Not a week goes by that I don’t see “the” question in my Twitter feed. Rarely does a week pass without our customer relations team having to answer it either. “What does the U in RDU stand for?” It seems everyone is curious about the meaning of our code.

Most people assume that the R stands for Raleigh and the D for Durham. Then what about the U? Is it because it’s the second letter in Durham? That makes sense, but there are other theories too.

A long time ago there was an article in one of the local newspapers, my colleagues tell me, that asked if the U stood for United. As in Raleigh-Durham United, reflecting an increased partnership between the cities. No, we can safely say that isn’t so. There are those who think it has something to do with Umstead State Park, adjacent to the airport. No to that one as well.

So here’s our official answer, and, unfortunately, it’s not very dramatic. In the 1960’s the Federal Aviation Administration began assigning three-letter codes to commercial airports in the United States. For our airport, they picked RDU. That’s it. Whoever was assigned this task decided that RDU best fit Raleigh-Durham International Airport. If there was a specific reason behind it, we really just don’t know.

The three-letter airport codes are created by using combinations of letters representing the airfield, city or region’s name. Small, general aviation airports may have a combination of letters as well as numbers.

RDU falls right in line with the pattern for codes like SFO for San Francisco International Airport and GSP for Greenville-Spartanburg International Airport. Other airports that serve a single city may take the first three letters of that city, such as DAL for Dallas Love Field or HOU for Hobby Airport in Houston.

Then there are those that are puzzling. ORD refers to Chicago-O’Hare Airport. This was selected because at the time of the designation that airport was known as Orchard Field. Same with MCO for Orlando, as the airport stands on the site of the former McCoy Air Force Base.

And while RDU is fine to us, people occasionally write or e-mail asking us to change our code to RDI or RDA. Though RDI seems to be open for the moment, the fine folks at Rockhampton Downs Airport in Australia, might have an issue with someone else trying to be RDA.

So there you have it. You now know what RDU doesn’t stand for. And, you’ve got some knowledge on airport codes that could be helpful at the next trivia night.