620 ILCS 25/12
The Department shall formulate, adopt and revise, when necessary, an airport approach plan for each publicly-owned airport in the State. Each such plan shall indicate the circumstances in which structures and trees are or would be airport hazards, the area within which measures for the protection of the airport's aerial approaches should be taken, and what the height limits and other objectives of such measures should be. In adopting or revising any such plan, the Department shall consider, among other things, the character of the flying operations expected to be conducted at the airport, the traffic pattern and regulations affecting flying operations at the airport, the nature of the terrain, the height of existing structures and trees above the level of the airport, and the possibility of lowering or removing existing obstructions, and the Department may obtain and consider the views of the agency of the Federal Government charged with the fostering of civil aeronautics, as to the aerial approaches necessary to safe flying operations at the airport.
620 ILCS 25/12