An object would be an obstruction to air navigation if of greater fight than 200 feet above ground at the site, or above the established airport elevation, which ever is higher

(a) within 3 nautical miles of the established reference point of an airport with its longest runway more than 3,200 feet in actual length, and

(b) that height increases in proportion of 100 feet for each additional nautical miles from the airport reference point up to a maximum of a 500 feet.

Note: heliports excluded

If your structure penetrates allowable height for surfaced analyzed, you can do the following to prevent a penetration:

Lower the height of your structure and/or change location by moving further away. Use the Airspace Utilities or the TERPS^® program to determine a new set of geological coordinates.