USAIR <U> AND UNIT REMAIN UNDER MOODY'S REVIEW Moody's Investors Service Inc said the 212.75 mln dlrs of debt of USAir Group Inc and its USAir Inc unit remain under review for possible downgrade. The rating agency cited USAir Group's proposed acquisition of Piedmont Aviation Inc <PIE>, as well as Trans World Airlines Inc's <TWA> proposed cash merger with USAir. However, the status of TWA's bid for USAir Group is currently uncertain. The U.S. Transportation Department has rejected TWA's application to acquire USAir on deficiency grounds, but TWA has said it will file a revised application, Moody's noted. Under Moody's review for possible downgrade are USAir Group's Baa-1 senior debt and Baa-2 subordinated debentures, along with the USAir unit's A-3 senior debt and Baa-1 subordinated debentures. Moody's said it would examine the effects of the proposed mergers on USAir Group's financial measurements, as well as potential damage to the company's financial flexibility because of the probability of increased debt-service requirements.