Columbia subject headings:
Aeronautics--United States--Safety measures.
Air traffic control--United States.
Airplanes--Collision avoidance.
Radar air traffic control systems--United States.
Harvard subject headings:
Aeronautics--United States--Safety measures
Air traffic control--United States
Airplanes--Collision avoidance
Radar air traffic control systems--United States.
Princeton subject headings:
Aeronautics--United States--Safety measures.
Air traffic control--United States.
Airplanes--Collision avoidance.
Radar air traffic control systems--United States.