Slotting In

‘More airport infrastructure and new ATM systems come with significant capital and operational costs’

Airlines, airports and Airservices are involved in the pre-tactical phase the day prior to the movement. In the tactical phase, Airservices’ air traffic controllers apply measures to separate and sequence aircraft.

In the past, highly tactical methods of providing airport infrastructure and air traffic services dominated operations and strategic planning. Airlines had discretion over when they preferred to operate, with airports and Airservices providing infrastructure and services to meet this demand as best they could. Aircraft delays on the ground and in the air were accepted as a natural consequence and managed by operational staff. These delays increased airline operating costs.

It had also largely been the responsibility of Airservices to manage movement capacity issues with airlines. Airports typically had a limited focus, undertaking airport master planning, addressing aircraft congestion at the terminals and on the ground, and supporting the management of the noise issues arising from increased air traffic with local communities.

‘The adoption of standard arrival speeds probably produced the greatest benefit’

The sharp increase in aircraft movements arising from the greater airline competition and large numbers of fly-in/fly-out (FIFO) operations resulted in extreme pressure on airport infrastructure and the air traffic management (ATM) system at peak periods. Solutions that involve providing more airport infrastructure and new ATM systems come with significant capital and operational costs and involve long lead times to plan, procure and bring into service.

In 2012, new strategic initiatives were introduced by airport companies and Airservices to better meet the demands of increased traffic levels. Initiatives took place at Perth, Brisbane, Sydney and Melbourne, termed network airports, to optimise airport movement capacity and operations in surrounding airspace.

Each of these airports regularly have aircraft demand that exceeded capacity. These initiatives comprised an airport directed slot management system, the Airport Capacity Enhancement (ACE) program, and Metron Harmony Air Traffic Management Flow Control.

Slot management schemes, sometimes termed the runway demand management scheme (RDMS), are the first gateway in balancing aircraft demand with the capacity of an airport and the ATM system. These schemes are typically based on IATA Worldwide Slot Guidelines with local rules defined for how slots are assigned. While airport companies set the rules for how RDMS will operate, day-to-day management is undertaken by Airport Coordination Australia.

At Brisbane, for example, assignment of airport slots begins when an airline applies to operate a service. Mark Willey, Brisbane Airport Corporation’s (BAC) Head of Airport Planning explains: “The process of allocating slots commonly occurs twice each year coinciding with the international scheduling season. It is a voluntary scheme, in contrast to the scheme at Sydney Airport, which is regulated. Since the RDMS was introduced in 2012, along with Airservices’ efforts, it has made a big difference to the consistent and on-time performance of airline services at Brisbane Airport. Although the RDMS is voluntary, the manner in which the scheme is managed and engagement with the airlines results in an extremely high level of compliance.”

The number of slots available each hour is based on the runway capacity of the airport. Initially, Brisbane Airport established movement metrics based on the demand that was presenting at peak periods. This figure was updated following a capacity study undertaken by NATS Consulting, an offshoot of the UK ATM provider. A similar capacity study was undertaken at each of the four network airports. The goal was to identify measures to extract latent capacity from inefficiencies in runway operations.

At Brisbane, the ACE program identified 23 initiatives that could improve capacity. The initiatives providing the greatest opportunity to increase runway capacity included reducing spacing between arriving flights, the adoption of standard arrival speeds and reducing runway occupancy times. Of these initiatives, the adoption of standard arrival speeds probably produced the greatest benefit. Standard arrival speeds provide predictability to air traffic controllers who can then have the confidence to reduce the spacing between arriving aircraft. They also enable gaps between arriving aircraft to be more effectively planned, and enable departures to take place. Some redesign of airspace around airports also occurred to improve the flow of arriving and departing aircraft.

At the time, Airservices predicted that the implementation of ACE initiatives could result in capacity increases of between 5- 15%, without major investments in airport infrastructure. Not only did these initiatives enable airports to optimise their slot management system, they provided greater predictability for the arrival and departure rates that are incorporated in the Metron Harmony Air Traffic Flow Management application operated by Airservices.

Willey explains: “Since its introduction, BAC has added a 56-hour look-ahead to determine the impact of adverse weather on operations. If the forecast suggests that system capacity will be lowered from adverse weather, BAC limits the availability of ad-hoc slots. This is to keep control of the on-time performance. These weather delays occur mostly during the storm season from early October to early January, particularly in the afternoons. Rather than setting an arrival rate of 24 aircraft per hour, when a high certainty of a weather event is likely this arrival rate will be lowered to 20 or 19 per hour, as well as denying itinerant slots.”

“New parking gates and improved passenger processing initiatives that have been implemented by Brisbane in recent years, such as kiosk check-in and bag drops, have also helped increase the declared capacity of the airport” states Willey. “Improvements by Border Force in their processing of departing international passengers has also contributed to improvements.”

