The thin magenta line
Easy but enigmatic, Class E airspace is Everyman's environment
Then came airplanes. Eventually, there were lots of airplanes. Some of them tried to fill the same airspace at the same time, and that caused problems. The authorities began organizing airspace into different categories with different names, with rules governing who could come into airspace and when. Eventually, there were lots of rules. The most recent complete overhaul of airspace, undertaken in 1993, assigned it to classes from A to G (absent Class F). It is safe to state that the restrictiveness of airspace control gradually diminishes as you move from A to B to C to D, and so forth.
The least controlled of controlled airspace is Class E. Yet for many student pilots and veteran flyers alike, Class E airspace is the most conceptually challenging of all the airspace classes. Perhaps that is because of its ubiquitous nature (E might well stand for "Everywhere controlled airspace is not otherwise designated"), its purpose, and its somewhat erratic vertical distribution. Near the ground its primary function is to keep aircraft operating under visual flight rules away from instrument-approach paths during conditions of marginal visibility. In the cruise altitudes Class E airspace serves as a sort of default form of controlled airspace, once again imposing stricter standards for visual flight than uncontrolled airspace (Class G), but demanding nothing more of the pilot than adhering to the appropriate ceiling, visibility, and cloud-clearance requirements -- depending on whether the Class E airspace in question is above or below 10,000 feet msl.
In no other controlled airspace is the pilot's burden of compliance so minimal: Class A airspace (above 18,000 feet msl, if you can get there) requires you to be flying on an instrument flight plan, period. Class B airspace, the most restrictive surface-based controlled airspace centered on the busiest hubs, requires a clearance, specific on-board equipment, and pilot certification or logged training. Class C airspace, also surface-centered around less-busy aerodromes with radar, makes communications and equipment demands of visual flights. Class D airspace, centered on tower-controlled airports lacking terminal radar service, still requires tower approval before you arrive or depart. All this is easy enough to grasp.
Of the four classes from A through D, one governs use of the so-called flight levels (18,000 feet msl and above), and the others (B, C, and D) are centered on airports. All have set procedures for coming and going, and the ground-based classes are easy to find on charts.
Class E is a hybrid. Unlike classes B, C, and D, it must be depicted three different ways on sectional charts. The other airspaces classes require only one method of depiction each. Not always centered on an airport -- and in certain places touching the ground but usually with a floor above ground level -- Class E serves a variety of purposes. Perhaps the best way to understand Class E airspace is to study how it appears in the vicinity of selected airports and think about how it might affect you if you are arriving, departing, or overflying them.
Typical of how Class E airspace depictions most often catch the eye when you open an aeronautical sectional chart is the meandering magenta boundary enclosing the complex of Arkansas airports that includes facilities in Osceola, Manila, and Blytheville, found on the Memphis Sectional (p. 36, top). Comparing the shading of this boundary with the three Class E airspace depictions shown on the chart's legend under Airport Traffic Service and Airspace Information shows it to be the one that outlines "Class E Airspace with floor 700 feet above surface." Inside the boundary, then, controlled airspace extends downward to 700 feet agl. Outside, the floor -- or bottom -- of the controlled airspace increases to 1,200 feet agl.
How do we know this? Look at the illustration above. Since, from your examination of the Memphis Sectional chart legend you know that this Class E airspace has a floor of 700 feet agl, it meets the following criteria given in the AIM: "There are Class E airspace areas beginning at either 700 or 1,200 feet agl used to transition to/from the terminal or en route environment." If you were taking off from one of these airports, you would be in uncontrolled airspace until climbing to 700 feet agl, and you would be able to fly under ceiling, visibility, and cloud-clearance requirements appropriate to uncontrolled airspace. For instance, if visibility were less than three miles but one mile or greater, and you could remain clear of clouds, you could fly below 700 feet agl. But once you were above 700 feet agl, controlled-airspace minimums would apply, requiring you to have at least three miles visibility and be able to maintain the well-known 500 feet below clouds, 1,000 feet above clouds, and 2,000 feet horizontal cloud clearances.
After departing the depicted area and remaining above 1,200 feet agl, you would stay in Class E airspace during your en route flying unless you specifically entered controlled airspace of a higher designation as shown on the chart, or passed a rare boundary between Class E airspace and uncontrolled (Class G) airspace (see chart legend for depiction).
Many student pilots ask why Class E airspace is lowered to 700 feet agl around some airports and not others. The answer is that these airports all have instrument approaches that allow aircraft on instrument flight plans to descend and land when the visibility is greatly reduced, or through a cloud cover. If the airspace were uncontrolled to a higher altitude (such as 1,200 feet) an aircraft flying under visual flight rules at, say, 1,000 feet with a mere mile of visibility, could risk a collision with an aircraft executing an instrument approach with a minimum descent altitude a few hundred feet above the airport. (Indeed this can still be an issue below 700 feet agl, so be wary in marginal weather.)
In certain places, Class E airspace centered on an airport extends all the way to the surface. Here the chart shows the boundaries as a dashed magenta line, sometimes with an odd shape or configuration. "When designated as a surface area for an airport, the airspace will be configured to contain all instrument procedures," explains the AIM. An example is Dade-Collier Airport in Florida (p. 36, lower left).
This same brand of surface-based Class E airspace is frequently tacked onto Class D airspace (tower-controlled airports), such as is the case at the Lebanon, New Hampshire, airport (p. 36, lower right); here it's also designed to contain all instrument ap-proaches. If the visibility in the Class E extension were, say, two and one-half miles, the Class E extension of Lebanon's Class D airspace would be off-limits to a flight operating under VFR, even though adjacent airspace outside the Class D circle and the Class E extension is Class G (uncontrolled) from the surface to 1,200 feet agl. On a good visual-flying day, would you need permission from Lebanon Tower to fly through the Class E extension? No.
In a more complex interweaving of airspace about 50 miles to the southeast, note how both the Class D airspace and Class E airspace at Nashua, New Hampshire, underlie the outer portion of Class C airspace centered on Manchester.
The marginal weather conditions posed above, although legal, are pretty iffy for flying around close to the ground under visual flight rules. In most cases this would be a good view of things, but a case could be made for flying in marginal visibility on a dual-instruction session in the traffic pattern.
Now take a student and flight instructor at one of those airports and confront them with a 900-foot ceiling and two miles of visibility. The plan was to practice takeoffs and landings at the home field without leaving the traffic pattern. Should they cancel? Hardly. Stay below the controlled airspace floor and work in the pattern, while giving the student pilot valuable experience seeing what the term marginal conditions really means. As long as you can maintain one mile of visibility and stay clear of clouds, it is a legal flight. (It would not be legal where the Class E airspace extends all the way to the surface, however.)
Some designated examiners have been known to pose hypothetical questions of this type to probe your understanding of Class E airspace -- not necessarily to encourage you to fly in marginal conditions. If you can answer the question properly, congratulations! You are ahead of many pilots who may be greatly senior to you in experience but far less aware of the nuances of the airspace in which they fly.
Dan Namowitz is an aviation writer and flight instructor. A pilot since 1985 and an instructor since 1990, he resides in Maine.
