Avgeek Alert: Time Zones and How They Affect Flights


If you’ve ever flown across multiple time zones – for example, an eight-hour flight between Madrid and New York – you’ve no doubt experienced the jet lag and disorientation involved. Well, here we’re going to get into a bit of detail on how time zones work.

Time Zones, International Time and the Prime Meridian

In aviation, international time is a widely adopted standard (actually it’s the one adopted by pretty much everything, including the internet). And it’s normal: talking about international time (or UTC, or GMT) is essential for air travel when flights cross different time zones. UTC (Universal Coordinated Time) is a time standard which in this case coincides with GMT (Greenwich Mean Time). To sum it up, this is the reference point to define the hours of the entire planet. The Greenwich meridian is also known as the prime meridian. Imagine the Earth as a plane (ie as reflected on a world map). From Greenwich Meridian to the right, times are recorded as UTC+1, UTC+2, etc., and negative (UTC-1, UTC-2) to the left.

The Movement of the Earth’s Rotation

Since the Earth rotates on itself from left to right (from west to east), to the left of its imaginary axis (west) is earlier and to the right (east) is later. The Earth takes approximately 24 hours to complete one turn on itself, a full 360 degrees. By convention, and because the exact solar time would be organisational chaos, it was concluded that a time zone should be established every 15º. This is the result of a simple mathematical operation: if we divide 360º by 24 hours, the result is 15, which is the number of degrees that the Earth rotates in one hour.

In Spain, for example, dawn rises earlier in Tarragona than in farther west in Lugo. But at both points it is the same time because they belong to the same time zone (a lthough Spain is precisely one of the exceptions to the time zones that we’re going to discuss now).

Time Zone Exceptions

When Countries Have Different Times
It happens, for example, that extensive countries such as the United States have different time zones throughout their territory; four, if we leave out Alaska and Hawaii. The time zones (Pacific, Mountain, Central, and Eastern) aren’t exactly aligned with the meridian that crosses them, and the some U.S. states have adjusted their time zone so as not to be split into two zones. The same thing happens in many other places on other continents.

The case of Spain is an peculiar exception due to the fact that in the 1940s the Franco régime aligned the country’s time zone with Nazi Germany, and this was never corrected. So while Spain should be on UTC, it’s still on UTC+1.

During Seasonal Time Changes
Then of course there’s “spring forward, fall back” time change in March and October each year in practically all of Europe, North America, Chile, Paraguay; and part of Australia. In Asia and Africa, however,  practically no country does this. And this must of course also be taken into account when flying. For example, if we travel from Spain to Argentina, the time difference will be four hours in winter and five in summer time, since we do change the time and there it no longer changes. In other words: Spain has UTC+1 in winter and UTC+2 in summer.


Pilots, when planning their flight, take all these factors into account in order to coordinate with the airport where they take off or land, so that each operation is perfectly monitored. The rest of the workers (flight coordinators, controllers, etc.) follow, of course, identical guidelines to find out what time it is around the world.


Photo | Yelizaveta Tomashevska