Cracking the Code: Breaking Down Flight Numbers
A flight number is an alpha-numeric protocol for identifying specific airline routes. The official term, as defined in the Standard Schedules Information Manual, or SSIM, is flight code or flight designator.
The International Air Transport Association, a trade organization that helps to regulate and support the airline industry, issues the letter-based code that represents the airline, which usually consists of two or three letters. These specify the airline.
The numbers that follow differentiate the routes. But assigning a flight code isn’t done in the same way as allocating a phone number. The numbers can represent different types of flights.
Most flights have a fixed route that goes between points A and B. Your flight number usually changes during a layover, however. That’s because you’re likely switching to a different carrier or different route. Although some flight codes are used for routes with three legs, not all of the passengers will continue to the third destination. If your next flight is with a different carrier, the airline code will change as well.
Air traffic control uses flight numbers to keep track of the paths of aircraft. Unique identifiers for the flight provide a way to organize, regulate and monitor air traffic flow.
Flight Number Conventions and Standards
Many airlines follow the same standards. However, there is some variation among carriers.
For example, many airlines use even numbers to indicate northbound and eastbound flights. Odd numbers are reserved for southbound and westbound flights. However, an airline may assign an odd number to an outbound flight and the next consecutive even number to its corresponding inbound flight.
Lower flight numbers are typically given to prominent routes. Long, popular and high-revenue routes often have low flight numbers, such as Delta’s DL1 flight, which provides service between New York’s JFK and London’s Heathrow airport, which was Delta’s first international destination. Because these flight numbers are low, they usually have fewer than three digits, although some are in a multi-digit format that starts with 0, such as 01 or 001.
Regional affiliate flights are often designated with a four-digit number between 3000 and 5999. Flight numbers greater than 6000 are typically codeshare flights. These are operated by partner airlines, which sell seats for the operating carrier to allow passengers to visit multiple destinations on a single itinerary.
When your boarding pass reads, “Operated by British Airways” beneath the American Airlines flight code, this indicates that it’s a codeshare flight. British Airways is the operating carrier—the company flying the plane. American Airlines is the marketing carrier.
Sometimes, an empty aircraft must be moved to a different location. These ferry flights, or empty leg flights, are identified with numbers between 8000 and 9000.
How Does Your Favorite Airline Use Flight Numbers?
American Airlines uses the same numbers for inbound and outbound flights on the same route. This may be confusing for some travelers because it requires them to make sure that they’re looking at the correct departure and arrival airports when they’re trying to identify the flight. However, it makes sense from an air traffic control standpoint because both flights can’t be airborne simultaneously.
When Southwest Airlines launched, the airline code SW was already taken by Air Namibia, which was originally called South West Air Transport. Southwest Airlines adopted the identifier WN. There are many theories about what WN stands for. Some say that one of Southwest’s executives was a Willie Nelson fan. Others wonder whether WN stands for “Why not” or “We’re nuts.”
United Airlines gives a nod to the Indy 500 with flight UA500, which flies between Indianapolis and San Francisco. Alaska Airlines identifies its Seattle-Pittsburgh flight with 412, Pittsburgh’s area code. Jet Blue, Spirit Airlines and Frontier Airlines run lucky flights with number 777, which land in Las Vegas.