Junkers airplane which is all metal made and seats 6 people.
During 1924-1925, 85,000 passengers were boarded on this kind of airplane ... and all were perfectly harmless.
Will board at Don Mueang Airport from 8:00 AM to 5:00 PM daily.
Will start for the first time on February 13th, 1925.
Drinks are sold at Don Mueang Airport.
There are also trams and trains to pick up passengers to Don Mueang Airport on schedule, which is very convenient.
Flying from Don Mueang ... around Pra Nakhon ... back to Don Mueang at a rate of 24 baht per seat per 1 trip.
On Sundays, fare tickets are sold at Don Mueang Airport.
For more details, please ask Windsor & Co.
(Probably this model, a Junkers F13;1919-1932)