Read airspace classes and chart symbols: FAA colours, line types, altitude limits, restricted-area blue hatching and MOA magenta hatching.
Read an airspace chart by identifying the authority and legend, tracing each boundary, then comparing its published floor and ceiling with your altitude. On FAA sectional charts, solid blue marks Class B, solid magenta Class C, dashed blue Class D; Class E uses dashed magenta or magenta or blue shading; Class G is inferred.
For Aviation & Real-World Flying, we use FAA sectional conventions below where the question concerns US charts. The chart’s own legend remains authoritative: ICAO airspace classes are international, but colours, line styles, labels and altitude conventions are not identical worldwide.
FAA airspace classification chart and legend
FAA sectional charts distinguish controlled airspace through a combination of colour, line style, shading and altitude labels.
| Class | Typical FAA sectional symbol | How to interpret it |
|---|---|---|
| Class A | Not normally outlined locally | Generally extends from 18,000 feet MSL through FL600 in the US and is operated under IFR. |
| Class B | Solid blue boundary | Read the floor and ceiling printed for each sector. Different shelves can begin at different altitudes. |
| Class C | Solid magenta boundary | Usually has a surface core and one or more shelves, but the actual shape and limits are charted rather than guaranteed. |
| Class D | Dashed blue boundary | Normally surface-based around a towered airport. A boxed number gives the ceiling in hundreds of feet MSL. |
| Class E | Dashed magenta, magenta vignette, blue vignette or labelled boundary | Dashed magenta means Class E begins at the surface. Magenta shading commonly marks a 700-foot AGL floor; blue shading or labels identify a 1,200-foot AGL or other designated floor. |
| Class F | Not used in the US system | Class F can appear in other countries, subject to their national rules and chart conventions. |
| Class G | Usually no dedicated boundary | Class G is the uncontrolled airspace below the base of the controlled airspace above it, where no other class applies. |
This table works as a quick US airspace map legend, but colour alone is not enough. A solid, dashed, hatched or shaded line can have a completely different meaning even when its colour is similar.
What colour and line type denotes restricted areas on sectional charts?
On FAA sectional charts, a restricted area is enclosed by a blue hatched or comb-style boundary and identified by an R-#### designator.
It is not the same as the dashed blue boundary used for Class D. At low resolution, the inward hatching can resemble dashes, so follow the line until you find the restricted-area identifier.
What colour and line type denotes military operations areas on sectional charts?
A military operations area, or MOA, is shown by a magenta hatched or comb-style boundary, normally with the area’s name and MOA printed nearby.
A magenta MOA boundary must not be confused with solid magenta Class C, dashed magenta surface Class E or a magenta Class E vignette. The hatching and the MOA label are the decisive features.
| Special-use area | FAA sectional marking | Operational meaning |
|---|---|---|
Restricted area R-#### | Blue hatched boundary | Hazardous activity may occur. Entry is subject to the published restrictions and authorisation. |
Prohibited area P-#### | Blue hatched boundary | Flight is prohibited unless specifically authorised. |
Warning area W-#### | Blue hatched boundary | Potentially hazardous activity, generally offshore; it is not legally identical to a restricted area. |
| Military operations area | Magenta hatched boundary | Military training may include high-speed or abrupt manoeuvres. An MOA is not automatically closed to VFR traffic. |
Alert area A-#### | Magenta hatched boundary | High-volume training or unusual aerial activity may occur. All pilots retain collision-avoidance responsibility. |
Special-use airspace is an overlay, not another Class A–G category. An MOA can occupy Class E airspace, for example, so both the MOA information and the underlying airspace rules matter.
The chart margin or associated aeronautical information gives the area’s floor, ceiling, scheduled times, controlling agency and other details. Status can change, and temporary flight restrictions may not appear on a printed or cached chart. The full-resolution FAA sectional chart downloads are useful when hatching is unreadable on a reduced moving-map image.
How do I read airspace altitude labels?
Airspace labels must be read as a vertical stack, with the ceiling normally shown above the floor on US Class B and C shelf labels.
| Chart notation | Meaning |
|---|---|
100/40 | Ceiling 10,000 feet MSL and floor 4,000 feet MSL. The figures are hundreds of feet. |
40/SFC | From the surface to 4,000 feet MSL. |
−25 in a Class D ceiling box | The ceiling is below 2,500 feet MSL; the minus sign means 2,500 feet itself is not included. |
700 AGL | 700 feet above the terrain directly below, not an altimeter indication of 700 feet. |
FL180 | Flight level 180, referenced to standard pressure rather than the local altimeter setting. |
Never compare an AGL limit directly with an MSL altitude. A 700-foot AGL Class E floor follows the terrain, while a 4,000-foot MSL Class B shelf remains fixed relative to mean sea level.
