Probable cause

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.

— NTSB Determination