How Daylight Saving Time Impacts the Airlines

Once again, it’s my least favorite time of the year . . . the end of Daylight Saving Time here in the US. Sure, there are good things about it. It was nice driving to work in the daylight this morning instead of the darkness I drove through last week, and having that extra hour in the day yesterday was fine as well. But when I leave work tonight and it’s dark outside, I’ll remember why I hate this day so much. I love summer, and this is the day that I’m reminded that winter is right around the corner. It’s time for me to start counting the days down until Daylight Saving and baseball return in March.

As you can imagine, airline schedulers see Daylight Saving Time as yet another headache. Domestically, yes, it’s a pretty simple process. Arizona and Hawai’i, the two states that don’t observe Daylight Saving Time, see all their flight schedules shifted one hour when the time changes, as shown below.

07_11_05 dstdemo

That’s easy enough, but the international world makes it a lot harder. You always have this problem when traveling between the northern and southern hemispheres since the seasons are reversed. Right now, for example, LA and Auckland are only three hours apart, but in March when the US springs forward and New Zealand falls back, the difference will be five hours. Most of Asia does not have Daylight Saving Time either, so twice a year, they see times shifting as well.

But this year is a special kind of year since the US changed when it observes Daylight Saving Time. See, until now, the US and the EU changed clocks on the same date, so everything was fine. [EDIT 11/6 @ 847a: I was wrong, there used to actually be a one week lag in the Spring, so this year it has just expanded in size.] But this year the US moved Daylight Saving up a couple of weeks in March and back a week in October/November, so now there are a few weeks, including last week, where times are really messed up in the extremely busy transatlantic market.

At most airports, that’s no big deal, because there’s room to move. But at congested airports like London/Heathrow or Frankfurt, the airlines don’t have slot flexibility so I assumed they’d have to just change around their flights in the US. But what about when that involves flights at New York/JFK or Chicago/O’Hare, also congested airports? This gets very tricky and the result is a hodgepodge of schedule changes for some airlines.

International carriers almost exclusively appear to change their US departure and arrival times by one hour during this period, as you might expect. So a flight that leaves London at say, 430p and arrives LAX at 730p would have arrived at 830p for last week only. US carriers, however, don’t seem to treat it the same way all the time.

Looking at American, for example, most flights do appear to change flight times in the US whether it be an arrival or departure. But the London to Chicago flights all change their London departure times in order to keep connections in the US. To make things even more confusing, the return flights from Chicago actually change their Chicago departure times. Look at JFK, however, and the London flights change both their US departure and arrival times. As you can imagine, arriving into the US an hour later means missed connections and longer waits for the next flight.

Delta deals with this by changing their non-US flight times. So, US connecting times remain intact. But this begs the question . . . how do they get Frankfurt to let them change times for a week? If anyone has more information on this, let me know in the comments section.

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13 Comments on "How Daylight Saving Time Impacts the Airlines"

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Chris Kerns

well, I don’t know how the airlines actually handle this, but if all the planners simply used Zulu time (GMT) for all route planning, then DST wouldn’t really matter at all.



Wow! I often wonder about the marvel behind running a modern day international airline, but the details of time change and how that may impact ops never really crossed my mind! Thanks for explaining it for us mere mortals! :)

I just found it fascinating that each airline handles it differently. With all the technology, one would think the optimal way has been shown to every company on a computer model. But I guess this goes to show that creativity in each airlines management still persists! Now if they could just be a little more creative in the service aspect…

Nick Barnard

Hmm. Yet another reason to pontificate on the stupidity of moving the daylight savings time thing around. I would’ve loved to have been a fly on the wall in those meetings.

Alex C

Just a correction–the US has been offset from Europe’s and Australia’s switch to/from DST for some time–at least 6 years, and probably more than that. The difference is, it used to just be a week instead of more.

It is indeed a bizarre time, in which int’l connections that used to work, no longer do.


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john swam

I strongly believe that this concept of daylight saving is meaningless. We simply do not save any day light but only change our watches and fool ourselves that we have saved day light!. It is high time that this practice is discontinued forthwith and avoid unnecessary confusion. To add to this confusion the dates on which this stupid act is committed changes every year I understand.


So I’m leaving from Phoenix, AZ on Sunday, Nov. 1 (daylight savings day) at 3:55 and arrive back in Ore. at 5:35 but since it’s daylight savings day it will really be 4:35, right??? But I should still arrive at airport for 3:55 flight home..


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