Expert: Colin Woehrle - 10/26/2005

Question
What is the reasoning behind some class E airspace starts at 700 feet AGL, and some starts at 1200 AGL. I know the rule and know how to identify which is which on a sectional, but what was the thought behind doing that by the FAA?

My only guess is at my home base we have an NDB approach which gets you down to 700 agl, thats why if our class E started at 1200 then on an IFR someone could go out in the pattern and using the "1 sm and clear of clouds" requirement for a class G airport and there may be some guy coming in on an NDB approach also, meaning a good chance for collision. Whereas, if the class E starts at 700, he cant just fly around the pattern because now hes in class E and needs 3 sm and 500 below clouds?

But there are plenty of class G aiports with no instrument approach that fall under the class E 700 ceiling?

Answer
Good question. The purpose of different airspace designations, as you were assuming, is to separate IFR traffic from VFR traffic via visibility and cloud clearance requirements. You will see controlled airspace floors decreasing as they approach airports with instrument approaches. Check again to see if there aren't any instrument approaches at the airports in question. Many new GPS approaches/departures are now in place at airports not previously served by "conventional" instrument procedures. Also check to see if these airports are located in close proximity to other airports served by approaches, as those procedures may require this airspace designation.
Hopes this helps to clear things up.

Thanks for the question,