International Airlines Group (IAG) said September traffic figures had been boosted by heavy promotional activity by British Airways during and after the Olympic Games.
However, it said that while trading conditions at its London hub remained 'firm', performance at Madrid, where Iberia is based, continued to be impacted by Spain's economic woes.
Short haul traffic from its Spanish base had been particularly affected, it said, as was the amount of cargo Iberia carried, which dropped 15.3%.
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In September 2012 the airline carried 8.7% more passengers than in the previous year, up 3.7% on a like-for-like basis.
The passenger load factor, which measures the percentage of available seats filled, was up 1.2% to 84%, or 1.5% on a like-for-like basis.
Across the group premium traffic grew by 8% in September compared to the previous year, with 4.6% growth in non-premium traffic.
"British Airways has been engaging in heavy promotional activity during and post the Olympic and Paralympic Games culminating in the 'Thank-you Great Britain sale', which ended on September 25th," the company said.
"This has positively impacted our volumes in both premium and non-premium cabins."
British Airways' September traffic, measured in 'Revenue Passenger Kilometres', was up 4.2%
Meanwhile Iberia traffic was down 0.8% on that measure.
