Airline blog View From the Wing listed the world's longest direct flights recently, though they considered miles traveled instead of hours spent in air. The longest flight, according to VFTW, is Qantas's direct flight from Sydney to Dallas, which covers 8,578 miles. Thanks to time zone changes, a flight that leaves Sydney at noon would arrive in Dallas about 20 minues later, even though it takes over 15 hours to reach Texas.
But if you measure length by the time it take to get to a destination, Delta takes the cake, with a 17 hour+ flight from Atlanta to Johannesburg that covers over 8,400 miles.
LAX can lay claim to numerous long-haul flights, with direct service from Los Angeles to Middle Eastern destinations like Abu Dhabi and Dubai that clock in at over 8,300 miles. Singapore Airlines once operated the undisputed longest flight, with direct service from Singapore to Newark's Liberty International Airport, until it ended the service in late 2013.