On July 7, 2017, an Airbus A320-211 operating as Air Canada Flight 759 was nearly involved in an accident at San Francisco International Airport in San Mateo County, California, United States. The flight, which originated at Toronto Pearson International Airport, had been cleared by air traffic control to land on runway 28R and was on final approach to land on that runway; however, instead of lining up with the runway, the aircraft had lined up with the parallel taxiway, on which four fully loaded and fueled passenger airplanes were stopped awaiting takeoff clearance. The flight crew initiated a go-around prior to landing, after which it landed on 28R without further incident. The aircraft on the taxiway departed for their intended destinations without further incident.^[1][2][3][4] The subsequent investigation by the National Transportation Safety Board (NTSB) determined that the Air Canada airplane descended to 59 feet (18 m) above the ground before it began its climb, and that it missed colliding with one of the aircraft on the taxiway by 14 feet (4.3 m).

The NTSB determined the probable cause was the Air Canada flight crew's confusion of the runway with the parallel taxiway, with contributing causes including the crew's failure to use the instrument landing system (ILS), as well as pilot fatigue. A retired pilot stated the runway confusion that almost happened "probably came close to the greatest aviation disaster in history"^[2][3][4][5] as five airplanes and potentially over 1,000 passengers were at imminent risk of a disaster greater than the Tenerife airport disaster.

At 11:46 p.m. local time, Air Canada Flight 759, carrying 135 passengers and 5 crew members,^[4] was cleared to land on Runway 28R. The adjacent Runway 28L had been closed at 10 p.m. local time and its lights were off,^[6] except for a 20.5-foot-wide (6.2 m) lighted flashing "X" at the eastern runway threshold.^[7] The captain was flying the aircraft and the first officer was monitoring.^[7] The two pilots of AC759 acknowledged that they mistook runway 28R for 28L and therefore lined up for landing on the parallel taxiway C,^[2][7][8][9] even though runways and taxiways are lit with different colors and intensities.^[6] Preliminary post-event investigation results noted that Runway 28R and Taxiway C were lit on default settings (in different colors), and the automatic terminal information service broadcast information was current and advised that 28L was closed and unlit.^[7] According to preliminary Transportation Board investigation results, as the weather was clear, the pilots of AC759 were not required to utilize the instrument landing system and relied instead on a visual approach, as typical for the prevailing conditions.^[10]

Taxiway C contained four airplanes, three from United Airlines and one from Philippine Airlines, queueing for takeoff.^[1] At 11:55:46 p.m. local time, upon spotting aircraft lights approximately 0.7 miles (1.1 km) from the runway, the AC759 pilot asked the tower if he was clear to land on 28R, to which the air traffic controller responded at 11:55:56 p.m., "There's no one on 28R but you,"^[1][3][11] when AC759 was approximately 0.3 miles (500 m) from the runway threshold.^[12] The AC759 pilots "did not recall seeing aircraft on Taxiway C, but something did not look right to them" according to a post-incident interview summary.^[7] The crew of Philippine Airlines 115 (PR115) turned on their landing lights to alert AC759 they were lined up on the taxiway.^[13][12] The pilot of United Airlines 1 (UA001), the first in line for takeoff, interrupted the radio traffic at 11:56:01 p.m. and asked "Where is this guy going? He's on the taxiway."^[1][3] The air traffic controller then ordered AC759 to abort the landing at 11:56:10 p.m. After AC759 acknowledged the go-around, the air traffic controller stated, "It looks like you were lined up for Charlie [Taxiway C] there."^[1][3] AC759 had already started to climb before the go-around order.^[12]

