Following the sale of Gatwick Airport to Global Infrastructure Partners last week, BAA has revealed a loss of £225m on the deal.
London's second-largest international airport was valued by accountants at £1.735bn, but was sold for £1.51bn.
According to reports, the deal has pushed BAA's pre-tax loss to £784.7m in the period up to the end of September, which compares unfavourably with the £519.5m recorded a year earlier.
Adding to this loss was the exceptional charge of £2.617m for the group's pension scheme deficit and a further £1.361m of losses on financial instruments, which are thought to be a result of interest rate swaps.
BAA, which was sold for £10bn in 2006 to a consortium fronted by Spanish support services group Ferrovial, claims that its underlying performance has been good. It has also said that the proceeds of the sale will be used to repay debt, which some sources believe stands at a net of £9.77bn.
The company faces further uncertainty as it continues to appeal against a ruling by the Competition Commission that it must also go on to sell Stansted and either Edinburgh or Glasgow Airports.