Most explanations of airspace authorization stop at “you need ATC approval for controlled airspace, use LAANC.” That’s true and it’s not enough. Two specific things about 14 CFR 107.41 catch people repeatedly — on the knowledge test and on real jobs — and neither is obvious from reading the section once.
The first is that airspace floors are measured in MSL while you fly in AGL. The second is that only some Class E requires authorization, and the chart symbol for the kind that does looks nothing like the kind that doesn’t.
Here’s what 107.41 actually says, then both traps in detail.
What the section requires
Under 14 CFR 107.41, you need prior ATC authorization to operate in:
- Class B
- Class C
- Class D
- the lateral boundaries of the surface area of Class E designated for an airport
Class G — uncontrolled airspace — requires no authorization at any altitude Part 107 permits. Most low-altitude drone work happens here.
Two things that are not substitutes for authorization: announcing your intentions on the tower frequency, and staying low. There is no altitude beneath which controlled airspace stops applying. If you’re inside Class C at 100 feet AGL, you need authorization.
LAANC (Low Altitude Authorization and Notification Capability) automates this, granting near-real-time approvals in Class B, C, D, and surface-area Class E — at or below the altitudes published in the UAS Facility Maps. Note what LAANC is not: it isn’t a flight-plan filing system, and it has nothing to do with Remote ID serial numbers.
Trap 1: airspace floors are MSL, and you fly AGL
This is the one that produces genuinely illegal flights by pilots who believe they’re compliant.
Controlled airspace floors are charted in MSL — feet above mean sea level. Your drone’s altitude readout is AGL — feet above the ground where you took off. To know which airspace you’re in, you have to add your terrain’s elevation to your AGL altitude.
Work two cases under the same Class C shelf, charted 40/12 (ceiling 4,000 MSL, floor 1,200 MSL):
Case A — terrain at 800 feet MSL, flying 350 feet AGL. 800 + 350 = 1,150 MSL. The shelf floor is 1,200 MSL. You are 50 feet below it, so you’re in Class G — no authorization required. Under a shelf, the airspace beneath the charted floor is not Class C.
Case B — terrain at 900 feet MSL, mission needs 380 feet AGL. 900 + 380 = 1,280 MSL. That’s above the 1,200 MSL floor. You are inside Class C, and you need authorization under 107.41 — even though your controller reads a perfectly ordinary 380 feet.
Same shelf, same charted numbers, opposite legal answers. The only variables were 100 feet of terrain and 30 feet of altitude.
In Case B you have two lawful options: get the authorization, or cap the flight at 300 feet AGL (1,200 MSL) — and in practice, cap it lower, because 1,200 MSL exactly is the floor, not a safe margin. Barometric drift and terrain variation across your operating area both eat margin.
The habit to build: before any flight near a shelf, look up your site’s field elevation and write down your AGL ceiling as shelf floor minus terrain minus margin. Do it on the ground, not while flying.
Trap 2: only surface-designated Class E counts
Class E exists in more than one form, and 107.41 sweeps in only one of them.
Requires authorization: Class E designated to the surface for an airport. On a sectional this is a dashed magenta line. The “keyhole” extensions protruding from a Class D boundary are also dashed magenta — those are Class E surface extensions protecting instrument approach paths, and operations inside them require authorization too.
Does not require authorization: Class E beginning at 700 feet AGL (shown by a shaded magenta vignette, not a dashed line) or at 1,200 feet AGL. These are aloft, not at the surface, and 107.41 doesn’t list them.
That distinction has a real consequence. Consider inspecting a 900-foot tower in an area where Class E begins at 700 feet AGL. You fly at 750 feet AGL, within 400 feet of the structure. Is that legal?
Yes. You’re in Class E aloft, which 107.41 doesn’t cover, so no authorization is needed. And 750 feet is lawful because 107.51(b) permits flight higher than 400 feet AGL when you stay within a 400-foot radius of a structure and no higher than 400 feet above its top. Two rules, both satisfied, no authorization required.
Get the Class E distinction backwards and you’ll either request authorizations you don’t need or, worse, assume a dashed magenta boundary is the harmless kind.
