Over Memorial Day weekend, American filed its “overlay” for post-Labor Day travel through September. This is the schedule the airline intends to fly, fixing the existing placeholder schedule which had been in place in some form since those travel dates went on sale, about 11 months prior to travel. There wasn’t anything particularly note-worthy about this schedule, but it seemed like a great opportunity for me to look at exactly how this process has changed in recent times. After all, schedule changes have become more complex thanks to last year’s Department of Transportation (DOT) rules which trigger the option of a refund if there is even something as small as a flight number change.
Here’s a look at a snapshot I took from Cranky Network Weekly right after the Memorial Day weekend filing.
These are daily departures with gray being existing and blue being the change this week. As you can see, there were some tweaks in August, but the real change was post Labor Day into early Oct where the day-of-week variation became much more apparent. (It’s very similar to what the airline flew last year.)
If you were booked to travel during that time, you probably got a schedule change notification that week telling you something had changed. That didn’t mean it was a big change, but it was something. And even the smallest change has to be notified.
On a high level, here’s what happened on a random peak day (Monday, September 22, 2025) for American’s mainline and regional operations:
Data via Cirium
Of the 6,500 flights that were filed to operate that day, only 481 (7.4 percent) saw no change at all. A lot of these are long-haul routes that change less frequently than domestic hops anyway.
The bulk of the changes involved the flight number staying the same but the time changed. This could have been a one-minute change or a 10-hour change, as long as the flight number stayed the same. There were 4,664 flights (71.7 percent) that saw this kind of movement.
Another 959 (14.7 percent) actually had a flight number change. In other words, that flight number no longer existed on the route it was previously on and something else took its place.
Then finally, we had 396 flight numbers (6.1 percent) that were just removed from the schedule. The total number of departures for mainline and regional flights after this change dropped to 6,104.
Geographically, this was pretty widespread, but it stayed close to the US. Here’s a look at the routes that saw flight numbers change or disappear.
American Flight Number Change Map generated by the Great Circle Mapper – copyright © Karl L. Swartz.
This is a lot, but it’s just the tip of the iceberg. See, this doesn’t even take into account codeshares. I don’t want to get into that in too much detail, but let me give you a sense of magnitude. The airlines have access to 9,999 flight numbers. Why not more? Because the systems were designed to support no more than 4 digits a very long time ago. Eventually, presumably, systems could be updated but it would be a painful and herculean task which nobody has wanted to take on yet.
Here is a visual look at how American breaks down its flight number ranges:
It is split roughly a third with mainline flying, a third with regionals, and a third with codeshares. The various ranges are assigned to the different operating airlines, but sometimes those ranges are no larger than 10 different numbers for smaller partners.
At the very end, there are a few hundred that aren’t assigned. I put a question mark, because this is potpourri. It could be charters or maintenance ferry flights… anything that doesn’t fit into regular schedule operations falls into that bucket. So when you hear of big airlines saying they are running out of flight numbers, they aren’t making that up.
In the long run, I understand that the International Air Transport Association (IATA) is working toward an enhanced interline solution so that airlines wouldn’t need to bother with codeshares. There’s a lot to be figured out before that happens, so for now, the airlines will have to work within these constrained ranges.
That is not easy, and the government just made it a lot harder last year when it required airlines to provide refunds without question if there was a flight number change. Even if the flight times and airplane stayed exactly the same, this would trigger a free, full refund. I won’t bother explaining how stupid this is, but suffice it to say that it makes airlines want to reduce the frequency of flight number changes when they can.
In American’s case, it has been pretty successful, apparently cutting flight number changes by about 50 percent. There were two main changes here that helped make that possible.
First, American worked on figuring out how to start with a better schedule. It now is more deliberate about its placeholder schedules, taking more accurate versions of schedules from the prior year in the same season and then applying them. This means fewer changes will need to happen during the overlay process about 100 days or so before travel.
On top of that, American has been using technology. It used to be that flight numbering was a pretty manual process. Maybe there was a flight number conflict or perhaps there was a through flight (single flight number on multiple flights) that needed to change. The team would then manually go look for a solution. Now just imagine how complex this can get, especially in the regional world.
Regional airlines fly airplanes under the mainline carrier’s brand, but when it comes to air traffic control, they are flying under their own callsign. So, there’s SkyWest flying for four different airlines. Let’s say American assigns a flight 5435 to a SkyWest flight at 3pm. If Delta already has a flight 5435 at that time operated by SkyWest, it will need to change. This thought just gives me a headache.
Now, technology can solve much of this. If there are conflicts, the tech American uses will automatically re-number. It also tries to keep flight numbers within certain time bands, working to keep it attached to the same bank in each hub even if the times shift. That way there will be fewer flight number changes for travelers.
The only hiccup here is that a flight number has to change if the operating airline does. Since each operating airline has a fixed range, if SkyWest was going to operate a flight but now it’s Envoy, there is no way around the need to change that number.
This is a technology that American has used for some time, but it didn’t use it consistently. For example, it used to manually do holiday flight numbering or non-standard days. Now it just feeds the tech and lets it do its magic.
Schedule changes are complicated, and nobody likes them, but they are inevitable. I don’t think most people care what their flight number is, but there’s better chance that they’ll keep it now.
