What is LRATFM?
The Australian Air Navigation Services Provider (Airservices) has identified that their Long-Range Air Traffic Flow Management (LRATFM) project will be an addition to their domestic air traffic flow management (ATFM) applications. LRATFM from Airservices’ perspective is a “collaborative decision-making project to enhance demand and capacity management through the integration of international flights into Australia’s air traffic flow management system”. They explain that conventional ATFM processes must evolve and improve to support the expected long-term growth and the resultant congestion in the Australian air traffic network.
ATFM measures are services established with the objective of contributing to a safe, orderly, and expeditious flow of air traffic by ensuring that ATC capacity is utilized to the maximum extent possible, and that air traffic volume is compatible with the declared airspace capacities. In essence, the LRATFM concept builds upon these measures.
What are the early concepts and trials?
CANSO’s 2019 document “Implementing Air Traffic Flow Management and Airport Collaborative Decision Making (ATFM/CDM)” introduces the LRATFM concept internationally. The document proposed that as cross border ATFM/CDM operations develop, there may be opportunities to effectively include long haul flights into current ATFM systems. CANSO notes that the Bay of Bengal Cooperative ATFM System (BOBCAT) and the NATS Extended Arrival Manager (X-AMAN) concept could be examples of LRATFM initiatives. BOBCAT introduces the use of calculated take off time (CTOT) and calculated time over (CTO) assignment to manage the flow of flights through restricted airspace. CTOT, CTO and Target Time Over (TTO) assignments as ATFM measures to integrate long haul aircraft into domestic ATFM networks have been further explored in the introduction of the X-AMAN concept in the UK, a 2011 CTO trial in Japan, and a 2017 LRATFM trial completed by New Zealand and Singapore.
BOBCAT is an ATFM initiative that commenced operation in July 2007 and was implemented to manage the passage of flights travelling westbound from Asia-Pacific through to Europe. BOBCAT manages the flow of traffic through Afghanistan (Kabul) airspace which restricts civil access to limited operating routes at specific flight levels. The system aims to manage flight times of aircraft intending to fly through Kabul during the peak period by assigning a CTOT. Entry time to Kabul is further managed through a Calculated Time Over (CTO) assignment with a target window of 5 minutes after CTO.
The Extended Arrival Management (X-AMAN/XMAN) is an ATFM solution that was introduced to extend arrival management coordination beyond current Arrival Manager (AMAN) target areas to allow for early sequencing of arrival traffic. The conventional AMAN target area is usually a range of 40-50 NM from an airport. The NATS X-AMAN concept, which became fully operational in 2015, is described as a Cross Border Arrivals Management system that extends the arrival manager range out to 350NM from Heathrow Airport. When delays at Heathrow exceed 7 minutes, the system communicates to surrounding ANSPs that inbound aircraft will need to slow down during cruise to streamline approaches into Heathrow. The concept was primarily introduced to reduce the airborne holding and stack holding in airspace surrounding congested airports. The system requires effective information sharing and communication between multiple ANSPs and FIRs with the aim to reduce fuel costs through efficient delay management within cruise phase of flights.
Industry research into the introduction of long-haul international flights into domestic ATFM systems has continued in the Asia Pacific Region. A CTO trial operated in Japan between August 2011 and September 2014, aimed to identify if the introduction of CTO operations would help alleviate airspace congestion into Tokyo International Airport. The trial was suspended in 2014 due to a number of issues with CTO compliance rates and ATC workload issues. Key CTO compliance issues were due to differences between ground based and airborne trajectory predictions. Trajectory prediction accuracy is dependent on various uncertainties such as weather prediction, navigation uncertainty, and pilot intent. CTO was assigned by ATC in this trial using ground-based trajectory prediction which was not using information such as airspeed, aircraft intent, and aircraft performance. Accuracy of this trajectory information was increased through synchronizing some airborne trajectory data into the system through downlinking key information such as estimated time of arrival computed on the flight management system (FMS). Once trajectory prediction is accurate CTO assignment can be applied to achieve require speed control within aircraft operating limits to manage demand capacity imbalances at congested airspace around airports.
In 2017, a LRATFM project was devised between United Kingdom (NATS), New Zealand (Airways), and Singapore (CAAS) ANSPs with the aim to provide operational research into the basic factors of a LRATFM concept to test the communication processes, the accuracy of estimates, and the interaction with and compliance of aircraft crew. The operational trials facilitated by Airways and CAAS focused on aircraft during the enroute phase of flight using a target time over (TTO) milestone approach to manage aircraft demand. TTO is comparable to CTO and will be used to explain this concept for consistency. The ANSPs developed 5 key phases of the LRATFM concept:
- Concept users establish an agreed time frame before a CTO metering fix within which LRATFM can be applied based on the operational environment, estimate accuracy, communication, and compliance capacity.
- Entry to the agreed time frame begins with the CTO metering fix where an accurate Estimated Time Over (ETO) is used to calculate the CTO reference point inclusive of ATFM measures.
- At the CTO metering fix the CTO reference is communicated to aircrew via agreed communication path.
- Aircrew confirm their ability/inability to comply with the CTO fix to the relevant authority.
- Aircrew manage the flight to reach the CTO fix at the CTO time or advise inability to comply with a revised ETO.
Figure 1 below shows an adapted diagram of the NATS, Airways, and CAAS LRATFM concept.
