Complications: High Altitude & Non-Standard Airspace

Class G, or uncontrolled airspace, is down low… most of the time, and not everywhere. There are areas of ‘high altitude‘ Class G airspace that we must also watch for lest VFR and IFR traffic meet.

Many of you have written with questions over the past few weeks during the series on airspace about the blue shaded line. Most of these questions have come from the Eastern United States where high altitude uncontrolled airspace is rare — pilots in the Western United States see it all the time. Look at Figure 1 to see how high altitude Class G airspace works.

This figure is taken from the Las Vegas Sectional Chart. First, look the area that I have marked with the number 1. A victor airway, V293, starts at the Bryce Canyon VOR and proceeds southeast on the 105-degree radial. Sectional charts usually only show a victor airway’s centerline. The airway itself is controlled airspace, but usually (above 1,200 AGL) the airspace adjacent to the airway is also controlled, Class E airspace, so the edge of the airway is not shown. But this particular airway, V293, cuts across an area that would otherwise be uncontrolled. As a result, the blue shading exposes the edge of the airway.


    : The airway has a controlled airspace — Class E — floor of 1,200 feet above the surface. Outside and beyond the blue shaded lines lies an area where uncontrolled — Class G — airspace exists from the ground all the way up to 14,500 above sea level.

Note: A military training route, IR266, cuts across V293 at almost a right angle. Figure 2 is a vertical cross section diagram of V293 taken where IR266 comes through.

Now go back up and look at the area of Figure 1 that I marked with the number 5. This area, between Victor 293 and Victor 257 (between the blue shading), is an area of high-altitude Class G airspace. This is where Class G starts at the ground and extends all the way up to 14,500 feet MSL. ‘Between the blue‘ is high altitude, uncontrolled airspace… which is very rare in the East.CLASS G — THE LOWS AND HIGHS
Most of the time the boundary between Class G and Class E is based on an AGL altitude and the floor of the Class E airspace would not be level — it would be a mirror image of the terrain features below. But in this case the boundary between Class G and Class E is an MSL altitude and therefore a level surface. Inside the Class G airspace from a point that is 1,200 feet AGL and up to 10,000 feet MSL, the rules for flying VFR are different than anywhere else.

Normal (low) Class G

  • Where Class G exists above 1,200 AGL and below 10,000 MSL a pilot can fly VFR in the daytime with only one-mile visibility (3 miles at night), but clouds have a buffer zone that VFR pilots must stay out of.
  • VFR pilots must stay clear of a cloud by 500 feet below, 1,000 feet above, and 2,000 horizontal feet.

High-Altitude Class G

  • In the Class G airspace that exists between 10,000 feet MSL and 14,500 feet MSL, the cloud buffer zone remains that same, but VFR flight — both day and night — requires 5 miles visibility.Note: Class E, controlled airspace, at this same high altitude (above 10,000 feet MSL) has the same visibility and cloud buffer requirements.

On the chart: Normal boundaries are shown with either magenta or blue shading. Inside magenta shading is a boundary between Class G and Class E at 700 feet AGL, while inside blue shading depicts the same boundary is at 1,200 feet AGL. Outside the blue shading (between V293 and V257 of figure 1) the boundary is 14,500 MSL.

Between area 2 and area 3, there is an unusual looking airspace symbol that I call the ‘chain-link.’ The symbol looks like overlapping dashed lines. Whenever you see the chain-link you know that non-standard airspace boundaries exist. Inside the chain-link, the boundary is something other than 700 AGL, 1,200 AGL or 14,500 MSL. Since the altitude of the Class G and Class E boundary is non-standard inside the chain-link, the altitude of the boundary is printed on the chart.

Example 1

    • : In

area 3

    • of

Figure 1

    • you can see the indication of ‘

9500 MSL

    • .’ In that area, the Class G airspace starts at the ground and extends up to 9,500 feet MSL. Class E airspace starts at 9,500 feet MSL and goes up to 18,000 feet MSL.

Example 2

    • : In

area 4

    • of

Figure 1

    the boundary between Class G and E jumps up to 12,500 feet MSL.

Class G, uncontrolled airspace, completely covers the ground in Figure 1. At no place on this portion of the chart does Class E come down and touch the surface. But the top of Class G (the altitude where Class G meets Class E) is different all over the chart.
Area 1 and 2 the Class G and Class E boundary line is uneven. The boundary line mirrors the terrain features below — rising with mountains and falling over valleys — but always remaining at 1,200 feet AGL. So for…

Area 3

    • the boundary line is level at 9,500 feet MSL

Area 4

    • the boundary line is level at 12,500 feet MSL, and

Area 5

    the boundary line is level at 14,500 feet MSL.

BOTTOM LINE: The rules of operation change depending on the type of airspace you are flying in. So it is important to recognize unusual and non-standard airspace boundaries… especially if you normally fly in the Eastern United States.