Four-dimensional tracks are based on longitude, latitude, altitude and time, and through hardware and software upgrades and transformations, the data itself is more accurate, data transmission is faster, and data usage is unified standards.

Before the outbreak of the new crown pneumonia epidemic, the busy air traffic and exponentially growing travel demand allowed the upstream and downstream of the aviation industry to explore technological upgrades and changes. Four-dimensional tracks are based on longitude, latitude, altitude and time, and through hardware and software upgrades and transformations, the data itself is more accurate, data transmission is faster, and data usage is unified standards. In recent years, Airbus has carried out four-dimensional track exploration and practice in Europe and China, making the operation based on four-dimensional tracks more mature and reliable.

Accurate data Safe and controllable

According to the traditional aircraft operation command mode, the controller needs to voice the pilot to inform the specific instructions. The pilot recitation after receiving the command from the controller, and the controller monitors the pilot to recitation to ensure the command is accurate. This will take at least more than 10 seconds to go back and forth. However, after adopting the four-dimensional tracking technology, the entire process will be very different - on the ground, the controller will issue instructions with just a click of the mouse; in the air, this instruction will be directly transmitted to the aircraft, and the pilot can see more standard digital instructions on the screen. This technology not only reduces the probability of wrong orders due to tongue errors, but also makes it easier to correct problems in a timely manner. The core of

4-dimensional track technology lies in the accuracy and controllability of time. The use of precise data based on four dimensions of longitude, latitude, altitude and time can make the aircraft operate safer. By carefully controlling the entire stages of flight takeoff, climb, cruise, near-advance, landing, etc., four-dimensional track operation can achieve "fixed-point and timed" flight, and the time accuracy is increased from minute level to even 10 minutes level to within 10 seconds tolerance.

For the civil aviation industry with rapidly developing market size, such "speed-up" is of great significance. Several data show that before the outbreak, the busyness of air traffic increased exponentially. From 2015 to 2019, China's total civil aviation transportation turnover, passenger turnover, and cargo and mail turnover have increased year by year, and the growth rate of civil aviation transportation has remained above 10% for five consecutive years. Taking 2019 as an example, transport airlines across the industry completed 4.9662 million aircraft takeoffs and landings, an increase of 5.8% over the previous year.

In this context, improving the level of automation is one of the effective ways to avoid large-scale flight delays and reduce costs. In recent years, the operation based on four-dimensional tracks has been one of the new technology applications that the Civil Aviation Administration of China and the Civil Aviation Administration of China and attach great importance to, and is also one of the specific application scenarios for the construction of smart civil aviation and smart air traffic control. Since 2016, under the guidance of industry authorities such as the Civil Aviation Administration and the Civil Aviation Administration of Air Control and Control Bureau, many civil aviation-related enterprises have carried out in-depth cooperation. After more than three years of collaborative research on industry, a series of four-dimensional track information processing systems (ATN data link processing system, four-dimensional track control automation system, etc.) have been developed. At the same time, in order to verify the system capabilities and control operation procedures of this technology, from 2016 to 2018, Airbus, a joint project team of China and a control operation unit carried out multi-level and comprehensive simulation verification work.

drawing/Wang Shixin

technology upgrade benefits a lot

When running, appropriate safe distances need to be maintained between aircraft according to their altitude. Since the information references used by air control departments, airports, airlines and aircraft are different, controllers must take into account the information lag caused by data transmission and loss when conducting commands, leaving room for safe distances. With the support of four-dimensional track technology, the data of each aircraft can be determined in advance, which not only improves the predictability of air traffic, but also better ensures flight safety. In addition, according to the optimized route flight, the aircraft can also reduce fuel use, reducing carbon dioxide emissions while reducing costs.

"The optimization of route intervals requires the sharing of track dynamic information between air traffic control departments, airports, airlines and aircraft. The unified use of four-dimensional tracks for management can greatly improve the safety margin of , improve management efficiency, and make the aircraft run safer." A relevant project leader of Airbus told reporters.

For flight, the value of four-dimensional tracks lies in providing the same data reference for all systems.After calculating the four-dimensional track, the aircraft flight management system (FMS) will transmit the relevant data to the air traffic control center, the airline operation control center, and the flow management system to ensure that all relevant parties refer to the same data within the closed loop. According to current standards, four-dimensional track technology can calculate up to 128 track points.

During the flight, after flight management system receives the Controlled Digital Command (CPDLC), it will dynamically update the predicted tracks in combination with the real-time data of the aircraft, thereby enhancing the track prediction capabilities and achieving accurate prediction and control of the aircraft. Behind the accurate prediction and control is a complex system project, involving the upgrading and transformation of airborne avionics systems, ground-to-air data links and air traffic control information systems. It is worth mentioning that Airbus has developed avionics system (FANS C) that meets airworthiness requirements. With aircraft equipped with FANS C systems, an air navigation service provider (ANSP) on the ground will be able to predict traffic flow more accurately.

