Los Angeles, CA, USA
N461WN
Boeing 737-7H4
Asiana Airlines flight 204 (AAR204), a Boeing 747-400 that had been cleared to land on runway 24L, initiated a go-around and overflew Southwest Airlines flight 440 (SWA440), a Boeing 737 which had been cleared into position and hold for takeoff on runway 24L. Radar reconstruction of the event found that AAR204 passed over SWA440 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. 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. Recorded voice communications of the position relief briefing indicated the LC2 controller informed the relief controller that the inboard runway (RWY 24L) was in use for landings, and that AAR204 was cleared to land on runway 24L. There was no indication from the relief controller that he did not understand or needed clarification from the relieving controller. The LC2 controller addressed all major areas on the LAX position relief checklist, and conveyed information accurately during the position relief briefing. About 30 seconds after the LC2 controller completed the briefing, he remembered additional information about helicopter operations and began relating that to the relief controller; however, this conversation was interrupted by another radio transmission, which effectively distracted both the LC2 controller and relief controller and likely exacerbated the difficulty the relief controller had in converting the briefing information in his short term memory to working memory. Immediately following the relief briefing, the LC2 controller left the postion. Based on what is known about the volatility of information held in short term memory, and the speed of decay in short term memory without rehearsal of the information, it is not surprising that the relief controller failed to recall every detail LC2 controller's position relief briefing with complete accuracy. The relief controller was briefed on the location and clearances for seven aircraft (seven pieces of information is about the limit that can be effectively retained short term memory), but was not given sufficient opportunity to rehearse this information in working memory until 13 seconds after the briefing was completed. The format and timing of the position relief briefing and its interruption by routine radio transmissions contributed to the relief controller's memory error. LAX tower controllers interviewed during the investigation stated that, because of the location of the tower, it was difficult to determine visually whether a single approaching aircraft was lined up for runway 24R or runway 24L. Controllers stated that destination runways were most difficult to determine visually for large aircraft, such as the Boeing 747. The LC2 relief controller believed this was the reason he did not recognize the conflict between AAR204 and SWA440. Although this may be true, it does not alleviate the controller of his responsibility to monitor the operation. In addition, the relief controller was aware the inboard runways were in use for landings and should have been alert to the possibility of aircraft arriving on runway 24L. To assist the controllers with visual observations, the LAX tower is equipped with Digital Bright Radar Indicator Terminal Equipment (DBRITE) displays. The relief controller stated that he saw AAR204's radar target on the DBRITE display during the position relief briefing, but that he did not specifically recall seeing AAR204's data block. A review of the radar replay indicated AAR204's data block displayed two sets of alternating aircraft information: runway assignment and aircraft type were presented for 5 seconds; followed by a 15-second presentation of altitude and ground speed data. The relief controller stated that he glanced at his DBRITE display before the runway incursion. However, he clearly did not perceive the critical information that AAR204 was assigned to land on runway 24L, and he therefore did not take action to eliminate the conflict. Time-sharing of runway assignment information on the aircraft data tag increased the likelihood that critical information would not be perceived when parallel approaches were being conducted on the north side of the LAX tower. LAX is equipped with (Airport Movement Area Safety System) AMASS, which is a computer software enhancement to the airport surface detection equipment. The LAX AMASS at the LC2 position generated an aural and visual alert only 12 seconds before a collision would have occurred, warning the controller to the impeding conflict; however, the flight crew of AAR204 had observed the Southwest Boeing 737 taxing towards the runway and, believing the aircraft was not going to stop, initiated a go-around before the AMASS alert activated. A collision was avoided, not by AMASS, but by the actions of the flight crew of AAR204. At the time of the incursion, five certified professional controllers and one operations supervisor were working in the tower cab. According to 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.
