US Airways has integrated many of the operations of the two airlines, but the US Airways and America West contingents of its pilot and flight attendant groups are still working separately. The company and union officials, who represent both US Airways and America West pilots, have been negotiating for nine months over a single contract that would cover employees of both carriers. The airline employs about 2,500 pilots, down from almost 6,000 before Sept. 11, 2001.