Periodic Reporting for period 2 - REIVON (Reduction of the Environmental Impact of aviation via Optimisation of aircraft size/range and flight Network)
Reporting period: 2022-04-01 to 2023-10-31
Many flights are operated with aircraft designed for ranges much longer than actual flight distances, to improve operational flexibility and interchangeability of aircraft in an airline’s fleet, albeit at the expense of increased fuel use and CO2 emissions. This leads to the question as to what extent the combination of a fuel-optimised flight network and size/range-optimised aircraft design can reduce CO2 emissions at the air transport system level, when such aircraft are design optimised for major operational range and payload capacity. This is very important in the Clean Sky 2 / Clean Aviation programme to identify the need of new emissions/noise-optimised aircraft for the future sustainable air transport system.
The objective of the Clean Sky 2 Technology Evaluator project REIVON was to investigate the CO2 emissions reduction potential at global air transport system (ATS) level through the optimisation of aircraft size/range and flight network. This reduction potential comes on top of the much more widely investigated improvements at aircraft and mission level.
The project approach was to first identify the theoretical CO2 reduction potentials of these optimisations through modelling various future global flight network scenarios, then to assess the impacts of a global air transport system with such optimisations on aviation stakeholders, and finally to assess potential measures to support the implementation of the ATS optimisations considered in the study.
The project investigated the theoretical potential of CO2 emissions reduction through various fleet and flight network optimisation measures. These are: (1) Intermediate Stop Operations (ISOs), whereby long-haul flights are split into shorter legs, avoiding “burning fuel to carry fuel”; (2) Frequency Reduction (FR) on busy routes through the utilisation of higher-capacity aircraft; and a combination of Cases (1) and (2). In all cases, aircraft with the most fuel-efficient size/range combination for each route are allocated, including combinations not existing in today’s fleet.
REIVON made use of an integrated approach involving experts from multiple disciplines, including aircraft design and performance, airline fleet and network optimisation, aircraft emissions modelling, air traffic demand modelling as well as impact assessment on local and global level. The analytical steps were carried out in four technical work packages (1. General methodology, data, models/tools/metrics, 2. Theoretical potentials for reducing CO2 via optimised ATS, 3. Impact assessment for stakeholders, 4. Analysis of potential measures) and a fifth work package for management. REIVON used various databases and a range of state-of-the-art models and tools to support the analysis.
The objective of the Clean Sky 2 Technology Evaluator project REIVON was to investigate the CO2 emissions reduction potential at global air transport system (ATS) level through the optimisation of aircraft size/range and flight network. This reduction potential comes on top of the much more widely investigated improvements at aircraft and mission level.
The project approach was to first identify the theoretical CO2 reduction potentials of these optimisations through modelling various future global flight network scenarios, then to assess the impacts of a global air transport system with such optimisations on aviation stakeholders, and finally to assess potential measures to support the implementation of the ATS optimisations considered in the study.
The project investigated the theoretical potential of CO2 emissions reduction through various fleet and flight network optimisation measures. These are: (1) Intermediate Stop Operations (ISOs), whereby long-haul flights are split into shorter legs, avoiding “burning fuel to carry fuel”; (2) Frequency Reduction (FR) on busy routes through the utilisation of higher-capacity aircraft; and a combination of Cases (1) and (2). In all cases, aircraft with the most fuel-efficient size/range combination for each route are allocated, including combinations not existing in today’s fleet.
REIVON made use of an integrated approach involving experts from multiple disciplines, including aircraft design and performance, airline fleet and network optimisation, aircraft emissions modelling, air traffic demand modelling as well as impact assessment on local and global level. The analytical steps were carried out in four technical work packages (1. General methodology, data, models/tools/metrics, 2. Theoretical potentials for reducing CO2 via optimised ATS, 3. Impact assessment for stakeholders, 4. Analysis of potential measures) and a fifth work package for management. REIVON used various databases and a range of state-of-the-art models and tools to support the analysis.
The DLR unconstrained high-growth forecast movements database for 2050 was used as the baseline for comparison with optimised cases. Flight routes with emission reduction potential (with distance > 3,000 NM for ISO or > 500,000 seats/year for FR) were first selected for optimisation. The well-established NASA FLOPS tool was used to generate an aircraft design response surface model and with this, new range-optimized and high passenger capacity aircraft designs, which were based on two reference aircraft (A320neo and B787), were determined. Sensitivity analyses were conducted to establish suitable constraints for the optimisation. These included minimum flight leg lengths for ISO, minimum number of seats offered, maximum number of new aircraft designs and maximum airport movements. Finally, emission inventories for the 2050 baseline and the three optimised cases were generated using the FAST tool and the global CO2 reduction potential calculated.
