Airspace overview: controlled and uncontrolled

Before every flight you must assess the local airspace and any flight restrictions (14 CFR 107.49(a)(2)). To do that, you need a clear picture of how the sky is divided and which parts of it need permission. This lesson builds that picture. The next lessons add detail on busy airport airspace, special use airspace, temporary restrictions and how all of it is drawn on a sectional chart.

How airspace is organized

The FAA sorts airspace into two categories, regulatory and nonregulatory, and four types: controlled, uncontrolled, special use and other airspace (FAA Remote Pilot Study Guide, p. 5). How each area is set up depends on how busy and complex the traffic is, what kind of flying happens there, the level of safety needed, and national and public interest (FAA Remote Pilot Study Guide, p. 5).

"Controlled airspace" is a general term for the classes of airspace in which Air Traffic Control (ATC) service is provided according to the class (FAA Remote Pilot Study Guide, p. 5). Classes A, B, C, D and E are controlled (AIM 3-2-1); Class G is uncontrolled (AIM 3-3-1). The controlled classes that matter most to a remote pilot are B, C, D and E (FAA Remote Pilot Study Guide, p. 5).

The six classes at a glance

• Class A: generally from 18,000 feet MSL up to and including flight level 600. It isn't drawn on sectional charts (AIM 3-2-2) (Chart Users' Guide, p. 16), and a drone flying under Part 107's limits stays far below it.
• Class B: generally from the surface to 10,000 feet MSL around the nation's busiest airports, built in layers that can look like an upside-down wedding cake (FAA Remote Pilot Study Guide, p. 5).
• Class C: generally from the surface to 4,000 feet above the airport elevation, around airports with an operating control tower and radar approach control (FAA Remote Pilot Study Guide, p. 6).
• Class D: generally from the surface to 2,500 feet above the airport elevation, around airports with an operating control tower (FAA Remote Pilot Study Guide, p. 6).
• Class E: the controlled airspace that isn't Class A, B, C or D. It covers a large part of the United States and typically extends up to, but not including, 18,000 feet MSL (FAA Remote Pilot Study Guide, p. 6).
• Class G: the airspace not designated as Class A, B, C, D or E. It runs from the surface up to the base of the Class E airspace above it (FAA Remote Pilot Study Guide, p. 6).

The rule that decides: 107.41

Part 107 says you may not fly in 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 you have prior authorization from ATC (14 CFR 107.41). That gives you four places that need permission before takeoff:

1. Class B airspace.
2. Class C airspace.
3. Class D airspace.
4. A Class E surface area designated for an airport.

Class G never needs ATC authorization (FAA Remote Pilot Study Guide, p. 6), and in most cases neither does Class E, as long as it isn't an airport surface area (FAA Remote Pilot Study Guide, p. 6). How you request an authorization is covered in the next lesson.

Class E: three floors to know

In most areas Class E begins at 1,200 feet AGL. In many other areas it begins at the surface or at 700 feet AGL, and some Class E starts at an MSL altitude printed on the chart. Where the chart shows no lower base, Class E begins at 14,500 feet MSL (FAA Remote Pilot Study Guide, p. 6).

• Surface area: Class E that starts at the ground around an airport with no control tower in operation (AIM 3-2-6). It is drawn with a dashed magenta line (Chart Users' Guide, p. 17). This is the kind of Class E that needs authorization under 107.41.
• 700 feet AGL: shown by a faded magenta band called a vignette (Chart Users' Guide, p. 17). These transition areas stay in effect all the time, whatever the airport's hours (AIM 3-2-6).
• 1,200 feet AGL: where this floor borders Class G airspace, it is shown by a blue vignette (Chart Users' Guide, p. 17).

Why does this matter? Part 107 limits you to 400 feet above ground level, unless you stay within 400 feet of a structure (14 CFR 107.51(b)). Under a 700-foot or 1,200-foot floor, then, a drone at or below 400 feet AGL is in the Class G airspace underneath.

Part-time airspace and overlaps

Some control towers close at night. When a part-time Class D surface area isn't in effect, it may become a Class E surface area or Class G airspace, and its hours are published in the Chart Supplement (AIM 3-2-5). When two airspace designations apply to the same airspace, the rules of the more restrictive one apply (AIM 3-1-3).

Uncontrolled doesn't mean unregulated

In the FAA's words, there is no such thing as "unregulated" airspace (FAA Airspace 101). The AIM makes the same point: all airspace is regulated, and certain rules apply throughout (AIM 11-4-6). In Class G you still keep the drone within visual line of sight (14 CFR 107.31), give way to all other aircraft (14 CFR 107.37), stay out of the way of airport traffic (14 CFR 107.43) and obey temporary flight restrictions (14 CFR 107.47).

Worked example

You are hired to photograph a farm about 4 nautical miles from Millbrook Municipal, a small airport with no control tower. On the sectional, the airport is ringed by a dashed magenta line, and the whole area, farm included, sits on the shaded side of a faded magenta band. The farm is outside the dashed line. You plan to fly at 250 feet AGL.

1. What starts at the surface? The farm isn't inside any Class B, C or D boundary, and it's outside the dashed magenta line, so it isn't in the airport's Class E surface area.
2. Where does Class E begin? The faded magenta band means Class E starts at 700 feet AGL (Chart Users' Guide, p. 17).
3. Where is the drone? At 250 feet AGL it is below that floor, in Class G. No ATC authorization is needed (FAA Remote Pilot Study Guide, p. 6).
4. The second job. The client also wants photos of the hangars, inside the dashed magenta line. That is a Class E surface area designated for an airport, so you need prior ATC authorization first (14 CFR 107.41), and you must not interfere with the traffic pattern (14 CFR 107.43).

Either way, your preflight check of the airspace and any flight restrictions still applies.

Common mistakes

• Thinking all Class E airspace needs authorization. Only the surface area designated for an airport does.
• Treating "uncontrolled" as "no rules". Class G removes the need for ATC authorization, not the rest of Part 107.
• Reading the Class C and Class D heights as feet above the ground. They are measured from the airport elevation and charted in MSL (FAA Remote Pilot Study Guide, p. 6).
• Forgetting that part-time airspace changes class. Check the airport's hours before you fly.
• Confusing the magenta vignette (Class E from 700 feet AGL) with the dashed magenta line (Class E from the surface).