Consultation Hub

We asked for feedback on the CAA’s view on Handling Rules for VTOL Aircraft Using Battery Power for Propulsion.

We received a total of 16 responses. Eight respondents have disagreed or expressed concern with our proposal to not allow recharging of batteries used for propulsion with passengers embarking, on board or disembarking. Some of the same respondents felt it is the operators that should decide if recharging with passengers onboard is appropriate, with manufacturers’ input.

Multiple respondents noted the proposal would have a negative impact on the business model of VTOL operators by resulting in longer turnarounds and ground handling times, risking the viability of the industry.

One respondent explicitly was in favour of equating swapping out of batteries to maintenance.

Two respondents stressed that approach to this issue should be risk-based, not prescriptive, to account for design, procedural, and ground mitigations that will be in place.

Two respondents asked for more specifics on firefighting and rescue standards and regulations, including which and how much of substance to use when putting out lithium-ion battery fires, and standardised firefighting techniques for this type of fire.

We have considered the comments submitted in response to the call for feedback on the proposed approach to Handling Rules for VTOL Aircraft Using Battery Power for Propulsion.

The CAA is committed to enabling new aviation business models in the UK, subject to appropriate levels of safety being maintained. The CAA’s approach to regulating these new business models remains risk and evidence based.  Due to the novelty of VTOL aircraft and their infrastructure we consider that there is insufficient data to support the use of some practices when handling batteries used for propulsion.

In its statement the CAA proposed that batteries used by VTOL for propulsion should not be recharged with passengers on board. We consider that recharging lithium-ion batteries with passengers on board a VTOL aircraft would be analogous to refuelling using avgas and wide-cut fuel with passengers on board.

Both avgas and wide-cut fuel are difficult to handle due to the amounts of explosive vapours that they generate. If a fire was to occur, it would result in high risk to passengers and likely damage the aircraft. Due to these risks, refuelling using these fuels with people on board is not permitted.

While a lithium-ion battery thermal runaway event is a low probability event, if it did occur, could result in a very powerful and fast-spreading fire and the outcome of that fire could be more significant compared to conventional fuels, such as wider area of damage and toxic byproducts. Academic research suggests that even if fire is not present, a lithium-ion battery experiencing a thermal runaway can generate large amounts of toxic fumes. This can have negative health consequences and inhibit efforts to evacuate passengers.

At times, the process of thermal runaway could last days. Even during recharging, lithium-ion batteries can create gasses that are toxic and flammable by nature. As the capacity of lithium-ion batteries grows, so will the potential damage that can be caused.

Lithium-ion batteries are therefore currently being treated as high risk. We will review our approach as more data is made available to us about the technologies being used and the mitigation methods applied to address the risks to persons and property on the ground.

We acknowledge that technological and procedural measures can go a long way to mitigate risks associated with recharging batteries used for propulsion. The CAA will therefore consider potential mitigations, such as a proposal by respondents to allow development of operating procedures by the OEMs and operators, but subject them to CAA review and approval. This statement will be reviewed to account for technological progress in energy storage where new types of batteries may have a lower risk profile compared to lithium-ion batteries.

We are aware of the challenges posed by lithium-ion batteries in VTOL aircraft, especially in the context of Rescue and Fire Fighting Services and are actively engaged in EUROCAE work on this topic. Future guidance for vertiports will include RFFS criteria and additional guidance will be released in due course.

The CAA will further clarify the statement to include the need for a qualified individual to attend the entire process of recharging unless it can be demonstrated that a certified system or appropriate procedure can be used to monitor the process remotely without diminishing safety levels.

Regarding possible divergence from other regulators, while we do learn from outputs of other regulators, we are firmly focused on introducing regulations that are appropriate for the UK environment. We will seek to remain aligned with our international partners, insofar as their approach is suitable for the UK environment.

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.
 

We asked for feedback on the CAA’s position on the adoption of 21 Special Conditions and 2 Means of Compliance, published by the European Aviation Safety Agency (EASA) after the United Kingdom left the European Aviation regulatory system.

We received 5 responses in total. All respondents agreed with the CAA approach to adopt the Special Conditions and Means of Compliance listed in the consultation. There were no comments on the technical content of the Special Conditions or Means of Compliance.

We acknowledge that all respondents supported this proposal, however we are also aware of the limited number of responses. The Special Conditions and Means of Compliance will be adopted and published on the CAA website in due course.