There may be no better example of overlapping airspace than Chicago; the Chicago airspace has it all — Class B, Class C, Class D, Class E, and yes even Class G airspace — all under one roof.
Consider flying to Chicago this summer to take in a baseball game. You can get to both the Cubs and White Sox games easily from the smaller airports using the elevated train. But if you do go, you must really be sharp on your airspace rules and recognition. Every baseball park has different outfield dimensions — and in congested areas the airspace will have different dimensions as well. The airspace around Chicago is a maze of different airspace types, and as a pilot you must be able to ‘see‘ the airspace boundaries both horizontally and vertically.
Figure 1 is a section of the Chicago Terminal Area chart. Look at the Class C airspace that surrounds the Chicago-Midway (MDW) airport. The inner circle of this Class C airspace is standard, but the outer circle is sliced off to the northeast to accommodate other surrounding airspace. There are also some unusual markings that designate the airspace at Midway. In the inner circle you will find (printed south of the MDW airport symbol) the letters SFC. These letters have a line over the top and the letter T above the line. The letters SFC stand for ‘surface‘ and indicates that the Class C airspace here starts at the surface — the letters SFC are normal. What is not normal is that letter T.
What exactly does the letter ‘T’ indicate? In this case, the letter T means that the ‘top‘ of the MDW Class C airspace is located where the floor of the overlying Class B airspace begins. The Class B airspace from Chicago – O’Hare completely overlaps the Class C at Midway — and there is no space between the two.
How high up then does the Midway Class C go? That depends on your exact location. Look back at Figure 1 and notice that two of the rings around Chicago – O’Hare cuts right across the Midway Class C airspace. One of the O’Hare Class B bands covers over the southeast portion of the inner circle at Midway. In this band, the class B has a top altitude of 10,000 feet MSL, and a bottom altitude of 3,600 feet MSL. We know this, because contained within this band is a symbol that shows the number 100 over a line and the number 36 below the line. This symbol is out over Lake Michigan and the numbers are in code — you must add two zeros to the number shown to get the correct MSL altitude for the top and bottom of the Class B airspace.
PUTTING IT ALL TOGETHER
Now, we know that the bottom of the Class B (in this case 3,600 feet) is also the top of the underlying Class C — so here the ‘T‘ means ‘up to but not including 3,600 feet MSL.’ But the airspace directly over the Midway airport is different, because this airport is under a different band of Class B airspace. The bottom of Class B — and therefore the top of Class C over the Midway airport — is lower, at 3,000 feet. At the extreme northwest side of the Midway inner circle is under yet another Class B band. That small area has a top of only 1,900 feet MSL.
The picture in your head: Shows the top of the Midway Class C airspace is a descending staircase toward O’Hare.
Important Notes: The chart used in Figure 1 is from the Chicago Terminal Area chart. Terminal Area charts are different from Sectional charts. The Terminal chart has a scale of 1:250,000, while the Sectional chart is 1:500,000. This means that the Terminal chart depicts the land and airspace twice as big as the Sectional.AIRSPACE ‘SLICE‘
Imagine a line cut across this Class C airspace from northwest through southeast — the diagram is a slice of the airspace along that line. Figure 2, above, is a diagram of that slice of Midway Class C airspace, as you would see it from the side.
When the airspace is extremely congested, as is the case in Chicago, it pays to buy a Terminal chart and study the airspace before the flight. Terminal Area charts are also available for the airspace around Boston, New York, Philadelphia, Baltimore/Washington, Charlotte, Atlanta, Orlando, Tampa, Miami, New Orleans, Memphis, Pittsburgh, Cleveland, Detroit, St. Louis, Kansas City, Minneapolis, Dallas/Ft. Worth, Denver, Phoenix, Salt Lake City, Las Vegas, San Diego, Los Angeles, San Francisco, Seattle, Honolulu, and San Juan. Charts are available from PilotMall.com at FAA Charts
BOTTOM LINE: Get a good look at the airspace before you go… then, have a great time at the ball game!