Alaska Air Group Inc expects it will be challenging to keep customers who are loyal to Virgin America Inc after the two companies merge, Alaska Air's chief executive said on an analyst call on Thursday. Alaska Air said earlier this month that it would buy Virgin America, a carrier with cult status among leisure and business travelers on the U.S. West Coast, for $2.6 billion. Chief Executive Brad Tilden said "the biggest challenge" ahead will be appealing to its own customers as well as Virgin America's passengers, after that airline is merged into the Alaska brand. Virgin America has a distinctive style, with in-flight mood-lighting and media-rich entertainment.