Guidance Control

Changi Airport is in a competitive environment for passenger and aircraft services. It faces aggressive competition from other airports in the South-East Asian region as well as the Middle East. One of the ways to meet this competition involves Changi Airport investingin infrastructure, services and technology to improve the safety and efficiency of aircraft operations.

Lee Kian Wei, manager engineering and master planning division of Changi Airport Group (CAG) highlights the reasons for undertaking the AGLCMS project. “Changi Airport undertook a major replacement of the old airfield ground lighting and control and management system as it had reached the end of its design lifespan. We also wanted to enhance operational efficiency and safety. The system overhaul included a newer generation airfield lighting system that operates with the existing single addressable lamps. An addressable lamp system means that each lamp is fitted with a command and monitoring system. Lights are then grouped into defined segments for operation,” Lee said.

“Having addressable lamp control then opened up new possibilities in the further enhancements that we could consider. Besides improving the assignment of aircraft ground routes and separation of aircraft, it also enables us to achieve greater integration with the main air traffic management (ATM) system and new docking guidance systems. ” The small geographical size of Singapore has enabled a very close operational relationship to develop between Changi Airport Group (CAG), the owner/operator of Changi Airport, and the Civil Aviation Authority of Singapore (CAAS), the air traffic control provider. This relationship is built upon a major air traffic control provider delivering services to only one major airport. (Seletar, the other civil airport in Singapore, has comparatively small movement numbers undertaken by general aviation aircraft. ) It sees CAAS and CAG having extremely close linkages and knowledge of eachother’s activities. Compared to other countries with multiple large airport operations, decisions to improve operations or to introduce new technologies can be taken promptly, with comparatively contained project scope.

CAG contracted Singapore Technical Electronics, whose software solution is provided by Safegate International, to deliver the project. Operational consultancy support was provided by AVISU, an ATM consultancy headquartered in the UK with an office in Australia.

The AGLCMS provides the aircraft and air traffic controller with the optimal route between the runway and a parking gate. For an arriving aircraft, gate information is inputted into the flight plan contained in the ATM system flight data processing system (FDPS). When the aircraft is on short final, taxiway lights are illuminated on each of the rapid exit taxiways the aircraft may use to vacate the runway. Only a short path to the main taxiway network is illuminated at this stage. When the surveillance system has

AGLCMS provides the aircraft and ATC with the optimal route between the runway and a parking gate.

confirmed which rapid exit taxiway the aircraft will use, the lights presenting the route to the gate are illuminated. All other rapid exit taxiway lights are automatically switched off. The air traffic controller is able to override the route functionality should a specific rapid exit taxiway be required.

‘Narrow’ route guidance is provided on the route between the runway and the gate. This narrow guidance activates taxiway lights only a short distance – 400m at Changi – ahead of the aircraft. This distance may change as more operational knowledge of the system is gained. Taxiway lights behind the aircraft are automatically turned off.

For departing aircraft, the preferred operation involves the route being activated from the gate to the runway holding point once surveillance sensors detect that the aircraft has commenced its push back. However, full ground surveillance coverage around all gate areas at Changi Airport requires additional multi-lateration and ADS-B sensors to be installed. A project is underway to provide this coverage over the next two years. Until full surveillance coverage can be assured, the ground controller undertakes manual activation of the route.

AGLCMS software algorithms determine the optimal route offered to the aircraft. These algorithms determine the optimal route based on the possibility of conflicts with other aircraft, the ability of taxiways to accommodate the size of aircraft and any unserviceable areas on the airport. The pilot sees a path of green centerline runway lights in front of the aircraft presenting the path the aircraft is to follow. A pathway can be changed by the control tower while the aircraft is taxiing by nominating points on the route to be followed. This is done by touch screen.

The taxiway network at Changi Airport includes a multitude of stop bars. Not only are the stop bars located on taxiway entry points to the runways, they are also located at major taxiway intersections. The AGLCMS provides automated control over the activation of these taxiway stop bars.

An important feature of the AGLCMS is the ‘look ahead’ function. Algorithms determine whether the routes of two or more aircraft will be in conflict at a taxiway intersection. This is calculated by processing surveillance data provided by A-SMGCS (Advanced SurfaceMovement Guidance and Control System), including the ground speed of the aircraft, along with the route to be followed. Once the system recognises that two or more routes will conflict, the algorithm will activate stop bars prior to the intersection on the route of the second or later aircraft. Taxiway guidance lights through the intersection for the second, or later, aircraft are turned off. The taxiway lights presenting the route for the first aircraft will still continue through the intersection. An alert is sent to the responsible ground controller when a conflict will take place. This assists the ground controller to maintain situationalawareness. Once the intersection conflict has ended, the controller turns the stop bar off and the route is automatically reactivated. An onward taxi clearance is given over the radio.

