POST-WAR ATC OPERATIONS
By the end of WW II, the Air Traffic control system in Canada was established. The low frequency 4-course ranges across Canada on the Trans-Canada Airway provided for non-precision approaches at airports as well as guidance along the airways. Centres had no air-ground radio channels. All their communications including clearances, positions and altitude reports had to be relayed through radio stations, Airline ground stations and towers. Direct pilot-to-controller communications had been attempted on a trial basis, but most controllers complained about the noisy frequencies.
The United States had developed the VOR/DME (VHF Omnidirectional Range and Distance Measuring Equipment) to replace the existing 4-course Low-Frequency Ranges. However, the United States Air Force advocated adoption of the Ultra-High Frequency TACAN (Tactical Air Navigation) system which was required for their emerging generation of jet aircraft. After months of heated controversy, the civil/military joint decision was to combine them into one system known as VORTAC which was accepted world-wide by ICAO on 30 August 1956.
A review of Separation Standards showed that the greatest delay was at Terminals due to the indirect centre communications. With the changeover to Very High Frequency Channels in the late 1940s, the heavy static problem was almost entirely eliminated, plus the VHF frequencies provided many more usable channels for ATC.
INTERNATIONAL COOPERATION IN AVIATION
Almost immediately following the cessation of WW II, civil aviation exploded in growth, fuelled by new, modern aircraft capable of long-distance instrument flights, and problems of standardization between countries suddenly appeared. Luckily, these problems had been foreseen and in early 1944, exploratory discussions had been held with United Nations members. As a result, fifty-five nations were invited to meet in Chicago in November 1944; fifty-two attended. From this grew the International Civil Aviation Organization (ICAO) which began to function in interim offices in August 1945, becoming an official UN organization in 1947. headquarters for ICAO were subsequently established in Montreal, Canada.
ACCEPTANCE OF RADAR INTO ATC OPERATIONS
Radar had been a closely-guarded secret during the war, but civil tests in 1945 showed that the search portion of Ground Controlled Approach was particularly applicable for Terminal Control. This use led ultimately to the purchase of Airfield Surveillance Radars for use in Terminal Control Areas. Looming on the horizon was long-range radars for use in the En route system. VOR airways were being instituted and this caused some problems. The old r-course radio ranges could be flown with right side separation along airways which would allow the clearing of aircraft up and down as needed through the altitude of opposing aircraft. VOR rules did not allow for such use.
Another vexing problem was Noise. Urban sprawl around airports, particularly under approach and departure paths resulted in strong protests from irate citizens. This necessitated a complete review of approach and departure procedures as well as minimum altitudes. This also brought into question safety factors as viewed by airline and commercial pilots.
In 1953, the military released the first secondary radar system to the Ministry of Transport. At that time 8 Mode Alpha codes were released for civil use. Advantages accrued immediately. The system provided a means of tracking targets through radar clutter, besides giving controllers a means of positive identification. When secondary radar was accepted into the full civil ATC system 64 identification codes were available. Later the Mode Alpha expanded to 4096 codes with 4096 codes available for Mode Charlie-Altitude readout capability.
Updated: November 28, 2004