British Airways carried 3.4 per cent fewer passengers last month than in April 2004.
However, the number travelling in the more-expensive seats rose 13.3 per cent on the same month last year.
A total of 2.9 million people travelled with BA in April 2005 compared with nearly 3m in April last year.
Overall, passenger numbers fell 5.1 per cent on UK and European routes last month, and numbers to North and South America declined 0.9 per cent. Africa and Middle East traffic was down 2.4 per cent.
But there was an increase of 7.5 per cent on Asia Pacific routes.
BA's planes were 74.7 per cent full last month compared with 75.5 per cent full in April 2004.
Low-fare airline Ryanair announced it had carried 2.6 million passengers in April 2005 - well up on the 2.1 million figure for April 2004.
The load factor on Ryanair's planes - the number of seats occupied on each flight - was 81 per cent compared with 82 per cent in April 2004.