WN1648 - Incident: Southwest B738 and Skywest E175 at San Diego on Jun 10th 2021

A Southwest Airlines Boeing 737-800, registration N8674B performing flight WN-1648 from Phoenix,AZ to San Diego,CA (USA), was on final approach to San Diego's runway 27 when tower cleared the aircraft to land.

A Skywest Embraer ERJ-175 on behalf of Alaska Airlines, registration N197SY performing flight AS-3371 from San Diego,CA to San Francisco,CA (USA) with 73 passengers and 4 crew, was taxiing for departure from runway 27. A short time after WN-1648 had been cleared to land, tower instructed the Embraer to line up runway 27 and wait. The Embraer lined up runway 27 and immediately vacated the runway again via taxiway C2 to the right (about 60 meters/200 feet down the runway). The aircraft taxied to the hold short line C1.

The Boeing continued the final approach for a safe landing.

The Embraer departed about 8 minutes later.

The NTSB reported: "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 3307 to line up and wait on the same runway." (editorial note: Flight SKW3307 is in error, it does not operate to or from San Diego). The occurrence was rated an incident and is being investigated by the NTSB.

On Sep 8th 2023 the NTSB released their final report concluding the probable cause of the incident was:

The blocked go-around radio instruction from the air traffic control tower to the arrival aircraft which resulted in the arrival aircraft continuing the landing approach. This led to a loss of separation between the landing aircraft and the aircraft awaiting departure on the runway.

Contributing to the loss of separation was the controller’s distraction communicating with a helicopter transitioning the airspace.

The NTSB analysed:

On June 10, 2021, about 1745 Pacific Daylight Time (PDT) a runway incursion occurred at the San Diego international airport when a SkyWest flight was positioned on Runway 27 for takeoff at the same time a Southwest flight was cleared to land on the same runway.

The SkyWest flight was instructed to Line Up and Wait (LUAW) on Runway 27.

According to FAA recordings, the Southwest flight was instructed to go around on an approximate 0.84-mile final (about 1.2 miles from the runway 27 displaced threshold); however, the transmission was blocked and the instruction was not heard by the crew. The air traffic control tower controller instructed the SkyWest flight to exit the runway at taxiway C2 about 11 seconds prior to instructing the Southwest flight to go around and to not overfly the SkyWest airplane. The Southwest flight maneuvered around the SkyWest flight exiting the runway and subsequently landed on Runway 27. The closest proximity was 0.18 miles laterally and 200 feet vertically.

A review of the FAA audio recordings indicated that the tower controller informed the Southwest flight that there would be traffic holding in position for takeoff on the runway following a preceding arrival aircraft. The controller then issued instructions to other uninvolved aircraft, including a helicopter that was transitioning the airspace. Just after the controller issued instructions for the SkyWest flight to exit the runway, and when the Southwest flight was on an approximate 1.2-mile final, the ASDE-X provided a mandatory goaround alert, and the controller issued go-around instructions to Southwest. The Southwest flight subsequently maneuvered and offset to the left of Runway 27, and then back to the right, and the aircraft aligned with and landed on Runway 27. The SkyWest crew did not hear the air traffic controller’s transmission to the Southwest flight to go around. The SkyWest crew reported they did hear the Southwest flightcrew’s query about the airplane on the runway.

According to the FAA, the tower controller was communicating with a helicopter transitioning the airspace after they had instructed SkyWest to LUAW. This additional communication likely distracted the controller from monitoring the position of the SkyWest and Southwest airplanes.

Although the FAA reported that tower communication was working normally at the time of the event, they were requested to conduct testing on the strength of the radio signal from the tower cab at various distances away from the airport. However, there was no indication that the FAA was able to conduct such testing and therefore it could not be conclusively determined if the control tower’s frequency strength was adequate to overpower an airborne aircraft’s transmission for other aircraft operating on the airport. Therefore, it is likely that the air traffic controller and the Southwest flightcrew’s simultaneous transmissions canceled each other with no indication to the controller, the arriving aircraft, nor any other aircraft on the frequency.

Related Flight: WN1648, Twitter: #WN1648, Southwest Airlines News