Air China's (SHA:601111, HKG:0753) available seat kilometers, which measure passenger capacity, rose 0.5% year on year in April, according to a Hong Kong bourse filing on May 15.
The airline's Hong Kong-listed shares were down nearly 4% in late-morning trade on Monday.
Revenue passenger kilometers, an indicator for combined passenger traffic, increased 5.8% from a year earlier during the month.
Cargo capacity, measured through available freight tonne kilometers, declined 3.6% from a year earlier.
Cargo and mail traffic, measured through revenue freight tonne kilometers, increased 4.2% from a year earlier.
The airline added six aircraft and retired one A320 aircraft in April, bringing its fleet size to 965 aircraft at month-end.