Air China's (SHA:601111, HKG:0753) available seat kilometers, which measure passenger capacity, fell 6.4% year on year in May, according to a Hong Kong bourse filing on Monday.

Revenue passenger kilometers, an indicator for combined passenger traffic, decreased 2.7% from a year earlier during the month.

Cargo capacity, measured through available freight tonne kilometers, declined 5.4% from a year earlier.

Cargo and mail traffic, measured through revenue freight tonne kilometers, increased 1.6% from a year earlier.

The airline added six A320 aircraft and one B737 plane in May while retiring one A320, bringing its fleet size to 971 aircraft at month-end.