The history of aircraft navigation
In 1952, when the SAS made the historic first flight between the United States and Scandinavia via the Arctic, navigation was a major challenge. The principal method was astronavigation, in which the sun, moon, and stars were used to determine position.
To be able to steer the right course at these high latitudes, navigators had to develop new tools, such as a high-precision polar gyro that made it possible to chart a route using a grid map that had been specially designed for use in the Arctic.
The navigation capability of today’s smartphones, with their built-in Global Positioning System (GPS), would make 1950’s navigators drop their jaws, but their pioneering work bore fruit in 1960 when the jets started flying the Arctic route.
Fixed radio beacons were rare in the Arctic, but by using ground-based pairs of radio transmitters that broadcast similar signals at identical intervals, the navigators could plot the route according to the time difference between the signals – a method that formed the basis of the LORAN system.
By the time SAS upgraded its fleet with Douglas DC-10s, navigation was done with the help of the Inertial Navigation System, which used accelerometers and motion sensors that detected the slightest movement of the aircraft. This system continually calculated the plane’s position independently of radio beacons or other equipment. That also spelled the end for navigators, who had until this point been indispensable.
Today the standard is GPS, originally developed in the 1960s to satisfy the navigational needs of the US military. Russia has its own GPS system called GLONASS, and soon China and the EU will have their own GPS satellites in operation.
In today’s modern aircraft, all systems are integrated under the Flight Management System. Navigation – including GPS, inertial navigation, and traditional radio beacons such as VOR – is incorporated in the autopilot system and controlled by another integrated part of the navigation system.
The pilots type data into their Flight Management Computer (FMC), and during flight the system calculates positioning with the data it receives from satellites, GPS, inertial navigation, and radio beacons.
An important part is the Controller Pilot Data Link Communications (CPDLC), which improves navigation, communication, monitoring, and traffic flow by using satellite data links, with full coverage over oceans. This system enables the aircraft and air traffic control to communicate via text messages through the FMC, a method the pilots consider seamless and smooth.
“The CPDLC is a massive help on transatlantic flights,” says SAS captain Per Elenborg.
“In the past, all communication, including positional reporting and other messages, was carried by HF radio on frequencies shared with many other aircraft, which could sometimes make simple messages unnecessarily complex to send.”
The current navigation system broadcasts automatic position reports, which removes the administrative burdens from the pilots and makes things easier for air traffic control as it gives them a more precise picture of exactly where an aircraft is. After all, there is zero radar coverage over the Atlantic.
The high precision of GPS navigation means that aircraft can fly in closer proximity to one another, thereby increasing airspace capacity.
“Thanks to CPDLC, aviation has become more efficient,” Elenborg says. “The bottleneck is no longer aircraft or air traffic control, but rather airport capacity. During periods of high traffic, some of the major airports quite often reach saturation point.”
A lot has happened since 1952 when a Douglas DC-6B set off across North America and the Atlantic toward Copenhagen. With a crew of 13 and a journey time of 28 hours, the flight between Los Angeles and Copenhagen was the embodiment of a major project.
Navigation was handled by two navigators who shared the burden of monitoring the course based on observations of celestial bodies. One of them wrote the forward speed of the flight on the chart and monitored the gyro. The second navigator checked the aircraft’s grid course every 20 minutes using a sextant and took observations of three stars every 30 minutes to determine position.
Today, the same journey takes a little more than 11 hours with a crew of three pilots.
Text: Staffan Erlandsson
Published: August 23, 2016