Update: January, 2016
The bus A3 has been canceled for about 2 months.
Starting from today (1st September), Euro Bus A3 will run from BTS Udom Suk to Suvarnabhumi Airport. The bus starts from BTS Udom Suk and stops only 5 points along the way: Bang Na Intersection, Central Bang Na, Lotus KM8, King Kaew Intersection, and Suvarnabhumi Airport. The service is available from 6.00 to 20.30 and the fare costs 30 baht throughout the route.
This is very convenient for passengers who want to go to Suvarnabhumi Airport from Sukhumvit Road or anywhere in Bangkok that connects with BTS. The fare is, of course, much cheaper than taking taxi.