Quote from US Airways website:
Proper travel identification and documents are required for all domestic and international travel. Also, you will need to show your photo identification at the ticket counter, security checkpoints and possibly when you board the plane.
Requirements for Domestic Travel (U.S. only):
Unexpired state-issued photo driver's license OR
Unexpired state-issued photo identification card OR
Unexpired passport OR
Employee ID issued by a Federal, State or local government agency