BOEING 737-8H4 near San Diego, CA — 2021-06-11

Probable cause

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.

Contributing factors

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

NTSB narrative

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 go-around 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.

Analysis

Primary failure mode

Human factors

First missed decision gate

ATC should have ensured clear communication before clearing both flights.

NTSB coding

• Comm system malf/failure · Approach

Evidence available

• ATC audio
• ADS-B / radar
• 23 docket documents

Docket documents23

• AIR TRAFFIC CONTROL - ATTACHMENT 1 LOCAL CONTROL AUDIO RECORDINGatc
• AIR TRAFFIC CONTROL - ATTACHMENT 2 GROUND CONTROL AUDIO RECORDINGatc
• AIR TRAFFIC CONTROL - ATTACHMENT 3 CERTIFIED FAA RADAR DATAatc
• AIR TRAFFIC CONTROL ATTACHMENT 4 MANDATORY OCCURRENCE REPORTatc
• AIR TRAFFIC CONTROL ATTACHMENT 5- EVENT RESPONSE REPORTatc
• AIR TRAFFIC CONTROL ATTACHMENT 6A��SYSTEM SERVICE REVIEWatc
• AIR TRAFFIC CONTROL ATTACHMENT 7A��CORRECTIVE ACTION PLANatc
• AIR TRAFFIC CONTROL ATTACHMENT 8A��LIVEATC AUDIOatc
• AIR TRAFFIC CONTROL SPECIALIST REPORTatc
• ATTACHMENT 3 - SOUTHWEST INCIDENT FLIGHT DISPATCHER AND ATC SYSTEM MANAGER STATEMENTS [EXCERPT]atc
• PILOT/OPERATOR AIRCRAFT ACCIDENT REPORT, NTSB FORM 6120.1 - SOUTHWEST AIRLINESform
• STATEMENT OF PARTY REPRESENTATIVES TO NTSB INVESTIGATIONform
• ATTACHMENT 4 - SKYWEST CREW STATEMENTSinterview
• ATTACHMENT 10 - RISK ASSESSMENT OF THE UNDETECTED SIMULTANEOUS TRANSMISSIONS PHENOMENON - EUROCONTROLother
• ATTACHMENT 5 - SAN AIRPORT AND APPROACH CHARTS [EXCERPTS]other
• ATTACHMENT 6 - SOUTHWEST AIRLINES AIRCRAFT OPERATIONS MANUAL [EXCERPTS]other
• ATTACHMENT 7 - SOUTHWEST AIRLINES FLIGHT OPERATIONS BULLETIN 20-38other
• ATTACHMENT 8 - SOUTHWEST AIRLINES FLIGHT OPERATIONS MANUAL [EXCERPTS]other
• OPERATIONAL FACTORS - SPECIALIST REPORT - CORRECTEDreport
• OPERATIONAL FACTORS - SPECIALIST REPORT ERRATAreport
• ATTACHMENT 1 - FLIGHT CREW INTERVIEW TRANSCRIPTS AND STATEMENTStranscript
• ATTACHMENT 2 - DIRECTOR OF FLIGHT OPERATIONS INTERVIEW TRANSCRIPTStranscript
• ATTACHMENT 9 - SOUTHWEST AIRLINES FLIGHT RELEASE [EXCERPT]wreckage