The Airways trial used an initial inbound CTO horizon of 2 hours out from destination which was chosen based on initial assumptions from the Flight Management System (FMS) and Oceanic Control System (OCS) estimate accuracy and aircraft compliance capability. Accuracy of wind data was identified as a major factor for accuracy and most long-haul flight planning information became increasingly inaccurate after departure due to limited or no weather data updating. The Airways trial also identified that communication was achievable through Controller-Pilot Data Link Communications (CPDLC) and that non-participation was mainly due to prohibitive fuel burn cost or airline scheduling requirements whereas noncompliance was mainly related unacceptable FMS performance calculation due to difference between forecast and actual winds.
The CAAS trial communicated with flights through their Airline Operating Centre (AOC) and informed them of the required ATFM delay through email up to 6 hours out from the CTO reference fix. The trial results identified that an ideal time frame for ATFM delay being distributed to flights should be at least 4-5 hours prior to CTO reference fix. It was identified that when no ATFM delay was required, accuracy provided by aircrew for the CTO fix was 90% to the 4–5-hour mark.
Both trials provide a basis for the continuation of the development of the LRATFM concept, with areas of further work including alternative communication paths, the integration of existing ATFM advisory information in CTOs, cross FIR feasibility, synchronization with existing tools such as GSP and AMAN, and use of the concept to link regional ATFM programs through shared information.
Airservices has identified that LRATFM will be an addition to their domestic ATFM applications. The LRATFM concept plans to extend the point of intervention for inbound aircraft out to 4 hours through the assignment of CTO at arrival waypoints. The point of intervention represents a rough time frame until arrival where ATC will begin to apply ATFM measures to aircraft. This will integrate long haul aircraft into the domestic ATFM system earlier and may assist to absorb required delay adjustments within the enroute phase of flight managing demand and capacity imbalances. The rough 4-hour horizon is currently used to manage early morning demand for Sydney Airport and allows for early sequencing where aircraft are required to reduce speed during cruise to ensure that flights are not reaching the airport prior to operational hours to reduce airborne holding requirements. The Australian LRATFM concept focuses on the management of long-haul arrivals and their integration into the domestic aviation network particularly during peak demand periods at key capital city airports. As domestic aircraft in Australia participate in the Harmony Ground Delay Program (GDP), this integration aims to allow for a reduction in ground delay due to additional assurances in speed control and delay absorption of international flights inbound to capacity congested airports or airspace.
All current interpretations of LRATFM initiatives have similar expected outcomes and problems to solve. Key concerns aiming to be addressed are the equitable distribution of delay through ATM networks and the increased predictability of arrival aircraft to allow integration into current ATFM systems.
What’s Next?
As LRATFM is still in its infancy, there is not yet an internationally recognized definition of the concept. The initial concepts and trials provide a basis of understanding of the crucial elements required to develop a concept of operations.
The academic literature surrounding ATFM optimization points to the dynamic nature of ATM and the importance of predictability of air traffic operations to ensure that the demand and capacity can be monitored and managed. The efficient and accurate sharing of information is crucial to facilitate the safe and efficient flow of traffic. From a LRATFM perspective the key areas of development include the increased accuracy of trajectory predictions and a developed understanding of the achievable delay through speed adjustments.
References
Aerothai. (n.d.). Air Traffic Flow Management. Retrieved from link
Airservices (2013). Collaborative Decision Making Program: Domestic ATFM, Long Range ATFM. ICAO ATFM Seminar. Hong Kong. Retrieved from link
Airservices (2017). Long Range Air Traffic Flow Management: A Perspective. Retrieved from link
Airservices. (2016). Air traffic flow management: Harmony for ANSPs. Retrieved from link
Airservices. (n.d.). Air Traffic Flow Management. Retrieved from link
Airways (2019). ATFM Progress – New Zealand. Ninth Meeting of the ICAO Asia/Pacific Air Traffic Flow Management Steering Group. Bangkok. Retrieved from link
Board of Airline Representative Australia (BARA). (2020). Airline Views: Long range air traffic flow management. Retrieved from link
CANSO. (2019). Implementing air traffic flow management and collaborative decision making. [pdf].
ICAO. (2016) Annex 11 to the Convention on International Civil Aviation: Air Traffic Services. [pdf].
ICAO. (2016) Doc 4444: Procedures for Air Navigation Services Air Traffic Management. [pdf].
ICAO. (2016). BOBCAT Operational Updates. 27th Meeting of the Asia/Pacific Air Navigation Planning and Implementation Regional Group. Retrieved from link
ICAO. (2018) Doc 9971: Manual on Collaborative Air Traffic Flow Management. Retrieved from link
ICAO. (2018). Long Range ATFM Concept Trials. The 8th Meeting of the ICAO Asia/Pacific Air Traffic Flow Management Steering Group. Retrieved from link
Kistan, T., Gardi, A., Sabatini, R., Ramasamy, S., & Batuwangala, E. (2017). An evolutionary outlook of air traffic flow management techniques. Progress in Aerospace Sciences, 88, 15-42. Doi: 10.1016/j.paerosci.2016.10.001
Lulli, G., & Odoni, A. (2007). The European air traffic management problem. Transportation Science, 41(4), 431-443. Doi: 10.1287/trsc.10700.0214
Matsuno, Y., & Andreeva-Mori, A. (2020). Analysis of achievable airborne delay and compliance rate by speed control: A case study of international arrivals at Tokyo International Airport. IEEE Access, 8, 90686-90697. Doi: 10.1109/ACCESS.2020.2994109.
NATS. (n.d.). Why new streamlined Heathrow arrivals start in Europe. Retrieved from link
Schultz, M., Lubig, D., Rosenow, J., Itoh, E., Athota, S., & Duong V. N. (2020). Concept of a long-range air traffic flow management. Proceedings of the SESAR Innovation Days 2020, 1-9. Retrieved from link
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