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.
23 comments on “The Times They Are a Changin’: Anatomy of a Schedule Change”
Thanks for the lesson on the “back end” of how commercial airline operations work.
Some people love reading trip reports, but for me, these are my favorite types of posts.
Thanks Cranky!
CF,
Great article. A couple of questions:
1. Do smaller carriers i.e., Sun Country, Frontier, etc have roughly the same scheduling process?
2. Would using AI help in this process?
3. Would the IATA look at using hexadecimal for flight numbers?
Angry Bob –
1) To varying degrees. Most airlines that sell 330 days out on a rolling basis have a process like this. But airlines like Southwest which have a hard end of schedule that gets extended every few months tend to be different. Those initial rollouts are more thoughtful and fewer changes are needed later on.
2) Sure. Or not. Who knows?
3) I have no idea what they’d look at, but anything would be a big and expensive change.
Doesn’t the Southwest “hard end” and traditional short selling window (which, to be fair, has gotten longer in the last couple of years) result from it’s inability to auto-reaccom? Someone in WN Network Planning told me once that every time they did a schedule change – until a couple years ago – they had to have reservations manually rebook anyone impacted. I know they have an auto-reaccom now and when they started using it, it didn’t work very precisely (like for one ticket I had, a MDW-MCI flight moved by 30 minutes, so they rebooked my CLT-MDW-MCI trip to CLT-BWI-MCI with an 8 hour connection, when there was a similarly timed connection via DAL that basically matched my original journey time, and another where I had a PHX-ABQ that changed later by 45 minutes and they rebooked me from a 60 minute connection in PHX to leaving my origin 9 hours earlier, when there were multiple ONT-PHX flights in between).
They’ve improved to be sure, but perhaps still taking baby steps due to system limits on other tools like aircraft routing or contract limitations?
NedsKid – That limitation ended years ago when they switched to the Amadeus Altea reservation system. But it’s true that before that they had to manually reaccomm any changes. I don’t know exactly why the decision was made to roll out in chunks like this, but it is far more customer friendly. Generally when you roll it out, you’ve been able to put together a nearly accurate schedule. There will be tweaks much more these days than there used to be, but the schedule remains largely intact. When you go so far out on a rolling schedule, you can’t do that as easily. Still, was that the reason for doing this? Who knows. My guess is it was just easier to deal with.
How crucial is it, nowadays, for airlines to continue their practice of assigning different number ranges for specific purposes? It was an obvious solution when numbers were largely assigned by hand. But if the process is largely computerized, I could imagine just throwing the whole 1-9999 range open to all types of flights, which would push back the “running out of numbers” issue.
Obviously a human would no longer be able to look at “3410” and conclude “Regional on Envoy!” But I have no idea whether this would be a practical problem or just a culture change.
grichard – I think it’s still important that they do it this way, but I can’t remember the exact reason. I know, that’s totally unhelpful, sorry.
Yes you do, it is another control to apply to corporate deal eligibility and therefore must be specified in contracts, not to mention the additional controls of listing flight application eligibility. Revenue accounting / settlement agreements for interline based on flight number. Keeping up with all the business impacts of flight number movement within a range for a codeshare partner or capacity purchase provider is easy with defined ranges. If they could use any number anywhere for any partner the impacted business processes would be extensive.
Sorry to be a broken record here but airlines were abusing the flight number change loophole (one AAirline in particular, in my experience) to gouge extra seat selection revenue. It was ripe for a regulatory fix, and it was their own fault.
Changing the flight number cleared the seat map even if the equipment & times didn’t change. My experience on several AA flights circa 2021-2022 was that a flight number change meant I had to make my main cabin seat selections again, but on the “new” flight the exact same seats I had previously selected for free (and pretty much all other desirable seats) were now “preferred” seats and required an up-charge to select again.
Felt very exploitative when your family of 4 has free seats selected but suddenly has to pay $250 to keep them or sit anywhere that isn’t back-middle on a 10 hour flight to Hawaii. I’m glad there’s a regulation to fix it, and clearly I haven’t forgotten the bAAd taste it left in my mouth. Flying United more these days…
Agreed. I had a similar experience. I booked 2 seats months ago when I had a higher status. Then AA made a change that required me to go back and select my seats again, but now my status had gone down! The exact same seats were available but if I wanted them I would have to pay additional! Not exactly “customer friendly”!
