Sectional Chart Decoder — Read Airspace, Airport Symbols & Numbers

Airport symbols

Blue vs. magenta tells you about the tower

Color is the fast read. Tap a symbol to see what it means for your flight.

Blue airport

Has an operating control tower

A blue airport symbol means the field has an operating air traffic control tower (Class B, C, or D airspace). The little tick marks are runways.

Authorization usually required

If the surface airspace around it is controlled (B/C/D), Part 107 ops there need ATC authorization — most easily through LAANC, otherwise FAA DroneZone.

Magenta airport

No operating control tower

A magenta airport symbol means no operating control tower at that field. It often sits in Class E or Class G airspace.

Check the surrounding airspace

No tower doesn't automatically mean "no authorization." If the airport sits inside a dashed magenta Class E surface area, you still need authorization. If it's in plain Class G, you don't — but you still follow all Part 107 rules.

Dashed magenta ring

Class E airspace to the surface

A dashed magenta circle is Class E airspace that starts at the surface, usually drawn around a non-towered airport that has instrument approaches. It is controlled airspace all the way down to the ground.

Authorization required

This is the classic trap: no tower, but still controlled to the surface. Part 107 ops here require ATC authorization. This is exactly the kind of question the chart-reading section loves.

Faded magenta vignette

Class E starting at 700 ft AGL

A soft, faded magenta shading (darker on the outside edge) marks Class E airspace that begins at 700 ft AGL — not at the surface.

No authorization needed below it

Because the controlled airspace doesn't start until 700 ft AGL, a normal Part 107 flight below 400 ft AGL is in Class G underneath — no ATC authorization required. (A faded blue vignette is the same idea but for Class E starting at 1,200 ft AGL.)

💡

Quick rule: solid blue or magenta lines = airspace boundaries you read for floors/ceilings. Faded shading = where Class E begins above the ground. A dashed magenta ring is the one that catches people — controlled to the surface even with no tower.

Airspace classes

Each class, and whether Part 107 needs a green light

Tap a class for how it's drawn, the numbers you'll see, and the authorization answer.

B

Class B

Solid blue lines · busiest airports

Drawn with solid blue lines in an upside-down wedding-cake of shelves around the busiest airports. Numbers like 100/SFC read as ceiling 10,000 ft MSL down to the surface.

Authorization required

LAANC is available at many Class B fields. No coverage there? Request through FAA DroneZone.

C

Class C

Solid magenta lines

Solid magenta lines, typically two rings around a moderately busy towered airport. Shelf numbers like 41/SFC = 4,100 ft MSL down to surface on the inner ring.

Authorization required

Get it via LAANC where available, otherwise DroneZone.

D

Class D

Dashed blue line

A dashed blue ring around a smaller towered airport. The blue boxed number (e.g. [25]) is the ceiling in hundreds of feet MSL — 2,500 ft MSL — down to the surface.

Authorization required

LAANC covers many Class D fields. The tower is only "operating" during published hours; outside them it may revert to Class E or G — but plan as if authorization is needed.

E

Class E

Magenta — surface or 700 ft AGL

Class E is controlled airspace that isn't B/C/D. Dashed magenta = starts at the surface (authorization required). Faded magenta = starts at 700 ft AGL. Faded blue = starts at 1,200 ft AGL.

Depends how it's drawn

Surface (dashed) Class E needs authorization. Class E that begins at 700/1,200 ft AGL leaves Class G underneath — no authorization for a sub-400 ft flight.

G

Class G

Uncontrolled — no boundary line

Class G is uncontrolled airspace. It has no special boundary line — it's simply what's there beneath the Class E floor (often up to 700 or 1,200 ft AGL, sometimes higher).

No authorization required

No ATC authorization needed — but every other Part 107 rule still applies: 400 ft AGL max, visual line of sight, see-and-avoid, weather minimums, and Remote ID.

The numbers

What the numbers on the chart actually mean

Floors, ceilings, tower heights, and frequencies — decoded.

100
SFC

Airspace shelf, ceiling over floor. Top number 100 = 10,000 ft MSL ceiling (in hundreds of feet). SFC = floor is the surface. So this shelf runs surface up to 10,000 MSL.

100
40

Floor that isn't the surface. 100 = 10,000 MSL ceiling, 40 = 4,000 MSL floor. The controlled shelf sits between 4,000 and 10,000 MSL — Class G is below 4,000.

[ 25 ]

Class D ceiling. A blue boxed number is the Class D top in hundreds of feet MSL — here 2,500 ft MSL — down to the surface.

1289
(287)

Obstruction height. Top = height above sea level (1,289 ft MSL). Bottom in parentheses = height above ground (287 ft AGL). Towers, antennas, and buildings use this.

Frequencies. CT = control tower frequency. The magenta Ⓒ marks the CTAF (Common Traffic Advisory Frequency) used at non-towered fields for self-announcing.

25 *L 72

Airport data line. Field elevation (25 ft), *L = lighting available (the * means see the Chart Supplement), and longest runway in hundreds of feet (72 = 7,200 ft).

⚠️

MSL vs. AGL is the #1 trap. Airspace floors and ceilings are in MSL (above sea level). Your 400 ft Part 107 limit is AGL (above the ground below you). Obstruction tops are given both ways — read which one the question wants.

Self-check

Five quick chart-reading questions

No supplement to flip to — just like the new format. Read it and answer.

Question 1 of 5Score: 0

Not sure if you need authorization?

Reading the chart tells you the airspace. The LAANC Required? tool walks the decision step by step — and kills the "5-mile rule" myth for good.

Do I Need Authorization? →

Chart reading is now half the battle.

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