How A to F works

I spent two years as a gate agent at Amsterdam Schiphol, and the question I heard most was “which side has the view?” The honest answer was always “it depends.” This site works out what it depends on.

1. The flight path

   One position per minute from takeoff to landing. For now this is the shortest route between the two airports at a typical cruising height. Real flights bend with the wind and air traffic control, which is why anything within 40 km of the line is marked as possibly on either side.

2. Where the sun is

   For every minute, the sun’s direction and height above the horizon at the plane’s position, using the standard NOAA solar formulas. At 11 km up the horizon sits about 3 degrees lower than on the ground, so you see the sun for a few minutes after it has set for people below. The calculation matches the open-source astral library exactly across 20,000 random times and places.

3. Left or right

   Compare the sun’s direction with the direction the plane is pointing. If the sun is to the left of the nose, it’s on the A side; to the right, the F side. A window shows you roughly what’s beside you, not straight ahead, so the sun has to be at least 20 degrees off the nose to count. Near sunset the coloured sky spreads wide, so golden light counts from 5 degrees.

4. What you can see

   51 landmarks along these routes: mountain ranges, canyons, lakes, islands, capes and big cities, each from Natural Earth with a Wikidata ID. Terrain only counts in daylight. Cities count at night too, because their lights are the view.

5. The answer

   Sunset or sunrise light wins first. Otherwise, the side with clearly more to see. Otherwise, in daylight, the side away from the sun: no glare, and the ground is lit from behind you. The same engine runs in Python for the data and in your browser for any date, and 320 test flights check that both give identical answers.

6. Where Claude fits

   Claude writes and reviews the code and the words: the window narration, the trip-planner plugin and the MCP server. It never decides which side something is on: the geometry does, and a separate checker rejects any sentence the geometry doesn’t support.