BAA's London airports, which include Gatwick, Heathrow and Stansted, have reported a combined loss of £550m in the initial half of 2009.
BAA claims the losses were due to a number of exceptional items, such as the depreciation of old terminals at Heathrow and an increase in its pension deficit.
The airport authority said that it was trying to sell Gatwick airport and was in negotiations with several interested parties.
As of the end of June, the authority had a debt of £9.7bn, which it believes can be handled even without the sale of Gatwick.
In the first half of 2009, BAA reported earnings of £469.9m before interest, tax, depreciation and amortisation (EBITDA), which is an increase from the result of £366.6m in 2008.
The number of travellers across BAA's airports has decreased by 7.4% on a year-to-year basis.