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Part I

In the early days of aviation, pilots navigated using visual aids such as rivers, lakes, hills, roads and other physical fixtures, aided by a compass, rudimentary maps and charts. The objective of the pilot was to get the aircraft safely to its intended destination without running out of fuel.

The uniqueness of air transport is that, unlike other modes of surface transport, the pilot cannot stop the aircraft in mid-air to refuel or check his maps and charts to see if the aircraft is on course.

A critical factor at that time was the adequacy of fuel for the flight, based on the aircraft fuel capacity, known as fuel endurance. Therefore, prior to take-off the pilot had to chart his course from the departure point to the destination point to ensure there was adequate fuel on board the aircraft for the flight.

Sometimes this required a refuelling stop, depending on the length of the flight. In that case, the pilot had to recalibrate his course once more. Even today, fuel endurance remains a critical factor for all flights.

Visual navigational aids had limitations for night flying and adverse weather, both of which impaired visibility. This gave rise to aviation meteorology, as pilots needed to know in advance what were the likely weather conditions along the planned route. This at times required diversions from the planned route and increased the fuel burn, which sometimes required another refuelling stop.

Advancements in radio technology saw the introduction of a myriad of ground-based non-visual navigational aids (navaids) making night-time and “all-weather” flying possible. These included non-directional beacons, distance-measuring equipment and VHF omnidirectional radio range, enabling the aircraft to derive its magnetic bearing from the station.

To use these radio navaids, aircraft are equipped with the appropriate wireless receivers for displaying the navigational data on cockpit instruments.

First-generation surveillance radar was used by air traffic controllers (ATC) to determine an aircraft's position, heading, speed and altitude in flight. Pilots and ATC maintained two-way VHF radio communication. However, radar and VHF radio navaids to this day have a range of approximately 250 nautical miles.

Further technological improvements in aircraft design caused incremental increases in the passenger-seating capacity of transport aircraft.

A major technological breakthrough was the introduction of jet engines in 1939, replacing piston engines on passenger aircraft. This permitted aircraft to fly greater distances at higher altitudes. This posed several challenges for air navigation, as the aircraft was at times “out of range” of ground-based navaids when the aircraft was flying over oceans, mountainous regions, jungles, and deserts, and led to the use of celestial navigation.

Celestial navigation is the practice of position-fixing using stars and other celestial bodies that enables a navigator to accurately det