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Nearly 400 airport codes from around the United States. Text size is based on their number of enplanements.  Designed by <a href="https://shop.nomodesign.com/collections/airport-runway-series/products/us-primary-airport-code-map-screen-print" target="_blank">NOMO</a>
Nearly 400 airport codes from around the United States. Text size is based on their number of enplanements.  (Designed by NOMO)

Why the 'O' in San Francisco's Airport Code, SFO?

Why the 'O' in San Francisco's Airport Code, SFO?

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That short “poem” is not just a string of random words. They’re all airport codes. But how do airports get these codes? To some, certain codes don’t seem to have any rhyme or reason. Which brings us to a question from listener Ruth Suter, who flies in and out of the Bay Area a lot.

“Why is the San Francisco airport called SFO?”

The SF seems obvious, but where did the O come from? Does it have to do with Oakland? We talked to John Hill at the SFO Museum.

Why the 'O' in San Francisco&rsquo;s airport code, SFO?

Why the 'O' in San Francisco’s airport code, SFO?

“It’s an interesting story, and it came from the three-letter code distinctions that were established by the International Air Transport Association. Also called IATA. That group was formed in 1945,” Hill says.

Before IATA, most airports were identified by the two letters used by the National Weather Service codes. It usually made sense. Los Angeles was LA, Phoenix was PH, San Francisco was SF.

“But as aviation quickly advanced, and more airports were established, two-letter codes sort of ran out of steam,” Hill says.

To have more options, IATA required airports to have three letters instead of two, increasing the possible combinations from 650 to 15,600.

“The only real requirement was that no two codes were the same. So as long as everybody had a distinct three-letter code, the system would work,” Hill says.

There was no universal naming convention, though there are some patterns.

A few airports just added an X to the end of their two-letter codes. Like Portland (PDX) and Los Angeles (LAX).

Other airports decided to use the first three letters of the city’s name, like OAK in Oakland.

Then there were airports that took the acronyms of their namesakes, like JFK for New York’s John F. Kennedy International Airport.

Other codes are inspired by places that are no longer there, or names that are no longer used. Chicago’s O’Hare airport (ORD) was once known as Orchard Field Airport, named after a small town that was once nearby, Orchard Place. In New Orleans, MSY got its name from the Moisant Stock Yards.

Then there are the codes that seemingly make no sense at all, like EWR for Newark Liberty International Airport. It’s like that because in the United States, codes starting with N can only be used by the Navy.

But what about Ruth’s airport? SFO? Turns out it has nothing to do with Oakland.

“You know, Oakland’s Airport started virtually the same time that San Francisco’s did. So it would have been confusing to put those together, and I think Oakland tried to get its own three-letter code from the same time frame as SFO,” Hill says.

“With S.F. they simply took an O, which we can assume was convenient to the fact that San Francisco has an O at the end of it,” says Hill.

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