Prior to the early 1930s, there was little need for an organized system of air traffic control in the United States. Almost all of the aerial traffic in this country was conducted in daylight with clear flying conditions.
Advances in aircraft control and navigation that would permit flight at night or during periods of restricted visibility had yet to be made.
The practice of “see and be seen” became the principal method of traffic avoidance. This meant that pilots could fly only on conditions that would permit them to see other aircraft and alter their flight path in time to avoid them.[1]
The earliest method of regulating takeoffs and landings required an air traffic controller to stand in a prominet location on the airfield and use colored flags to communicate with the pilots. If the controller waved a geen flag, it meant that the pilots were to proceed with their planned take off or landing. But if the controller if the controller waved a red flag, the pliots were to hold their position until the controller had determined that it was safe to continue.
