TWA <TWA> SUES USAIR <U> OVER POISON PILL Trans World Airlines Inc said it filed suit in Delaware Chancery Court against USAir Group Inc and its board of directors seeking to invalidate its "poison pill" anti-takeover plan. TWA vice president and general counsel Mark Buckstein said TWA also sought a declaratory judgement from the court that its 52 dlr per share takeover offer for USAir would in no way interfer with USAir's possible buyout of Peidmont Aviation Inc <PIE>. Buckstein said TWA asked the court to enjoin the enforcement of USAir's shareholder rights plan, or "poison pill." Such provisions, which typically allow for the issue of securities to shareholders in the event of a hostile takeover bid, are aimed at deterring takeovers by making them more expensive. USAir earlier today rejected TWA's offer, saying TWA's bid was an attempt to interfer with its buyout of Piedmont. USAir also had said its counsel would investigate the matter. Tonight, a spokesman for USAir said the airline had no comment on TWA's lawsuit. USAir did respond, however, to a TWA request to the Department of Transportation for permission to buy up to 51 pct of USAir stock and place the stock in a voting trust pending approval of a takeover. USAir said the request was "hastily pasted together in order to take advantage of a regulatory anamoly that would allow TWA to accomplish in a regulated environment actions that would be impermissable in the non-regulated economy at large." USAir called on the transportation department to reject TWA's request.