Different types of new civil supersonic aircraft are currently under development, and may be in-service as early as the mid-2020s. The design process to develop and certify such aircraft faces various environmental challenges.
When an aircraft transitions through and flies faster than the speed of sound (Mach 1), the phenomenon of ‘sonic boom’ occurs. For this reason the Concorde was limited to subsonic speeds when flying over land and near coastlines. In recognition of this problem, the ICAO 39th Assembly adopted, in October 2016, an ICAO Resolution ‘ensuring that no unacceptable situation for the public is created by sonic boom’. A flight demonstrator is currently being built in the USA to research specifically shaped aircraft designs that may reduce the sonic boom, and to establish a noise dose-response relationship through community noise tests. A European research study known as RUMBLE is also supporting the development of new regulations for low-level sonic booms .
Compared to subsonic aircraft, these supersonic aircraft will operate at higher cruise altitudes in the sensitive high troposphere and stratosphere (15-18 km altitude). Although future civil supersonic project aeroplanes will be more fuel-efficient than Concorde, their fuel burn is still expected to be higher in comparison with current subsonic aircraft of a similar size because drag increases with speed. Research also suggests that the climate change effects due to non-CO2 emissions from supersonic aeroplanes, operating at significantly higher altitudes, could be considerably greater than the non-CO2 effects from subsonic aeroplanes.
The noise and emissions produced from supersonic aircraft operations in and around airports is also a critical aspect. Engines optimised for supersonic operation typically have a trade-off between lower noise during take-off (high bypass ratio) and lower drag / higher fuel efficiency in supersonic cruise (low bypass ratio).
There are currently no noise or CO2 certification requirements for supersonic aircraft in Europe, and the existing supersonic engine emissions standards are considered to be outdated according to ICAO guidance material. Europe is therefore actively working to update these standards.