Spirit Airlines has revised its preliminary second-quarter revenue estimate to $1.28 billion, citing lower-than-expected non-ticket revenue and competitive pressure on baggage fees. This revision comes as the airline industry faces challenges from excess capacity and intense competition, leading to a forecasted bigger quarterly loss. United Airlines, which reports earnings soon, has also acknowledged the capacity glut and is preparing for its impact, though its third-quarter profit outlook is below analyst estimates. Meanwhile, Alaska Air Group has lowered its third-quarter profit forecast due to a new flight attendant contract deal, despite topping market expectations for the second quarter with a 15.8% adjusted pretax margin.