No airport, no matter where, can use another’s code.

Dear Mr. Alice: My friend James and I have discussed the possibilities and can reach no logical conclusion. We simply wish to know the meaning of X as it is used in LAX or for that matter the meaning of O in SFO. What are these airports doing with Os and Xs.? The personnel at the airports don’t know either. I’ve asked. — Michelle Priestly, San Diego

The possibilities are dizzying. Maybe Fogtown’s is “San Francisco? Outrageous!” or “San Francisco? Ooooo, baby!” Perhaps Smogtopia’s airport is commemorative, named for L.A. and Malcolm X. Or some visitor’s assessment of the place, “L.A. Ick(s)!” I’ve always believed Chicago-O’Hare was abbreviated ORD because it’s such an ordeal to change planes there.

But junk the logic; the feds are in charge of the system. When air travel began in the 1920s, airports used the two-letter code of the local weather station, which often was an abbreviation for the city name. When that system was overwhelmed in the late ’30s, the FAA went to three letters, and some of the old two-letter airports were given one more (arbitrary) letter. Case in point, LAX. The X has stood for nothing for nearly 60 years.

If somebody gave you a ticket for BOS or DEN, PIT, BUF, ATL, CLE, or SEA, you’d probably be able to figure your destination. But if a city’s first three letters weren’t available for some reason, the FAA sometimes did the next best thing — initials or pieces of the city’s or airport’s name: DFW, PHX, JFK, and SFO. So think of SFO as “San FranciscO.” But suppose you’re jetting off for a passionate weekend at EPCOT, and the clerk tags your bags MCO. Afraid you’re heading for Orlando, but your edible underwear will languish in Macon? Macao? McMurdo Sound? Naw. Orlando International Airport’s identifier has been MCO since the days when the field was McCoy Air Force Base. Many codes belong in that category, which we might call “The Airport Formerly Known As....” There’s Nashville, BNA (Barry Field); Knoxville, TYS (Tyson Field); Spokane, GEG (Geiger Army Air Field); and the arduous ORD, originally Douglas (Aircraft) Field, then Orchard Field, and eventually O’Hare.

At some point, the U.S. Navy appropriated all unused airport codes that begin with N, which explains the civilian ports of EWR (Newark); IAG (Niagara Falls); and the fiddling with Nashville as well. The FCC needed the unused Ks, Ws, Xs, and Qs, leaving us with EYW (Key West) and the letter swap in MKC (Kansas City, MO).

With no Ws and Ns available, Washington, D.C.’s National Airport became DCA. But soon DCA-bound luggage (and the occasional muddled pilot) were misrouted to nearby DIA (Dulles International Airport), so the FAA changed Dulles to IAD and made a rule that no airports within 200 miles of one another could have such easily confused identifiers.

So you’d figure by now they’d have all the bugs worked out of the system. And they pretty much do, except that the assignments are now coordinated globally by the International Air Transport Association, based in Canada, which also coordinates airline code letters and other air-traffic-related identifiers. No airport, no matter where, can use another’s code, they say, though the IATA is just a trade association of member airlines and not a lawmaking body. The edict makes sense when you’re dealing with big airports, but there are limits. When Baltimore-Washington International Airport opened in Maryland, Baltimore and state legislators wanted to swap the old BAL code for BWI, to remind folks that they, too, served the lucrative District of Columbia market. After some political maneuverings, the FAA unilaterally okayed the switch. When the IATA heard about the change, they harrumphed that the hamlet of Bewani, Papua New Guinea, was served twice a week by air service, and Bewani already claimed BWI. Everyone else was unimpressed, figuring there was little risk of confusion.

So, armed with more airport identifier information than you ever wanted, can you figure the names of these local stops? I’ll get you started. SAN is Lindbergh Field. What’s MYF, NZY, CRQ, SDM? And if your bags are marked FAT or YUM, are you off to Hershey, PA?

And here are the answers to the “Can I Get a Cab Home from CRQ?” quiz. Get ’em all right and we’ll award you our usual stunning prize, a year’s worth of free Readers. They’re Montgomery Field, North Island Naval Air Station, McClellan Palomar Airport (Carlsbad), and Brown Field (oiice San Diego Municipal). FAT condemns you to a flight to Fresno; YUM is a weekend in Yuma.