92 Ill. Adm. Code 16.100
Circling Approach Surface
Section 16.100 Circling Approach Surface
a) A
circling approach surface is a circular area that is 200 feet above natural
ground level or above the established airport elevation (whichever is greater)
within three nautical miles of the established ARP of the airports listed in
Section 16.Appendix A. It increases in height at a proportion of 100 feet for
each additional nautical mile of distance up to six nautical miles from the
airport reference point up to a maximum height of 500 feet (see Section
16.Illustration C).
b) Beyond
the six nautical mile criterion in subsection (a) of this Section, an object
would be an obstruction to air navigation if at a height greater than 500 feet
above ground level at its site (see Section 16.Illustration D).