Operational initiatives

This section contains some examples of the numerous operational initiatives being implemented at the network level [16] .

Free route airspace (FRA) is a SESAR solution (see section 5.5), that is defined as a volume of airspace within which users may freely plan a route between any defined entry and exit points, subject to airspace availability [17] . This fosters the implementation of more efficient routes and more efficient use of the European airspace. FRA has been implemented in most European airspace already. Since 2018 additional Member States and Area Control Centres reported on FRA implementation, including: Maastricht Upper Area Control Centre, Greece, Romania, Bulgaria, Slovakia, Czechia, Poland, Iceland, parts of the United Kingdom and France. In addition, cross-border free- route activities, where the most significant potential benefits lie due to the defragmentation of European airspace, have been implemented in Italy, North Macedonia, Albania, Georgia, Armenia and parts of the United Kingdom and Ukraine. In Europe, according to Common Project 1 regulation [27] , mandatory final FRA implementation with cross-border dimension and connectivity to terminal manoeuvring area should be fully implemented by 2025.

The proportion of flight time flown in free route airspace was 68% in 2021, compared to 8.5% in 2014. The Network Manager (NM) estimates that 10 million tonnes of CO2 have been saved through the implementation of FRA since 2017. This is equivalent to around 170,000 round-trips between Madrid and Riga. In order to advance the roll-out of FRA across borders the NM should increase its efforts in the implementation of cross-border projects by ANSPs. In addition, the implementation of new airspace design projects out to 2030 [18]  is expected to provide an additional 2.5-3.5% per flight CO2 reduction as the flight efficiency of the network is further enhanced.

During the peak traffic periods of 2019, the NM also introduced the so-called “file it, fly it” measure to reduce en-route delay in operational airspace sectors which arose due to insufficient staffing levels in Central Europe. Whilst such measures reduced delay from around 4.0 to 2.3 minutes per flight, the corresponding re-routing of flights resulted in additional CO2 emissions of approximately 60 tonnes per day for the defined traffic period. The measures also resulted in an additional benefit of encouraging aircraft operators to fly the filed flight plan which enabled enhanced predictability and fuel planning.

Along with Free Route Airspace, Continuous Climb Operations (CCO) and Continuous Descent Operations (CDO) are SESAR solutions often considered to be one of the best options for fuel (CO2) savings and/or noise reduction in the climb and descent phases. Following an agreement on harmonised definitions of CCO and CDO together with a metric and measurement criteria, their implementation has been supported by the release of the European CCO / CDO Action Plan in 2020 [19] .

The CCO / CDO performance dashboard has been measuring fuel and noise benefits at European airports since 2019 [20] . The fuel CCO/CDO measures the vertical flight efficiency, in terms of fuel and CO2, for the entire climb and descent profile respectively. The noise CCO/CDO measures the vertical flight profile efficiency up to 10,500 ft for CCO and from 7,500 ft for CDO, which are the phases of flight where the major environmental impact is considered to be noise.

As reported in EAER 2019, there is greater potential for fuel burn and noise reductions in CDO than CCO. Figure 5.7. shows the progression in the ‘average time in level flight’ for the fuel and noise CDO during 2019-2021. With the removal of network constraints at the height of the COVID pandemic, the average time in level flight for the fuel CDO fell by around 50% from 200 seconds to 100 seconds, only to subsequently slowly increase to around 150 seconds by the end of 2021. The impact on the noise CDO values is not so clear with average time in level flight reducing from around 70 seconds in 2019, to between 50-60 seconds during the pandemic. This suggests that there is an inefficiency captured below 7,500 ft that is less influenced by traffic levels.

In 2021, the average duration of level flight flown at the top 40 airports is 25 seconds for departures (CCO) and 137 seconds for arrivals (CDO), the latter decreasing from a high of 189 seconds in 2019. This compares to 31 seconds across the network for CCO and 135 seconds for CDO. Figure 5.8. indicates that there is a relatively high amount of level flight at airports within the European core area, indicating a link between CCO/ CDO and airspace complexity. 

The potential savings in the European Civil Aviation Conference (ECAC) area from the implementation of CCO / CDO are estimated to be up to 320 thousand tonnes of fuel (up to 1 million tonnes of CO2 emissions) per year based on the peak traffic of 2019. However, it should be noted that it may not be possible to fly 100% CCO or CDO for a number of reasons such as safety (i.e. time or distance separation), weather or capacity. To realise significant savings, constraints should be minimised, especially in the descent phase, and aircraft should descend from their optimal top of descent points.

The Common Project 1 mandate requires that from 2027 all aircraft must be forward fit with the capability to downlink the Extended Projected Profile (EPP), thereby providing visibility on the ground of the optimum descent profile as calculated by the avionics, including the optimal top of descent point. The SESAR very large demonstration DIGITS (2016-2020) [21]  assessed the potential benefits to the descent profiles of making EPP information available to controllers in real time. This work continues in the ADSCENSIO project [29] , which is considering potential metrics based on the difference between the EPP and the actual climb/descent profile to detect inefficiencies that may not be captured by the length of level segment metrics, for example in case of a long thrust descent that is continuous but sub-optimal.

Pilot environmental awareness is critical in the implementation of operational initiatives, such as CCO / CDO. In order to support this, the Aircrew Training Policy Group (ATPG) has issued an advisory paper on Environmental Awareness Training for Pilots that calls for mandatory training in all categories of pilot licences through academic knowledge and practical training, thereby integrating it into the established threat and error management philosophy and process. In addition, the European CCO/CDO Task Force has developed training for ATCOs and Flight Crews that detail best practices on how to collaborate in enabling optimum vertical profiles [22] .