Daylight Saving Time, or DST, for most people in the U.S. and Canada, ends on Sunday at 2 a.m. Remember, at that time, to turn all clocks back to 1 a.m. local time. For airline schedulers, Daylight Saving Time is yet another headache.

The schedule will need to be adjusted quite a lot when international traveling is involved, especially from Northern to Southern Hemisphere since the seasons are reversed. In March the U.S. will spring forward and Australia fall back. This will mean a difference of two hours. Also most of Asia does not have DST either, so twice a year, they see airlines times shifting as well.

U.S. states or territories that do not observe DST are Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands and most of Arizona except for the Navajo Reservation.

The Energy Policy Act of 2005 decrees that DST begin on the second Sunday of March and end on the first Sunday of November. So there will be a few weeks, where times are really messed up in the extremely busy transatlantic market.

At congested airports like Heathrow or Frankfurt, the airlines don’t have slot flexibility. When the travel is from one congested airport to another, say from London to Chicago, the rescheduling gets extremely tricky.

Most flights do appear to change flight times in the U.S., whether it is an arrival or departure. But the London to Chicago flights all change their London departure times in order to keep connections in the U.S. The return flights from Chicago actually change their Chicago departure times. However, for JFK , the London flights change both their U.S. departure and arrival times. As one can imagine, arriving into the U.S. an hour later means missed connections and longer waits for the next flight.

All these have led to the practice of DST being widely criticized.