Air Traffic Control - Part 1
by Roger Meyer
Until the mid 1930s, there was no formal wireless organisation or control of air traffic in Australia. Few aircraft apart from the all-metal DC2 carried two-way radio equipment. The few which did could communicate with Coastal Radio Stations and with the fledgling Aeradio organisation. The first Aeradio stations at Darwin, Essendon and Launceston were temporary rigs, operated by the RAAF and AWA Ltd.
In 1937, the Civil Aviation Branch appointed Aerodrome Control Officers (ACOs) at Archerfield, Mascot, Parafield and Essendon. Their function was to regulate air traffic at aerodromes, provide a meteorology service, and give advice to pilots of aircraft engaged in cross-country flights. The personal qualities required of Aerodrome Control Officers were mature age, discipline, power of command and level-headedness. The salary range was £306 - £384 (about $17,000 in 2003 dollars), being slightly above that of a Rifle Range Superintendent. The first appointments were: Commander H.T. Bennet and Flt. Lt. A.A. Poole (Mascot); A.V. Lauchland (Archerfield); and Sq.Ldr. A.E. Hempel (Essendon).
Lacking radio communications, ACOs used visual signalling devices - the Aldis signalling lamp and Very cartridge pistol. At Essendon and Mascot they operated from rudimentary Control Towers on the roofs of the Aero Clubs. From these Towers hung red and cream cane balls, which were raised or lowered to indicate aerodrome conditions. A signalling square located in front of the Tower conveyed information on wind speed and direction and general aerodrome conditions. Using a combination of red and green flare cartridges, and white or red signalling lights they gave instructions to aircraft when to land or takeoff, and to taxi safely. These signals had an effective range of two miles, and were based on RAAF procedures of the time.
Following the crash of ANAs DC2 aircraft Kyeema in October 1938 it was revealed that two major weaknesses existed in the ground control organisation. A radio beacon to provide pilots with a positive course along which to fly was soon introduced. This was the Lorenz 33 MHz Radio Range, the precursor of the VAR and todays VOR.
The other major innovation was the appointment of Flight Checking Officers whose job it was to maintain a watch on the progress of flights on the main air routes. This was to guard against a pilot making a grave miscalculation of his position, as had happened with the Kyeema.
Flight Checking Officers (FCOs) were introduced in August 1940 and were at the same locations as Aerodrome Control Officers. They were selected from experienced airline pilots and provided what would become known as a uniquely Australian aviation service - Operational Control. Their duties were to check flight plans and ensure that adequate fuel was carried, to divert aircraft if conditions at the destination were unsafe, close airports if weather conditions deteriorated below minimum standards, and to keep pilots informed of changing flying conditions.
After an aircraft took off, the pilot was instructed by the Aerodrome Controller to call Aeradio on a given frequency, on which he transmitted his position to Aeradio every half hour. Aeradio passed the position report on a slip of paper through a chute to the FCO who recorded the position, making sure that the it was reasonable for the pilot to be where he claimed to be. It was not unknown at times when Aeradio was busy for the FCO to receive a report that an aircraft was over Benalla just as the aircraft was taxying past the Essendon control tower! Such were the limitations in this form of position reporting.
During the war, the widespread installation of radio facilities made it possible to take positive control of flights en route. A ground organisation capable of exercising such control, including positive separation between aircraft, was established. The first Flight Control Manual was published in 1943, and in early 1944 the use of radio for Aerodrome Control purposes made it possible to exercise greater control over aircraft operating in the vicinity of aerodromes.
Aircraft were separated by the most rudimentary rules: northbound aircraft flew at odd thousands of feet and those southbound at even thousands. This was the NOSE rule. Also, aircraft flying at the same height along an air route had to be separated by ten minutes flying time. With aircraft of vastly different speeds on the same trunk air routes, a procedure was needed to maintain this longitudinal separation.
was presented in 1944 by a Sydney FCO, Mr Norman Rodoni, who invented
a form of computer, known as the Rodoniscope.
It comprised a rotating circular glass disk 60 cm in diameter, under
which was a chart showing aircraft reporting points. At the outer edge
of the chart was a clock face. By marking the position reports and circulating
the glass disk in real time, the controller could see at what time Aeradio
was likely to receive a position report and would then mark the actual
position when the radio report was received. Thus is was possible to
accurately predict when a faster aircraft would overtake a slower machine.
At the end of the War, Australia had to decide on a peacetime air traffic organisation, having cognizance of the fact that radio had developed enormously over the past five years, and that new higher-speed piston engined aircraft were being designed. Whatever decision was made had to be the right one. Aviation could not wait.
In the Part 2, we will see the role of ICAO in setting international standards for air traffic control, and the introduction of two indispensable tools for ATC: the Flight Progress Board and the use of radar.
Click here to read Part 2
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