Prior to the 1930's, there was little or no need to organize air traffic as aircraft flew under the "see or be seen" rules of Visual Flight. Thus they flew only in good weather and never at night. But by the late 1930's the capability of aircraft to fly at night and in bad weather had made a quantum leap. With instruments that allowed the pilot to control the aircraft without visual reference to the ground and ground-based navigational aids (radio ranges) being installed, pilots could take-off, cruise and land in weather conditions which would not allow them to see and avoid other aircraft.
Because all these planes had to land eventually, it was inevitable that the airspace around airports would become congested and some form of local control would be needed. But the airport of that era only slightly resembled the airport of today. The 1920's airport rarely had designated runways and usually consisted of a large rectangular plot of land covered with sod or cinders.
After flying over the airport, the arriving pilot would observe wind direction, local traffic and runway conditions. He would then decide in what direction they would land. Others would follow the first arriving aircraft, allotting sufficient time for the previous plane to land, brake to stop and taxi clear prior to their landing. Additionally, pilots needed to continuously scan the airport area for aircraft taxiing for take-off. Usually, of course, aircraft took-off into the wind. But on calm days, aircraft could be seen departing from all directions of the compass. It was immediately apparent some form of control would be needed around airports or the accident rate would be increasing alarmingly.
THE FIRST NORTH AMERICAN AIR TRAFFIC CONTROLLER
The earliest method of air traffic control required a person to stand in a prominent location on the airport and use coloured flags to communicate with the pilot. If the controller waved a green flag, it meant that the pilots were to proceed with their planned take-off or landing. But, if the controller waved a red flag, then the pilots were to hold their position until the controller had determined that it was safe to continue. At that time, the controller would wave a green flag advising the pilots that they could continue. The first airport to hire such a controller was St. Louis, Missouri in 1929; that controller was Archie League who controlled traffic from a wheelbarrow on which he had mounted a beach umbrella. He would daily wheel his equipment to the approach end of the runway, where he would use his flags to advise the pilots whether to continue their approach or hold until the traffic was clear. Archie performed these tasks in both winter and summer. Other large cities soon saw the advantages of this system and began to employ controllers at their airports.
Although a workable system, this early, crude form of control had obvious drawbacks. Since the controller was usually near the approach end of the runway, he was far more likely to attract the attention of departing rather than arriving aircraft. Pilots inbound for landing found it difficult to see the controller's location to determine which direction they were to land. If more than one aircraft was inbound, it became difficult, if not impossible, for the controller to give different instructions to each plane. Additionally, the controller could not be assured the pilots had seen and understood the intended instruction. Finally, it was impossible to use this type of control in stormy weather of at night. Fortunately, few aircraft flew during such weather conditions.
LIGHT GUNS
In an attempt to rectify some of these problems, the controller's flags were replaced by light guns. A light gun is a device that permitted the controller to direct a narrow beam of high-intensity coloured light to a specific aircraft. Light guns were equipped with a gun-sight that let the controller accurately aim the beam of light at one particular aircraft. The gun was also equipped with different-coloured lenses to permit the controller to easily change the light colour.
The light signals were similar to the flag colours. A red light advised the pilots to hold their aircraft, while a green light authorized them to proceed. Initially, the guns were used from a portable light station at the arrival end of the runway. Soon, however, the various airfields built control towers on top of one of the highest structures. Controllers working in the tower now had an unobstructed view of the airport and the surrounding airspace. A side benefit was, of course, that controllers did not have to stand at the side of the runway, exposed to the elements.
Light guns are still used today in most control towers to communicate with pilots when either the tower radios or the aircraft radios become inoperative or when an aircraft is not radio-equipped. The light gun code has not changed significantly since the 1930's.
VISUAL LIGHT SIGNALS IN 1920
Steady Green Light:
Cleared for take-off: Cleared to land.
Steady Red Light:
Do not take-off: Hold position: Do not taxi.
Intermittent Green Light:
Cleared to taxi: When on approach, land long and clear runway immediately.
