Prohibition of Supersonic, Transonic and Hypersonic Flight over land

We asked for feedback on the proposal to prohibit instrument flight rules (IFR) flights to be undertaken at supersonic and hypersonic speeds over land (to bring the rules into line with those for visual flight rules (VFR) flights) and to prohibit VFR flights to be undertaken at hypersonic speeds over land without express permission from the CAA.

We received 42 responses in total. Overall, there was support for the proposals which are designed to mitigate the environmental effects on the ground from ‘faster than sound flight.’

The principal areas where respondents considered that there may be negative impact were in efficiency and financial impacts. The concerns centred around aircraft that are designed to be more efficient at supersonic or hypersonic speeds having to fly subsonic over land, therefore impacting on their efficiency and fuel utilisation, potentially leading to greater cost.

A couple of respondents believed there would be a negative impact to safety due to the requirement for these aircraft to “operate in sub optimal flight regimes which could compromise their handling characteristics and thus reduce safety.”  Additionally, another suggested that as “supersonic aircraft are designed to cover long distances at high speed. If they have to reduce to subsonic speed every time they pass over land this manoeuvre, perhaps necessitation [sic] large altitude changes, may be hazardous and would reduce fuel reserves.”

It is important to highlight that it is not the intent for a prohibition of supersonic and hypersonic flight to remain in place for the long term. It is intended to mitigate the environmental effects of ‘faster than sound’ flight and provide protection to those on the ground whilst aircraft are developed that have less of an environmental impact from noise. Moreover, aircraft capable of supersonic and hypersonic speeds will be required to reduce speed at some point during their flight to enable a return to an appropriate approach and landing speed, and their handling characteristics will facilitate this in a safe manner.

One respondent believed that supersonic flight would benefit the air traffic management (ATM) network by getting aircraft to their destination faster, whilst another believed that the additional workload for ATM created by dealing with supersonic flight would offset any benefits of their faster flights. 

Where respondents considered there was a negative impact, this was mainly due to concerns over the inability of developers to conduct flights for research and development (R&D) purposes, especially when those flights were looking to reduce the noise impact of faster than sound flight.  Additionally, there were several concerns over the financial impact should developers of supersonic aircraft look to move away from the UK due to limits being placed on their trial flights.

However, the proposal specifically allows for R&D flights to continue through the power afforded to the competent authority to authorise such flights, whilst still ensuring the protection of people on the ground. It is intended that the proposal to prohibit ‘faster than sound’ flights over land is an interim measure which provides the flexibility to support R&D and the subsequent certification of ‘low-boom’ aircraft.

It is likely that future ‘low-boom’ aircraft will have a far lower noise profile than earlier generations of ‘faster than sound’ aircraft, and thus be much less noticeable to people on the ground. Consequently, they will not need to be limited in the same way as which will allow us to review these requirements accordingly.
 

To facilitate the ongoing development of new aircraft types capable of supersonic and hypersonic speeds, whilst taking into account the impact on citizens on the ground from noise impacts, the Civil Aviation Authority (CAA) will proceed with the task of developing rules which limit when and where aircraft can fly at speeds ‘faster than sound.’

These rules will not affect transonic IFR flight and, where there is a requirement for ‘faster than sound’ flight over land for R&D purposes, the CAA will have power to authorise these where appropriate.

As technology advances and the impacts of ‘faster than sound’ flight on the ground diminish, these rules can be revised to ensure innovative technologies achieve their full potential both in terms of speed and efficiency.