Reading it off the chart
The symbols matter because this is how the question is actually posed — and how you’ll actually plan.
| Symbol | Airspace | Authorization? |
|---|---|---|
| Solid blue, stepped rings | Class B | Yes |
| Solid magenta rings | Class C | Yes |
| Dashed blue | Class D | Yes |
| Dashed magenta | Class E to the surface | Yes |
| Shaded magenta vignette | Class E from 700 ft AGL | No |
| Solid black outline | TRSA (radar service overlay) | No — only the Class D/E inside it |
| No boundary markings at all | Class G | No |
Two readings worth memorizing:
40/SFCon a Class C core — from the surface to 4,000 MSL. Any flight inside this ring needs authorization regardless of altitude.- An airport with no dashed boundary and no vignette sits in Class G at drone altitudes. No authorization needed — but 107.43 still prohibits interfering with operations at that airport, and right-of-way duties under 107.37 still apply fully.
A TRSA deserves its own note because the solid black outline looks official and alarming. It’s a legacy radar-service overlay around a Class D core. The rings themselves trigger nothing under 107.41; only the Class D (and any surface Class E) inside them does.
Above the grid value
One more thing people get wrong about LAANC. The altitudes in the UAS Facility Maps are the ceilings for automatic approval, not advisory suggestions and not the legal limit.
If your mission in Class D needs to exceed the grid value for that area, LAANC won’t auto-approve it. You submit a further-coordination request through LAANC, or an authorization request via FAA DroneZone — and you wait. What you may not do is proceed because “the grid values are advisory,” or announce intentions on the tower frequency and launch.
Rules stack — authorization covers only airspace
Worth stating explicitly, because it’s the same structural error that shows up everywhere in Part 107: a 107.41 authorization resolves the airspace requirement and nothing else.
A night flight in Class D over your own crew requires 107.41 (authorization), 107.29 (night training plus 3-statute-mile anti-collision lighting), and 107.39 (permitted only because those people are directly participating) — three separate compliance items, no umbrella. Similarly, Class G means no authorization, but Remote ID under Part 89 still applies to registered aircraft everywhere outside a FRIA.
Practice questions on this
1. Under 14 CFR 107.41, prior authorization from Air Traffic Control is required to operate in which airspace?
A. Class G airspace at any altitude
B. Class E airspace beginning at 700 feet AGL
C. Class B, Class C, or Class D airspace, or within the lateral boundaries of the surface area of Class E designated for an airport
Answer: C. 107.41 requires authorization (typically via LAANC or FAA DroneZone) for Class B, C, and D, and for surface-designated Class E areas. Class G needs none, and Class E beginning aloft at 700 feet is not included.
2. A site lies under a Class C shelf charted 40/12 (MSL). Terrain is 900 feet MSL and the mission requires 380 feet AGL. This flight:
A. Needs no authorization, since drone altitude is measured AGL
B. Penetrates the shelf and requires Class C authorization under 107.41
C. Is legal because shelves apply only to manned aircraft
Answer: B. Airspace floors are MSL: 900 + 380 = 1,280 MSL, which exceeds the 1,200 MSL floor, putting the aircraft inside Class C. Either obtain authorization or cap the flight at 300 feet AGL with margin.
3. A remote pilot needs to operate in Class D airspace above the UAS Facility Map grid value for that area. The pilot should:
A. Broadcast intentions on the tower frequency and proceed
B. Proceed, because grid values are advisory only
C. Submit a further-coordination request through LAANC or an authorization request via FAA DroneZone
Answer: C. Grid values are the ceilings for automatic LAANC approval. Above them, the operation requires further coordination or a DroneZone authorization, and the flight waits until it’s granted.
The short version
- 107.41 covers: Class B, C, D, and surface-designated Class E. Class G needs no authorization at any altitude.
- Airspace floors are MSL; you fly AGL. Add terrain elevation. Under a 1,200 MSL shelf, 800 ft terrain + 350 AGL = legal Class G; 900 ft terrain + 380 AGL = inside Class C.
- Dashed magenta = Class E to the surface = authorization required. Shaded vignette (700 ft AGL Class E) = no authorization.
- LAANC grid values are automatic-approval ceilings, not advisory. Above them: further coordination or DroneZone.
- Staying low is not a substitute for authorization, and neither is a radio call.
- Authorization covers airspace only — night (107.29), people (107.39), and Remote ID (Part 89) all still apply on their own terms.
Want to practice the whole regulations section this way? The free 90-question Regulations drill runs in your browser, and every answer names the section it comes from — so you can check any of the above against the regulation itself.
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Study aid only. Not flight instruction and not legal advice. Regulations change — always verify against current FAA publications and current charts before you fly. These are original questions written to the ACS standards from public FAA material, not FAA exam questions.