1.1 HISTORY OF FLIGHT On August 19, 2004, about 1455 Pacific daylight time, an Asiana Airlines Boeing 747-400, HI7415, overflew a Southwest Airlines Boeing 737-7H4, N461WN, while the Southwest airplane was in position on the active runway 24L, at Los Angeles International Airport, Los Angeles, California. Southwest Airlines operated the Boeing 737 under the provisions of 14 CFR Part 121, and Asiana Airlines operated the Boeing 747 under the provisions of 14 CFR Part 129. There was no damage to either airplane nor injuries to the combined total of 417 passengers and 29 crewmembers. Visual meteorological conditions prevailed and an instrument flight plan had been filed. On August 24th Southwest Airlines safety personnel reported to the National Transportation Safety Board investigator that the captain of Southwest flight 440 (SWA440) reported that an Asiana Boeing 747 (AAR204) came with in 200 feet of his airplane while it was executing a go-around on runway 24L. Southwest flight 440 had been cleared for takeoff on runway 24L. The captain stated that he became concerned when the Asiana airplane did not come in to his view, as it should have, when landing on the parallel runway 24R. He began to move his airplane off the runway when the Asiana airplane overflew his, coming within 200 feet. The captain of AAR204 stated that he and his copilot identified the runway conflict while they were on the short final approach for landing and executed a go-around about 400 feet above ground level (agl). At 2151:21, the LAX local 2 (LC2) tower controller cleared AAR204 to land on runway 24L, and the flight crew acknowledged the landing clearance. AAR204 was conducting an ILS runway 24L approach and radar data indicated the aircraft was 9.3 miles east of the airport. About this time, the LAX operations supervisor on duty asked the local assist 1 (LA1) controller (hereafter referred to as the "LC2 relief controller") to relieve the LC2 controller, who needed a break. At 2153:08, the LC2 controller began a position relief briefing for the LC2 relief controller. He stated, "Alright uh both runways available. Let's see you got the board you said. Got a lot of flow up there, a lot of flow. Better study up on that." The LC2 relief controller stated, "uh huh, I do I came from assist one." The LC2 controller continued, "Alright. They're on the boards, the inboards I should say, both runways available, PIREPs none, you can visual out. Uh, rolling out on the right is Southwest, cleared to land is Asiana on the left. Southwest on the pad is a LAXX I haven't tried to coordinate. You got a King Air, I'm sorry, he just left, so right now you're back to released. These two have been approved, but not run down or released…" The LC2 controller continued, "This one is awaiting approval," then stated, "and that's all I can think of." At 2153:43, the LC2 relief controller advised, "Alright well I've got it." The LC2 controller responded by saying, "Uh helicopters I'm sorry you have one more." The LC2 relief controller asked, "Oh and who is it?" As the LC2 controller began to say the helicopter's call sign, "Coast Guard six five...," he was interrupted by a transmission from a Southwest Airlines flight crew who had just landed runway 24R and requested permission to exit the runway at a different location than instructed. The LC2 controller approved the request, and after he received an acknowledgement from the Southwest crew, he continued briefing the LC2 relief controller. At 2153:55, the LC2 controller completed the briefing by informing the LC2 relief controller of the Coast Guard helicopter's call sign and location on the airport, and that no other helicopters were operating in the vicinity of the airport. During the interview, the LC2 controller stated that at this time he unplugged his headset from the position and left to speak briefly with the supervisor about his break. At 2154:06, the LC2 relief controller issued his first radio communication from the LC2 position, "Southwest four forty runway two four left position and hold." SWA440's flight crew acknowledged the instruction stating, "Position, and hold southwest four forty." At this time, AAR204 was 1.81 miles from the 24L runway threshold and the aircraft's altitude was 700 feet. According to the SWA440 Captain's statement, he turned onto taxiway V, which is perpendicular to runway 24L; he saw the Boeing 747 on final approach but believed the aircraft was landing on runway 24R. The LC2 relief controller spent the next few seconds coordinating SWA440's southwesterly departure via the landline with the LAX local one (LC1) controller. At 2154:18, the LC2 relief controller stated, "Southwest four forty turn left heading two one zero runway two four left cleared for take off." The flight crew replied, "we'll turn two one zero cleared for takeoff runway two four left southwest four forty. AAR204 was 1.26 miles from the runway threshold and at 500 feet. At 2154:26, the LC2 relief controller issued a wake turbulence advisory to the flight crew of UAL961, the lead aircraft on final approach to runway 24R and advised, "caution wake turbulence heavy seven forty seven short final." Radar data and recorded voice communications indicated UAL961 was not following any other aircraft to runway 24R. The wake turbulence advisory was in reference to AAR204 who was approximately 3 miles ahead of