Airlines may be struggling with higher gas prices, ticket-price competition and rising labor costs. But airports? Profit city. That's why the consortium of investors called Airport Development Corp. bid for BAA, the world's largest airport operator, in a $30-billion deal this February. London-based BAA operates seven airports in Britain including Heathrow and Gatwick, and manages or owns part of 11 more in Australia, Hungary and the U.S. (including Logan Airport in Boston). BAA archrival Ferrovial, the Spanish construction company, has a majority stake in Airport Development.