ILS approach. Normally 3 degs vertical from the runway threshold. It’s too let you know but if it’s outside controlled airspace then you can fly legally within although be careful.
I have had been spoken to by Farnbourgh atc whilst flying fixed wing through the ils approach (not much choice as it’s a pinch point) as if I had breached there controlled airspace. I told them I was squawking there listening code and was outside there airspace but listening in.
They backed down and admitted I had done nothing wrong