UAL961 but on final approach to runway 24L. The LC2 relief controller believed AAR204 was landing runway 24R, and therefore, a wake turbulence advisory would have been required. At 2154:40, an aural and visual alert was generated by the Airport Movement Area Safety System (AMASS) at the LC2 position. AAR204 was .4 miles from the runway at 300 feet. At this time, recorded voice communications indicated the LC2 relief controller was issuing a landing clearance to Sky West 6040, the second aircraft on final approach to runway 24R. According to the Asiana captain's statement, he observed the Southwest B737 approaching runway 24L but believed the aircraft 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 he was passing through 400 feet. At 2154:48, a voice of unknown origin stated on the frequency, "is that four seven going around?" AAR204 was .18 miles from the runway at 200 feet. At 2154:50, the LC2 relief controller advised the flight crew of SWA440, "cancel take off clearance hold in position." The flight crew responded by saying, "holding in position southwest four forty." The controller then instructed the flight crew of AAR204, "fly heading two five zero climb and maintain two thousand." The flight crew replied, "heading two five zero climb and maintain two thousand asiana two zero going around now." Radar data indicated AAR204 had flown over SWA440, clearing the aircraft by about 200 feet, and was now .32 miles past the runway threshold and climbing out of 500 feet. At 2155:07, the flight crew of SWA440 advised the LC2 relief controller, "we're going to go to echo eight and come back southwest four forty." The LC2 relief controller approved the request and instructed the flight crew to taxi and hold short of runway 24L at the full length. Echo eight is a designated taxi way off of runway 24L. At 2156:23, the flight crew of SWA440 asked the LC2 relief controller, "what happened up there sir." The controller replied, "well he apparently was lined up for the wrong runway." The flight crew responded by saying, "ok yeah the runways are so close together we looked at it and it was so big we thought he was on the right side as well." In response, the LC2 relief controller said, "yep, I did the exact same thing." Upon hearing the AMASS alert, the operations supervisor who was located on the south side of the tower cab began walking to the north side of the tower cab, and saw AAR204 in a nose-high attitude, 200 to 300 feet above the runway. The aircraft appeared to be executing a go-around. The supervisor continued to the LC2 position, and began monitoring the actions of the LC2 relief controller. The operations supervisor looked at the DBRITE display and saw information indicating that AAR204 was assigned to land on runway 24L. He asked the LC2 relief controller if he knew AAR204 was landing on runway 24L. The controller responded, "I did not know he was on the left." The LC2 controller, who was leaving the tower cab, also heard the AMASS alert. He also began walking toward the LC2 position, observed AAR204 climbing in a go-around attitude, and saw SWA440 turning onto the runway below AAR204. The operations supervisor asked the LC2 controller if he had told the LC2 relief controller AAR204 was landing on the left side. The LC2 controller advised that he had done so, and that SWA440 had been awaiting a takeoff clearance on the concrete pad adjacent to the approach end of the runway. The LC2 controller asked if he should relieve the LC2 relief controller. The supervisor advised him to do so. 1.5 PERSONNEL INFORMATION 1.5.1 The LC2 Tower-Controller The LC2 controller held an air traffic control tower operator certificate and a current medical certificate. He entered on duty with the Federal Aviation Administration (FAA) on November 2, 1982. He was assigned to LAX in 2000, and received facility certification in 2002. Before his assignment to LAX, he previously worked at Kansas City Air Route Traffic Control Center (ARTCC), Los Angeles ARTCC, Los Angles TRACON, and Southern California TRACON (SCT). On the day of the incursion, he had been working the LC2 position for about 1 1/2 hours before the relief LC2 controller relieved him. 1.5.2 The LC2 Relief Tower-Controller The FAA hired the LC2 relief controller as an air traffic controller in 1987. After completing his initial training at the FAA academy, the relief LC2 controller was assigned to Fullerton Tower (FUL) until 1990. In 1990, he was assigned to Orange County Tower (SNA) and remained there until he was assigned to LAX in 2000, where he received facility certification in 2001. The LC2 relief controller had no history of operational errors or disciplinary action in the FAA. His supervisor described him as "the best controller on his crew," adding that he was a "conscientious controller" who "gave 100 percent." The LC2 relief controller's coworkers also spoke favorably about his performance. The LC2 controller said he had "a lot of confidence" in the LC2 relief controller. He said if someone else had relieved him, he might have remained at the LC2 position longer after the position relief briefing was completed. The LC2 relief controller's most recent second-class medical certificate, dated May 28, 2004, included a limitation stating "must have glasses for near vision in his/her immediate possession while performing ATC duties." He reported having glasses