Thai Airways International has posted a 5% fall in RPKs in May, largely due to the political unrest in Bangkok.
Capacity, as measured in ASKs, grew 4%, says the Star Alliance carrier.
As a result, the passenger load factor fell 8.9 percentage points to 56.7%, it adds.
Thai attributes the operating performance to the off-peak tourist season and the anti-government rallies in the country.
On the cargo front, revenue freight tonne kilometres (RFTKs) rose 61%, says Thai.