UTC vs LMT

In the PPL exam in the NAV section you may encounter questions that require you to convert local times to universal times or vice versa. Be careful when you encounter them and ensure you know what is being asked!

Here is a sample question:

The time UTC is 0100Z. What time is it at a location 60 degrees longitude west of Greenwich England?

1. 2100LMT
2. 2100Z
3. 0500LMT
4. 0500Z

Ok, so what do we know about the time zones?

Well, standard time zones are made up of Earth's 24 equal parts bordered by meridians each 15° longitude apart.

So, in the example above, 60 degrees divides nicely by 15 to give you 4, meaning you are 4 hrs west of Greenwich England (that of course happens to be the location of the the mean solar time at longitude 0° also called the Prime Meridian. )

When converting LMT (local mean time) to UTC (universal coordinated time), remember:

• East is least - subtract one hour for every 15 degrees of longitude, if the location is east of the prime meridian.
• West is best - add one hour for every 15 degrees of longitude, if the location is west of the prime meridian.

Using the rule above you may be compelled to add the 4 hrs to 01:00 as west is best? NOPE...

Please note that above the time given is 1 o'clock UTC, so you do not need to convert to UTC but rather to LMT.

Therefore, you use the reverse rule of the above to convert from UTC to LMT.

100 UTC minus 4 HRS = 2100 LMT (or 9PM)

Viola, the answer is 1.

Here is a great time zone map for your review

Test your knowledge in this example:

A location that is located 45 degrees longitude east of the prime meridian has an LMT of 1000. The Universal coordinated time would be

1. 0600Z.
2. 0700Z.
3. 1000Z.
4. 1300Z.

Answer?





1000 minus (east is least) 3 hrs (45 divided by 15) = 700Z (UTC)

Therefore: 2