At certain key points there are other types of equipment designed mainly to enable aircraft to approach an airport safely. Distance measuring equipment (DME), which is installed at certain points including Wellington and Christchurch, enables a pilot to read on an instrument in the aircraft his exact distance from a selected point which he is approaching. Radio ranges, installed for example at Whenuapai (Auckland) and Christchurch, provide radio beams along which an aircraft can be steered to approach an airport. Mangere Airport will be equipped with the instrument landing system, which, by radio, provides the pilot with a visual indication of a glide path and tells him not only whether he is travelling in the right direction but also whether he is at the right height and descending correctly.

Wellington is equipped with an extremely advanced form of radar. Radar (radio detection and ranging) works by emitting a train of very short pulses of radio frequency energy which are reflected back from distant objects to a sensitive receiver near the transmitter. Distance is measured by the time taken for each pulse to return to the receiver. These reflections, appearing on a sort of television screen, enable the operator to see where the objects (in this case aircraft) are, and how far away they are. The operator can then inform the pilot of his position, his direction of flight, and of any other aircraft in the vicinity. He can keep a continuous watch on any aircraft and, by talking to the pilot, can bring the aircraft to its destination when the pilot cannot see.

Wellington employs radar in two main forms–surveillance radar and precision approach radar. Surveillance radar enables the operator (radar director) to observe and control all aircraft within about 100 miles of Wellington. An aircraft wishing to land at Wellington may be taken over at a certain point (between 6 and 10 miles from Wellington) by precision approach radar which enables the radar director to watch the aircraft so closely that he can “talk it down” virtually to the runway threshold; the final landing is made by the pilot who can then see the runway and, if it is at night, the runway lighting. Other forms of radar in use in New Zealand provide aircraft with warning of storms ahead and, by tracking balloons from ground stations, provide information on wind speed and direction at different heights. The navigational aids described above can only be used by aircraft fitted with the necessary equipment. Other aircraft may use visual aids (landmarks or aerodrome markings) and obtain advice by radio, but their operations are necessarily restricted in conditions of poor visibility.

The navigational aids are backed up by a network of radio communications, which enable aircraft to keep in touch with the Department of Civil Aviation's officers and provide direct radio communication between airports and the Department's control officers and others throughout most of New Zealand. Hence aircraft know where they are, thus enabling them to pursue their flights in safety. But they also know that, when an aircraft files a “flight plan” with the Civil Aviation Administration, all the airports and traffic controllers along its route are warned in advance to expect it and to keep watch for it. In addition, weather reports from places ahead are relayed by radio. The complete system of navigational aids and communications means that the captain of an airliner, flying between main centres, is never out of touch with ground stations which advise, warn, and direct him. A Viscount airliner flying from Auckland to Wellington, for example, is in touch throughout the flight with ground controllers, first at Auckland and then, through successive relay stations at Mount Egmont and Colonial Knob (Porirua), at Wellington. When the aircraft is about 100 miles from Wellington it may be picked up on a radar screen there and watched all the way to the airport.

New Zealand is unusual in that the same air traffic control organisation provides control both of Air Force and of civilian aircraft. Other countries which have separate control systems have had some unfortunate experiences, with the result that they are now considering common control, as in New Zealand.

Piston-engined aircraft on the main route (Dunedin-Christchurch-Wellington-Auckland) flying at lower altitudes than the Viscounts and Friendships follow prescribed routes known as airways, and they also are constantly in touch with the ground. They maintain prescribed heights in order to avoid collisions with aircraft going in the opposite direction. Aircraft flying away from the main routes are not kept under such continuous control, although information on weather conditions, serviceability of navigational aids, state of destination aerodromes, and location of other traffic is passed to flight captains to enable them to plan their flights accordingly.

Aircraft which are unable to use comprehensive navigational aids (either because the aircraft are not equipped or because the route is not adequately provided or because the pilot has not obtained the necessary instrument qualifications) must fly under visual flight rules. This means broadly that the pilot must be able to see where he is going and, therefore, may not fly in cloud or darkness. He must keep at least 500 ft away from the nearest land or water; this is specially important in hilly country. If he flies above 3,000 ft, then, like aircraft under instrument flight rules, he must keep to certain prescribed heights in order to avoid collisions.

by Donald Frederic Toms, Divisional Controller Air Services, Department of Civil Aviation, Wellington.