Have you ever wondered why the departure procedures from Oshkosh and its surrounding airports are so brief compared to the complex arrival procedures that govern airplanes heading into the show. It’s an easy explanation.
Think of airplanes as being water flowing to Oshkosh and of Oshkosh as being a big puddle of airplanes located directly beneath that funnel. Air traffic control is concerned primarily with airplanes not running into each other. At Oshkosh, they’re not even particularly concerned about them not getting too close--the air show has reduced separation standards or else all those airplanes would never be able to make it in.
Mathematically, the worrisome parts of the operation, when airplanes might collide, is when there are a lot of them in close proximity to each other. That is, when they are flowing down the neck of the funnel to the runways.
On departure, ATC has a lot more control over things, because they control when the airplanes take off--there’s a lot less control when those airplanes are coming in to land, as their pilots can do any number of unexpected and potentially frightening things.
So when airplanes are leaving the airport, they are under ATC control for long enough to allow them to disperse naturally into the airspace. The biggest concern, really, is that they don’t collide with arriving airplanes. That’s why the notam directs airplanes to climb above the altitude of arriving traffic before turning toward the arrival routes.
Here it’s a reverse funnel. After just a few minutes, your chances of encountering and colliding with another airplane are very remote.
What this means is that you should pay attention to the notam’s guidance to climb and to just get out of Dodge. They really do care about you hitting another airplane, but they know that the chances of that happening when you’re heading out the other end of the funnel are extremely slim.