The impact of these improvements on the declared airport capacity is first reviewed internally by BAC then taken to the twice-yearly seasonal coordination meetings with airlines for review. This capacity is provided to Airport Coordination Australia to allocate slots for scheduled airline services. Airport Coordination Australia handle the strategic assignment of slots up to 24 hours prior to service. Closer to departure, slot assignment is undertaken by Airservices’ Network Coordination Centre (NCC) as part of their Metron Harmony process. BAC provides tables to Airport Coordination Australia and Airservices that reflect the impact on capacity from anticipated weather events.

Metron Harmony is a tool used to undertake the pre-tactical activities. It is designed to balance capacity and demand within the ATM environment. This system is reliant on the foundation provided by an airport’s slot management system, which already regulates the time most scheduled airline operations take place. Metron Harmony is managed centrally from Airservices’ NCC in Canberra.

On the evening prior to operations (at 0700 UTC), aircraft schedules are sourced from airport slot management schemes and uploaded into the Metron Harmony system. Anticipated weather conditions for the upcoming day are also incorporated. Jesper Bronsvoort, Airservices Network Strategy and Development Manager explains: “Airservices works collaboratively with major airlines in determining the next day capacity for an airport. Meteorologists from airlines and Airservices hold daily discussions to get common agreement about the impact of next day weather conditions on traffic capacity at the four network airports. This process is termed Meteorological Collaborative Decision Making.” The nominal capacity of the airport is also adjusted to reflect other activities that will hinder operations in and around the airport, such as taxiway or runway works.

Metron Harmony then integrates the proposed flight schedules with the predicted arrival and departure rate. The outcome sees departing aircraft assigned a departure time, while arriving aircraft are given a target arrival time. In the case of more than one aircraft seeking the same time, Metron Harmony randomly chooses the order and places other aircraft into slots as close as possible to their requested time. A ground delay program, holding aircraft at their gate, is initiated when the ATM system capacity is significantly lower than the traffic demand. “When significant delays are being experienced, airlines can swap flights to different slots assigned to their company to meet operational and commercial needs”, says Bronsvoort. “Should operational conditions change significantly throughout the day the NCC holds teleconferences with airlines to review and adjust ATM capacity and aircraft operations.”

Domestic flights within 2,600 nm of network airports on the eastern seaboard are provided with an arrival time. At this distance, aircrew can often adopt measures to absorb a delay. Paddy Goodall, Airservices’ Network Services Manager says “Due to their route length, international flights in-bound to Australia have not had an arrival time pre-determined by Metron Harmony. In the future, however, international traffic will be given a notional delay depending on how they are tracking, between four and six hours prior to their destination. Imposing a delay well in advance of their arrival time enables these aircraft to adopt measures, such as speed reduction, which are more fuel-efficient and provides more predictability to the flight crew.”

At the moment, new measures are being introduced to improve capacity through greater integration between Airservices, airlines and airport companies. A new program termed Airport Collaborative Decision making (A-CDM) is being developed for the four network airports. Goodall explains: “At the moment Airservices has a good field of view of traffic operating in the airspace and taxiways of the four network airports. While airports and airlines have information about activities within the terminal building and at the gate, any problems that may result in ATM delays are not visible to Airservices. Airport companies, at the moment, only receive limited flight information from the ATM system that could impact their operations.”

A-CDM is an information sharing platform that incorporates the performance of landside and airside functions. It takes over some of the activities being performed by airport companies, by providing more accurate information and disseminating it to more impacted parties. “The ground delay program will become a component of the A-CDM process” says Goodall. “At the moment airport companies plan for an aircraft arrival at a gate the day prior, based on schedules. A-CDM will continue updating an aircraft’s arrival time. Very accurate information about an aircraft’s gate arrival time will be available to airport companies and others once it has departed its origin airport.”

‘The goal is to enable all parties to view the same information’

“A key metric that will be measured as part of A-CDM is the reduction in aircraft taxi times,” adds Goodall. “A-CDM will focus attention on the points at an airport that are causing aircraft delay, such as gate or taxiway congestion. This program will focus on achieving a reduction in fuel burn from the time an aircraft commences its taxi to the runway holding point. A 7% reduction in the taxi time during congested periods has been established as a target. It is intended to have the four network airports using A-CDM by 2021.”

While continental Australia may have lower traffic volumes than North America or Europe, it has very high traffic volumes in the triangle linking Brisbane, Sydney and Melbourne. If a disruption occurs at one of these airports, it quickly impacts operations at the other airports. With A-CDM, the impact of delays at one airport can be quickly shared with the other stakeholders as well as providing greater options within the entire network to address problems.

In forthcoming years, substantial new infrastructure will become available at the four network airports, such as new runways at Brisbane and possibly Melbourne and Perth plus a new airport serving the Sydney basin. The introduction of new runways shifts the bottleneck outward to the airspace serving the airport. It also places pressure on airport technology platforms to manage gate utilisation as well as the various support functions required for aircraft turnaround. The new OneSky ATM system will enable the airspace to be reconfigured and air traffic controllers allocated to sectors to match different arrival and departure paths.

