When do you need to file an alternate airport?

Answer 1

A) If your destination airport does not have an instrument approach or

Does not meet the 1 2 3 Rule.

1 hour before to 1 hour after ETA the destination airport must have at least a 2,000 ft ceiling and 3 miles visibility.

B) If your destination airport has ONLY a GPS approach .

And to file that alternate , - if you're shooting a precision approach (which requires that you do have the appropriate equipment in your airplane) .. the forecast weather at the destination has to be 600 foot ceiling and 2 SM visibility at the ETA (estimated time of arrival)

- if you're shooting a non precision approach .. the forecast weather at the destination has to be 800 foot ceiling and 2 SM visibility at the ETA

- if that airport doesnt even have an instrument approach , the weather there has to be VFR at the ETA

P.S - a precision approach is an approach that has vertical guidance , so it makes sense that on precision approaches you have lower minimums because vertical guidance enables you to get kinda closer to the ground .