Lacking both 'W' and 'N' Washington National has a code of DCA for District of Columbia Airport. The newer Dulles airport just outside D.C. was DIA (from Dulles International Airport); however, the DIA and DCA were easy to confuse, especially when hastily written in chalk on a baggage cart, scribbled on a tag or a handwritten air traffic control strip, so we are stuck with the backwards IAD. Now one of the rules of the game is "the first and second letters or second and third letters of an identifier may not be duplicated with less than 200 nautical miles separation."
Houston has HOU for the William B. Hobby airport. The 200 mile rule lead to the airport label of IAH, for the new Intercontinental Airport Houston. Louisville, Kentucky, already had an airport with the logical code of LOU; therefore, the letters for the new airport had to be something radically different: SDF stands for Standiford Field.
The airport ciphers sometimes don't originate with the city or airfield name but with the county in which it resides. Longview/Kilgore in Texas is GGG, from Gregg county airport. The 'W' in Detroit's DTW comes from Wayne county; the 'P' in Greenville's PGV comes from its location in Pitt County, North Carolina. However the John Wayne Airport serving Orange County takes its call letters from the less recognized Santa Ana (SNA).
A little more geography cracks the code for CVG, MDT and GTR. Cincinnati, Ohio, has its airport located in northern Kentucky (look at a map if you don't believe me!); therefore, Cincinnati's ID actually comes from the town of Covington - CVG. Harrisburg International is physically located in Middletown, Pennsylvania (MDT). Any Mississippi State Bulldogs' fan can tell you that Columbus, Starkville, and West Point form the Golden Triangle of Mississippi, with airline service at the Golden Triangle Regional Airport (GTR).
History, rather than geography, solves the puzzle of BNA, TYS, GEG, OGG and MCO. The main airport in Nashville, Tennessee, was named in honor of Col. Harry Berry who helped build it: BNA. Knoxville, also in Tennessee, doesn't have a single letter in common with its tag of TYS; however, a historian would know that the Tyson family donated the land in honor of their son killed in World War I. The current Orlando International Airport stands on the land that used to be McCoy Air Force Base (MCO). Spokane International Airport is coded as GEG in honor of Major Harold C. Geiger, a pioneer in Army aviation and ballooning. Geiger field was renamed in 1960 but the code was not changed. Kahului Airport, Maui, was designated as OGG in honor of aviation legend, and Lihue native, Capt. Bertram J. Hogg (pronounced Hoag).
One of the world's largest airports, JFK, is also one of the very few that changed call letters. A change is rare because an identifier becomes so well known to airline staff that changes are not normally permitted. Interestingly the John F. Kennedy airport's former code also came from the name of the field IDL for Idlewild airport. If you knew that Fort Myers used to be called SouthWest Florida Regional, the RSW moniker starts to make sense. A code used by American Airlines/American Eagle but never seen by the traveling public is GSW. Pilots spend months at GSW, but no planes land or take-off there. The mystery is solved when you discover that Americans' Flight Academy, with its many simulators and classrooms, is in Ft. Worth on the former site of the Greater SouthWest Airport.
Years ago, entire metropolitan areas were given a code to include many airports; NYC covered New York City and LON signified London. Unfortunately there are no new metropolitan area codes due to the scarcity of letters. These codes provide the ability to quickly look up in a computerized reservation system all the flights to a certain city without using separate codes for each airport. Entering WAS as a designation will give me the next few flights to BWI, IAD and DCAthe Washington, D.C. area. In fact, three letter codes are so scarce that after a year they can be recycled: when Idlewild Airport became JFK, the old IDL tag was retired then reused for Indianola, Mississippi.
Airlines use the three-letter codes internationally in their own network, Sita, for messages such as passenger loads and departure times. World ATC and weather agencies use a separate teleprinter network, the Aeronautical Fixed Telecommunications Network (AFTN), which uses a four-letter "location indicator." Going from large area to actual airport, the first letter relates to the part of the world and the second letter the country. The third letter is a group of airports within that country. Most countries who use this particular convention use a letter to denote the FIR in which the airport is located. So F is Frankfurt FIR in Germany, M is Munich; P is Paris FIR, M is Marseilles. Other ways to use the third letter include identifying a group of airports with a common factor. For example, A was used in Germany for all Canadian and American air force bases. The last letter positively identifies a specific airport.
Thus Aberdeen, Scotland, has the International Civil Aviation Organization (ICAO) location indicator of EGPDE for Northern Europe, G for United Kingdom, P for Scottish region, and D for Dyce field. Want to figure out LFPG? It's L for southern Europe, F for France, P for Paris FIR, and G for Charles de Gaulle airport. Easy! One more example is EDMM. E for northern Europe, D for Deutchland (Germany), M for Munchen (Munich) FIR, and M again for the Munich airport.
So if London Heathrow has two codes and it does, LHR and EGLL how come I've heard Chicago O'Hare only called ORD? The answer is unique to the United States. In the 48 contiguous States the ICAO code is formed simply by adding a "K" to the FAA code. This explains why international flight plans refer to KORD, KMIA, KJFK, etc. A meeting of two rules is Key West, the FAA code is EYW (lose the 'K') and the IATA code is KEYW (add a 'K') which works great for KEY West.
Other airports within FAA jurisdiction have ICAO codes usually formed by taking two letters from the FAA name and prefixing them with PA for Alaska, PH for Hawaii, or PG for Guam. PT appears to be Pacific Trust Territories (Pohnpei, Yap, Chuuk, etc.), and there are various random other P codes like PWAK for Wake Island.
Instrument pilots are familiar with another type of identifier, not for an airport or navigation aid but simply for a point in space. Every airway intersection is a five letter, supposedly pronounceable, combination, from AADCO to ZZARP. Just like airports, some fixes are named after towns: close to Raleigh, N.C., are DUHAM (over Durham) and CHAPL (over Chapel Hill) intersections. Some are named after people or events, and others are named just for fun: BORED, BUILT, BUTCH. The excellent book Chasing The Glory, by Michael Parfit, introduces us to the woman who names intersections, Macho Irene. She dreams of some pompous B-747 captain saying, "Roger, will report MUMMI."
From LA to DUHAM, identifiers have grown in complexity and are now used as computer codes in vast reservations systems and flight management computers. The latest trend in bag-tagging technology is laser printed bar codes for automated luggage systems. Will # ## # ## ever completely replace DFW? The answer may be found at DIA, the new Denver International Airport, which, when open, will inherit the familiar DEN code.
Oh, still wondering about the world's busiest airport, O'Hare International, and its ORD code? Well once upon a time, before the editor and publisher of the Chicago Tribune, Colonel Robert McCormick suggested a name change as tribute to pilot Lt. Cmdr. Edward "Butch" O'Hare, United States Navy, there was an airstrip well to the northwest of Chicago with a quaint, peaceful nameOrchard Field.
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