The Air Traffic Control Service - c. 1950
|This pamphlet outlining the establishment and function of the Air Traffic Control Service was produced by DCA's Education and Information Branch, c. 1950. Today it is of interest for its descriptions of equipment and procedures that have vanished into history, as well as for those that have stood the test of time and are with us still.|
The problems in handling air traffic differ from those applying to other transport methods due to the fact that aircraft are restricted to the use of one road (runway) for the take-off and landing, whereas railway and sea transport is usually routed to a number of roads (platforms or piers) at the terminals, while road traffic is even less restricted in this regard.
following paragraphs outline how order is achieved in the air transport field
|Before departing from Sydney for Melbourne, a pilot carefully calculates his flight plan. His flight is planned by sections and, having considered the forecast weather conditions along the route, the pilot estimates the time of flight on each section. The total of these times will govern the amount of fuel he will require, to which amount is always added sufficient for at least an additional hours flight. The flight plan is submitted to an Air Traffic Control Officer who checks it carefully.|
In the matter of determining which altitude may be allotted to an aircraft, the consideration is that of ensuring an aircraft will be at least 1000 ft. above ground along the route. Secondly, an arbitrary rule is followed which provides an automatic separation of 1000 ft. between aircraft. To confine our attention to the congested Sydney-Melbourne route, it will be seen that aircraft flying in opposite directions must always be separated by at least one thousand feet, and aircraft flying in the same direction will either be separated by at least 2000 feet or will be at the same altitude.
|In the latter circumstances flights are so controlled - with the aid of a computor invented by an Air Traffic Control Officer - that a following aircraft is always at least ten minutes behind a leading aircraft.|
En route, therefore, the movements of aircraft are carefully followed by Air Traffic Control, so that no collision risk may arise. Changes of speed or altitude which may be desired by a pilot are not approved until it is certain that such a change will not bring two aircraft into dangerous proximity.
It will be remembered that a comment was made earlier to the effect that air routes are provided with detours. It sometimes happens that the weatherman predicts the worst weather in the book, along the normal route. In these cases, Air Traffic Control will authorise the pilots to adopt an alternative route which will take aircraft clear of the rough weather belt.
It is apparent by this time that we have dealt with the middle portion of a flight first. To return to a reasonable sequence, we can now examine firstly the departure, and secondly the arrival, portions of a flight.
At busy aerodromes a particular type of control must be provided to prevent aircraft operating on and around the aerodrome from colliding with each other. Arrivals and departures are blended into an orderly stream by Aerodrome Control. The Aerodrome Controller, overlooking the aerodrome and its approaches from a high tower, directs aircraft by radio telephone and, in the case of light aircraft not fitted with radio apparatus, with signalling lamps.
To consider a departure, a departing aircraft before leaving the tarmac area calls Aerodrome Control by radio telephone and requests permission to taxi. In granting such permission, the Controller nominates the runway to be used for take-off, describes the path the aircraft must follow to arrive at the end of the runway, and provides information such as wind speed and direction, obstructions to be avoided and so on. On arrival at the end of the runway, the pilot will test his engines and generally ensure that his aircraft is performing normally, after which he will request permission to take-off. If the runway is clear, and if no other aircraft is approaching to land, such permission will be granted. After take-off, when the Controller is satisfied that the aircraft will not conflict with others around the aerodrome, the pilot will be instructed to report his departure to the aeradio station through which any route instructions will be issued.
Departing aircraft are usually instructed to climb away from the aerodrome in a direction which diverges from the path followed by arriving aircraft, which are descending towards the aerodrome. The system ensures that there will be no conflict between climbing and descending aircraft.
|At busy aerodromes, the arrival of an aircraft is considered to commence some 60 or 70 miles out. At a specified position, usually identified with a radio beacon, the aircraft is placed under the personal control of an Approach Controller.|
As a result of instructions issued by Aerodrome Control, the aircraft will join an orderly rectangular pattern around the aerodrome, this pattern having as one of its long sides the runway in use.
In due course the aircraft will be given permission to land, and, having landed, will be directed in its taxiing from the runway to the tarmac area.
The arrival of an aircraft may be considerably less complicated, in as much as weather conditions may be perfectly clear. On the other hand, greater complications may be encountered.
If weather conditions - height of cloud, visibility, or both - deteriorate below certain specifications, the aerodrome will be closed, and an aircraft will not be permitted to land, or even to make an attempt to land. In such a case arriving aircraft will be directed to proceed to another suitable aerodrome. On the basis of the weather forecast issued at the departure point, this circumstance would have been provided for. The result of such a diversion, of course, is that passengers find themselves on the ground at an aerodrome at which they have no desire to be. However, it is far better to spend a few hours at another aerodrome than to commence at the destination an instrument approach which, due to unfavourable weather, might end in disaster.