3 ms·

From reading the article, it seems like it occurs when the runway is precisely running east to west and the airplane is coming in westward. And also the latitud

From reading the article, it seems like it occurs when the runway is precisely running east to west and the airplane is coming in westward. And also the latitude/longitude is somehow involved. You can see one of the airports here. Notice how it is exactly horizontal, i.e parallel of latitude. https://www.google.com/maps/place/Wiley+Post-Will+Rogers+Memorial+Airport/@71.2835378,-156.7756877,14.08z/data=!4m5!3m4!1s0x50c327fff620aae7:0x936de8c8fd2d094b!8m2!3d71.2874212!4d-156.7802701 https://www.google.com/maps/place/Wiley+Post-Will+Rogers+Mem...

Scoundreller 7y ago
My thought is some combination of that and magnetic deviation. Runway headings are always magnetic headings, so what the runway says and what GPS calculates (at the lowest levels) are two different things. So maybe the issue only occurs at airports where you’re landing on 27 AND mag deviation is some specific value? Would explain why it happens at only some US and some S. American airports: https://en.m.wikipedia.org/wiki/Magnetic_declination#/media/File%3AWorld_Magnetic_Declination_2015.pdf https://en.m.wikipedia.org/wiki/Magnetic_declination#/media/...
- theideaofcoffee 7y ago
  > Runway headings are always magnetic headings... This is incorrect, while most runways are aligned with the magnetic heading, that changes when you have a field with multiple parallel runways. Atlanta Hartsfield comes to mind first, with its five parallels in the East-West directions, 8L/26R, 8R/26L, 9L/27R, 9R/27L, 10/28. One would naively expect these to be not parallel by just reading the name, while in fact they are all in line.
  - Scoundreller 7y ago
    Okkkk, good point. And they're only magnetic until they get updated because the declination changes over time. Other exceptions: near the poles where the magnetic declinations change rapidly, so they use something else.

Scoundreller 7y ago

My thought is some combination of that and magnetic deviation. Runway headings are always magnetic headings, so what the runway says and what GPS calculates (at the lowest levels) are two different things. So maybe the issue only occurs at airports where you’re landing on 27 AND mag deviation is some specific value? Would explain why it happens at only some US and some S. American airports: https://en.m.wikipedia.org/wiki/Magnetic_declination#/media/File%3AWorld_Magnetic_Declination_2015.pdf https://en.m.wikipedia.org/wiki/Magnetic_declination#/media/...

theideaofcoffee 7y ago
> Runway headings are always magnetic headings... This is incorrect, while most runways are aligned with the magnetic heading, that changes when you have a field with multiple parallel runways. Atlanta Hartsfield comes to mind first, with its five parallels in the East-West directions, 8L/26R, 8R/26L, 9L/27R, 9R/27L, 10/28. One would naively expect these to be not parallel by just reading the name, while in fact they are all in line.
- Scoundreller 7y ago
  Okkkk, good point. And they're only magnetic until they get updated because the declination changes over time. Other exceptions: near the poles where the magnetic declinations change rapidly, so they use something else.