On 19 August 2004, a Boeing 747-400 operated by Asiana Airlines, was given a landing clearance for runway 24L at Los Angeles (LAX). At the same time, a Boeing 737-800 operated by Southwest Airlines was given line up and wait instruction for the same runway. The B744 initiated a go-around as the crew spotted the B738 on the runway.
According to the National Transportation Safety Board (USA) (NTSB) Report on the Serious Incident,
"Radar reconstruction of the event found that AAR204 (Asiana B744) passed over SWA440 (Southwest B738) at 200 feet during the go-around. At the time of the incident, a controller change for the LC2 position had just occurred and the relief controller was responsible for the air traffic control handling of both AAR204 and SWA440."
At 2151:21, the LC2 controller who was being relieved cleared AAR204 to land runway 24L. At this point, the Boeing 747 was 9.3 miles from the runway. About 2 minutes later, while AAR204 proceeded inbound on the approach, the LC2 controller provided a relief briefing to the LC2 relief controller and advised him that AAR204 was landing on runway 24L, which the relief controller acknowledged. After assuming the responsibility of the position, the first transmission from the LC2 relief controller was to SWA440 instructing the flight crew to taxi into position and hold on runway 24L (NOTE: the RTF used in United States differs from the ICAO phraseology “Line up RWY… and wait”). AAR204 was 1.81 miles from the runway at 700 feet. According to the SWA440 captain's statement, he saw the Asiana Boeing 747 on final approach but believed that the aircraft was landing on runway 24R. Twelve seconds later, the relief controller cleared SWA440 for takeoff. Radar data indicated AAR204 was 1.26 miles from the runway and about 35 seconds from reaching the landing threshold. Data retrieved from the SWA440's flight data recorder indicated the airplane was on taxiway V approaching runway 24L when given the takeoff clearance. This meant that the flight crew had less than 35 seconds to taxi on to runway 24L, begin a departure roll, and travel 6,000 feet before AAR440 crossed the landing threshold, which would be impossible. According to the Asiana captain's statement, he observed the Southwest Boeing 737 approaching runway 24L but believed the airplane would hold short of the runway. Once he recognized the aircraft was entering the runway, he initiated a go-around and estimated it was about the time his airplane was passing through 400 feet approaching the runway.
The relief controller said that contrary to the recorded relief briefing where he clearly acknowledged that AAR204 was cleared for the left runway, he fully believed AAR204 was landing runway 24R, and therefore, was unaware of the conflict. He first became aware of the problem when the Airport Movement Area Safety System (AMASS) generated an alarm. At this point, AAR440 was only about 12 seconds from colliding with SWA440, and without the prompt actions of the Asiana flight crew a collision would have likely occurred. When the relief controller recognized the problem, he canceled SWA440's takeoff clearance and AAR440's landing clearance. However, AAR204 had already overflown SWA440 on the go-around, clearing the aircraft by about 200 feet. Although the relief controller believed AAR204 was landing runway 24R, this did not alleviate his responsibility to properly monitor the operation and ensure separation was maintained.
The Investigation conducted by NTSB reveals:
At the time of the incursion, five certified professional controllers and one operations supervisor were working in the tower cab. According to the facility personnel, there would normally be 10 people available to work on this shift but injuries and illness had reduced the available shift staff to five. It is common for ATC to combine positions to accommodate facility and/or operational needs. Controllers routinely work combined positions and are specifically trained to do so. However, in this situation, the absence of a local assist controller eliminated an additional safety net established to assist local controllers. The staffing decisions made by the Federal Aviation Administration supervisor on duty at the time of the incursion decreased the likelihood that the relief controller's error would be detected and corrected prior to the runway incursion.
In its evaluation of fatigue, the investigation determined that the relief controller had only 8 hours off between the end of his August 18 evening shift at 2330, and the beginning of his morning shift at 0730 on the day of the accident. As a result, the relief controller reported sleeping just "5 or 6 hours" the night before the incursion, and described his shift leading up to the incursion as a "hard day." This acute sleep loss resulted in a slight decrease in cognitive performance on tasks involving working memory and reaction time.
The National Transportation Safety Board determines the probable cause(s) of this incident as follows:
- a loss of separation between Southwest flight 440 and Asiana flight 204 due to the LC2 relief controller's failure to appropriately monitor the operation and recognize a developing traffic conflict. Contributing factors included the FAA's position relief briefing procedures, the formatting of the DBRITE radar displays in the LAX tower, controller fatigue, and the tower supervisor's staffing decisions on the day of the incident.