Heathrow saw a fall in passenger numbers in the same month that the government approved expansion of the airport to cope with growth in demand.
The London airport handled 1.2% fewer passengers in October compared with October 2015.
The figures were released today, two weeks after the government announced it was backing Heathrow for a third runway.
The airport blamed the drop in traffic in October partly on cancellations caused by Hurricane Matthew in the US.
Overall, it handled 1.6% more flights during the month, carrying 6.48 million passengers, and cargo traffic was up 7%.
Meanwhile, Stansted enjoyed its busiest ever month, carrying 6% more passengers than in October 2015, pushing its moving annual total to more than 24 million.
Manchester Airport saw its numbers rise almost 12% year-on-year in October, pushing its rolling 12- month total to 25 million passengers for the first time in its 78-year history after 31 months of consecutive growth. The airport said it had seen the equivalent of 9.3% year on year growth, driven by a host of new long-haul routes and additional capacity on short-haul services.