Intermittent White Light:
Emergency-Taxi Clear of runway immediately.
Although the light-gun was a major improvement over the coloured-flag system of control, a number of important deficiencies still remained. Inbound to the airport, the pilots were usually busy flying their aircraft and were unable to maintain a constant lookout for changing light-gun signals. As a result, the controller might not be able to transmit critical safety instructions to the pilot whose attention was rivetted on performing a landing task. The light-guns were also unusable in bad weather since particles of dust and/or moisture would diffuse the light-beam. Finally, the controller was never assured the pilot had received or properly interpreted the light signal. Thus, control instructions were one-way only, - controller to pilot!
RADIO COMMUNICATION
The present system of airport control was initiated at Cleveland, Ohio. A control tower was constructed and equipped with radio-transmitting and receiving equipment-15 watt radios that had a range of 15 miles. With these radios, controllers could issue instructions, pass weather information and airport landing conditions to pilots who had radio-equipped aircraft and the pilots could respond to the instructions or initiate communication with the tower. This control could be carried out in good weather or bad, night or day.
The light-gun remains today, as a legacy of those times and for backup communications in event of tower or aircraft radio malfunction. However, the use of radios allowed a higher degree of safety in the control of sequencing departures and arrivals. It was only a short time before other airfields in the USA and Canada followed the examples of Cleveland by constructing towers and equipping them with radios.
Despite the dramatic safety improvement of these new towers, their effectiveness was still limited. Since radio equipment was bulky, unreliable and relatively expensive, compared to today's equipment and prices, the airlines were reluctant to install these items in their aircraft as they would reduce revenue-producing payload. Additionally, smaller aircraft were not equipped with the electrical systems capable of powering these radios. Controllers and pilots alike were hampered by the lack of a standardized set of rules or phrases to be used for inter-communication. Some pilots would contact the tower 5 to 10 miles away from the airport while others would wait to contact the tower until almost ready to land. While controllers were federally certified, pilots had no legal obligation to contact the towers. Finally, even though radio contact might be established, there were few rules of standardized procedures which were followed. Still, this early form of traffic control worked reasonably well, although a great deal of standardization was still needed.
AIRPORT CONTROL IN CANADA
Canadian Air Traffic Control policy was closely meshed with that of the United States as it was realized that a continental standard was preferential to two distinct systems side-by-side. On November 1, 1936, the government established the Department of Transport. Now the process was complete! Civil aviation had been separated from military aviation and could now be administered by the same organization which dealt with railway, canal, marine and highway services. Stability in the organisation of Canadian aviation was at last achieved.
By 1939 air Traffic had increased at major airports to the point where it was necessary to introduce some measure of control. On the urging of Mr. J.A. Wilson, Secretary of State for Air, the Air Traffic Control service of the Department of Transport was established and it's 1939-1940 report contains the following:
"Airport Traffic Control - The increase in air traffic in and around many of the larger Canadian airports has made it necessary, in the interests of public safety, to institute a system of control of traffic in the vicinity of such airports, both on the ground and in the air. An assistant inspector who had been involved in earlier airport work had been sent to the USA to study their airport control systems and regulations were drawn up embodying the best accepted practice on this continent. These regulations, amongst other things, require that an officer in charge of the control of air traffic at an airport must be licensed by the Department of Transport.
It was decided to install control on all the larger departmental airports and applications for the position of Airport Traffic Control Officer were invited by the Civil Service Commission. The selection of a group of 10 candidates was made from this list and the initial group was trained on contact training at the St Hubert Airport, after which licences were issued to the successful 10 candidates." See Appendix C.
Within two years a system of Airways Control was deemed necessary and to ensure the safety of the numerous aircraft en route over an airway system especially at night or in conditions of poor visibility. It must be noted that the Air Administration of the USA and Canada followed a common policy in airport planning, airways planning, control standards, radio communication etc. so that there would be one system universally used throughout North America. It was necessary to establish a school to train Control Officers and assistants. Initially, the first DOT Air Traffic Control School was established at Malton near Toronto.
Updated: November 23, 2004