As the plane carrying your correspondent from Hong Kong to Singapore started its descent to the Changi airport, the world's fifth busiest, it started flying circles. Shortly afterwards, the captain explained that multiple aircrafts were on holding pattern and the queue was changing quickly. That, I was assured, had nothing to do with the official launch of the airport's new US $300-million air traffic control system. Instead, the delay was due to the final day of the Chinese Lunar New Year holidays, and it probably would have been a lot worse without the new system.
Soft launched in October and jointly developed by French engineering firm Thales and Singapore's aviation authorities, LORADS III is the latest iteration of a proven air traffic control system called TopSky-ATC. And it's main strength is that it gives controllers better information, faster.
To understand how, you have to remember that air traffic control actions in many places are still done by recording flight data— airplane call signs, speed, bearing, altitude, and other information—on strips of paper, and instructions.
Like all modern ATC systems, LORADS III does without paper strips. That's all been digitized, but Thales is looking at doing without strips altogether, paper or digital: the ideas is to move towards much richer labels and a management system that give at a glance a clearer, more complete picture of the congestion status of a given airspace.
Hovering the mouse over each track symbol allows the controller to see a plethora of data and issue commands that can get relayed to the aircraft via satellite. The new commands pop up in the on board navigation and communication instruments and the pilot can decide whether to implement it or not. (They usually do, unless they have a good reason not to—they are too heavy to climb to a higher level or they are cruising already at their fastest, for example.)
Usually these commands are radioed in when in radio range — and it's fair to assume they still will be for some time — but this sort of command-by-text-messaging would reduce controllers workload, according to Thales. This will also reduce the radio chatter, which at busy airports and on certain frequencies is up to capacity and represents a bottleneck for more efficient operations. For control of the skies over oceans it's even more important. Long distance communications between ground controllers and aircrafts goes over HF radio, notoriously finicky and with a range that depends on weather conditions. Controllers can instead transfer small amounts of data via satellite or by HF or VHF radios, because, as anybody trying to make a call on a busy cell network has noticed, it's much easier to slip a small text message through, than place a voice call.
The commands and subsequent execution, together with key flight data are stored in a central system called the Flight Data Processor, which calculates in real time everything pertaining to the position and trajectory of each aircraft. Every work station is connected to it, so all controllers have an up-to-date view of who's going where and how fast.
"It a simple change, but it's also very complicated, because there are more than a hundred positions in the Singaporean Traffic Center and training facilities", says Andrew Nabarro, business development manager for air operations at Thales. "Now, each person can have access to customized information at different times."
The first step, though, is knowing where aircraft are. This involves both active and passive sensing. Airplanes beam out their name, location, route and whatnot through an ADS-B feed, or automatic dependent surveillance broadcast. ADS-B is a type of transponder that beams out the GPS position of the aircrafts about once per second.
There's radar too, of which there are two kinds: primary radar sends out a burst of energy and waits for a reflection from an aircraft. Secondary radar instead interrogates a receiver placed aboard the airplane, which in turns answers with its identifier and altitude. Secondary radar has a longer range, about 250 nautical mile (460 kilometers); primary reaches less than half that distance. But primary works with any type of aircraft whether or not they've been equipped with the transmitter needed for secondary radar.
LORADS III has to make sense of all those signals to come up with a single set of information about the aircraft above Singapore. Thales' proprietary solution, called Multi Sensor Track Processing, "takes all the different tracks from all the different radar, many ADS-B receivers, many wide area multilateration receivers, which is another type of surveillance, and turn it all up and says 'of all the sensors that we have, this is the actual position of the aircraft'," says Nabarro.
Most air-traffic control systems are customized to manage a particular type of airspace; there are approach airspaces (think the area above and around a major airport) and en route ones (the skies of the North Atlantic, through which the bulk of Europe to U.S. traffic flies). Singapore, by virtue of its position in the middle of the "Kangaroo route" connecting the UK and Europe to Australia and several South East Asian countries, happens to need a system that can do both. The portion of sky under Singapore's control covers an area of three quarters of a million square kilometers and its controllers preside over 220 000 annual movements.
As the deluge of flights approaches for arrival at Singapore, the system's Arrival Manager kicks in. So "instead of having a human being trying to sequence a whole bunch of airplane coming from all sorts of directions, at different speeds and altitude, the system will calculate the best sequence", says Nabarro. Here, "best" means the sequence that gives the least amount of holding time for everybody.
Holding costs airlines thousands of dollars per flight in wasted fuel. Usually, airplanes begin their descents from cruise level when they are about a hundred nautical miles (185 kilometers) from the airport, but they only learn of congestion as they get closer and reach a much lower altitude. At low altitudes, jet engines are much less efficient. With the Arrival Manager, controllers are able to tell approaching but still cruising airplanes to slow down or speed up a bit in order to sequence them in a way that reduces low-altitude holding. The order can, of course, be changed manually and the system will then recalculate the best sequence, showing the relevant controller what commands must be sent to which aircraft, in order to minimize disruptions to the flow of approaches.
But what's good software, without the ability to back all the data up? The main system has a dual, fully redundant set of servers that make the Changi control room fail safe; controllers can switch from one to the other simply pressing a button. While this has been implemented before, Singapore officials wanted another layer of safety: at a neighboring training facility, there's a replica of the control room with yet another set of dual servers. This second set runs simulations for training of new controllers, but with minimal software tweaking it could be transformed into a fully autonomous back up control room, if anything catastrophic were to happen to main one. The two locations are a few kilometers apart, providing an added layer of strategic safety, as well.
