Passenger traffic at BAA's six UK airports fell by 1.3% in October 2011, compared with the same month in 2010.
Heathrow reported a 1.3% decline and Southampton a drop of 3%.
Passenger numbers at the operator's Scottish airports rose by 2.1%, with Aberdeen recording a 7.6% rise and Glasgow a 0.3% increase.
BAA reported a 0.8% fall in the total number of commercial aircraft movements, while Heathrow recorded a 0.5% rise.
The operator's cargo volumes fell by 7.5% for October this year.