How do I determine which airspace the aircraft is in?
Determine the aircraft’s horizontal position first, then compare its altitude with every floor and ceiling at that position.
- Confirm the chart source. Check the country, chart type, edition, effective period and legend before interpreting any airspace markings.
- Plot the horizontal position. Use coordinates, landmarks, a navigation fix or a simulator position display, then transfer that position accurately to the chart.
- Trace the complete boundary. Follow the line to its label rather than deciding from a short coloured segment. Roads, routes, borders and other airspace boundaries can look similar when zoomed out.
- Read the floor and ceiling. Expand figures in hundreds of feet and distinguish
MSL,AGL,SFC,GNDand flight levels. - Build the vertical stack. Identify what lies below, at and above the aircraft’s altitude. A position inside a Class B outline is not inside Class B when it remains below that shelf.
- Check status and rules. Account for tower hours, special-use activation, temporary restrictions, communications, weather minima and equipment requirements.
For example, beneath a Class B shelf labelled 100/40, an aircraft at 3,500 feet MSL is below Class B because the shelf starts at 4,000 feet MSL. It is not necessarily in Class G; the underlying airspace may be Class C, D or E. Our step-by-step method for reading a US VFR sectional covers the airport, terrain, obstacle and navigation symbols needed to complete that interpretation.
Does identifying the symbol tell me whether I may enter?
An airspace symbol identifies the volume, but entry clearance, communications, equipment and flight-rule requirements must be checked separately.
- Class B: US operations require an explicit ATC clearance before entry.
- Classes C and D: Two-way radio communication must be established before entry under the applicable US rules.
- Class E: It is controlled airspace even though VFR entry does not normally require a specific clearance.
- Class G: “Uncontrolled” does not mean rule-free; weather, visibility and other operating requirements still apply.
- Restricted areas: Published restrictions and active status determine whether transit is authorised.
- MOAs: VFR flight is not automatically prohibited, but obtaining the activity status and exercising extra caution are sensible operational steps.
Tower operating hours can also change the answer. When a Class D tower closes, the surrounding airspace may revert to Class E or Class G according to its published arrangement; the dashed blue boundary alone does not prove that Class D is active.
How are control zones shown on ICAO charts (wie sind Kontrollzonen in ICAO-Karten dargestellt)?
An ICAO control zone is normally labelled CTR, begins at the surface and has a charted lateral boundary and upper limit, but its colour and line style depend on the national chart specification.
Kurzantwort auf Deutsch: Kontrollzonen sind in der Regel mit CTR, einer seitlichen Begrenzung sowie der Obergrenze gekennzeichnet; sie beginnen am Boden. Farbe und Linientyp richten sich nach der Legende der jeweiligen nationalen ICAO-Karte.
A CTR may be assigned Class C, D or another class according to the state concerned. Do not assume that every control zone is Class D, or apply the FAA blue-and-magenta sectional legend to a German, British, European or other national chart.
Which mistakes cause airspace symbols to be misread?
Most wrong answers come from reading an aviation map as a flat picture instead of a labelled three-dimensional stack.
- Using colour without line style: Dashed blue is Class D; blue hatching is restricted, prohibited or warning airspace.
- Reading a reduced image: Hatching and vignettes can disappear or look dashed. Use the full-resolution chart and trace the line to its label.
- Assuming every ring has the same floor: Class B and C shelves can change by sector, not just by distance from the airport.
- Mixing MSL and AGL: Convert each limit using the correct reference before comparing it with the aircraft’s altitude.
- Assuming outside B, C or D means Class G: Much of the remaining US airspace is Class E.
- Treating special-use airspace as a class: An MOA or restricted area overlays the surrounding Class A–G structure rather than replacing it.
- Using an old chart or ignoring notices: Boundaries, frequencies, operating times and temporary restrictions can change.
Why might a simulator map disagree with the chart?
A simulator moving map may use a different navigation-data cycle, simplify boundaries, hide labels through decluttering or omit temporary and activation information.
Use the simulator map for position awareness, not as proof of the legal airspace structure. Our guide to applying aeronautical charts in a flight simulator explains how to match chart type, data age, altitude references and the aircraft’s simulated position.