Behind the scenes of the proposed $11 billion merger between American Airlines Inc. and US Airways Group Inc. are groups of in-house and outside counsel struggling with the myriad legal issues involved in creating the world’s largest airline. But they won a unique victory in December when marathon negotiations ended in an agreement with both companies’ pilot unions.

"This deal culminated after a fairly dramatic, two-week, round-the-clock, multiparty negotiating process in a room in Dallas over the Christmas [holidays]," recalled labor lawyer Robert Siegel. He is a partner at O’Melveny & Myers and was representing US Airways.