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HISTORY OF FLIGHTOn June 10, 2021, about 1745 Pacific Daylight Time (PDT), a runway incursion occurred at the San Diego International Airport (SAN), San Diego, California, when air traffic control cleared Southwest flight 1648 to land on runway 27 and subsequently instructed SkyWest flight 3371 to line up and wait on the same runway. Both flights were being operated under Title 14 Code of Federal Regulations (CFR) Part 121. There were no injuries reported to the occupants of either flight or damage to either airplane. Daytime visual meteorological conditions (VMC) prevailed at the time of the incident.

Southwest flight 1648 push backed from the gate at Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona about 1647 and was airborne about 1656. The original departure time was 1630. According to the flight crew interview transcripts there were no issues with their airplane that would affect their landing and that everything was “normal.” For the event flight the first officer was the pilot flying and the captain was the pilot monitoring.

The Southwest flight’s arrival into SAN was the LUCKI1 arrival and then the Area Navigation (RNAV) Z approach to runway 27 (see section 5.0 for details on the arrival and approach). According to the flight crew “it was VMC, clear” and they were going to follow the RNAV approach for lateral and vertical guidance to the airport. Air traffic control (ATC) was going to sequence another aircraft in front of them on the approach; however, after the other aircraft went south of the extended final to the runway, the ATC controller vectored that flight off the approach and the incident flight became the number one aircraft for the airport. They were cleared to the initial approach fix for the approach to runway 27 “near the end” of the LUCKI1 arrival. The flight crew stated that once they reported the airport in sight, they were cleared for the visual approach to runway 27.

At 1741:54, the Southwest flight contacted the SAN ATC tower inside of the VYDDA waypoint. The ATC tower controller cleared Southwest flight 1648 to land on runway 27 and informed them that there was going to be an airplane in the takeoff position on runway 27. The flight crew accepted the landing clearance and acknowledged that there was to be an airplane in position on the runway.

At 1744:00 the ATC tower controller advised the SkyWest flight that Southwest was on a 5-mile final and instructed them to line up and wait on runway 27. As the Southwest flight got closer to the runway, they observed the SkyWest airplane at the beginning of the displaced threshold for runway 27 and they had not heard the tower controller issue a takeoff clearance to the SkyWest flight.

At 1745:47 the tower controller instructed SkyWest to exit the runway, first at Bravo then corrected the clearance to Charlie 2 (C2) which was read back by the SkyWest flightcrew.

At 1745:58, the Airport Surface Detection System – Model X (ASDE-X) alerted the tower controller that runway 27 was occupied and provided a mandatory go-around alert. The FAA audio recording captured the pilot of the Southwest flight starting to transmit with “Ah” followed by the tower controller instructing the Southwest flight to go around. However, immediately after the tower controller stopped transmitting the audio recording captured the Southwest flight crew stated, “Southwest sixteen forty-eight.” However, LiveATC audio recording of the event captured the pilot of SWA1648 transmitting, “Ah, is that an airplane on the runway, for Southwest sixteen forty-eight.” Radar data of the event indicated that the Southwest flight was less than 1 nautical mile from the end of runway 27 at the time of those transmissions.

At 1746:02 The ATC tower controller stated, “do not overfly the aircraft on the runway.” According to the Southwest pilots’ interviews, the pilot monitoring unknowingly keyed the transmit button and stated, “how are we going to do that.”

According to written statements from the SkyWest flight crew, the captain, after receiving clearance from the controller to line up and wait on runway 27 and that there was traffic on a 5-mile final, taxied into position for departure. The flight crew reported hearing several transmissions from the tower to several other aircraft including an aircraft requesting a clearance into the airspace and to fly near “Petco Park.” They heard several airlines receive a landing clearance after they reported on the frequency with the tower controller. However, there was no takeoff clearance issued to them and the next instruction they were issued was to exit the runway. While their flight began moving to exit the runway, they heard the Southwest plane ask if that was a plane on the runway. The controller transmitted that the airplane was exiting and not to overfly them, to which Southwest queried about how they are going to do that. The crew reported that the controller’s response was “just off-set.” After they exited the runway, they heard several transmissions between the controller and the Southwest flight crew. After the SkyWest flight stopped and was holding short of runway 27, they informed the tower controller that they did not hear a go-around instruction for Southwest.

