VTOL using battery for propulsion

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.