US Airways Group, Inc. operates a network air carrier through its ownership of the common stock of US Airways, Inc. (US Airways), Piedmont Airlines, Inc. (Piedmont), PSA Airlines, Inc., Material Services Company, Inc. and Airways Assurance Limited, LLC. US Airways is the Company's principal operating subsidiary. Effective July 1, 2004, Allegheny Airlines, Inc. merged with Piedmont, with Piedmont as the surviving entity. US Airways is a certified air carrier engaged in transporting passengers, property and mail. As of December 31, 2004, US Airways operated 281 jet aircraft and 22 regional jet aircraft and provided service at 89 airports in the United States, Canada, Mexico, France, Germany, Italy, Spain, Ireland, the Netherlands, the United Kingdom and the Caribbean. On September 12, 2004, US Airways Group and its domestic subsidiaries, including its principal operating subsidiary, US Airways, filed voluntary petitions for relief under Chapter 11 of the United States Bankruptcy Code.