During the UN Climate Change Conference (COP26), in November 2021, the international
aviation community agreed to advance actions to reduce CO2 emissions. Adopting more
fuel efficient routes, now that full global satellite coverage is available, could achieve this
quickly and economically. Here flights between New York and London, from 1st December, 2019 to 29th February, 2020 are considered. Trajectories through wind fields from a
global atmospheric re-analysis dataset are found using optimal control theory. Initially,
time minimal routes are obtained by applying Pontryagin’s Minimum Principle. Minimum
time air distances are compared with actual Air Traffic Management tracks. Potential air
distance savings range from 0.7 to 16.4%, depending on direction and track efficiency.
To gauge the potential for longer duration time minimal round trips in the future, due
to climate change, trajectories are considered for historic and future time periods, using
an ensemble of climate models. Next, fixed-time, fuel-minimal routes are sought. Fuel
consumption is modelled with a new physics-driven fuel burn function, which is aircraft
model specific. Control variables of position-dependent aircraft headings and airspeeds or
just headings are used. The importance of airspeed in finding trajectories is established,
by comparing fuel burn found from a global search of optimised results for the discretised approximation of each formulation. Finally, dynamic programming is applied to find
free-time, fuel-optimal routes. Results show that significant fuel reductions are possible,
compared with estimates of fuel use from actual flights, without significant changes to
flight duration. Fuel use for winter 2019–2020 could have been reduced by 4.6% eastbound and 3.9% westbound on flights between Heathrow and John F Kennedy Airports.
This equates to a 16.6 million kg reduction in CO2 emissions. Thus large reductions in
fuel consumption and emissions are possible immediately, without waiting decades for
incremental improvements in fuel-efficiency through technological advances
