United's new 17.5-hour flight is third longest in the world

United Airlines has launched a 17.5-hour Houston-Sydney flight, which spans a distance of 13,834 kilometres and is the third longest flight in the world by scheduled flight time. The world's longest flight is Qatar Airways' Auckland-Doha flight, which takes 18 hours and 20 minutes. It is followed by United Airlines' Los Angeles-Singapore flight, which takes 17 hours and 55 minutes.