Chart Reading Part 1 – Understanding Airspace

For years I’ve been recycling my old charts to use as wrapping paper for the Christmas gifts I give my friends and family, using the most interesting/complicated looking areas of Sectionals, IFR Low, and TACs. Usually, if it’s the first time they’ve seen one, they’ll stare at the map for a couple of minutes and say something along the lines of “this looks so cool, but how the hell do you read it?”, and that is a very good question. Unlike most maps, where what you see on the map is something that you can physically see in the real world, aeronautical charts are covered in lines and symbols for things that aren’t physical and cannot be seen, but still exist. As a pilot, you have to be able to interpret and visualise those lines and symbols in order to fly safely and efficiently, and adhere to the regulations.

In this article we’re going to take a look at the National Airspace System and the elements that it consists of, including:

  • The different airspace classes, their operating rules and requirements;
  • VFR weather minimums;
  • Special use airspace; and,
  • Other airspace areas.

Cheat Sheet

If you’re in a hurry and just need a quick refresher then check out this airspace summary.

Summary of different airspaces and their requirements/regulations.
Airspace Summary. Source: Instrument Flying Handbook

Airspace Classes, Rules & Requirements

In the US the National Airspace System is made up of controlled airspace (Class A, B, C, D, and E), uncontrolled airspace (Class G), special use airspace, and other airspace areas. The airspace designated by letters are the ones that you need to know and memorise the regulations and requirements for as these are the most common that you will encounter whilst flying. Special use and other airspace you should know of, but you don’t necessarily need to memorise all the information about them unless you think you may be flying through or near one on your route.

Before we get into the details of each airspace class, here’s a short description of each one and the nicknames I used for them that helped me remember when I was learning.

AAirlinersIFR traffic only, above 18,000 ft MSL (mean sea level).
BBusyVery busy/large airports (e.g. LAX).
CCitiesFull time tower, but not busy enough to be class B.
DtowereDBusy small airports, used primarily by general aviation.
EEnrouteControlled airspace, provides services for IFR aircraft.
GGroundUncontrolled airspace.

Class A – IFR Only “Airliners”

If you’ve just started learning to fly then it’s unlikely that you’ll be going anywhere near Class A airspace, even if your home airport happens to be Lake County (KLXV) with an elevation of 9933 ft MSL. But, it’s still important to know that Class A starts at 18,000 ft MSL and goes all the way up to FL600 (that’s 60,000 ft MSL) throughout the contiguous United States and Alaska, including the airspace overlying the waters within 12 nautical miles of the coastline.

To enter Class A, you will need to have an instrument rating, be flying under an IFR flight plan, and have an ATC clearance; VFR flight is not allowed. You will also need to be flying an aircraft that is capable of two-way radio communication with ATC and is equipped with a mode C transponder (plus ADS-B Out after 1 January 2020).

Class A is not depicted on charts.

Class B – “Busy” Airports

Ah, Class B airspace, that scary looking mess of lines and numbers on your chart that the AIM tries to innocently describe as resembling an “upside-down wedding cake”. This airspace is reserved for the nation’s busiest airports in terms of IFR operations or passenger enplanements (i.e. airlines), and generally starts at the surface and extends up to 10,000 ft MSL. Each Class B airspace is individually tailored for the airport it belongs to and consists of a surface area and two or more layers extending outwards from that; being designed to contain all published instrument procedures once an aircraft enters the airspace. Another factor unique to Class B is the Mode C Veil, extending from the surface upwards to 10,000 ft MSL in the airspace within 30 nautical miles of the airport, it indicates that you must have a Mode C transponder within that zone.

Class B airspace
Seattle Class B Airspace

If you are going to fly inside Class B then you should also have the relevant Terminal Area Chart (TAC), along with the Sectional Chart. TACs have a scale of 1:250,000 (versus the Sectional scale of 1:500,000) and give you a more detailed image of the area you will be flying, providing information that wouldn’t fit on your Sectional.

Operating Inside Class B

In order to operate within Class B under VFR, you will need to comply with the following requirements:

  • Minimum pilot qualifications – private pilot, or a student pilot with an endorsement (14 CFR §61.95)         .
  • Entry – ATC clearance*.
  • Equipment – Mode C transponder and two-way radio.
  • VFR weather minimums – 3 statute miles (SM) visibility, clear of clouds.
  • Speed restriction – No more than 200 knots when in the airspace underlying Class B or in a VFR corridor through Class B (14 CFR §91.117).

*Note – ATC clearance is not guaranteed, especially if they’re busy with airliners; always have a plan B (pun intended) just in case you can’t get in to or through the airspace!

ATC services:

  • Separation is provided for all aircraft operating inside Class B.

Class C – “Cities”

Class C airspace usually covers airports that are medium-large in size and deal with a mixture of airlines and general aviation traffic. These airports have a full-time control tower and are serviced by a radar approach control. Typically, the airspace consists of two layers: a 5 NM radius core surface area that extends from the surface up to 4,000 feet above the airport elevation, and a 10 NM radius shelf area that extends no lower than 1,200 feet up to 4,000 feet above the airport elevation.

