Every year in the UK, we set our clocks an hour forward in March and then set them back again in October as British Summer Time (BST) begins and ends. British Summer Time is a type of Daylight Savings Time and today, about 40% of countries worldwide use it to make better use of daylight and to conserve energy (and for many pilots, it makes those 4am reports a lot easier).
Even though everyone tries to remember to set their alarms correctly, it always catches a few people out – one of the reasons that the aviation world does not observe daylight savings time.
Daylight savings time will affect local scheduled flight times the same way it will affect your live television schedule. It will affect apparent flight duration if the departure and arrival airports switch to DST on different days of the year, but actual time in the air will remain the same. All communicated times within the aviation community observe one time, which will not be affected…
Aviation observes UTC (Coordinated Universal Time)
The international standard on which the world regulates time. Flight plans and air traffic control clearance, weather forecasts and maps all use UTC to avoid confusion about time zones and daylight saving time. UTC is just like GMT, (in fact the aviation world used to run on GMT but it took over in 1960) and there are two distinct differences, one, as we’ve already mentioned, it does not observe daylight savings time and, two, it’s slightly more accurate.
Hang on, why is it not known as CUT?
The answer is, it’s a compromise between the English (Coordinated Universal Time) and French phrases (Temps Universel Coordonné)
UTC is often seen written as ‘z’ and referred to by pilots and aviation professionals as ‘zulu’ time.
Where does ‘Z’ come from?
You may have noticed how each time zone is expressed as a certain number of hours "+ UTC" or " -UTC"? (For example, UTC -5 is Eastern Standard Time in the USA.) Well, the letter "z" refers to zero hours (UTC + 0).
And why Zulu?
Since the NATO phonetic alphabet ("Alfa" for A, "Bravo" for B, "Charlie" for C...) word for Z is Zulu, pilots and aviation professional will refer to it as "zulu time”, as per This is especially true in aviation, where "Zulu" is the universal standard. This ensures all pilots regardless of location are using the same 24-hour clock, thus avoiding confusion when flying between time zones.
Know your daylight when flying
Time is of the utmost essence in aviation. Time and speed together relate to distance show us how to calculate how long a flight will take, estimate our time of arrival and provide us with our fuel consumption.
Being aware of daylight savings time is important when flying with visual flight rules (VFR) as many airfields close at or just after sunset.
Atmospheric conditions and altitude also have a pronounced effect on the duration of daylight, which can influence your VFR flight near the end of the day.
Sunlight
Sunlight occurs between sunrise and sunset. Sunrise is the exact time where the top part of the sun becomes visible on the horizon and sunset is where the top part of the sun disappears under the horizon.
Daylight
Daylight starts when the centre of the sun is just below the horizon in the east and ends when the centre of the sun is just below the horizon in the west.
Twilight
After the sun sets below the horizon at certain times of year, and depending where you are in the world, there might still a bit of daylight left - the same happens in the morning just before the sun peeks over the horizon. These short periods are called twilight and are measured when the centre of the sun is just below the horizon. The time the sun spends in these small (6 degrees either side, to be precise) varies considerably depending where you are flying in the world. If you’re fortunate enough to be flying in the tropics, closer to the equator evening darkness sets in abruptly, which means you’ll get a much shorter period of twilight.