Flight punctuality at 10 major UK airports - including Stansted and Luton - fell in the first part of this year.
The number of scheduled flights arriving and departing on time, between January and March 2013, was 78% - a 4% dip on the same period last year.
The average delay across scheduled flights was 13 minutes - three minutes more than the first three months of 2012.
The Civil Aviation Authority statistics relate to flights at Heathrow, Gatwick, Luton, Stansted, London City, Manchester, Birmingham, Newcastle, Edinburgh and Glasgow airports.
Iain Osborne, from the CAA, said: "Passengers have a right to expect their flight to get them to their destination on time, so it's disappointing to see that flight punctuality fell during the first quarter of this year."