The agency said the second wave of Covid-19 caused airlines to adjust or cancel flights in line with tourism demand and virus-containment measures.
Air traffic volume in January totalled 23,536 flights. Of these, 5,244 were international flights, 10,170 domestic, 2,657 flights across Thai airspace and 5,465 military and government flights.
"Air traffic volume in January slumped by 15,970 flights or 40 per cent compared to December last year," Aerothai said.