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Airspace Overlap -- Part 2

When airports and their associated airspace are in close proximity to each other, there can be congestion, confusion and conflict.When airports and their associated airspace are in close proximity to each other, there can be congestion, confusion and conflict.

CHANGING NEEDS, CHANGING AIRSPACE...
Last week we saw that having two airports near each other can create complicated airspace problems. Many cities will have a large airline airport and a second general aviation airport near each other. Other cities will also have a military airbase in the area. As time goes by, aircraft traffic to these airports will change, and this causes airspace needs to evolve. Looking at many cities, you will see that airports and airspace have grown up together -- and airspace accommodations have been made.

- Click here to view the Nashville example.

Use Nashville, Tennessee as an example. Figure 1, above, is the Nashville area and its four airports.

  1. Nashville International Airport (the airport was originally named Berry Field -- Nashville, which explains why its three-letter identifier is BNA) is the larger airline airport with one 11,000-foot runway.
  2. The John C. Tune airport (JWN) is the newer general aviation reliever airport.
  3. Cornelia Fort Airpark (M88 -- named after the female flight instructor who first saw the Japanese attack planes coming through the valley toward Pearl Harbor) is the older general aviation airport, and
  4. Smyrna Airport (MQY), which was originally the Sewart Air Force Base. The airspace of these airports is a confluence of congestion and compromise and quite enough to confuse the most veteran pilot.
...ADDED COMPLEXITY
In order to really understand the airspace and its complextity, the pilot must develop the unique skill of mentally creating a 3-D image from the chart's symbology. Figure 2, below, is just such an image. Both Figure 1 and Figure 2 are of the Nashville area airspace, but Figure 2 is how pilots should see it in their mind's eye.
Figure 2
BUILDING AN IMAGE
First look at the relationship between the Nashville Class C airspace and the Class D airspace at Smyrna. The Class C overhang in the area of Smyrna begins at 2,100 feet MSL and has a top at 4,600 feet MSL. It just so happens that the outside edge of the overhang cut right over the top of the Smyrna airport. The Class D airspace at Smyrna starts at the surface, but the northwest portion of the Class D is replaced by the overhanging Class C.

Figure 2 illustrates that the top of the Smyrna Class D airspace is uneven. In the southeast, the part that in not under the Class C, the top of Class D is 3,000 feet MSL. (We know this from the number 30 in the four cornered brackets shown just south of the Smyrna airport.) But in the northwest portion -- under the Class C ledge -- the Class D's top is 2,100 feet, which is the Class C's base.

    Important: Whenever two types of airspace attempt to occupy the same spot -- the airspace with the letter closer to the front of the alphabet trumps any other. In this case, the Smyrna Class D is trumped by the Nashville Class C airspace.
SEEING THE DANGER...
Smyrna has an ILS approach to its runway 31. The missed approach, sends the pilot out on the runway heading (toward Nashville) until reaching 1,500 feet. This is followed by a climbing right turn to 2,500 feet. The airplane, while climbing to 1,500 feet, flies under the Class C overhang, then in the turn and climbing to 2,500 feet, they often enter Class C airspace from below as they climb through 2,100 feet. Nashville air traffic controllers will tell you that this area is where the greatest number of Class C airspace incursions take place. Very often this ILS approach is used by pilots for practice and without coordinating with the Nashville controllers -- and entering Class C airspace from below without communicating with ATC is an airspace violation.

...AND STAYING SAFE
Now look at the Cornelia Fort Airpark on Figure 1. You can see that Cornelia Fork (M88) is only about four miles from BNA. Ordinarily the area where M88 sits would be swallowed up by the surface area of the Class C airspace -- but not in this case. You can see that a half-circle cut-out has been made around M88. This makes it possible to takeoff, land and fly a close traffic pattern at M88 without actually being inside the Class C airspace. Look at the cut-out on Figure 2 and remember that this is how it actually looks when flying to that airport.

DEFINING THE STACK
Figure 3 illustrates the airspace over Cornelia Fork Airpark. You can see that there are several layers of airspace that form a stack.

Figure 3
This entire area is surrounded by a magenta shading, which means that the boundary between Class G and Class E is at 700 feet AGL. Look carefully at Figure 3 and be sure you can match up the symbols on the chart with the airspace designations. If you can do that, the only thing you'll have to worry about... is the pilots who can't.

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About This Author:
Paul A. Craig is a Gold Seal Multiengine and Instrument Flight Instructor. He currently holds a total of 11 Flight Certificates including his ATP. Craig is a previous winner of the North Carolina and Tennessee Flight Instructor of the Year award, the NCVT Outstanding Teacher award and has served as the regional representative of the National Air and Space Museum. Craig is an FAA Aviation Safety Counselor and the author of eight books, including Pilot In Command, The Killing Zone: How and Why Pilots Die, and Controlling Pilot Error: Situational Awareness (all from McGraw Hill).
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