Let’s pick this up right where the chapter’s logic is heading: interpolation — Page 426, Lesson 387

Let’s pick this up right where the chapter’s logic is heading: interpolation. If the date you need isn’t one of the dates actually listed in the Air Almanac, you don’t guess — you interpolate, and you only ever interpolate to the nearest minute. That’s the stated rule: interpolation is only required to the nearest minute. So the whole business of sunrise and sunset problems is really just ordinary time problems, and the starting point is always the Local Mean Time — the LMT — of sunrise or sunset at your given position. You extract that LMT from the Air Almanac, then convert it to UTC or to Standard Time using the methods from the previous chapter. Let me walk you through the worked examples, because they show the exact sequence. Example 1: Standard Time of sunset at Innsbruck, Austria, at 47°15'N, 011°20'E, on 5th September. From the Air Almanac, sunset at 47°15'N is given as 18:33 LMT on the 5th. Now I convert arc to time for the longitude, 11°20'E. Since Innsbruck is east of Greenwich, local time is ahead of UTC, so I subtract the arc/time — that gives 17:48 UTC on the 5th. Then I apply the Austrian Standard Time offset, which is +01:00, from List 1, giving 18:48 Standard Time on the 5th. So the sunset Standard Time at Innsbruck is 18:48. Example 2: Standard Time of sunrise at Keflavik, Iceland, 64°00'N, 22°30'W, on 14th October, and Summer Time is not being kept. From the Air Almanac, sunrise at 64°N is 06:45 LMT on the 14th. Keflavik is west of Greenwich, so local time is behind UTC — I add the arc/time for 22°30'W, which is +01:30, giving 08:15 UTC on the 14th. Iceland’s Standard Time offset is 00:00, from List 2, so the Standard Time of sunrise is 08:15 on the 14th. Example 3 is the one that matters for real operations: an aircraft lands at Goose, Labrador, Canada, at 53°20'N, 060°20'W, at 18:41 Standard Time on 20th September. Is it a day or a night landing? Ignore Summer Time. Here’s the key definition: the Air Navigation Order defines the period of night flying as from 30 minutes after sunset to 30 minutes before sunrise at the surface. And note the caution — this is not necessarily the same as when it gets dark. So I work out the sunset at Goose. From the Air Almanac, sunset at Goose is 18:05 LMT on the 20th. Goose is west, longitude 060°20'W, so I add the arc/time, +04:01, giving 22:06 UTC for sunset. Then I apply Labrador Standard Time, which is −04:00, from List 3, giving sunset at Goose as 18:06 Standard Time on the 20th. The landing is at 18:41 ST, which is 35 minutes after sunset. Since night flying begins 30 minutes after sunset, this landing is 5 minutes inside the night period — so it’s a night landing according to the ANO definition. Notice the pattern in all three: extract LMT from the Air Almanac, convert arc to time for the longitude, apply the sign correctly — east subtract, west add — to get UTC, then apply the Standard Time offset from the appropriate list to get local Standard Time. And for the night-landing question, the 30-minute buffer after sunset is the trigger, not darkness itself.