MUAC pioneers digital connectivity between ground and air with ADS-C

Air traffic controllers in MUAC are now using ATS B2 ADS-C datalink to provide airlines with optimised climb and descent procedures. By using datalink to directly access the aircraft’s flight management system (FMS), controllers can now allow pilots to climb or descend on their most optimal trajectories better than before.

“This new functionality allows controllers to see when the aircraft actually wants to descend,” said Viktor Jagasits, an air traffic controller at MUAC and coordinator of the Systems Monitoring and Revision Team (SMART). “At the end of 2022 we implemented a new controller-pilot datalink communications (CPDLC) functionality – ‘Descend When Ready’. Normally, as a controller you would not give a vertical rate of more than 1,500 or 2,000 feet a minute for a descent, but we could suddenly see through the ADS-C downlinked profile that there are aircraft which were cleared to descend on their most optimal descent path and they are happily descending at a rate of 3,500 or 4,000 feet a minute. This means that many of these aircraft can now stay at the cruising level for an additional two, three, four or even more minutes and save fuel.”

The functionality of ATS B2 ADS-C’s Extended Projected Profile (EPP), which essentially means downlinking 4D trajectory intent information directly from the aircraft’s FMS, has been in place for some years. Following the practical use cases discovered during the validation period at MUAC, the MUAC crew reached out to Airbus to calculate potential fuel savings that might be possible in these scenarios. Based on the feedback, the MUAC Datalink Team began the detailed work of coupling the ATS B2 CPDLC function to the ADS-C data exchange for more optimised descent profiles.

“When Airbus gave us some numbers that showed this could be a very feasible use case, then we started,” said Viktor Jagasits. “We set up our data warehouse in Maastricht which merges data from all the servers to cross-reference all the information we needed from all the different sources (radar tracks, CPDLC logs, etc). Once we realised that we could expect a descent rate well beyond 2,500 feet per minute we saw that we could save something like 50-110 kg of CO₂ emissions per flight on certain descent profiles.”

It is a small but significant step in the process of providing automated digital communications between the ground and the air and connecting airborne and ground-based data processing systems – an initial step in the implementation of trajectory-based operations (TBO). But the work involved to reach even this small milestone has taken over 10 years, suggesting just how difficult it will be to implement TBO on a grand scale.

But for those that did, the EPP functionality allowed them to see aircraft’s intentions in terms of flight levels, speeds and detailed flight path – data directly from the aircraft’s FMS – with the system providing warnings in case of deviations between the 2D route known on the ground and the one actually stored on-board. ATS B2 ADS-C is often mixed up with ADS-C via FANS1/A connections: “ADS-C on FANS 1/A equipped aircraft, which is used over the ocean, only has a projected profile of one point ahead,” said Viktor Jagasits. “EPP can contain up to 128 points ahead, which is great. If I look at 20 points on a flight from Frankfurt to the USA, I can see all the way to Gander in Canada.”

The process of converting ADS-C downlinked data into a form which could be read and understood by controllers was rather complex. The data arrives in a standardised format as defined by the industry standards of the EUROCAE ED-228, -229, -230, -231 documents and their revisions. They describe the complete message structure and all the functionalities. All that had to be turned into data which a controller could understand and wants to use. EUROCONTROL developed its Initial Trajectory Sharing Guidance document which could be used for new implementers of the technology as ADS-C EPP will be mandatory by the European Commission’s CP1/AF6 regulation from 2028.

At the moment only Airbus aircraft are equipped with ATS B2 ADS-C, therefore these are the only aircraft that can benefit from the optimised trajectory management procedures. MUAC handles around 5,500 aircraft a day in busy periods and currently there are only around 130 ADS-C connections per day.

The original ATS B2 standard became available in 2013 and was used in the initial 2014 SESAR i4D trials. In 2015, Revision A was introduced, which became the basis of the current implementation and is now available in around 300 aircraft. A new Revision B standard, with enhanced functionalities such as an active frequency downlink, was published in late 2023 and work is expected to begin soon on a further Revision C standard.

ADS-C will be mandated in Europe for new aircraft starting 31 December 2027, which should speed up the implementation of ADS-C procedures and open the door to more TBO operations. But it will also mean the European ATM system will have to manage traffic where some aircraft will have different versions of datalink equipment available: some will have full ATS B2 (including ADS-C and CPDLC) complying with Revision A/B/C standards, some will have a mixed ATS B2 ADS-C with legacy ATN B1 CPDLC, while others will have only ATS B2 ADS-C EPP or no ADS-C at all but legacy ATN B1 CPDLC – or not even that.

“We expect about 800 aircraft to be equipped in two years,” said Viktor Jagasits, “which will result in substantial fuel savings even if we only optimise the Top of Descents. The question the airlines ask though is: should we invest in new technology if it is only used by Maastricht? If other air navigation service providers (ANSPs) start receiving and processing this data then it will make more sense to equip more aircraft. The ground and the network will only start to see system-wide benefits when quite a lot of aircraft are equipped.

“And of course it will be better for the airlines when all the European ANSPs implement this as a common service, with one single entity to downlink this data from the aircraft. Everybody will see the same data, so it's not going to be as fragmented as CPDLC is right now with different implementations in every country.”