The goal is to enable all parties to view the same information so decisions can be made for the health of the network, not just their immediate area of interest. Bronsvoort notes: “At the moment, while Airservices may view capacity as runway utilisation, airports often consider it to be gate availability. We need broader system wide thinking about how to optimise the use of available capacity. At the moment, this is difficult to do since Airservices, airlines and airports only have part of the total picture. It may mean that everyone may need to give a little to achieve optimum operation across the entire network.” This broad information exchange and dispersed decision-making is termed Network Collaborative Decision-Making.

On the other hand, decision-making is likely to become more complex. Airservices is currently undertaking work with McLaren, the motor racing company, and Deloitte about how to manage and make decisions based on greater volumes of information and the increased number of variables that will be available.

It is important to recognise a key difference in the highly strategic time horizon of airport companies compared to the pre-tactical and tactical orientation of Airservices. Willey explains: “The best outcome for an airport is for an aircraft to arrive and leave in accordance with its scheduled times. International gates are a scarce resource that are heavily booked, particularly in peak periods. When early or late arrivals occur, it becomes very challenging. It is very frustrating for passengers when an aircraft arrives ahead of schedule and is required to wait for another aircraft to vacate the intended parking gate. The ATM system and modern generation aircraft have technologies that can yield significant reductions in long-haul flight time. Aircraft can choose a route to take advantage of favourable high level wind conditions that yield significant time and fuel savings. It can mean, however, that the aircraft arrives with no gate available, resulting in the airborne time savings being eaten away waiting on the apron. A-CDM will help identify latent capacity at gates as a means of alleviating the impact of ground delay resulting from early arrivals.”

BAC gate usage is peaking in nature. At peak periods gate occupancy is highly subscribed – for the international precinct this extends from 6am through 10am. There is limited opportunity to have airlines adjust schedules to operate outside these peak periods to gain greater infrastructure efficiency. International schedules are established based on arrival and departure slots airlines have obtained at major hub ports.

Brisbane’s airport capacity will significantly increase once its parallel runway begins operation. Willey says “Brisbane’s new runway will become operational in mid 2020. Although capacity will double from around 48 arrivals and departures per hour up to around 100 movements per hour, Brisbane will still be impacted by the operation of major supply ports, particularly Sydney and Melbourne.”

Accompanying the introduction of the new runway is airspace redesign of the Brisbane area. Neil Hall, BAC’s Airspace and Airfield Capacity Manager explains: “Over the past four years Airservices and BAC have been finalising the airspace design for the parallel runway system. First airspace plans were presented to various agencies in 2006-07 as part of an Environmental Impact Statement in the Major Development Plan (EIS/MDP). The final airspace design had to incorporate new routes based on satellite based navigation, which was only in its infancy at the time the EIS/MDP was prepared. Routes are separated from one another based on performance based navigation, which also enables continuous climb and descent from points close to the runway. The new route structure was also developed to maintain operational efficiency at Sunshine Coast and Gold Coast airports.”

The parallel runways are 2 km apart and slightly staggered, enabling independent operations to take place. Aircraft operations to the north and west will take place on the northern runway. Those to the south and east will operate from the existing southern runway. “The airport terminal zone being located between the two runways means that aircraft do not need to cross a runway while taxiing” explains Willey. “Simulations of ground operations, undertaken by Airservices and BAC, showed that airport capacity can operate comfortably at 90 movements per hour. It also highlighted that the closure of two rapid exit taxiways, in each direction, on the existing runway would remove the potential of aircraft bottlenecks.”

Noise concerns with the new runway are highly sensitive. Finalised airspace design has now been approved and BAC is now undertaking an intensive community update program. Residential areas in the sector from the west to the north of the new runway are likely to be most impacted. Willey says “BAC have assured that these residential areas will not be over-flown at night. An online tool is also available whereby any person can enter their address and receive information about the height and frequency of operations at this position – termed the BNE Flight Path Tool. To date, BAC records show that this online tool has been accessed 90,000 times at an average of three minutes per visit. It shows a very high level of community interest and engagement.”

When conditions permit, aircraft at night will takeoff over Moreton Bay with up to 5 kt tailwind. With a single runway, these operations reduce capacity to 10 movements per hour due to restrictions of head-on traffic. When the parallel runway is operational, avoiding the problem of head-on traffic, the capacity will increase to 40 to 50 movements per hour. In the long term, between 10pm and 6am, Brisbane will use ‘over the bay’ operations as much as possible. Only the southern end of the existing runway will be used when tailwind conditions prevent departures and arrivals over the bay.

Slot management activities are rapidly evolving whereby airports, airlines and Airservices share greater volumes of information and make decisions collaboratively.