Gatwick is worth about £1.8bn, regulators have said
BAA will appeal against an order to sell three of the seven UK airports it runs at a hearing starting later.
The Competition Commission ruled in March that BAA must sell Gatwick, Stansted and Edinburgh or Glasgow airports within two years.
BAA will argue there was an "apparent bias" due to a link between a member of the ruling panel and an organisation interested in buying the airports.
The hearing at the Competition Appeal Tribunal is set to last three days.
As well as arguing the commission had a conflict of interest, BAA will also say the commission did not properly take into account the effect the recession would have on the airports' sales.
In making its ruling, the commission decided that the lack of competition in the south-east of England, where BAA also operates Heathrow, and in lowland Scotland was bad for passengers and airlines.
At the start of this year BAA said its annual profits had fallen by 18.4% as the economic downturn dented passenger numbers.
It reported a profit of £582m before tax and interest, down from £713m in 2007, as the number of travellers going through its UK airports fell by 2.7%.
BAA was bought by Spanish firm Ferrovial for more than £10bn in 2006.
A ruling on the appeal is expected in the next few months.