We Asked the FAA About Facility Map Ceilings Outside Controlled Airspace. Here Is the Answer.

If you have ever opened a LAANC app at a spot miles from the airport and seen a 0 ft ceiling, you have met the question this post is about. The FAA's UAS Facility Maps are the grid LAANC answers from. Each cell carries a ceiling, the highest altitude LAANC will approve automatically there. What the cell does not carry is a floor. So when a 0 ft cell sits well outside the airport's surface area, under a shelf of Class B or Class C airspace whose floor is thousands of feet up, the map alone cannot tell you whether a flight at 400 ft needs authorization or is in Class G.

We built SkyCheck to refuse to guess in the permissive direction. For most of 2026 it disclosed every such cell, held the ceiling, and told you to read the floor from the sectional. That was honest, and it was also unsatisfying at places like Boulder City, Nevada, 17 miles from Las Vegas under a shelf that begins at 6,500 ft MSL. So on October 13 we asked the FAA.

The question

We sent the FAA UAS Support Center (UASHelp@faa.gov) three real cells from the October 2026 maps and one question: for a Part 107 operation at or below 400 ft AGL at a point where the controlled airspace above has a floor higher than 400 ft, is ATC authorization required because the map ceiling governs the cell, or is no authorization required because the operation is in Class G beneath the shelf?

The answer

The reply came the same day. Two sentences settle it, quoted here with the Support Center's permission:

"No authorization needed under the controlled airspace floor. Authorization is required within the lateral boundary of controlled airspace at your altitude."

And on the map ceilings themselves:

"'Map ceilings' are how high you may fly with automatic approval. Above that, you need further coordination. If you are inside controlled airspace boundary at your altitude, you must file."

Of the three example points, the Support Center put one inside the Las Vegas Class B surface area and the other two, near Los Angeles and Allentown, in Class G under a shelf.

This is a help-desk answer to a question, not a rule. The rule is 14 CFR 107.41, which requires authorization in Class B, C or D airspace and within a Class E surface area. What the FAA's answer does is say how to read a facility map against that rule: the map applies inside controlled airspace. Below the floor of a shelf you are not inside it.

What "at your altitude" means for you

The second sentence is the one to keep. A shelf is three-dimensional. At Allentown the Class C shelf begins at 2,200 ft MSL, about 1,800 ft above the ground. A drone at 400 ft AGL is in Class G there. A drone that somehow climbed to 1,900 ft AGL would be inside the Class C, where the map's 0 ft ceiling applies and LAANC will not help you. The floor is the boundary, and the boundary is measured against the ground under you.

That is why the ground elevation matters as much as the chart. A shelf floor of 2,000 ft MSL is 2,000 ft above the ground at sea level and 500 ft above the ground on a 1,500 ft ridge. Boulder City sits about 1,300 ft higher than the Lake Mead shore a few miles away.

What changed in SkyCheck

Since October 13, SkyCheck carries the FAA's own shelf outlines, with each floor as the FAA filed it, and reads them at your point:

• Under a shelf, SkyCheck reads the ground elevation at your exact coordinates and clears the cell as Class G when your planned altitude is under the floor by at least 500 ft. The Allentown cell that used to read CHECK LOCAL RULES at 0 ft now reads CLEAR TO FLY at 400 ft, and the FAA's answer is printed on the cell.
• If the floor is within reach, SkyCheck caps your altitude at the Class G under it and says so.
• If the floor is within 500 ft of the ground, or the elevation cannot be read, nothing is cleared: the ceiling stands and you are sent to the sectional, as before.
• Cells inside a Class E extension, and cells where the FAA draws no controlled airspace at all (most of them around military fields), keep their ceiling. The FAA's answer was about shelves, and we apply it to shelves.

The 500 ft margin is deliberate. Terrain models have error, you move around within a cell, and the cost of being wrong in the permissive direction is a violation. We would rather send a few pilots to the sectional than clear one who should not have been.

The map now draws the shelf over your point as a dotted outline in the class color, with its floor in the popup, so you can see where it begins and ends.

Before you fly under a shelf

1. Know the floor. The sectional chart prints it, and SkyCheck draws the shelf and names the floor on the map.
2. Know your ground elevation. The floor is MSL; your altimeter reads AGL.
3. Keep the margin. If your planned altitude plus the ground elevation comes within a few hundred feet of the floor, treat the point as inside the controlled airspace and get authorization.
4. If the cell is 0 ft and you need to be inside the shelf, LAANC will not authorize it. The route is a manual request through FAA DroneZone.

Run the check at uas-skycheck.app/check to see the shelf over any point, its floor, and whether your planned altitude is under it. For the background on Class B shelves, read Class B airspace drone rules; for what CHECK LOCAL RULES means elsewhere, why we changed 2,200 zones from red to yellow; for how LAANC works, what is LAANC.

Informational only; not legal advice. The FAA UAS Support Center's reply was given in answer to a specific question on October 13, 2026 and is quoted with its permission; it is not an endorsement of UAS SkyCheck. Rules change. This post reflects the regulations as we understood them on the date above and is not updated automatically. Verify current federal rules at faa.gov/uas, and any state or local rules with the relevant authority, before you fly.