United Airlines has reported higher profit in the second quarter, thanks to record crowds at U.S. airports. United said Wednesday that its profit rose 23% to $1.32 billion in the three-month period that ended June 30. However, the airline warned that its third-quarter results will fall short of Wall Street expectations. That's because airlines are adding more flights than the market can handle, creating a glut of seats that is keeping prices from rising. Airlines are trimming their schedules for mid-August and beyond, which United says will help reduce the oversupply of flights.