One of the most practical and heavily tested skills for any FAA Part 107 remote pilot is the ability to look at a sectional chart, identify the class of airspace overhead, and determine exactly where that airspace begins and ends — both horizontally (laterally) and vertically. Unlike manned pilots who can ask ATC for advisories, small UAS operators must proactively determine their operating environment before the motors spin. A single mistake about where Class D airspace ends, or whether a surface area extends to a certain GPS coordinate, can mean an unauthorized incursion — triggering certificate suspension, civil penalties, or worse, a collision with an arriving airliner on short final.
This article walks through how each class of controlled airspace is shaped, where to find its boundaries on a sectional aeronautical chart, and the specific numbers and techniques the FAA expects you to know for the Part 107 Aeronautical Knowledge Test.
How Airspace Boundaries Are Defined
The FAA defines airspace boundaries in two dimensions: lateral (the footprint on the ground, measured in nautical miles from a reference point or depicted on charts as rings and lines) and vertical (expressed as altitudes in feet mean sea level, or MSL, or as AGL — above ground level — for surface areas). For Part 107 purposes, your operating ceiling under a standard waiver-free authorization is 400 feet AGL, so most UAS operations happen well below the bases of most en route airspace, but surface-based controlled airspace is the critical concern.
Class B Airspace
Class B surrounds the nation's busiest airports (think major hubs). Its lateral and vertical structure looks like an upside-down wedding cake: a core surface area at the primary airport ringed by successively wider layers that start at increasing altitudes. Each layer is depicted on a sectional chart with a solid blue line. Inside those blue rings you will see altitude numbers formatted as upper limit/lower limit — for example, 100/SFC means the airspace extends from the surface to 10,000 feet MSL, while 100/40 means it runs from 4,000 to 10,000 feet MSL.
For drone operations, Class B requires prior authorization from ATC before flight. The lowest shelf of Class B may begin at 1,200 or 2,000 feet AGL, which is far above a typical UAS flight, but the innermost ring extends to the surface. A remote pilot who operates anywhere inside any Class B ring — even at 50 feet AGL — without authorization is in violation. Always check all rings, not just the one closest to the airport.
Class C Airspace
Class C surrounds airports that have an operational control tower and radar approach control, with a significant volume of instrument operations. Its standard shape on a sectional is two concentric magenta circles. The inner circle has a radius of approximately 5 nautical miles and extends from the surface to 4,000 feet above the primary airport elevation. The outer circle has a radius of approximately 10 nautical miles and typically begins at 1,200 feet AGL and extends to 4,000 feet above the primary airport elevation.
Because the inner circle extends to the surface, any UAS operation within roughly 5 nm of a Class C airport requires authorization. The outer ring base of 1,200 feet AGL is usually above the 400-foot AGL UAS ceiling, so operations in the outer ring may be permissible — but you must confirm the exact altitudes on the chart rather than assume the standard dimensions apply, because Class C airspace is often modified to fit the local terrain and traffic pattern.
Class D Airspace
Class D airspace exists around airports that have an operational control tower but no radar approach control. On a sectional chart, it appears as a dashed blue rectangle or irregular polygon with the ceiling printed in hundreds of feet MSL inside brackets — for example, [27] means the ceiling is 2,700 feet MSL. Class D always begins at the surface. The lateral boundary typically extends about 4 to 5 nautical miles from the primary runway, though the exact shape is tailored to instrument approach procedures and depicted on the chart.
A critical nuance: Class D is only in effect when the control tower is operational. When the tower is closed, the airspace typically reverts to Class E or Class G. Check NOTAMs and the Airport/Facility Directory (now called the Chart Supplement) for tower hours. Many Part 107 test questions hinge on this: if the tower is closed, authorization for that specific Class D designation is no longer required — though other airspace rules may still apply.
Class E Airspace
Class E is the most common controlled airspace and can be the trickiest for drone pilots because it often starts at the surface near smaller airports that have instrument approaches but no control tower. On a sectional, a dashed magenta line indicates that Class E begins at the surface within that boundary. A faded magenta vignette (magenta shading) indicates that Class E begins at 700 feet AGL — usually in the vicinity of an airport. Without any special depiction, Class E begins at 1,200 feet AGL, which is generally above the UAS operating ceiling.
