What is the difference between 0000Z and 2400Z

[pelmet]

There is a difference. Anybody know?


Admittedly, I only discovered this recently.

[photofly]

I don’t believe there’s any such time as 2400Z, unless maybe they’re adding a leap second to the year as they sometimes do...?

[Outlaw58]

2400Z is not supposed to be used 0000Z. is the correct manner to code that time of the day.

The difference between the two would be the date you are referring to in that case if you code the entire time group 240012 would be the same as saying 000013 but 2400 is not to be used.

58

[Flying Low]

Actually saw 2400Z on the FMS today. I think it's a way of distinguishing a rounded number. In this case we were going to arrive at a waypoint sometime between 2359:31 and 2359:59 and it rounded it up and displayed as 2400Z. The same thing happens in METARS. If you've ever seen -0 then the temp is above -.5 but below 0.

[Schooner69A]

If I remember correctly, in the old days in the RCAF, things stopped on 2359 hours and started on 0001 hours. Did away with the problem.

[iflyforpie]

I imagine 2400Z is like heading 000 or 18,000 feet.

[Outlaw58]

I imagine 2400Z is like heading 000 or 18,000 feet.

+1

[lownslow]

2400 was late last night, 0000 was early this morning. Next question.

[AirFrame]

Pedantics.

[photofly]

ISO8601 is the most widely recognized standard for writing dates and time. I can’t find the txt online (ISO publications are $$$$$) but this page
https://www.cl.cam.ac.uk/~mgk25/iso-time.html
says:

As every day both starts and ends with midnight, the two notations 00:00 and 24:00 are available to distinguish the two midnights that can be associated with one date. This means that the following two notations refer to exactly the same point in time:

1995-02-04 24:00 = 1995-02-05 00:00

In case an unambiguous representation of time is required, 00:00 is usually the preferred notation for midnight and not 24:00. Digital clocks display 00:00 and not 24:00.

[pelmet]

0000Z is the beginning of the day while 2400Z is the end of the day, so they are separate times in any given day running from midnight to midnight. For example......in the military, you might report for duty at 0000 on January 7th and your duty might end 24 hours later at 2400 on January 7th. They are separated by 24 hours on the same day, so one does not necessarily equal the other.

https://www.militarytime.us/midnight-military-time/

[pelmet]

Now the question is......why the term Zulu for UTC time?

[Outlaw58]

Now the question is......why the term Zulu for UTC time?

The way military express time is by way of a date time group like this: DDHHMMT MON YEAR where DD=date, HH hour, MM=min, T=time zone ie 241900Z JAN 2019.

each of the time zone is coded with a letter and GMT is coded Z (I think in eastern Canada the letter is Q or R, something like that)

That way is a remnant of the message system, still in use but way less and this way of coding time has still lingered.

58

[pelmet]

Now the question is......why the term Zulu for UTC time?

The way military express time is by way of a date time group like this: DDHHMMT MON YEAR where DD=date, HH hour, MM=min, T=time zone ie 241900Z JAN 2019.

each of the time zone is coded with a letter and GMT is coded Z (I think in eastern Canada the letter is Q or R, something like that)

That way is a remnant of the message system, still in use but way less and this way of coding time has still lingered.

58

Sounds pretty good but there are 24 time zones and 26 letters in the alphabet. What gives? and why Zulu for GMT/UTC?

[photofly]

https://en.m.wikipedia.org/wiki/List_of ... time_zones

[Outlaw58]

https://en.m.wikipedia.org/wiki/List_of ... time_zones

That. As to why Zulu, I don't know. I guess the folks who put this system forward would have a story about how they picked "Z" instead of "A" or any other letter...but as far as I know, it probably is pretty arbitrary.

58

[photofly]

Zulu for zero hours offset?

[pelmet]

Zulu for zero hours offset?

Pretty close...Zulu is named after zero longitude. This is the Z military time zone.

Keep in mind, Zulu(Z), GMT, and UTC are interchangeable.

OK, for those in training for a pilot's license, don't worry. These letters used for time zones are military time zones where each of the 24 zones around the world has its own designated alphabetic letter. You don't need to know this except for the Zulu time zone while straddles the zero line of longitude and is 0 hours UTC(Zulu time).

But you should know which time zone you are in or going to figure out weather, notams, etc for your flight. For example, In the CFS, it might say for operating hours of an airport...UTC-8.

The first 12 time zones going east from Zulu(GMT) are....+1, +2, +3. etc which coordinate with military time zones A, B, C, all the way to the M time zone which is at +12 from Zulu(GMT or UTC). There is no UTC +13, +14. etc. Instead, the time zones going the other way from Zulu are -1. -2, -3, etc. Going eastbound, we stopped at M which is +12. Where is N and the second half of the alphabet? It goes the other way from Z. GMT -1 is N, GMT -2 is O, etc. The Pacific time zone is military time zone U. Of course. This is all easier to see when using a diagram.


So does anybody know which is the only military time zone with two letters?

[wannaflyguy]

Well, since we start counting at 0,
plus 12 and minus 12 would have to be the same time zone since there are 24 hours , not 25 hours in a day.

So when traveling east you would arrive at Zulu plus
Mike Time Zone M +12

And when traveling west you arrive at Zulu minus
Yankee Time Zone Y −12

Thanx for the thread.