PIEDMONT <PIE> AGREES TO USAIR <U> BUYOUT USAir Group Inc said Piedmont Aviation Inc has agreed to be acquired for 69 dlrs per share. The company, in a newspaper advertisement, said it has started a tender offer for all Piedmont shares at that price, and the Piedmont board, with two directors absent, has unanimously approved the bid. The offer and withdrawal rights are to expire April Three unless extended, and the bid is to be followed by a merger at the same price. USAir said Piedmont has granted it an irrevocable option to buy up to 3,491,030 new shares under certain circumstances. Piedmont now has about 18.6 mln shares outstanding. USAir said the tender is conditioned on receipt of enough shares to give USAir at least a 50.1 pct interest in Piedmont on a fully diluted basis and approval by the U.S. Department of Transportation of a voting trust agreement permitting USAir to buy and hold shares pending review of its application to gain control of Piedmont. The company said its merger agreement with Piedmont provides that the offer is not to be amended without Piedmont's prior written consent in any way that would be adverse to Piedmont shareholders, but it said it could cut the number of shares to be bought without Piedmont's consent. USAir said it could reduce the number of Piedmont shares to be purchased in the offer to no less than the minimum number needed to cause the voting trust condition of the bid to be satisfied. In that case, it said if more than that minimum number of shares were tendered, it would buy shares on a pro rata basis. In February USAir had offered to pay 71 dlrs per share in cash for 50 pct of Piedmont's stock and 1.55 to 1.90 USAir shares for each remaining Piedmont share. Last week, Carl C. Icahn-controlled Trans World Airlines Inc <TWA> made a conditional offer to acquire USAir for 52 dlrs per share, a bid that was rejected by the USAir board. The Transportation Department on Friday rejected TWA's application to acquire USAir on the grounds that the application failed to comply with department regulations by omitting necessary information. TWA said it would refile today, providing the information needed. On Friday TWA said it had already acquired four mln shares or 15 pct of USAir.