 At about eight miles out, FlightAware shows the plane dropped to an altitude of 525 feet. It flew over the top of Yukon, Oklahoma, setting off that low altitude warning. The tower did ask the pilot if everything was OK. The pilot replied, yes, then aborted the landing and went around and landed safely. So in a statement, Southwest tells NBC News it is, quote, in contact with the FAA to understand and address any irregularities with the aircraft's approach.