London Heathrow airport's EBITDA rose 9.6 percent to GBP£922.9 million in the nine months to the end of September on revenue 8.2 percent higher at GBP£1.84 billion, helped by an increase in tariffs it charges airlines.
But Heathrow warned that full-year earnings would fall short of its target, after fewer passengers travelled through Europe's busiest airport this summer.
In June, the group predicted it would report adjusted earnings before interest, taxes, depreciation, and amortization (EBITDA) of around GBP£1.27 billion (USD$2 billion) for 2012.
The company, owned by Spanish infrastructure group Ferrovial, said Heathrow, Europe's busiest airport, handled 53 million passengers in the first nine months of 2012, up 0.6 percent on last year.
However, traffic at London Stansted, which is predominantly a low-cost leisure travel airport and more exposed to domestic economic conditions, fell 4.6 percent to 13.5 million in the same period.
"Traffic over the summer months was lower than expected, particularly in July and August when passenger traffic was down about 400,000 on the same period in 2011," chief financial officer José Leo said on Monday, referring to London's Heathrow airport.
The operator said the sale of Stansted, which handled 18 million passengers last year, was now underway after Britain's competition regulator forced it to sell the airport to loosen the group's grip on the UK.
"The sale of Stansted will take a matter of months," said Leo, who added that it would "probably be next year" before a deal was completed.
Single runway Stansted is based 50 km (31 miles) northeast of central London and is the fourth-busiest airport in the UK.
Manchester Airports Group, Macquarie, J.P. Morgan Asset Management and Morgan Stanley Infrastructure are expected to bid for Stansted, according to sources.
Plans for additional runways at Stansted and Heathrow were dropped by BAA after the Conservative-Liberal Democrat coalition came to power in 2010 and the future of the airports is unclear.
Leo dismissed the idea of connecting Heathrow and Stansted with the Crossrail line that will run between east and west London to create a 'dual hub' as a way to solve the air capacity shortage in London and the south east of England.
"Airlines won't operate a dual hub easily because the transfer time will be too long, killing the competitive advantage a hub airport has," he said.
Heathrow Ltd also owns Southampton airport in southern England and Glasgow and Aberdeen airports in Scotland.