For drone pilots, surface-area Class E (inside a dashed magenta ring) requires authorization just like Class D or C. Operations in the 700-foot transition area (magenta shading) are typically fine at or below 400 feet AGL because the airspace floor is above you, but confirm the specific altitude numbers. Class E has no upper boundary until it reaches Class A at 18,000 feet MSL.
Class G Airspace
Class G is uncontrolled airspace — no ATC authorization is required. In most of the continental United States away from airports, Class G extends from the surface up to 1,200 feet AGL (where Class E begins). In remote areas, Class G may extend to 14,500 feet MSL. For the vast majority of Part 107 operations in rural or suburban areas without surface-area controlled airspace, you are flying in Class G and need no airspace authorization, though all other Part 107 rules still apply.
Why It Matters
Unauthorized entry into controlled airspace is one of the most serious violations a remote pilot can commit. Manned aircraft rely on the integrity of controlled airspace boundaries for separation from other traffic. A drone operating near an airport without authorization — even at low altitude — can distract controllers, trigger TCAS alerts in airliners, and create a collision hazard. Beyond safety, the FAA actively enforces these boundaries through radar track data and reports from pilots and controllers. Civil penalties under 49 U.S.C. can reach thousands of dollars per violation, and the remote pilot certificate can be suspended or revoked.
Key Numbers and Rules
- Class B inner ring: Surface to approximately 10,000 feet MSL; depicted with solid blue lines; read altitude as upper/lower in hundreds of feet.
- Class C inner ring: Surface to 4,000 feet above the primary airport elevation, radius approximately 5 nm; outer ring approximately 5–10 nm, from 1,200 AGL to 4,000 feet above the primary airport elevation; depicted with solid magenta lines.
- Class D: Surface to ceiling shown in brackets (e.g., [27] = 2,700 ft MSL); roughly 4–5 nm radius; dashed blue line; only active when tower is operational.
- Surface-area Class E: Dashed magenta line on sectional; requires authorization for UAS operations.
- 700-foot Class E transition area: Magenta shading; floor is 700 ft AGL, typically above UAS altitude — but confirm on chart.
- Standard Class E floor away from airports: 1,200 ft AGL — above the Part 107 400-ft ceiling in most cases.
- Class G: Uncontrolled; no authorization required; extends from surface to Class E floor.
- LAANC and DroneZone: The FAA's Low Altitude Authorization and Notification Capability (LAANC) provides automated, near-real-time authorization for many Class B, C, D, and surface E airports — use it before every flight in controlled airspace.
Reading the Chart: A Practical Method
When planning a drone flight, plot your intended location on a current sectional aeronautical chart (or an FAA-approved app using current data). First, identify the nearest airport and note what color depicts its airspace boundary: solid blue = Class B, solid magenta = Class C, dashed blue = Class D, dashed magenta = surface Class E. Then read the altitude data associated with the boundary you are inside. Compare those altitudes to your planned operating altitude. If any portion of controlled airspace sits at or below your planned altitude at your location, you need authorization before flight. If the floor is above 400 feet AGL at your specific location, you are operating in Class G or in the airspace below a Class E transition area and no authorization is required — though you must still remain below 400 feet AGL.
Common Test Traps
- Assuming all Class C outer rings require authorization: If the outer ring floor is at 1,200 feet AGL and you are flying at 400 feet AGL, you are below the airspace and no authorization is needed — but you must verify the actual altitude, not assume the standard.
- Ignoring Class D when the tower is part-time: Class D only exists while the tower is open. Check the Chart Supplement for hours and check NOTAMs for temporary closures.
- Misreading the altitude format in Class B: The notation 100/40 means 10,000 MSL ceiling and 4,000 MSL floor — not 100 and 40 feet. Each number represents hundreds of feet.
- Confusing dashed blue (Class D) with dashed magenta (surface Class E): Both require authorization, but they are different classes with different rules and chart colors. Know which is which.
- Forgetting that authorization covers only a specific location and altitude: A LAANC approval for 200 feet AGL at one spot does not give blanket permission across the entire airport's airspace. Always operate within the grid tile and altitude that was approved.