Routes accounting for 28% of global fuel burn were shown to be suitable for ISO optimisation, and routes accounting for 65% of global fuel burn for FR. CO2 emissions reductions range between 7% to 25% were obtained for flights suitable for ISO optimisation, and reductions between 10% and 24% for flights suitable for FR optimisation. On a global level, ISO has the potential to reduce aviation CO2 emissions by 2%-7%, FR 7%-16% and ISO & FR combined 8%-19%, all results including range/size-optimised aircraft.
A thorough study of the impact of REIVON concepts on stakeholders was done. Ten representative airports for ISO and FR were selected for detailed studies of the impact on noise, local air quality and airport capacity, based on the modelling of future optimised traffic scenarios. On hub airports with many busy routes suitable for FR, a significant reduction of noise and NOx emissions was found. On ISO stopover airports, most of which have very little traffic in the baseline scenario, movements and consequently noise and NOx increased significantly, but still to a moderate level. A significant reduction in movements of around 30% (international) to 40% (domestic) was observed globally due to FR, reducing the number of airports expected to be above capacity limits in 2050 from 93 to 12. The emissions reduction potential was greatly influenced by the use of the new range-optimised aircraft (mainly large narrow and large wide-bodies), which would make up about 50% of the global fleet in 2050. Total travel times of 14% longer on average for ISO flights would have an impact on passenger acceptance, as well as the lower choice of departure times with FR. As long as there are non-stop alternatives, airlines may be reluctant to introduce ISO to remain competitive.
One of the main implementation barriers is the identification of suitable ISO airports, which for major intercontinental routes are often located in sparsely populated, climatically challenging or politically sensitive regions. International coordination and funding for airport development would be needed to overcome this. The other main obstacle is the large investment needed from manufacturers to develop and produce a large fleet of new range-optimised aircraft, and from airlines to purchase them. Also, new slot regulations might be needed to encourage airlines to reduce the number of flights on specific routes. These challenges and measures were discussed with the stakeholders in the Advisory Board.
Routes accounting for 28% of global fuel burn were shown to be suitable for ISO optimisation, and routes accounting for 65% of global fuel burn for FR. CO2 emissions reductions range between 7% to 25% were obtained for flights suitable for ISO optimisation, and reductions between 10% and 24% for flights suitable for FR optimisation. On a global level, ISO has the potential to reduce aviation CO2 emissions by 2%-7%, FR 7%-16% and ISO & FR combined 8%-19%, all results including range/size-optimised aircraft.
A thorough study of the impact of REIVON concepts on stakeholders was done. Ten representative airports for ISO and FR were selected for detailed studies of the impact on noise, local air quality and airport capacity, based on the modelling of future optimised traffic scenarios. On hub airports with many busy routes suitable for FR, a significant reduction of noise and NOx emissions was found. On ISO stopover airports, most of which have very little traffic in the baseline scenario, movements and consequently noise and NOx increased significantly, but still to a moderate level. A significant reduction in movements of around 30% (international) to 40% (domestic) was observed globally due to FR, reducing the number of airports expected to be above capacity limits in 2050 from 93 to 12. The emissions reduction potential was greatly influenced by the use of the new range-optimised aircraft (mainly large narrow and large wide-bodies), which would make up about 50% of the global fleet in 2050. Total travel times of 14% longer on average for ISO flights would have an impact on passenger acceptance, as well as the lower choice of departure times with FR. As long as there are non-stop alternatives, airlines may be reluctant to introduce ISO to remain competitive.
One of the main implementation barriers is the identification of suitable ISO airports, which for major intercontinental routes are often located in sparsely populated, climatically challenging or politically sensitive regions. International coordination and funding for airport development would be needed to overcome this. The other main obstacle is the large investment needed from manufacturers to develop and produce a large fleet of new range-optimised aircraft, and from airlines to purchase them. Also, new slot regulations might be needed to encourage airlines to reduce the number of flights on specific routes. These challenges and measures were discussed with the stakeholders in the Advisory Board.
While extensive work on aircraft fuel efficiency and flight route optimisation is done in aviation R&D, little attention has been devoted to the environmental optimisation of the global flight route network. REIVON has for the first time identified the theoretical potential for reducing the CO2 emissions via an optimisation of the ATS including not only network and frequency changes, but also treating aircraft design range as an optimisation variable. Also, for the first time, REIVON carried out a comprehensive assessment of the impact of an air transport system with optimised aircraft, flight network and frequencies on stakeholders (passengers, manufacturers, airlines, airports and airport neighbours). The CO2 saving potential identified in REIVON is highly compelling and comparable to the cumulative impact of all other operational measures aimed at emissions reduction. Further research is needed to consolidate and expand upon the findings of REIVON, incorporating aspects like non-CO2 emissions and the impact of future propulsion technologies such as hydrogen. Therefore the methodology developed in REIVON is considered highly suitable as a comprehensive approach for comparing various operational measures for climate impact mitigation.