Why does class E airspace floor start at 700’ above some airports, and 1200’ above others?

Zaphod Beeblebrox

A 700 foot Class E floor constitutes a transition area for IFR approaches. If an uncontrolled airport has an IFR approach the airspace will either extend down to 700 feet AGL if there are only non-precision approaches or all the way down to the surface if there is at least one precision approach but no control tower. Otherwise, with a tower, it would be Class D. If there isn't an instrument approach, the floor of Class E is 1200 feet.

Anonymous

Mousefarts