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Zulu Time


With all the time zones in the world, pilots need a way to reference the current, past or future time, and not have to worry about what time zone they are in. 

This is where Zulu Time comes into play.  Because a pilot may cross several time zones during a flight, a standard time system has been adopted. It is called Universal Coordinated Time (UTC) and is referred to as Zulu time. UTC is the time at the 0° line of longitude which passes through Greenwich, England. All of the time zones around the world are based on this reference.  It is presented in the local Military time at Greenwich, England

To convert to this time in the United States, a pilot should do the following:

  Standard time Daylight saving time
Eastern Add 5 Hours Add 4 Hours
Central Add 6 Hours Add 5 Hours
Mountain Add 7 Hours Add 6 Hours
Pacific Add 8 Hours Add 7 Hours

For daylight saving time, 1 hour should be subtracted from the calculated times.

Taken from the Pilots handbook of aeronautical knowledge (FAA-8083-25)

In order to determine Zulu time, you must first convert the local time into military time:

To obtain Military time from local time:

After 12 PM, add or subtract 12
Before 12 PM, do nothing

Example:

2:00 pm: 2 + 12 = 14 or 1400 Military time

10:00 am = 1000 (ten hundred hours)
8:00 am = 0800 (zero eight hundred hours)

To obtain local time when Zulu time is known:
Zulu Time - Factor = Local Military time

To obtain Zulu time when local time is known:
Local Military Time + Factor = Zulu Time

Factor is the offset from GMT (Greenwich Mean Time). It can be obtained from the Airport / Facility Directory (A/FD)

 

Local Time  Local Military Time Zulu Time (Summer +5)  Zulu Time (Normal +6)
12:00 AM 0000 0500 0600
1:00 AM 0100 0600 0700
2:00 AM 0200 0700 0800
3:00 AM 0300 0800 0900
4:00 AM 0400 0900 1000
5:00 AM 0500 1000 1100
6:00 AM 0600 1100 1200
7:00 AM 0700 1200 1300
8:00 AM 0800 1300 1400
9:00 AM 0900 1400 1500
10:00 AM 1000 1500 1600
11:00 AM 1100 1600 1700
12:00 PM 1200 1700 1800
1:00 PM 1300 1800 1900
2:00 PM 1400 1900 2000
3:00 PM 1500 2000 2100
4:00 PM 1600 2100 2200
5:00 PM 1700 2200 2300
6:00 PM 1800 2300 0000
7:00 PM 1900 0000 0100
8:00 PM 2000 0100 0200
9:00 PM 2100 0200 0300
10:00 PM 2200 0300 0400
11:00 PM 2300 0400 0500

For example, the Texas A/FD shows that the offset for Houston is -6(-5DT).  This means that this time zone is 6 hours behind Greenwich, and when daylight saving time is active, it is 5 hours behind.


Examples:

Determine Zulu time for a local time of 3:45 PM, and time zone of Central Standard Time (CST) (UTC-6(-5DT))

3pm is after 12pm, so we add 12 (3 + 12 = 15), so 3:45 PM = 1545 Military

To obtain Zulu time when local time is known:
Local Military Time + Factor = Zulu Time

1545 + 6 Hours = 2145Z

Determine Zulu time for a local time of 9:30 AM, and time zone of Central Daylight Time (CDT) (UTC-6(-5DT))

9 AM is before 12 pm, so we don't add or subtract anything to get military time:
9:30 AM = 0930 Local Military Time

To obtain Zulu time when local time is known:
Local Military Time + Factor = Zulu Time

0930 + 5 hours = 3:30 PM

(Note we used 5, and not 6.  In this example, we are on daylight saving time. (CDT))

3pm is after 12pm, so we add 12 (3 + 12 = 15), so 3:30 PM = 1530 Zulu Time

Determine local time for a Zulu time of 1710Z, and time Zone of Eastern Daylight Time (EDT) (UTC-5(-4DT))

To obtain local time when Zulu time is known:
Zulu Time - Factor = Local Military time

1710 - 4 hours = 1310 Local Military time

(Note we used 4, and not 5.  In this example, we are on daylight saving time. (EDT))

13 is greater than 12, so our time will be in PM.  We subtract 12, and get 1

1310 Local Military time = 1:10 PM


NACO has made the A/FD digitally available to the public.  You can download and print excerpts from any A/FD in print from the internet:

www.naco.faa.gov/index.asp?xml=naco/online/d_afd

For more information, follow the link below to the FAA's AIM (Aeronautical Information Manual) article on Time:

www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/Chap4/aim0402.html#4-2-12