Forum: aviation.stackexchange.com
Tags: <time>
Title: Why does aviation use Zulu time instead of the local time?
Question: When reading aviation literature, it's common to find references to  Zulu Time .   What is  Zulu Time ?  Why does aviation use Zulu Time instead of the local time?

Answers:
sents: text: Zulu means the letter Z in radio communication.
text: The letter Z designates UTC time.
text: There is actually a list of time zones for each letter of the alphabet (except J ):
text: Alpha time zone:
text: UTC + 1 Bravo time zone: UTC + 2 ... India time zone: UTC + 9 Kilo time zone: UTC + 10 Lima time zone: UTC + 11 Mike time zone: UTC + 12 November time zone: UTC - 1 ... X-ray time zone: UTC - 11 Yankee time zone
text: : UTC - 12 Zulu time zone:
text: UTC + 0 However, the other time zones are seldom referenced in aviation.
text: Why do we use UTC time instead of local time?
text: Because flights often cross time zones.
text: Imagine this: the time now is 11:59.
text: We will takeoff at 12:30 and fly west.
text: Afterwards, at around 11:48, we will be 15 nautical miles away from the airport.....................
text: Huh?
text: Even more confusing
text: : We takeoff at 12:30 and land at 13:00 ==
text: > we only need 30 minutes of fuel.
text: Wrong!
text: We actually cross a time zone and the actual flight time is 90 minutes.
text: But we've taken off with 60 minutes less fuel than we need.
text: What do we do?
answer_details: author: aviation.stackexchange.com/users/3386/kevin
score: 31
sents: text: Zulu time, as others have pointed out, refers to UTC.
text: We use this time in aviation (and meteorology and surely others) because it is easier and it is standard.
text: It's the same time everywhere on earth.
text: If you are flying along the border between Arizona and New Mexico in the summer and given a hold:
text: Cessna 1234 hold at FIX, right turns, 10 mile legs, expect further clearance at 1630, time now 1602 If that were local time, you'd have to now determine if that fix is over AZ or NM, because NM observes daylight saving time and is in MDT/-0600 and AZ does not observe daylight saving time and is in MST/-0700.
text: This is a needless check that is distracting and can cause confusion all due to using a local time.
text: Instead, we know the times given are Z/UTC time and "1630" has an unambiguous meaning no matter where on earth our plane is located.
text: It is a similar situation when checking pre-flight weather.
text: Weather is reported in Z time and this makes it easy to calculate when you will get to your destination and what forecast is valid for that time.
text: If it were in local time you'd have to know additional information about time zones, which again could be a source of error and is needless.
text: Adding to potential confusion are regions of earth that keep odd adjustments.
text: For example, St. Johns, NL, Canada is GMT-0330 in the winter and GMT-0230 in the summer.
text: There are even a few that are off by 15 minute adjustments (e.g. Nepal).
text: Combine this with knowing where DST is observed and where it isn't, and more importantly when it is
text: (USA DST has different start/end dates than other places)
text: then it becomes very complicated to work in local time.
text: Working in universal time solves these problems.
answer_details: author: aviation.stackexchange.com/users/258/casey
score: 21
sents: text: Zulu time is UTC time .
text: The reason for the name zulu is because there is a hour shift of Zero sometimes denoted with a Z and in the nato alphabet Z is Zulu.
text: Many times a route will cross timezone so to avoid confusion about which timezone a time is in controllers and pilots will use zulu time by default.
text: It also avoids daylight savings issues.
answer_details: author: aviation.stackexchange.com/users/609/ratchet freak
score: 11
sents: text: Zulu time, used in aviation quite often, is another name for UTC (Coordinated Universal Time (French: temps universel coordonné)).
text: It is the primary time standard by which the world regulates clocks and time.
text: It is, within about 1 second, mean solar time at 0° longitude; it does not observe daylight saving time.
text: It is one of several closely related successors to Greenwich Mean Time (GMT).
text: For most purposes, UTC is considered interchangeable with GMT, but GMT is no longer precisely defined by the scientific community.
text: Edit
text: To answer the second part of your question : Its called Zulu time as UTC does not have daylight savings, hence Zero hour shift.
text: Now Zero starts with Z and NATO call-sign for Z is Zulu.
text: Hence the name. Source
answer_details: author: aviation.stackexchange.com/users/8547/Victor Juliet
score: 5
sents: text: Zulu time, sometimes called Greenwich Time or UTC time, is the local time at the Prime Meridian, that is on the 0° Line of Longitude, which also happens to run through Greenwich, England.
text: This local time has been adopted as International Standard Time and used as the official time on Earth.
text: Other local times are utilized by local principalities or nations as a relative standard time for that area of the Earth.
text: It is offset a certain number of hours from Zulu time.
text: As aircraft may be operating over several time zones during a cross country or international flight, it makes sense to file flight plans with departure and arrival times listed in Zulu time for easy reference.
answer_details: author: aviation.stackexchange.com/users/15637/Carlo Felicione
score: 1

Summary of the answers:
Zulu time is UTC or GMT. It is used for easy reference as planes often fly across timezones. 
Zulu time is another way of describing UTC time. It is used in aviation because it is standard around the world and therefore easier, particularly as flights may cross time zones.