United Airlines is airing its first TV spots in nearly a year this fall with its “Go. Go. Stay.” promotion with Hilton Hotels Corp. The offer gives leisure travelers fare discounts and free nights at Hilton hotels. Passengers who buy two or three tickets with the same itinerary get bigger price cuts. (Flights and hotel rates require a Saturday night stay.) TV support runs through Aug. 22 in Boston, Chicago, Denver, Los Angeles, New York, San Francisco, Seattle and Washington, DC. Print ads in national publications support.