According to the flight crew interview transcripts, the Southwest first officer, who was flying, queried the captain if he wanted him to move a little to the left to not fly over the SkyWest airplane, which the captain agreed. Prior to landing, the ATC controller queried the flight with “are you going around.” However, according to the crew, the transmission trailed off just as the main landing gear was touching down. The flight landed on the runway and the first officer reported he applied “normal thrust reversers” and at some point, prior to exiting the runway onto a taxiway, he transferred control to the captain to taxi. During the rollout, the ATC controller told Southwest 1648 “I told you to go around” to which the captain responded they did not hear him say that and that they were only told not to overfly the aircraft. The controller then told them to go ahead and contract ground control. The flight taxied to the gate uneventfully.

The first officer reported that after they returned to Dallas that night, he listened to a publicly available transmission recording of their flight. He stated that on one recording he could hear the controller issue a go-around to their flight and as soon as the controller’s transmission ended the remainder of the captain’s transmission was heard, which was their call sign only. He further heard another recording in which he could not hear the controller’s transmission but only the captain’s transmissions. PERSONNEL INFORMATIONSouthwest Flight Crew Information

Documentation provided by Southwest Airlines indicated that since 2015 the pilots had flown with each other on 10 flights, including the incident flight. The most recent time they flew together before the day of the incident was on December 7, 2019; however, other than the incident flight no other flights they operated together were to SAN. Documentation further indicated that since 2010 the captain had operated flights into SAN a total of 88 times including the incident flight. The most recent flight into SAN prior to the incident was on September 27, 2020. The first officer had operated flights into SAN a total of 42 times, including the event flight, with the most recent prior to the incident being on May 15, 2021.

Captain

The captain was 56 years old and held an Airline Transport Pilot (ATP) certificate with rating for multiengine land, commercial privileges airplane single-engine land, and type ratings on the B-737, CE-500, DC-9, HS-125, and LR-JET which included limitation of DC-9 Circling approach – VMC only, CE-500 Second in Command required. He held a flight instructor certificate with airplane single and multiengine, and instrument airplane rating, and a mechanic certificate with an airframe and powerplant rating. He held an FAA first-class medical certificate dated February 23, 2021, with a limitation of “must wear corrective lenses”. At the time of the incident, he reported that he was wearing contacts. His date of hire with Southwest Airlines was May 10, 2000. He was based at Dallas Love Field Airport (DAL), Dallas, Texas.

His most recent training event occurred in January of 2021 with a return-to-service training on the B-737 Max. Prior to that his most recent recurrent training was accomplished in October 2020. The Captain further provided that he had approximately 9,000 total hours of flight experience as a captain in the B737 series aircraft.

First Officer

The first officer was 41 years old and held an ATP certificate with a rating for multiengine land, commercial privileges airplane single-engine land, and a type rating on the B-737. He held an FAA first-class medical certificate dated February 1, 2021, with no limitations. His date of hire with Southwest Airlines was April 2, 2014. He was based at DAL.

Following a voluntary leave of 6-months from Southwest Airlines, he requalified on the B-737 in March of 2021 following a checkride. The requalification training included a day of ground school, maneuver observation training and line observation training, followed by a few days off. Then he did the Southwest Airlines Advanced Qualification Program (AQP) qualification which included a day of ground school, maneuvers in the simulator, a checkride, and then B-737 Max return-to-service training. ADDITIONAL INFORMATIONOn February 2, 2021, Southwest Airlines produced a Flight Safety Alert for SAN, specifically for runway 27 approaches. The alert stated that data indicate a potential for “unstable approaches” and “GPWS Terrain/Obstacle Warnings.” It further provided conditions that may result in an unstabilized approach with those conditions being “a steeper glidepath,” “Parking garage approximately 0.4 NM from RWY 27 threshold” and “high gross weight and...