Too close for comfort (Credit: Flight Aware)

DISCUSSION: On the evening of Friday, July 7,2017 at approximately 11:15 PM PDT, an Air Canada Airbus A320 operating as Air Canada flight 759 was preparing to land onto Runway 28R at San Francisco International Airport after a nearly five-and-a-half-hour flight from Toronto’s Pearson Airport. However, Flight 759 was instead lined up with taxiway C (Charlie). However, the taxiway had two United Airlines Boeing 787s, a Philippine Air Lines Airbus A340 and a United Boeing 737 on it all lined up for Runway 28R. The Air Canada Airbus A320 nearly missed the four waiting jets by about 60 feet above one of the 787s as it pulled up in time to circle around. This near-miss could have been possibly the worst air disaster in history as the total number of passengers in all the jets would be twice as many as those who died in the Tenerife Accident in 1977. This incident also comes two days after the fourth anniversary of the Asiana Airlines accident in San Francisco, coincidentally on the same runway, Runway 28R.

However, the weather played a role in preventing this near-miss into being a repeat of Tenerife. Prior to the incident, several of the local Bay Area airports were calling clear skies in the hourly METARs. Also, there was a steady west-northwest wind that was roughly 7 knots, according to the KSFO METAR nearest the time of the accident. Normally, during the summer, there would be a layer of stratus coming in about the time of the near-miss. However, this was not the case as there were clear skies due to a very strong ridge and mainly dry conditions aloft.  A stratus deck would have increased the likelihood of the crash as it would make it impossible for the pilots on Air Canada to have a visual of the runway lights or the approach lighting. Also, the air traffic controllers would not have been able to see the A320 and its approach. Wind was not an issue as it was oriented with Runway 28R in a way that crosswinds would be minimal which would not affect the direction of the plane.
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Therefore, in the end, weather may have been the reason that the worst aviation disaster in the United States and the world was averted. Moreover, the primary catalyst for this incident was quite plausibly due to pilot error as weather conditions was favorable and visibility affected.  You can read about more aviation and other applied meteorology topics here. 

© 2017 Meteorologist JP Kalb