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.
