The pace of growth was unchanged from the previous month, but was less than half the five-year average growth rate of 5.1 per cent, IATA said.
Freight capacity, measured in available freight tonne kilometres, grew by 4.5 per cent year on year in August.
This was the sixth month in a row that capacity growth had outstripped demand growth. Yields, however, appeared to be holding up, IATA said.