What is Zulu Time and why is it used in aviation?

Zulu Time is the “Universal Time Zone” used in the aviation world. But why do we use Zulu time in aviation?

Zulu Time is used in aviation because it is unaffected by geography or traditional time zones. It is a 24-hour timekeeping system that is the same worldwide at all times, and is used to coordinate scheduling, weather forecasts, and trip planning across the aviation industry.

In this article we will explore why it’s called “Zulu” Time, why aviation uses Zulu time, practical considerations you should keep in mind when planning your next flight, and the science and history of time zones.

Why is it called Zulu Time?

In aviation the phonetic alphabet is used (“A” and “B” are pronounced “Alpha”, “Bravo”, etc.) to ensure clarity in communications. Zulu is the phonetic pronunciation for the letter “Z”. In this case, Z stands for Zero, the number of hours offset from the Universal Time Zone in Greenwich, England.

Today, all time zones are referenced off of a Universal Time Zone which is defined as the local solar noon in Greenwich, London, England.

Greenwich is located on the Earth’s line of zero longitude, the prime meridian. The zero meridian and zero-time zone are defined arbitrarily, unlike the equator.

The time zone based on local solar time in Greenwich is known as Greenwich Mean Time, or GMT.

Other time zones are defined as having an offset from Greenwich Mean Time.

For example, Pacific Standard Time where I live is 8 hours behind GMT, notated as GMT+8.

Put simply, GMT, Zulu Time, and UTC (Coordinated Universal Time) are all different names for the same time zone.

When beginning your pilot training, the first time you are likely to see Zulu Time is in weather forecasts. For example, look at this METAR (METeorological Aerodrome Report) below. 

KBDN 072154Z 12005KT 10SM FEW040 10/04 A3013

The relevant part of this weather report is the letter Z in “072154Z”, meaning Zulu Time. 072154Z means the 7th day of the month, 21:54 Zulu Time.

Remember that Zulu Time is a 24 hour clock, there is no AM or PM. Hence why you see 21:54 instead of 9:54pm like we would say in normal conversation in the United States.

Because KBDN (Bend, Oregon Municipal Airport) is in the Pacific Time Zone, we subtract 8 hours from Zulu Time to get the local time. 21:54 minus 8 hours is 13:54.

In other words, this weather report is from 1:54 pm local time. During Daylight Savings Time this conversion is slightly different, as we’ll discuss later in the article.

Why Does Aviation Use a Universal Time Zone?

Having a universal time zone has many advantages in aviation. Pilots can know that weather reports, weather forecasts, fuel burn calculations, and flight schedules are all calculated with respect to a constant reference clock.

Imagine an airline has a scheduled trip from Newark, New Jersey (EST, GMT+5) to Phoenix, Arizona (MST, GMT+7). The trip should take 4.5 hours, and fuel and weather planning are done with this figure in mind.

The flight departs Newark at 7:00am local time, and arrives in Phoenix at 9:30am local time. How is this possible? Remember, you are flying two time zones to the west. 

It is much easier and there is less room for error when pilots, dispatchers, weather forecasters, and air traffic controllers use one universal time zone.

In this case, departure time from Newark would be 1200Z and arrival in Phoenix would be 1630Z. No time zone conversion is necessary. 

Practical Considerations for Aviation

I’ll be the first to admit that I struggle with converting from Zulu Time to local time in my head easily and I often lean on the automatic conversion feature in ForeFlight for things like interpreting weather Forecasts.

Here in Oregon, we are in the Pacific Time Zone. To convert from Zulu time to local time, I need to subtract 8 hours from Zulu time. During Daylight Savings time (the summer months), I subtract only 7 hours.

To find your local conversion factor, Google “(Your Local Time Zone) convert to GMT”. Offsets for the continental United States’ 4 time zones are listed below.

Keep in mind some areas (certain countries, states, and other geographies) don’t observe Daylight Savings Time. It’s not a bad idea to double check local conversions if you’re in an unfamiliar area.

Zulu (Universal) Time Used to be Unnecessary 

The history of time zones might not sound particularly interesting but it has some significance in the aviation world you should learn as part of your pilot knowledge base. Plus, you’ll be the life of the next party you attend when you steer the conversation toward this exciting topic.

Time zones are a relatively novel idea in human history. When transportation and communication methods were relatively slow, there was no need for time zones.

Local towns or states would set their own time by the local solar noon. Coordinating appointments and schedules was relatively easy as it was impossible to communicate over hundreds of miles or travel more than a few dozen miles per day.

The invention of the telegraph and faster transportation methods like trains changed this. When railroads were making schedules, each town having its own local time made things confusing and inefficient. 

That is why in 1883, the United States and soon the entire world started using “time zones.” Greenwich England was chosen arbitrarily as the line of zero longitude and therefore the zero-time zone.

Believe it or not, some time zones operate on half-hour offsets from GMT.

For example, India’s time zone is GMT+5.5 hours, and there even exist 15-minute time zones in some rare cases (Nepal’s time zone is GMT+5:45)!

All this nuance, special exceptions and quirky rules have led to the need for a simple, consistent, worldwide timezone for critical operations such as aviation.

If you’re still awake you probably have a burning question, namely why is Coordinated Universal Time not abbreviated as UTC and not CUT? 

This came about as a compromise between French speaking and English speaking scientists. English speakers would abbreviate it as CUT, whereas the French speakers would abbreviate it as TUC (Temps Universel Coordonné). The compromise UTC was reached.

Time Zone Summary

If there is one takeaway from this article, remember GMT, Zulu Time, and UTC (Coordinated Universal Time) are all different names for the same time zone.

A universal time zone in aviation is important so that scheduling, weather forecasts, and trip planning are done on a consistent clock.