(Refer to Figure 20, area 1.) You’re hired to inspect a group of structures that are under construction 9 statute miles (SM) south of Norfolk Intl airport. What’s the highest you’re allowed to fly if inspecting the topmost part of the tower?
A) 470 ft. MSL
B) 853 ft. AGL
C) 1,200 ft. MSL

The answer to this question is B.

While the Part 107 regulations state a maximum altitude of 400 ft. AGL, you’re allowed to fly higher than that as long as you’re within 400 ft. of a tower / obstruction. You’re even allowed to fly up to 400 ft. over the topmost part of that tower. In this case, the height of the structures under construction 9 statute miles (SM) south of Norfolk Intl airport is 453 ft. AGL. If you’re flying “as high as allowed under Part 107,” you’d be flying 453 ft. AGL + 400 ft., or 853 ft. AGL.

For the intellectually curious students out there, here’s a follow-up question you might enjoy:

If you’re flying a drone at 853 ft. AGL, what airspace would you be in, and would you need authorization from the FAA to operate there?

At first glance, the structures sit in Class G airspace at the surface, and Class C airspace from 1,200 ft. MSL to 4,000 ft. MSL. But if you zoom out, it looks like the whole area is actually enveloped in the thick, fuzzy magenta line indicating Class E airspace starting at 700 ft. AGL.

So that means, and here’s where it gets fun:

• From the surface to 700 ft. AGL, it’s Class G airspace
• From 700 ft. AGL to 1,200 ft. MSL, it’s Class E airspace
• From 1200 ft. MSL to 4,000 ft. MSL, it’s Class C airspace

So at 853 ft. AGL, that would be Class E airspace. Because you’re flying vertically up into Class E airspace (i.e., entering a Class E transition area), you do NOT need airspace authorization as long as you’re within 400 ft. of the tower / obstruction that you’re inspecting.