Prohibiting supersonic flight over land: AEF responds to CAA proposals

8th February, 2024

AEF has responded to a CAA consultation on prohibiting supersonic – and transonic and hypersonic – flight over land by civil aircraft. 

Supersonic flight creates air pressure waves that result in an effect called a ‘sonic boom,’ with significant environmental impacts felt on the ground below. Following the retirement of the previous supersonic commercial aircraft, Concorde, policies relating to supersonic flight over land have not been reviewed. However, with manufacturers keen to develop a new generation of supersonic and hypersonic commercial aircraft and some major airlines showing an early interest, the CAA has asked for comment on prohibiting supersonic flight over land. 

We support the proposal to prohibit aircraft operating over land at hypersonic, supersonic and transonic speeds to avoid exposing communities to sonic booms. With aircraft noise already posing a serious risk to public health, and previous studies documenting community opposition to supersonic overflight, communities will find the prospect of sonic boom exposure unacceptable. 

Based on industry projections of the potential number of new supersonic aircraft, ICCT (2019) found that parts of Western Europe and the United States could be exposed to sonic booms as frequently as once every five minutes if declared 2035 sales targets are met. Specifically, “operations departing or landing in London Heathrow, particularly to and from Dubai, would expose parts of Ireland, Germany, Austria, Hungary, Romania, and Turkey to between 150 and 200 sonic booms per day after combining with other cross-European traffic”.

While previous evidence of annoyance and health impacts relates to the operation of Concorde and military jets, there is currently no published evidence to demonstrate that future supersonic operations will be more acceptable. NASA’s research indicates a ‘sonic thump’, as distinct from a boom, but the technology being developed for its low-boom demonstrator aircraft will not be deployed for near-term supersonic designs.

In relation to emissions, a new generation of supersonics is expected to burn between 7 to 9 times more fuel per seat-km flown than subsonic aircraft. Given the challenges that the sector already faces in reaching net zero by 2050, and the fact that plans by supersonic manufacturers to use so-called ‘Sustainable Aviation Fuels” (SAFs) will divert an already finite supply away from the subsonic fleet, reducing the time spent flying at supersonic speeds is expected to have a positive impact. 

In addition, supersonic aircraft operating at higher altitudes are expected to have larger non-CO2 impacts than equivalent subsonic aircraft (IPCC, 1999). The ICCT found that while representing less than 1% of available seat kilometres, a new generation of supersonics using synthetic kerosene (to reduce net carbon emissions) could still increase the net radiative forcing from commercial aviation by two-thirds in the future.

As well as responding to the CAA’s consultation, AEF and the NGO coalition ICSA have been arguing at the environmental committee of the UN’s International Civil Aviation Organisation that a new generation of supersonic aircraft should have to meet at least the same noise and emission standards as subsonic aircraft.