Okay, but first you have to tell us what this "Pipper" you've flown is.
I think the most profound
operational effect 9/11 had on G.A., in my opinion, is seen in the form of the numerous Temporary Flight Restrictions (TFR's) that are often established with little or no warning. Also, TFR's like the ones around Camp David and the Bush ranch in Texas have changed size and shape several times...again, with little or no warning. I don't have any statistics, but I'll bet the number of violations against pilots crossing into TFR's has jumped significantly since 9/11. Even some military pilots have gotten into trouble over this.
You can probably search the major news outlets (CNN, MSNBC, etc.) for more information on these violations.
Now the U.S. economy is certainly having a big effect on G.A., but I suppose you can argue that was coming whether the Al Qaeda attacks happened or not...which I assume is what your paper is addressing.
Anyway, that's my two cents.