A (US domestic) carrier can obviously stop flying a flight, or some legs of that flight, for a host of reasons. But - occasionally it makes more significant changes, like re-numbering many flights, or changing a bunch of routes on offer etc.

My question is: Are there rules, or is there an established custom, regarding when this happens? Specifically, do operators always align these changes to the beginning of years, quarters, or months? Or do they just happen at arbitrary times and not even bunched together?

I'm interested in the period between 2000 and the present time.

  • $\begingroup$ Daylight savings time is a HUGE headache for airline schedules because some jurisdictions change over on different dates or don’t change at all. It is even worse for international flights between North and South America as the summer/winter change over dates are all over the place. $\endgroup$ Commented Feb 19, 2021 at 16:09
  • $\begingroup$ @MikeSowsun: Ok, but those are still "minor" changes: +1/-1 hours. I'm more interested in reassigning of flight numbers to different routes. $\endgroup$
    – einpoklum
    Commented Feb 19, 2021 at 16:51

1 Answer 1


At my carrier, there are no rules along the lines asked about; the rules that apply are generated by the Schedule Planning department, and will change as they see fit. They produce many schedules each year, and how much "this" one differs from the previous one depends on lots of factors regarding fleets and markets and priorities. Some things are seasonal, many aren't.

The change-over dates are similarly "whatever makes the most sense" as the schedules are being built. One carrier may be on a 6-week cycle, with another on a calendar month cycle; ours seems to change at not entirely regular intervals. Some schedules are longer than others - mid June thru mid-August may be one fairly constant schedule, but November & December may see 4 distinct schedules, as travel fluctuates around the two major holidays.

Increasing automation over the last 20 years has probably contributed to this variability.

There may be some "sacred cows" in the schedule, that flight 1 always is the first departure from (big east coast hub city) across the country to LAX or SFO, perhaps, or flight 711 always serves Las Vegas (dice roll of 7 or 11 is a winner), etc. But much of the schedule is, whatever makes sense to the planners this month or this quarter or this year.

The closest you'll come to having predictable guidelines would be to study one airline's schedules over time & observe enduring patterns... but even those may not be written in stone.


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