For the air traffic control and support department, four-dimensional track aircraft data can free up more space for controlled capacity. It is reported that four-dimensional track aircraft data will be applied to various control automation tools to provide traffic monitoring, organization and sorting services for designated airspace and even further areas, effectively reducing the work intensity of controllers.

"Four-dimensional tracking technology can not only allow controllers to understand the pilot's intentions better, but also enhance their capabilities in conflict detection, traffic situation awareness, capacity and demand balance, and complexity management." A relevant project leader of Airbus said, "For example, in conflict detection, two aircraft may conflict during scene taxiing, flight and other processes. After obtaining the four-dimensional track data of the two aircraft, ground air traffic control personnel can timely compare and analyze, predict possible problems in advance, and command and avoid early, thereby greatly improving safety margin. In addition, the situation awareness of multiple aircraft involves traffic management, capacity and demand balance. This is not only the management of a single aircraft, but also the macro control of the flight system."

International Cooperation The future is promising

For the civil aviation industry, four-dimensional trajectory is the general trend of future development.

At present, the traffic management system has taken into account data from four dimensions: longitude, latitude, altitude and time. However, due to the constraints of low data accuracy and slow transmission speed, it still seems unsatisfactory when dealing with large-scale flight delays. In comparison, four-dimensional track technology can provide the system with more accurate and timely data, which is of great benefit to improving the traffic management system.

However, the four-dimensional track operation is not yet mature, and if it wants to play its full role, it still requires joint efforts from all countries. At present, Europe, the United States and Asia-Pacific countries have reached an agreement on the concept of four-dimensional tracks. At the 12th Global Navigation Conference, ICAO released the AS-BU Aviation System Upgrade Block Plan, which listed efficient tracks as one of the four major blocks. Four-dimensional tracks, as an important part of the key performance field, are planned to be gradually implemented in four stages by 2028.

In order to further verify the reliability of four-dimensional tracks, Europe launched the SESAR 2020 PJ-31 DIGITS ultra-large-scale four-dimensional track verification flight project in 2017. The focus of this project is on real-time transmission of four-dimensional tracks, and better solutions to realize air traffic control information interaction through analysis. After the project was launched, a total of 91 Airbus A320 aircraft from 6 airlines participated in the verification operation, with a cumulative flight volume of more than 20,000 and recorded flight ADS-C information of more than 1.4 million.

In China, in March 2019, Airbus participated in and supported China's civil aviation to successfully complete the first initial four-dimensional track operation verification project in Asia-Pacific . During this verification flight, the Airbus A320 aircraft with four-dimensional track flight management capabilities and communication capabilities took off from Tianjin Binhai Airport, headed to Guangzhou Baiyun Airport , and returned to Tianjin after arriving. The flight route passes through 6 major controlled units, with a total journey of more than 3,800 kilometers. During the entire process, the airborne system, ground system and air-ground data link communication system worked normally, and the air-ground flight control was implemented smoothly as planned.This verification flight fully verified the capabilities of four-dimensional track technology for digital coordinated control of air-ground and air-ground track sharing, and conducted aircraft timing arrival (RTA) capability tests at 3 waypoints, with the deviations controlled within 5 seconds, achieving "fixed-point timing" flight.

In promoting the four-dimensional track operation technology, China and Europe have been working together. After the successful test flight, technical seminars and other activities on the theme of four-dimensional tracks and ground-to-air communication data links were continuously carried out, and China and Europe fully exchanged their respective experiences. In the future, my country's smart air traffic control construction will be based on four-dimensional track management, establish an advanced air traffic control operation model with track management as the core, improve the flow management capabilities at the strategic, pre-tactical and tactical levels, promote refined control of the entire life cycle of flights, improve safety levels, and achieve capacity expansion and efficiency enhancement.

word explanation

CPDLC: Controller Pilot Data Link Communications, i.e. controller-pilot data link communication, can be used to make up for the shortcomings of voice communication, such as crowded voice channels, poor sound quality, misunderstandings caused by misinterpretation and interference caused by simultaneous speeches.

contract automatic correlation monitoring (ADS-C): Automatic Dependent Surveillance-Contract, which automatically sends data such as location, altitude, speed, intention and weather collected by the onboard system to the air traffic service unit that signed a contract with the aircraft in the form of a report, for monitoring the aircraft location and route compliance.

Flight Management System (FMS): Flight Management Computer System refers to advanced area navigation, guidance system and performance management system with computer as the core. Its main function is air flight planning management, and various sensors are often used to determine the position of the aircraft.