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The weird world of clock changes and daylight saving

By: Virgin Atlantic

October 24, 2019

Some of us are looking forward to an extra hour in bed when the clocks go back this weekend.

But for our on-duty pilots and crew in the air, it’s irrelevant. With just a few days to go until British Summer Time ends in the UK, we look at the concept of daylight saving time around the world – and how the aviation industry deals with it.

What is daylight saving time? And who observes it?

Daylight saving time is the process of moving clocks forward by an hour at the beginning of spring to gain an extra hour of evening daylight, at the expense of normal sunrise times. Currently, around 70 countries observe some form of DST, including most countries in Europe, some parts of the Middle East and much of North America. While some have observed it in the past, most Asian, African, and Central and South American countries do not observe DST, as proximity to the equator means light levels are steady throughout the year.

While the original idea is often credited to US Founding Father Benjamin Franklin (who gave the world the expression “Early to bed, early to rise, makes a man healthy, wealthy and wise”) it didn’t gain serious momentum until the First World War, when it was adopted by many countries simultaneously in an attempt to preserve energy.

When does it happen?

The short answer is, at different times, depending on where you are in the world. In the UK, British Summer Time starts on the last Sunday in March and ends on the last Sunday in October. In the United States, daylight saving time starts on the second Sunday in March and ends on the first Sunday in November, meaning the time difference between the UK and the various USA time zones alters for a brief period twice every year.

With six time zones, at least most of the USA now sticks to the same changeover date. For much of the last century, there was no federal standard at all, so the decision to observe DST – and when to enact it – was taken at state, or even at individual city level. Inevitably, this caused chaos. Take the state of Iowa: By 1962, it had 23 separate combinations of dates for starting and ending DST and these frequently changed, causing mass disruption and confusion.

Similar situations occurred across the country. The madness didn’t end until 1966 when, under pressure from the transport industry, President Lyndon Johnson introduced the Uniform Time Act which standardised DST dates across the nation. But even that had an exemption at the state level, and both Arizona and Hawaii chose to opt out – Hawaii because of its geographical location (the sun rises and sets at roughly the same time every day), and Arizona because of its swelteirng summer temperatures. Most residents are only too pleased to see the sun go down at the end of another 100-degree day, even if it means less daylight. But get this, pub quiz fans: Arizona doesn’t observe daylight saving time, but the Navajo Nation – which lies mostly within Arizona – does. And the Hopi Reservation – an enclave surrounded entirely by the Arizona section of the Navajo Nation – also does not, meaning you could potentially need to reset your watch up to four times on a road trip through a single US state.

Why is it controversial?

For all kinds of reasons. There’s little evidence it preserves energy any more. We can light our homes efficiently now, and when DST is observed in hotter climates people are more likely to rely on air conditioning later into the evening – contributing to even greater energy use. In terms of health, there’s an argument that more exposure to sunlight increases levels of vitamin D, an important nutrient for bone strength. But studies have found the risk of heart attack increases after clocks go forward in the spring, and depression rates increase after they go back again in autumn, and at both times, sleeping patterns can be negatively impacted for weeks.

Glencoe, Scotland, where a change to daylight saving time rules could lead to darker mornings © LoboStudio Hamburg/Unsplash

Here in the UK, a government proposal in 2011 suggested a three-year trial of Central European Time (an hour forward from where we are now) resulting in lighter evenings and darker mornings. Motoring organisations say it would lead to a decrease in accidents, but some parts of Scotland and northern England are opposed as they wouldn’t see daylight until much later in the morning.

And – without opening a can of worms! – EU member states polled overwhelmingly in favour of abolishing daylight saving time in a recent public consultation. In light of this, the European Parliament has voted to abolish the practice in 2021, with individual countries able to choose whether to remain on ‘permanent summer time’ or ‘permanent winter time’. Post-Brexit, this could lead to different time zones on the island of Ireland, unless the UK follows suit.

What about aviation?

Pilots don’t observe daylight saving time. The changeover does affect local timetables, but if airlines were to observe DST then – during periods when the arrival and departure countries switch DST on different dates – flight durations would appear to change, despite hours in the air remaining the same.

Instead, the whole of aviation runs on UTC (Coordinated Universal Time), the international time standard by which the world regulates clocks and time. UTC removes all the confusion of differing daylight saving time periods around the world, and is used by air traffic controllers, flight planners, weather forecasters and, of course, pilots and crew, who all use the same 24-hour clock when flying to avoid confusion when travelling through different time zones. Of course, although actual flying is done on UTC it can be a different matter for airports when the clocks change. Local take off and landing times may have to be adjusted, along with staff shift times. But whatever it takes, our clever schedulers and planners work tirelessly to ensure our passengers and cargo are unaffected.

All pilots use the same 24-hour clock when flying to avoid confusion when travelling through different time zones.