Afterwards, the pilot of UA001 radioed the tower saying, "Air Canada flew directly over us," and the air traffic controller responded, "Yeah, I saw that, guys."^[1] During the first approach, AC759 flew for 1⁄4 mile (400 m) over Taxiway C, descended to an altitude as low as 81 feet (25 m) and approached as close as 29 feet (8.8 m) laterally to the four airplanes waiting on Taxiway C before being ordered to abort the landing.^[11][14][15] According to the flight data recorder, the pilots advanced the thrust levers when the airplane was 85 feet (26 m) above the ground. The airplane descended as low as 59 feet (18 m), approximately 2.5 seconds after the thrust levers had been advanced.^[7] Following a reconstruction of events, one pilot not involved in the incident noted that had the crew waited five more seconds before pulling up, it would have collided with the third airplane (UAL 863) on the taxiway.^[15] There was also less than 10 to 20 feet (3 to 6 m) separation between the bottom of the Air Canada aircraft and the tail of the Philippine Airlines A340.^[16]

SFO was the first airport in the United States to install an Airport Surface Surveillance Capability (ASSC) system,^[17] which should have alerted the tower of a potential conflict between runway and taxiway movements.^[10] AC759 disappeared from the local controller's ASSC display for twelve seconds, between 11:55:52 and 11:56:04 p.m. local time (from shortly after the AC759 pilot asked for confirmation that 28R was clear, to the time the UA001 pilot noted that AC759 was lined up for Taxiway C), as AC759 was too far off-course from 28R.^[12]

AC759 completed its go-around and landed without incident after the second approach.^[1] A single air traffic controller was monitoring ground and tower frequencies, which would typically be handled by two controllers.^[10][12]

The aircraft flying AC759 that night was C-FKCK, an Airbus A320-200.^[11][18] The aircraft was 24.5 years old on the day of the incident, first flying in December 1992.^[19]

The incident was not considered reportable under then-current federal regulations,^[21] but former NTSB chairman Jim Hall called it "the most significant near-miss we've had in this decade" and urged the NTSB to re-evaluate those reporting requirements.^[22] The United States National Transportation Safety Board (NTSB) was informed of the incident on July 9, and took the lead on the investigation, with assistance from the Federal Aviation Administration (FAA). The Transportation Safety Board of Canada (TSB) served as a facilitator to convey information between Air Canada and the NTSB.^[4] TSB released preliminary information from Occurrence No. A17F0159 on July 11, 2017.^[11][18] NTSB assigned identification number DCA17IA148 to the incident.^[23]

A retired pilot stated that SFO requires "precision flying" as the two runways (28R and 28L) are laterally separated by 750 feet (230 m), and Taxiway C is separated from 28R by less than 500 feet (150 m).^[24] Other pilots pointed out that some airlines require all aircraft to use the instrument landing system (ILS) regardless of weather or visibility, which would have led the crew to realize that they were not lined up with runway 28R.^[2] Dave Jones, then California Insurance Commissioner and a passenger on AC759, wrote a letter to Air Canada a week after the incident requesting their cooperation with the investigation.^[6][15]

Preliminary NTSB investigation results from flight data recorder telemetry, released on August 2, 2017, indicate that AC759 reached a minimum altitude of 59 feet (18 m) above ground level, comparable to the 55 ft 10 in (17.02 m) tail height of a Boeing 787-9, two of which were on Taxiway C.^[7][25] The cockpit voice recorder had been overwritten before the investigation was launched,^[12] as C-FKCK flew three more flights on July 8 before the NTSB was informed of the near-miss on July 9.^[22]

Following the incident, in early August the Federal Aviation Administration modified nighttime landing procedures at SFO, forbidding visual approaches at night "when an adjacent parallel runway is closed" and replacing them with instrument approaches, either ILS or satellite-based, and requiring two air traffic controllers in the control tower "until the late-night arrival rush is over".^[32]

As of December 2023, Air Canada no longer uses flight number 759 on its Toronto to San Francisco routes, instead using four different flight numbers. Flight number AC737 is used for the morning flight, flight numbers AC741 and AC743 are used for the afternoon flights, and the flight number AC745 is used for the evenings. Additionally, Air Canada only uses the Airbus A320 on the morning flights, while the two afternoon flights uses the Boeing 737 MAX and the evening flight uses the Airbus A220 instead.^{[33][34][35][36]}

• Accidents and incidents involving the Airbus A320 family
• Tenerife airport disaster