Only some countries use Daylight Saving Time. In Canada, some provinces use and don't use DST (such as Saskatchewan). However, in remote and local regions where this is not observed, what would happen?

What happens when areas that do not observe DST are controlled by areas that do. (Cleveland controls parts of Southern Ontario). How does this affect local airspace? Does it affect global airspace as well? What are the safety implications? How does it affect Air Traffic Controllers operating these different spaces?

  • $\begingroup$ @Zizouz212: Just pick one at random to accept then. Accepting one of the answers will make the question show up as 'answered satisfactorily' in the list of questions. $\endgroup$ Commented May 9, 2015 at 3:05
  • $\begingroup$ There is no such thing as "Daylight Saving Time" in the first place. Daytime is the same regardless of what your clock is set to show. $\endgroup$ Commented Jul 5, 2022 at 13:52

7 Answers 7


Aviation always uses UTC time. This is from the FAA's AIM, but other countries do the same for obvious reasons:

4-2-12. Time

a. FAA uses Coordinated Universal Time (UTC) for all operations. The word "local" or the time zone equivalent must be used to denote local when local time is given during radio and telephone communications. The term "Zulu" may be used to denote UTC.

This question covers in much more detail why UTC is used in preference to GMT, and this question explains why pilots need to know the time in the first place, at least under IFR (which applies to almost all airline flights).


Does daylight saving time affect local airspace?

Yes and No.

In aviation Flight plan information, weather, etc. all use Zulu Time (UTC). This provides a single time standard everyone in the world can use, and avoids misunderstandings based on various national rules for "Daylight Saving Time", "Summer Time", etc.
The airline / airport / travel agent / etc. are responsible for properly converting UTC times to the local timezone for passenger convenience.

Similarly active times for restricted airspace, TFRs, etc. are all published as UTC times to eliminate any possible ambiguity in this regard.

Not everything is based on UTC however: The (FAA-operated) tower at the field I fly from operates from 0700–2300 Local Time. When the United States messes with the clocks twice a year the UTC hours of operation/effective hours for the Class D airspace will change to remain aligned with the same "local time" operating period.


Air Traffic Control uses UTC or Zulu time which is the same, all the time, the whole world over.

Local only flights will use local time.


Yes it does, some Major international airports, notably SYD, have a curfew in place. Commercial passenger aircraft land between 0600 and 23:00 AEST or face sanctions. This in turn affects patterns in Dubai, Singapore, KL, LAX, DFW etc. This is a "must depart by" issue for some of these.

This is a politically motivated rule to appease voters in the flight path and is tied to "local" time. Aircraft arriving early are slowed and fly laps over suburbs, sharing the joy.


It does have an effect, look in St-Hubert, they have to work an hour longer in the summer! That might be true anyway, but when reading times in the CFS there are always adjustments for the time change. Essentially the airport (or parts thereof) opens and closes at the same local time but the zulu time changes.

TWR St-Hubert 118.4 352.5 (E) 1045-05Z‡ Apr-Oct; 1045-04Z Nov-Mar

You may think that doesn't happen in Sask., but look-

TWR Saskatoon 118.3 244.7 (E) 1200-0445Z Mon-Fri Mar 11-Nov 3, 1245-0445Z Sat-Sun Mar 11-Nov 3, 1245-0445Z Nov 4-Mar 10

They also have to make adjustments to their times to accommodate traffic from other provinces. They also work longer in the summer.

This is from an old CFS I found online, don't land and say I said they would be open.


In all air traffic control systems, all time is UTC (called "Zulu time"), which doesn't have daylight savings. Local time is only used when communicating with passengers (departure/arrival boards, announcements, boarding tickets, etc).


Some class D towers are only open part time based on local time. So yes, daylight savings time will impact when the tower and class D airspace is active.


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