History of Flight
On June 10, 2021, at about 1745 Pacific Daylight Time, a runway incursion occurred at San Diego International Airport (SAN), San Diego, California. 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 operated under Title 14 Code of Federal Regulations Part 121. No injuries to occupants or damage to either airplane were reported. Daytime visual meteorological conditions prevailed.
Southwest flight 1648 departed Phoenix Sky Harbor International Airport (PHX) at about 1656 after pushback from the gate at 1647, with an original departure time of 1630. According to flight crew interview transcripts, there were no airplane issues affecting landing, and everything was "normal." The first officer was pilot flying; the captain was pilot monitoring.
The Southwest flight arrived via the LUCKI1 arrival and the Area Navigation (RNAV) Z approach to runway 27. The flight crew stated conditions were VMC and clear, and they planned to follow the RNAV approach for lateral and vertical guidance. Air traffic control sequenced another aircraft ahead but vectored it off the approach after it went south of the extended final, making the incident flight number one. They were cleared to the initial approach fix near the end of the LUCKI1 arrival. After reporting the airport in sight, they were cleared for a visual approach to runway 27.
At 1741:54, Southwest contacted SAN tower inside the VYDDA waypoint. The tower controller cleared them to land on runway 27 and informed them an airplane would be in the takeoff position on the runway. The flight crew accepted the clearance and acknowledged.
At 1744:00, the tower controller advised SkyWest flight 3371 that Southwest was on a 5-mile final and instructed them to line up and wait on runway 27. As Southwest approached, they observed the SkyWest airplane at the beginning of the displaced threshold and had not heard a takeoff clearance.
At 1745:47, the tower instructed SkyWest to exit the runway, first at Bravo then corrected to Charlie 2 (C2), which was read back.
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. FAA audio captured the Southwest pilot starting to transmit with "Ah" followed by the tower controller instructing a go-around. Immediately after the controller stopped transmitting, the Southwest flight crew stated, "Southwest sixteen forty-eight." LiveATC audio captured the pilot transmitting, "Ah, is that an airplane on the runway, for Southwest sixteen forty-eight." Radar data indicated Southwest was less than 1 nautical mile from the end of runway 27 at the time.
At 1746:02, the tower controller stated, "do not overfly the aircraft on the runway." According to Southwest pilots' interviews, the pilot monitoring unknowingly keyed the transmit button and said, "how are we going to do that."
According to SkyWest flight crew statements, the captain, after receiving line up and wait clearance and traffic on a 5-mile final, taxied into position. They heard several transmissions to other aircraft, including one requesting clearance near "Petco Park." No takeoff clearance was issued; the next instruction was to exit the runway. While moving to exit, they heard Southwest ask about a plane on the runway. The controller transmitted that the airplane was exiting and not to overfly them; Southwest queried how to do that. The crew reported the controller responded, "just off-set." After exiting, they held short of runway 27 and informed the tower they did not hear a go-around instruction for Southwest.
Southwest first officer queried the captain about moving left to avoid overflying the SkyWest airplane, to which the captain agreed. Prior to landing, the ATC controller asked "are you going around," but the transmission trailed off as the main landing gear touched down. The flight landed, and the first officer applied normal thrust reversers. During rollout, the controller told Southwest 1648 "I told you to go around"; the captain responded they did not hear that and were only told not to overfly. The controller then directed them to contact ground control. The flight taxied to the gate uneventfully.
The first officer later listened to a publicly available recording and heard the controller issue a go-around, but the captain's transmission overlapped immediately after. Another recording captured only the captain's transmissions.
Personnel Information
Southwest Flight Crew
Documentation from Southwest Airlines indicated that since 2015, the pilots had flown together on 10 flights, including the incident flight. The most recent prior flight together was December 7, 2019. Since 2010, the captain had operated flights into SAN 88 times; the most recent prior to the incident was September 27, 2020. The first officer had operated into SAN 42 times, most recently May 15, 2021.
Captain
Age 56, held an Airline Transport Pilot (ATP) certificate with multiengine land, commercial single-engine land, and type ratings on B-737, CE-500, DC-9, HS-125, and LR-JET (DC-9 limitation: circling approach VMC only; CE-500 SIC required). Held flight instructor and mechanic certificates. FAA first-class medical dated February 23, 2021, with limitation "must wear corrective lenses" (wearing contacts at incident). Hire date with Southwest: May 10, 2000. Based at Dallas Love Field (DAL). Most recent training: January 2021 (B-737 Max return-to-service); prior recurrent training October 2020. Approximately 9,000 total hours as captain in B-737 series.
First Officer
Age 41, held ATP with multiengine land and commercial single-engine land, B-737 type rating. FAA first-class medical dated February 1, 2021, no limitations. Hire date: April 2, 2014. Based at DAL. After a 6-month voluntary leave, requalified on B-737 in March 2021 via a checkride, including ground school, maneuver observation, line observation, and AQP qualification.
Additional Information
Southwest Airlines Flight Safety Alert
On February 2, 2021, Southwest produced a Flight Safety Alert for SAN runway 27 approaches, noting potential for "unstable approaches" and "GPWS Terrain/Obstacle Warnings." Conditions that may result in unstabilized approaches included a steeper glidepath, a parking garage approximately 0.4 nautical miles from runway 27 threshold, and high gross weight with tailwinds requiring vertical speeds exceeding 1,000 feet per minute during final approach.
General Approach Policies
The Southwest Airlines B737NG Operating Manual (Section 11.1.3.1) provided guidance for following glidepath guidance on final, using electronic glideslope, RNAV glidepath, or visual glideslope. Pilots may fly slightly above the glidepath for wake turbulence avoidance during visual approaches. The Pilot Flying (PF) and Pilot Monitoring (PM) are to position hands and feet on controls prior to the final approach segment.
Go-Around/Missed Approach
Section 11.5.1 listed conditions requiring a go-around, including any flight deck crew member direction, ATC direction, unstabilized approach, loss of visual references, or inability to safely land in the touchdown zone. The manual stated that the Pilot Flying must execute a go-around immediately when called for.
Stabilized Approach Criteria
The Flight Operations Manual (July 23, 2020) defined criteria: by 1,000 feet above touchdown zone elevation (TDZE), the aircraft must be in landing configuration, within VTARGET speed range (VTARGET +10/-5 knots), on appropriate glidepath with normal descent rate (700-800 fpm, up to 1,000 fpm for normal maneuvering). By 500 feet above TDZE, wings essentially level on final approach course. If criteria not met, execute or direct a go-around.
Intended Touchdown Point
Flight Operations Bulletin 20-38 (December 28, 2020) advised planning to touch down between 1,000 and 1,500 feet from the landing threshold on centerline in the Touchdown Zone (TDZ). If touchdown occurs beyond 1,500 feet, the latest touchdown point is determined by the most restrictive of 1,500 feet plus PWB stopping margin, 3,000 feet, or one-third of usable landing length, and a go-around is required if past that point.
FAA Guidance
The FAA Aeronautical Information Manual (Chapter 4, Section 2) emphasized listening before transmitting, thinking before keying, and being alert to sounds or lack thereof to avoid unintentional transmitter operation.
Undetected Simultaneous Transmissions Phenomenon
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