BAA Ltd, the owner of London's Heathrow, Stansted and Gatwick airports, was assigned "preliminary" ratings to as much as 50 billion pounds (US$100 billion) of debt under a new program, Standard & Poor's said yesterday.

The debt sold through BAA Funding Ltd would have ratings of A-, S&P's seventh-highest investment grade ranking, and two steps lower at BBB, the New York-based credit company said in an e-mailed statement obtained by Bloomberg News.

The world's biggest airport operator is proposing to swap about US$9.6 billion of bonds for new notes backed by London's airports and it got backing from nine banks to refinance as much as US$15.2 billion of existing debt.

"This is a landmark corporate securitization transaction," S&P analysts led by Alexandre de Lestrange said in the statement. BAA "expects to improve its financial flexibility, reduce its debt costs and standardize its secured financing covenants."

The ratings become final after the securities are sold.

The program would allow BAA, controlled by Spanish builder Grupo Ferrovial SA, to raise money through bonds and bank loans, S&P said.

The debt would be backed by revenue BAA collected from fees it charged to airlines and passengers.