In a report for View from the wingTravel expert Gary Leff has found that American Airlines, Delta and United are in danger of running out of flight numbers. They, too, have no solution to this problem. Each airline is given four-digit flight numbers (the numbers listed after the airline, such as AA0420 for the American Airlines flight from Dallas to Denver). The 9,999 number options (there is no flight zero) seems like a lot. It’s apparently not enough.
After a second-quarter earnings call, an American Airlines IT employee asked executives a pointed question: “We’re running out of flight numbers. Are we looking at 5-digit or some other solution?” The airline has about 6,700 flights a day but would like to number more than 9,999 flights due to codesharing with partner airlines, responded Brian Znotins, senior vice president of network planning at American Airlines.
Changing the numbering system to accommodate more flights on each airline is not as simple as adding another digit. It is reminiscent of the calendar change from 1999 to 2000. Computer systems were not designed to understand that “00” at the end of a year meant “2000” instead of “1900,” and healthcare, banking and many other services that ran on the still relatively new Internet collapsed.
That obviously didn’t happen. But that doesn’t mean harmless mix-ups don’t happen to this day. A woman born in 1922 has had repeated problems with airlines because the airlines issued her tickets for “infants” after reading only the last two digits, assuming she was born in 2022, not a century earlier. Air traffic control and other key agencies operate on systems that understand four digits, no more, no less. Needless to say, mixing up the complicated computer systems for detecting flight codes, introduced more than half a century ago, would cause serious problems.
“Technically, we’re working with systems that date back to the ’60s,” Znotins said on the quarterly earnings call. “We have two-digit airline codes and four-digit flight numbers. If you remember that, you can think of it as a millennium problem. It’s tremendously difficult to find ways to add another digit to that field, and it’s really only a problem for three airlines in the world. The rest of the airlines don’t have that problem.”
So far, airlines have implemented some workarounds, such as reusing a flight number for multiple flights where there can never be any overlap. American Airlines CEO Robert Isom added on the conference call: “We’re looking to get much bigger, so let’s write that out as a project over time.”
This is just another factor that airlines must grapple with in order to continue flying as safely as they have in recent years despite aging infrastructure. And I for one will never take these four numbers for granted again. 
