In regard to:
103.17 OPERATIONS IN CERTAIN AIRSPACE No Person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.
What does lateral boundaries mean?
I see this question everywhere there are part 103 related discussions. Here's my take based on word etymology, which is how the legal definition will be derived.
Lateral comes from Latin "lateralis," meaning 'belonging to the side.' If you look at a map you see the horizontal boundaries of air space. Not the lateral boundaries. There are no sides depicted on a map, only the magenta boundaries right on the horizontal plane.
If you look at a 3D depiction, only then do you see the sides, or lateral boundaries of the airspace. The sides of the surface area of class e airspace extend from the ground up to where it joins regular class e. Part 103 liturally means the airspace between the sides. Those sides typically extend up 1200 ft above an airport where class e extends down to the ground, commonly referred to as the surface area of class e airspace. Above 1200ft it is no longer the surface area, it's just regular class e airspace above an airport.
So yes, you can fly in regular class e above the lateral boundaries of the surface area of class e as long as you are not between them, or within them, which is why the article says within the lateral boundaries. Within is synonymous with between, not above.
