Why do arlines change schedules by piddling amounts?
 

My morning flight went for 6:53 to 6:57. I have often noticed that the schedules change by times of less than 10 minutes or so.

Why do they do that?

At least they're updating it. It's probably the same amount of work to change it by 30 minutes as it is for 3 minutes and no one is questioning so small a change.
Chalk it up to insignificance and enjoy the extra four minutes. However, they might move it back so you have to keep watching!

May have to do with your airline attempting to optimize for 'on-time departure' with given takeoff/ATC slots.

Also sometimes there is an equipment change to a slower/faster aircraft.

There are dozens of variables that come into play in airline scheduling. These include (not every variable applies in every case) block times, gate availability, runway slots, terminal capacity limitations, handling equipment availability, customs/immigration availability, noise curfews, crew rest periods, crew duty times, etc...

I've always wondered (on a related note)... Why do North American airports schedule down the nearest minute, whereas European airport only do so to the nearest 5?

IATA reccomended practice for scheduling is 5 minute intervals.

Slot allocations are made by 5-minute blocks but are limited only by 15-minute capacity limitations and then again by 60-minute capacity limitations. Sounds confusing, but you get the hang of it once you have been working with it for a while. :)

I sometimes wonder if they make 1-4 minute changes in order to reduce reportable delays in the DOT statistics.

the summer/winter wind has an effect on east west flights.

Isn't there a Sinatra song about that? :cool:

6:53. Oh wait, 6:57. Oh, never mind, it's 6:53. And doors close 10 minutes before. And it's 6:43:01. Sorry, you can't board. You're on your own, bye.

One reason is that they are adding more and more time for the flights, so they are not late.

The simplest answer is that the schedules are ultimately computer generated, and the computer program doesn't particularly care whether it is a 1 minute change or a 2 hour change. It would probably involve a good deal more work NOT to show the revised times.