On the sectional chart Class C airspace is represented by solid magenta lines, with the upper and lower limits indicated inside each section of airspace. Sometimes, like in the case of Portland airspace, there will be an inset on your sectional chart showing the airspace in greater detail.

Class C airspace
Portland Class C Airspace

Operating Inside Class C

VFR requirements:

  • Minimum pilot qualifications – student pilot.
  • Entry – established two-way radio communication*.
  • Equipment – Mode C transponder and two-way radio.
  • VFR weather minimums – 3 SM visibility; separated from clouds by 500 ft below, 1,000 ft above, 2,000 ft horizontal.
  • Speed restriction – No more than 200 knots when at or below 2,500 ft AGL and within 4 NM of the primary airport, unless ATC approves a higher speed.

*Note – “established” in this case means that ATC has responded to you with your aircraft callsign.

ATC services:

  • Separation of IFR aircraft from other IFR and VFR aircraft.
  • VFR flight following (i.e. radar traffic information service AIM 4-1-15) – this provides VFR aircraft with traffic advisories but is only available on a workload permitting basis; if the controllers get too busy then they can terminate the service.

Class D – “towereD”

Chances are that you probably started your flight training out of a Class D airport as it’s quite common throughout the US at small, but relatively busy, airports that are used primarily for general aviation. Class D airports have either full-time or part-time control towers, and when a part-time control tower is not in use then the airspace becomes either Class E or Class G. This information is available in the Chart Supplement, so it’s important to check that for each airfield you fly in or out of.

On the sectional chart Class D airspace is represented by dashed blue lines, with the upper limit indicated inside a dashed blue square and lower limit being the surface unless otherwise noted. The airspace lines usually circle the airfield at a 4 NM radius but could be modified to fit with other airspace boundaries or instrument approaches.

Class D
Pendleton Class D Airspace

Operating Inside Class D

VFR requirements:

  • Exactly the same as Class C, except you don’t require a transponder.

ATC services:

  • Separation provided for runway operations.

Class E – “Enroute”

Class E exists to provide controlled airspace services to IFR traffic, without imposing a communications requirement on VFR traffic. This is probably the most common type of airspace you’ll be flying in when you’re learning to fly, in most areas it extends from 1,200 ft AGL, up to, but not including, the floor of Class A airspace at 18,000 ft MSL; in other areas the base is either the surface or 700 ft AGL (the airspace above FL600 is also Class E, but good luck getting to that altitude!). Even though Class E doesn’t affect you much when you’re flying under VFR, it can help your situational awareness to know the boundaries, especially near airfields where you might expect IFR traffic.

There are a few different ways that Class E is represented on the Sectional Chart. In the example below you’ll see a staggered blue line, indicating a boundary between two Class E airspaces; dashed magenta line, indicating Class E beginning at the surface; and a shaded magenta line, indicating Class E beginning at 700 ft AGL on the soft side, and 1,200 ft AGL on the hard side. There’s one more way to depict Class E, but we’ll get to that in the next image.

Class E airspace
Class E Airspace near Bowerman

Operating in Class E

VFR requirements:

  • Minimum pilot qualifications – student pilot.
  • Entry – no requirements.
  • Equipment – no requirements.
  • VFR weather minimums when below 10,000 ft MSL – 3 SM visibility; separated from clouds by 500 ft below, 1,000 ft above, 2,000 ft horizontal.
  • VFR weather minimums when at or above 10,000 ft MSL – 5 SM visibility; separated from clouds by 1,000 ft below, 1,000 ft above, 1 SM horizontal.
  • Speed restriction – No more than 250 knots when below 10,000 ft MSL.

ATC services:

  • Separation of IFR aircraft from other IFR aircraft.
  • VFR flight following – available on request depending upon ATC workload, and whether you are in radar coverage.

Class G – Uncontrolled Airspace “Ground”

Once upon a time there was huge swathes of uncontrolled airspace across the US, but that has been whittled down over time by the increase in IFR traffic and number of airports so that now Class G only exists almost exclusively in thin slithers of airspace near the ground. You won’t find it explicitly depicted on your Sectional, but it’s the portion of airspace that hasn’t been designated as one of the airspaces we’ve already talked about and almost always has Class E lying above it.

In the image below you’ll see one of the very, very few areas in the US where Class G extends above 1,200 ft AGL. In this case, the shaded blue line indicates that Class E begins at 1,200 ft AGL on the soft side, and 14,500 ft MSL on the hard side of the line (Class G lies below each of those).

Class G greater than 1,200 ft AGL
A rare example of Class E airspace beginning at 14,500 ft MSL, with Class G below it.

Operating in Class G

VFR requirements:

  • Minimum pilot qualifications – student pilot.
  • Entry – no requirements.
  • Equipment – no requirements.

VFR weather minimums:

Class G VFR reqs
Source: 14 CFR §91.155

ATC services:

  • VFR flight following – available on request depending upon ATC workload, and whether you are in radar coverage.


Developing a better understanding of the different airspace classes, their rules and requirements, and how to differentiate them on your charts will improve your situational awareness, help make you a safer pilot, and demonstrates good airmanship. If you’re flying somewhere unfamiliar then I recommend that you study the charts (and chart legend) beforehand to familiarise yourself with the airspace you expect to be flying through or near on your route.  

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