The key recommendation is to lay problems out logically and always work… — Page 402, Lesson 352

Let's pick up with the LMT/UTC problems, because that's where the real skill comes in. I want to show you the recommended method, and I want you to notice something important right away: in basic LMT problems, the latitude is completely unimportant. For instance, all points on the 75°W meridian have the same LMT — that includes Ottawa in Canada, Philadelphia in the USA, Kingston in Jamaica, Bogota in Colombia, and Lima in Peru. So when you see a latitude given, you can ignore it for the time calculation. The key recommendation is to lay problems out logically and always work through UTC. Let me walk you through Example 1. We have LMT at point A, which is at 40°N 137°50'W, equal to 1812 LMT on 18 August. We want the LMT at point B, at 30°S 121°12'E. Here's the layout. We set up columns for Day, Hour, and Minute. Start with LMT at A: Day 18, Hour 18, Minute 12. Now we convert the longitude arc to time. For A, that's 137°50' West. The arc-to-time conversion — which you'll find on the last page of the Air Almanac — gives us +9 hours and 11 minutes. Adding that to our LMT at A gives us UTC: Day 19, Hour 03, Minute 23. The note there is "long. West, UTC best" — meaning when you're west of Greenwich, you add the time to get UTC. Now we go from UTC to LMT at B. B is at 121°12' East. The arc-to-time conversion for that is +8 hours and 05 minutes. Adding that to UTC gives us LMT at B: Day 19, Hour 11, Minute 28. The note is "long. East, UTC least" — east of Greenwich, you add again to get local time. So the answer is 1128 LMT on the 19th of August. Now, I want to be honest with you: this question could have been completed without UTC. The change in longitude between A and B is 259°02', which converts to 17 hours 16 minutes later than A's LMT. But the method through UTC seems longer — and it is — yet it's far too easy to make a mistake if you try to take short cuts, especially if the date changes. So always use the method above and work through UTC. That's the professional habit. Let me do Example 2 with you. If it is 1012 UTC on 15 December at 50°N 030°W, what is the LMT in Singapore and in Hawaii? First, note that UTC is the same all over the world. Giving the initial position as 50°N 030°W is a red herring — it doesn't matter for the calculation. For Singapore, at 00°30'N 105°00'E: we start with UTC, Day 15, Hour 10, Minute 12. The arc-to-time conversion for 105°E is +7 hours. Adding that gives LMT Singapore: Day 15, Hour 17, Minute 12. The note is "long. E, UTC least." For Hawaii, at 22°00'N 155°00'W: again start with UTC, Day 15, Hour 10, Minute 12. The arc-to-time conversion for 155°W is -10 hours and 20 minutes. Subtracting that gives LMT Hawaii: Day 14, Hour 23, Minute 52. The note is "long. W, UTC best." Notice the date went back to the 14th — that's exactly the kind of date change that makes short cuts dangerous. Now let's move to a new concept: Zone Time, or ZT. Although UTC is the worldwide time datum for aviation purposes, it has little civil use far from the Greenwich meridian. Think about it — humans tend to rise in the morning and go to bed in the late evening. On a cruise ship in the mid-Pacific, it would be disappointing if you chose to go up on deck to sunbathe when your watch was reading 1000 hours UTC! This problem was recognized centuries ago, and the system of Zone Time was used to keep ships' time in synchronization with the periods of light and dark. Zone Time is based on the fact that the Sun transits 15 degrees in one hour. The datum for the Zone Time system is the Greenwich Meridian, 0°E/W. All ships within longitudes 7.5°W and 7.5°E keep a Zone Time the same as GMT, which is UTC. The correction from Zone Time to GMT is zero. Now here's the numbering system. Ships between longitudes 7.5°E to 22.5°E have a Zone Time one hour later than GMT. This zone is numbered -1 — that's the correction to be applied to Zone Time to calculate GMT. Similarly, ships between longitudes 22.5°E to 37.5°E are in the zone numbered -2. The numerical labels continue as minus values up to 180°E. For the Western hemisphere, a similar system applies but reversed. Ships at longitudes between 7.5°W and 22.5°W are in the zone numbered +1 — the zone time is earlier than UTC, and 1 hour must be added to Zone Time to calculate UTC. The numerical labels increase as plus values up to 180°W. So the pattern is: east zones are negative numbers, west zones are positive numbers, and the zone number tells you the correction from Zone Time to get UTC. That's the core of Zone Time.