This incident involved Southwest Airlines (SWA) flight 708, a Boeing 737-700, and Federal Express Corporation (FedEx) flight 1432, a Boeing 767-300, which were involved in a runway incursion at Austin-Bergstrom International Airport (AUS), Austin, Texas. The local controller had cleared the SWA airplane for takeoff on runway 18L and instructed the FedEx airplane to continue its approach to the same runway. The controller was unable to see the SWA airplane on the taxiway and runway because of dense fog, and the AUS air traffic control tower (ATCT) did not have surface detection equipment to aid the controller in monitoring ground traffic.
Federal Aviation Administration (FAA) procedures required the controller to apply a 2-mile separation between the airplanes. However, when the SWA airplane lined up with the runway 18L centerline and came to a complete stop (so that the flight crew could perform an engine run-up), the FedEx airplane was 1.5 miles away. The separation between both airplanes continued to decrease until the FedEx flight crew saw the outline of the SWA airplane through the fog and began a missed approach. At that time, the FedEx airplane had just crossed the runway 18L threshold, and the SWA airplane was 1,020 ft down the runway. The airplanes were separated at their closest point by 150 to 170 ft (which was less than the 180-ft length of the FedEx Boeing 767 airplane).
The FedEx airplane continued to climb, and the SWA airplane continued to accelerate, which increased the separation between the airplanes. The SWA airplane lifted off and continued to its planned destination. The FedEx airplane circled to the left and landed on runway 18L without further incident.
We determined that the probable cause of this incident was the local controller’s incorrect assumption that the Southwest Airlines (SWA) airplane would depart from the runway before the Federal Express airplane arrived on the same runway, which resulted in a loss of separation between both airplanes. Contributing to the controller’s incorrect assumption were
- his expectation bias regarding the SWA airplane’s departure,
- his lack of situational awareness regarding the SWA airplane’s position when the flight crew requested takeoff clearance, and
- the air traffic control tower’s lack of training (before the incident) on low-visibility operations.
Contributing to the incident was the SWA flight crewmembers’ failure to account for the traffic that was on short final approach and to notify the controller that they would need additional time on the runway before the takeoff roll. Also contributing to the incident was the Federal Aviation Administration’s failure to require surface detection equipment at Austin-Bergstrom International Airport and direct alerting for flight crews.
As a result of this investigation, we made seven new recommendations to the FAA. In addition, we reiterated the five safety recommendations that were previously issued to the FAA.