A conservative approach was adopted in establishing procedures for intersections not protected by stop bars. AVISU director Stephen O’Flynn explains: “For the early stages of operation, at intersections not protected by stop bars, aircraft will be held at the nearest stop bar prior to the intersection. At some parts of the airport this could mean that aircraft are held quite a distance from a conflicting intersection. Once confidenceis gained in the operation of the AGLCMS and safety case material developed, a ‘black hole’ concept could be used. This black hole concept means that for the second aircraft to arrive at an intersection, the taxiway lights are turned off 400m prior to the intersection. The aircraft stops at the point where the taxiway lights have been turned off. As well as intersection protection the black hole will be used for aircraft following one another. In this case, the lights 400m behind the leading aircraft are turned off. This ensures that a minimum spacing is maintained between the aircraft. At all times the controller remains in the loop of what the system is proposing and can intervene as appropriate. Clearance limits are still issued to the flightcrews by voice. ” The AGLCMS is able to quickly incorporate unserviceable areas on the airport that are unable to be used by aircraft. Polygons to depict these areas can be drawn by the air traffic controllers through screen touch. Once activated these areas influence the routes generated and provide alerting for aircraft that may seek to enter these unserviceable areas.

A new operating environment is able to be created for the control tower. AGLCMS functionality enables areas of responsibility, similar to ‘control sectors’, to be created. For example, areas of responsibility can be created for runway controllers and different ground controller positions. The functionality enables position and alerting information of aircraft and vehicles to be provided only to those controller positions that require this information. This reduces clutter on controller screens and ensures that controllers are better able to focus on pertinent information. There is clear delineation over the responsibilityfor an aircraft and transfer of control is undertaken automatically.

Implementation of the area of responsibility concept is an issue that presents some procedural issues. To now, control tower staff have been used to receiving information about all aircraft and vehicles on the airport. Alerts are also provided to all positions. There is concern that implementation of the area of responsibility concept will limit the capability of controllers to react to the dynamic nature of control tower operations and thereby reduce operational efficiency.

The Single European Sky Air Traffic Management Research (SESAR) program is currently undertaking an assessment, via simulation, of automated taxiway guidance systems. A project called ‘Follow the Greens’ was undertaken for Frankfurt Airport during August last year to assess the benefits of these systems. Further simulations will be

Combined with increased aircraft operational fluency while taxiing, a reduction of up to 40 per cent in fuel emissions was achieved.

undertaken for another five major airports to develop European-wide standards.

The main objective of implementing automated taxiway guidance systems is to make the taxiing procedure between the runway and gate more safe and efficient, thereby reducing the aircraft time involved in ground running. In having only the lights of the taxiing route turned on, it is considered that pilot errors will be minimised. There is less chance of confusion than at present where large sections of taxiway lights remain turned on at night.

Some performance benefits from the ‘Follow the Greens’ simulation at Frankfurt have been reported in Airports International magazine. Fuel consumption is reduced through an uninterrupted taxi route. At the moment aircraft are directed by verbal communication with air traffic controllers to holding points short of major crossing points. This can involve an aircraft repeatedly slowing down or stopping, then accelerating during the taxiing. Fuel consumption is reduced by a shorter taxiing time as well as from fewer repeated power up requirements. Reports of the simulation state the taxiing times reduced by a minimum of 10 per cent. Combined with increased aircraft operational fluency while taxiing, a reduction of up to 40 per cent in fuel emissions was achieved. The greatest reduction occurs in low visibility conditions. Time spent conducting radio communications is reduced by up to 50 per cent.

Implementing a ‘world first’ technology presents a number of challenges. O’Flynn highlights some issues: “Our role was to provide an operational perspective in the development of the AGLCMS. This role is important to ensure that the system is ableto be used effectively by air traffic controllers in their operational environment. It is impossible for a large sophisticated airport like Changi to buy new air traffic management systems ‘off the shelf’ and bring them into operation unaltered. Considerable customisation is needed in how air traffic controllers are presented with information and interact with the system. We also had to assist Changi control tower management in identifying the operational procedures and operating practices that could be changed to get most benefit from the AGLCMS, and understand those that could not. ” The AGLCMS also needs to incorporate airport movements such as by vehicles and towed aircraft. Route generation can then take into consideration the position of these vehicles when determining the guidance provided to scheduled aircraft movements. Capturing these movements required some software customisation and new operational procedures.

