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FAR 77.23(a)(2), Obstruction Standards

 Criteria:

An object would be an obstruction to air navigation if the object has a height greater 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.

Please Note: heliports are excluded

 Diagram  
 Ways to avoid surface penetration

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

(1) Lower the height of your structure

(2) Move the structure further away from airport

(3) Use Airspace OMS software to determine new location that is ideal for your needs.