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In Europe, we have Daylight Saving Time, but a few years ago, the European Commission decided that must stop and instructed their members to choose a permanent time zone. For various reasons that hasn't happened yet, and this night we moved from 'summer time' (CEST, UTC+2) to 'winter time' (CET, UTC+1), which always leads to a couple of articles being published. I read one from a well-respected Dutch news website and was curious about this part:

It is better for our health that the Netherlands opts for permanent winter time, and it is even better if we stick to the British time, according to the RIVM. It's an hour earlier there. For aviation, on the other hand, it is better to keep the current situation, and for the economy and road safety it is better to permanently introduce daylight saving time.

Original quote in Dutch:

Voor onze gezondheid is het beter dat Nederland kiest voor de permanente wintertijd, en het is zelfs het best als we ons aan de tijd van de Britten gaan houden, aldus het RIVM. Daar is het een uur vroeger. Voor de luchtvaart daarentegen is het beter om niets af te schaffen, en voor de economie en verkeersveiligheid is het juist beter om de zomertijd permanent in te voeren.

I understand why winter time may be better for our health (we need sunlight in the morning to properly wake up and get started; if the sun rises at 10am that will be difficult) and why summer time may be better for road safety (because rush hour will be in daylight more often). I just can't think of a reason why aviation would benefit from the current situation. What would they lose if we opt for permanent winter time or permanent summer time?

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  • Related: in 2010 the BBC reported that in UK summer time (DST) was in continuous effect from 1968 to 1971. But "A White Paper published in 1970 said it was impossible to quantify the advantages and disadvantages of British Standard Time. The experiment was debated in the Commons on 2 December 1970 and - by a vote of 366 to 81 - the experiment was discontinued." Oct 31 at 15:39
  • It makes things more complex. It is already bad that your timezone could change with every landing. Flights schedules are in the local departure and arrival airport and to make things more complex not all countries change the timezone the same day. In fact it is traditional to publish your flights twice a year in what is called the the Winter or Summer season just to avoid the problem. Just imaging programing the edge cases or just creating an Excel
    – borjab
    Nov 1 at 16:49
  • 1
    Other Dutch news outlets reporting on the same story suggest that it is not that aviation industry benefits from the current arrangement, but that making any changes to due that arrangement would cause issues (something vague about time slots). They don’t cite any sources either, hence not an answer.
    – mmeent
    Nov 4 at 21:07
  • It is always difficult to understand a third party interpretation of a complicated matter. Most probably someone is referring to a report. And not fully understanding it. My guess is that the statement is about curfew times at airports outside the Netherlands. Many airports have limitations on opening times, say only allowing flights between 06.00 and 22.00. If that airport changes times due to Daylight saving time, this would work for airlines IF all included airports changes these times in the same way. Guessing, the reference could be to London which I guess will stay as now.
    – ghellquist
    Nov 6 at 15:32
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A brief web search suggests that aviation would have no benefit or disadvantage from either regular clock changes or their abolition – at least when it comes to reporting time itself.

This is because aviation generally uses 'Zulu time' – a.k.a. UTC for all communications except for the departure and arrivals boards that are displayed directly to passengers using local time. The AOPA (Aircraft Owners and Pilots Association) writes:

Aviation Time

Greenwich Mean Time (GMT) is international time, the basis of the world time clock. It helps eliminate confusion across multiple time zones. It is also known as UTC (Coordinated Universal Time). Aviators commonly refer to it as Zulu time.

Aviators use this worldwide, 24-hour time to eliminate confusion about "a.m." and "p.m." and different time zones. It makes time comparisons and conversions easier.

There has been a question over at Aviation.SE asking about the reasons for using Zulu time in aviation which user Casey answered:

If you are flying along the border between Arizona and New Mexico in the summer and given a hold:

Cessna 1234 hold at FIX, right turns, 10 mile legs, expect further clearance at 1630, time now 1602

If that were local time, you'd have to now determine if that fix is over AZ or NM, because NM observes daylight saving time and is in MDT/-0600 and AZ does not observe daylight saving time and is in MST/-0700. This is a needless check that is distracting and can cause confusion all due to using a local time. Instead, we know the times given are Z/UTC time and "1630" has an unambiguous meaning no matter where on earth our plane is located.

As this approach completely nullifies any effect that clock changing might have on schedules and such, the local time will have zero influence on aviation.

On the other hand, for long-distance flights that cover two different DST areas – e.g. transatlantic flights where European and US clock changes are not synced or flights from Europe to East Asia where DST is not observed at all – the clock changes cause scheduling problems. Namely: In which time zone does the airline wish to keep its departure/arrival time constant and are there slots available at the respective airport. Summarised well by CrankyFlier:

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.

Taking a random example, I looked up the flight data for JL 408 (Japan Airlines flight from Frankfurt to Tokyo-Narita) on Flightradar24 and noticed that its departure time in Frankfurt remained the same but its arrival time in Japan shifted back by an hour, reflecting the fact that its 19:40 local departure time used to be 17:40 UTC but has been 18:40 UTC since Sunday.

Taken together, I fail to see any advantage that aviation has by changing the clocks.
(The answer may vary for general aviation, but its effect should be exceedingly small so I decided to disregard it.)

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  • not just that there is very little advantage, that advantage would be undone completely by the reverse clock change at the start of DST, leaving a net zero all around.
    – jwenting
    Nov 2 at 12:44
  • I agree it's not really significant, but kudos for managing to find a plausible reason (other countries / continents keeping DST, thereby causing scheduling problems)...
    – Glorfindel
    Nov 3 at 21:17
  • This answer sounds to me like something that a computer program should be able to handle relatively easily – unless there's a hidden layer of complexity. I'm thinking along the lines of designing flight plans with night flying restrictions in mind: a plane scheduled to arrive at 06:30 DST might be allowed to land regularly, but due to local regulations there might be a problem if the arrival is now scheduled to be at 05:30 after the end of DST (assuming that the local time of departure doesn't change).
    – Schmuddi
    Nov 4 at 14:26

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