An early challenge was to ensure that requirements to guide the software development of the system were operationally robust. O’Flynn says: “A new system does not have a past track record of operational use to guide development. In these circumstances a combination of operational, technical and integration expertise is particularly important to ensure that the system development can be implemented into the ‘live’ environment. We needed to add considerable detail to the initial requirements to ensure that the AGLCMS could be implemented in the operational setting. ” An essential component is the integration of data received from the A-SMGCS for processing by the AGLCMS. The A-SMGCS processes surveillance data received about an aircraft from avariety of sources. These sources include primary, secondary and surface movement radar, plus multi-lateration and ADS-B sensors. The A-SMGCS sends this data about the aircraft’s position to the AGLCMS for route processing. Importantly the A-SMGCS also sends various alerts to the AGLCMS, for presentation on air traffic controller screens in the tower eg, runway incursion, wrong route and impaired operations.

The emergence of AGLCMS will almost certainly see a change in the strategic-competitive positions held by various airport systems suppliers. Suppliers of the AGLCMS systems are integrating outward to take over the role performed by A-SMGCS suppliers. Safegate has a foundation as one of the leading organisations in airfield lighting systems, which is a core element on every airport. As the sophistication of these lighting systems have evolved, from relatively ‘dumb’ large circuit activation to single addressable lamp control, Safegate has increased its software development capability.

Suppliers of A-SMGCS systems fuse surveillance data from various sensors to generate position and information about an aircraft. Invariably different separate suppliers provide the surveillance sensors. The A-SMGCS system integrates on-ground aircraft data with surveillance and flight data processing undertaken by the main ATM system. This information is then presented on a screen for air traffic controllers in the tower.

The new AGLCMS integrates surveillance data with route generation software. Alerting functionality generated by the A-SMGCS is also able to be presented through the AGLCMS.

Recently Safegate acquired AviBit, an A-SMGCS systemssupplier. This acquisition has provided Safegate with in-house surveillance data fusion capability. It enables Safegate to incorporate surveillance fusion capability into their system’s AGLCMS without the need to integrate with another A-SMGCS supplier. The capability also enables the AGLCMS to integrate with the main ATM system. From a customer perspective, the opportunity to reduce the number of organisations involved in providing different systems significantly minimises the integration risks. The experience at Changi suggests that A-SMGCS suppliers at major airports will come under competitive pressure from organisations developing sophisticated route guidance systems.

The AGLCMS site acceptance test (SAT) was completed at Changi in April 2013. An estimated period of two years has been set aside before the advanced automatic routing functions of the AGLCMS will come into full operation. During this period optimising surveillance coverage, system tuning, controller training and final operational acceptance are expected to take place.

In the meantime, a semi-automated routing system is in operation, which enables air traffic controllers to initiate a taxiing route for an aircraft between the runway and gate. Air traffic controllers need to nominate the start and end points. The system activates the taxiway lighting system, including stop bars, on the whole route but requires air traffic controllers to deactivate lights once the aircraft has passed. There is no surveillance data incorporated in the semi-automated solution and limited alerting information.

Singapore commissioned a new Thales ATM system, termed Lorads III, in October 2013. Theproject includes new systems and information provided to the tower.

A single screen on each air traffic controller position will now present position information of the aircraft, alerts received from A-SMGCS and route guidance functionality from the AGLCMS.

Changi Airport Group has also recently decided to purchase an advanced visual docking guidance system (A-VDGS). Edwin Hulst, safegate’s system engineering director explains: “For arriving aircraft, the A-VDGS scans the area 150m out from the gate using laser technologies. These sensors activate A-VDGS functionality, which guide the aircraft to its designated stop position at the gate. For departing aircraft, the pilot receives information from the apron management system on the A-VDGS display, including a countdown to the assigned departure time. ” The future prospect of integrating the information flows between the new ATM system, AGLCMS and A-VDGS provides a platform to

An automated route guidance system presents the opportunity to achieve a step change in improving the efficiency.

increase operational efficiency and improve collaborative decision making (CDM) amongst various airline, airport and ATM functions.

“Once A-VDGS laser sensors identify when the push back commences it can then trigger theentire outbound routing system, both for the AGLCMS and the flight data processing system (FDPS) of the ATM system,” Hulst says. “In particular, the sensors are able to initiate the generation of automated taxiway routes and the activation of aircraft flight information. A-VDGS functionality is able to overcome limitations in the surveillance coverage around gate areas, where sensors do not always determine when an aircraft has commenced its push back. Information received about inbound aircraft can enable the gate to be prepared and activated for operation. ” Full integration of the three systems at Changi Airport is still likely to be some years away.

Nonetheless, the implementation of an automated route guidance system at Changi Airport, which can be integrated with advanced docking guidance and airborne ATM systems, presents the opportunity to achieve a step change in improving the efficiency and safety of airport operations.