with him at the time of the incursion, but stated that he was not wearing them and did not need them for the tasks he was performing. He stated that he did not take prescription medications, and said he took no medications of any kind in the 72 hours before the incursion. He said he did not smoke and reported only occasional light use of alcohol. He reported no significant recent changes in his finances or personal life. The LC2 relief controller's residence was a 45-minute drive from LAX. Mondays and Tuesdays were his regular days off. He rarely slept or took naps during the day. On his days off, he said he usually went to bed about 2200 and woke up between 0800 and 0900. He said he treated his weekends as recovery time, attempting to get at least 9 hours of sleep per night. The LC2 relief controller's normal weekly work schedule included afternoon shifts on Wednesday and Thursday, early morning shifts on Friday and Saturday, and either a midnight or early morning shift on Sunday. The LC2 relief controller had modified his schedule for the day of the incursion, working a shift that began in the early morning rather than in the afternoon. He did this for personal reasons. This change afforded him a rest period of 8 hours on Wednesday night. The controller referred to this rest period as a "quick turnaround." A review of tower watch schedules indicated that the 8-hour rest period the LC2 relief controller received the night before the incursion was his shortest in the previous 30 days. His next shortest rest periods were 9 hours long. The LC2 Relief Controller's 72-Hour History On Monday, August 16, 2004, the relief controller had a scheduled day off. He engaged in routine activities and went to sleep about 2200. On Tuesday, August 17th, the relief controller had another scheduled day off. He woke about 0800, engaged in routine activities, and went to sleep about 2200. On Wednesday, August 18th, the relief controller woke about 0800, and engaged in routine activities at his home. He said he felt fully rested when he began his shift at 1530. He finished his shift at 2330, drove home, and slept for "five or six hours." On Thursday, August 19th, the relief controller woke about 0600, got ready for work, drove to the tower, and began his shift at 0730. He described his shift leading up to the incursion as a "hard day." He felt tired because he had not received enough sleep the night before and worked several busy positions during the shift. Tower position logs for August 19, 2004, showed the relief controller spent 5 hours 36 minutes on position, out of a total of 7 hours 25 minutes on duty before the incursion. 1.9 COMMUNICATIONS The Los Angeles Air Traffic Control Tower is a Level 12 ATC facility. The tower is centrally located on the airport between the north and south complexes. The tower can accommodate up to 13 positions; 2 local control (LC1/LC2), 2 local assist (LA1/LA2), 3 ground control (GC1/GC2/GC3), 2 clearance delivery (CD1/CD2), 1 helicopter position (HC), 1 traffic management coordinator (TM), and 2 supervisors (AS1/AS2). On the day of the incursion, LAX was in a west configuration, the north complex was landing and departing runway 24R/24L, and the south complex was landing and departing runway 25R/25L. 1.9.1 Equipment The LAX tower is equipped with 7 DBRITE (Digital Bright Radar Indicator Terminal Equipment) systems, which are located at the LC1/2, GC1/2/3, helicopter, and traffic management positions. The system displays primary and secondary radar returns of aircraft and alphanumeric target symbols generated by the LAX ARTS IIIE system. The data is derived from the Los Angeles ASR-9 radar located on the airport. The DBRITE displays aircraft target symbols each with a corresponding (Automated Terminal Radar System) ARTS data block. The data block provides aircraft information to the controller. Line 1 of the data block indicates the aircraft call sign. Line 2 contains current altitude (in hundreds of feet) and ground speed (in tens of knots). These two items of line 2 data are time shared with two other items, which are referred to as "scratch pad" information. At LAX the scratch pad items are: current runway assignment or type approach (e.g., ILS runway 24L approach is displayed as "I4L") and aircraft type (e.g. Boeing 747-400 is displayed as "B744''). Information displayed in the scratch pad area alternates between altitude/ground speed and assigned runway/aircraft type. A review of the radar playback of the LC2 DBRITE display indicated that at the time of the incursion AAR204's altitude and ground speed were displayed for 15 second intervals, alternating with displays of assigned runway and aircraft type, which lasted 5 seconds. The LAX tower's AMASS is a computer software enhancement to the airport surface detection equipment. The system provides logic predicting the path of aircraft landing and/or departing, and aircraft and/or vehicle movements on runways. Visual and auditory alerts are activated when logic projects a potential collision. AMASS alerts controllers to a potential collision when an aircraft or vehicle is occupying a runway and when arriving or departing aircraft cross a certain threshold or attain a certain speed. The syst
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.
Source: NTSB Aviation Accident Database
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