I have no Ultralight experience other than several friends that fly them at my local airport.. I am also not familiar with FAR 103 other than recently reading it..
My question arrives from FAR 103.17 and "the lateral limits of Class E airspace" ..
Straight up question.. What is "lateral surface area of an airport"...
I believe this but want clarification...
The intent here is a "control zone" .. an area depicted by a by a magenta dashed circle...
I can't find the definition of the "control zone" I grew up with ... seems to have been replaced by the term "surface area"

Anyone want to offer a opinion???