The DOT rule also discourages flight number changes for the purpose of burying bad on-time performance for a given flight. With a new flight number, a message such as “There is no recent record of delay and cancellation percentages for this flight” appears on the carrier’s website when a flight’s “On-Time Performance” (or similar) is clicked . . . instead of, say, a disclosure that the flight at that time of day is late 50% of the time. So, by giving passengers the option of a full refund for a mere flight number change, DOT is discouraging such chicanery.
I’m old. And my dad worked for Delta. I remember how, (mumbly-mumble) years ago when there were spinny-things at the front of the engines, DL’s flight numbers told you the equipment being used.
A number starting with “4” was a Convair 440; “6” was a DC-6; “7” was a DC-7. As jets came aboard, “8” was a Convair 880 and “9” was a DC-9. All three digits, of course, because there weren’t that many flights or integrated regional carrier operations.
Ozark used to do the same thing. 700/800 were FH-227Bs and 500/900 were DC-9s.
while you didn’t specifically note the change in ASMs, the reduction in number of flight numbers post Labor Day indicates that AAL is going through w/ capacity reductions that the industry was expecting.
Any early read on AA’s planned capacity changes post Labor Day as well as those of other carriers, Cranky?
I thought he said it was similar to last year’s schedule?
Incorrect. The process always includes these reductions. The placeholder schedule rarely has significant day-of-week variation. That gets threaded in later as we see here. This has nothing to do with larger macroeconomic concerns. Those cuts tend to happen at a different time, if they’re going to happen. AA ASMs are up 2.2% in Sep YoY.
thank you for this, CF.
“AA ASMs are up 2.2% in Sep YoY”
The part that I am trying to reconcile is:
“The total number of departures for mainline and regional flights after this change dropped (from 6,500 flights that were filed) to 6,104.”
so what drove the reduction in the number of AA/AA regional flights?
Is this happening this year but hasn’t happened in the past?
Is AA being more conservative in publishing long-range schedules that end up having to be pulled down?
thanks for breaking it down.
I read somewhere that AA may be pushing against some scope limits. That would explain it, but I can’t really reconcile it into evidence.
Tim – I’m not sure what you aren’t understanding. This is a normal process that happens every single month. The placeholder schedule is given an overlay that adjusts it to what it wants to fly. You seem to be looking for some smoking gun on American’s view of capacity that does not exist. This is entirely normal and you can see it in the chart at the top of the post.
This fascinated me when my dad would bring home a “sky guide” with all the schedules & hub cities. Would read it to figure out the patterns of codes/ flight numbers etc. As a rule, a flight number that started at 3000 was a regional & those over6000 were codeshares depending on the carrier.
International flights are interesting in that3-digit numbers are always in use such as BA 001 instead of 1. From what I remember, it is a global standard.
Delta hit a milestone last year or year before where for the first time they had mainline flight numbers in the 3000 range. It was kind of a big deal as internally a lot of documents had to change, some system corrections, etc. I’ve noticed mostly they are short haul 717/737 flights.
Thank you for this Cranky! Very interesting especially the flight number part. Weren’t things easier once upon a time when each regional/mainline relationship just had a block of flight numbers? I guess we first saw recycling of flight numbers on round trips like HUB-OUT-HUB as first iteration of running low on numbers. And now I read somewhere (maybe here?) that any UA/B6 further codeshare is limited by UA not having enough available flight numbers.
I think the 5 digit flight number will be the Y2K of airline planning. Buy your cans of beans now!
I dread AA schedule changes as they tend to foul up interlines and codeshares something awful. Even just straight AA itineraries will go into a no-mans land of “a schedule change is in progress” where you can’t rebook or fix it until they are completely done. I have some upcoming trips where I’ve purchased with segments on interline partners (like Contour – so that if one leg is late I don’t have everyone throw their hands up… now they just point fingers at each other as to who has to fix it) where when the AA flight changes any time (even with a legal connection like 92 changing to 91 minutes at DEN) the AA segment cancels and refunds back to Contour. The Contour segment is there… then they reinstate the AA segment but the fare changed and it shows a balance due, which cancels the whole thing again. It’s obnoxious. I’m guessing an issue on the Contour/Crane side of things?
I had an issue this week with an Alaska/AA itinerary… booked with Alaska miles on AA and the AA schedule change somehow canceled the segment, which thankfully Alaska was able to fix through escalation as the new mileage amount was 10k higher. I will say it’s so pleasant dealing with Alaska… especially as a MVP75k but even back when I was a base member.