Roundtable Discussion: Certification and Safety in eVTOL Aircraft Engineering

Senior Aerospace Engineers from Stirling Dynamics discuss how to meet the unique challenges of certification and safety in the Advanced Air Mobility industry. 

The unique challenges of eVTOL development 

eVTOL innovators around the world are dealing with a range of unique challenges throughout their programs. Shorter development timeframes driven by funding round milestones; start-up and scale-up sized organisations requiring outsourcing of a much broader range of disciplines; the infancy of local and national operational infrastructure; and the unchartered territory of certification for aircraft which don’t fall neatly into any of the regulators’ existing aerospace categories. 

Against this backdrop our Stirling Dynamics eVTOL team delivers engineering and certification support to Advanced Air Mobility (AAM) pioneers across Europe, the Americas, and Asia. We asked some of our most experienced safety and certification team about the key issues facing these customers and to understand their approach in overcoming the industry’s collective obstacles.  

1. Why is certification in AAM so difficult? 

Mark Suter, Principal Safety Engineer explains, “Essentially there is no defined eVTOL standard to follow for certification. This means you are borrowing elements from existing certification standards, ultimately using a hybrid of standards across CS 23, 25, 27, and 29, but doing so cautiously”.  

Luke Bagnall, Head of Engineering, continues, “As well as this, some aircraft are being developed for a pure demonstration phase, and others are working towards full certification for airworthy flight, so there is not only the mix of certification standards, but also vast differences between the vehicles themselves. How we deal with those from a safety perspective can be very different from aircraft to aircraft.”  

“There is not only a mix of certification standards, but also vast differences between the vehicles themselves” 

Take landing for example, for some they are leveraging the CS 27 and CS 29 (rotary) approach, but in a scenario where the aircraft is losing power, how does the pilot land? Others lean more towards the fixed wing (CS 23) approach, but this necessarily determines a lot of system requirements and definitions. As a result, this triggers a requirement for a larger range of aircraft trade studies that need to be fully explored, before you can consider safety requirements at a system and equipment level.  

Another facet of AAM complexity is the blending of previously distinct technology, such as vertical take-off with a conventional landing. Mark explains, “For example, the brakes will be applied for the vertical take-off, but then the onus is on the pilot to ensure they are released before a conventional landing. These aircraft seem to rely heavily on flight control laws, requiring a lot of work on the software that sits behind this.”

So, how can the AAM industry develop a set of regulations that can apply to all these different configurations? 

European Union Aviation Safety Agency (EASA) and the Federal Aviation Authority (FAA) are the two main regulators driving certification bodies in the development of these standards. They are working to provide clarification, but with such a complex set of parameters, it's far from ready.

“Manufacturers should initiate technical discussions with regulators” 

Jean-Pierre Alfano, Head of Office Airworthiness at Stirling Dynamics explains, “If you’re an eVTOL manufacturer, you should be selecting the regulators you want to work with and initiating technical discussions with them.  

“It’s important to consider the standard you agree with. For example, the FAA may align with EASA a few years later, so you need to have a strong handle on your requirements today but keep one eye on how it will evolve over the next 2-5 years.” 

2. How to tackle shortened development time and its impact on certification?

The timeline of traditional aircraft development has increased from around 5 years in the 1940s to around 10 years for modern aircraft. A major factor is of course the increased complexities of today’s flight technology, but the practices and structures of the AAM industry are forcing heavy timeline reductions for aircraft, with arguably greater complexities, to just 5 years from concept to flight.  

The demand of such a profoundly accelerated time-to-market is forcing manufacturers and engineers to challenge the conventional processes of aerospace design. 

Mark says, “When it comes to certification and safety, we encourage our customers to involve safety experts in a program as early as possible. It saves time to factor in safety considerations from the start, rather than re-working a design at a later stage, which can delay a project.”

“Involve safety experts as early as possible rather than re-working a design at a later stage and delaying your project” 

With a market that mainly comprises start-ups and scale-ups, Stirling Dynamics is supporting customers with completely different business models from traditional aircraft programs. eVTOL manufacturers are under pressure to deliver projects and program milestones against a series of funding rounds, which often include ambitious timeframes to achieve the first flight.   

Simon Hancock, Head of eVTOL suggests, “A key way to reduce the timeline pressure is to be selective about what you design from scratch, and re-use existing airworthy elements so you’re not always working from a blank sheet of paper. For example, why re-invent the wheel with a new landing gear design when you can use an existing CS 23 landing gear that's already certified? Manufacturers can instead put their stamp of innovation where it makes the greatest difference – such as the battery, the propellers and the safety systems.” 

Luke adds, “The dilemma of course is accelerating speed to market through the use of existing certified parts and balancing this with the need to meet the particular requirements of eVTOL – battery life, flight time and a much greater need to minimise weight than even traditional aircraft might demand.”  

Every eVTOL manufacturer needs to tread this difficult line between optimising the performance of the aircraft versus reaching the first flight milestone. And whilst some of this rings true for traditional aircraft, there isn’t the luxury of using the same processes and methods from 20 years ago to achieve certification.

There is also the challenge with modern working practices of different disciplines or domains working in silos and there’s a lot to be said for the benefits of being more collaborative to make a project run as efficiently as possible.  

3. What is The distinction of eVTOL missions and operating conditions, and what this means for certification?

eVTOL aircraft will predominantly serve customers who want to improve the efficiency of short trips that might otherwise be done by road. These journeys will mainly be for local / domestic travel within built up areas, and potentially from rooftop to rooftop. 

One of the main challenges is the development of infrastructure. Mark explains, “If you do have a failure and require a diversion to a nearby airfield, how do you get there? And how can we ensure that there is a place available to land once you get there? The other aspect to consider is the recharging facilities on rooftops.”  

AAM development is more than just vehicle development – it's establishing new infrastructure too. 

If the projections are correct, there could be thousands of eVTOL vehicles flying around in the years to come, most of which will be in built-up areas. Luke points out, “There’s a combination of challenges from a safety point of view – how air traffic control is managed, co-ordinating large amounts of vehicles which share the same space, and this space consisting primarily of built-up areas. A lot of thought needs to be put into how this is organised, so these populated areas are not put at risk.” 

Mark adds, “There is also the question of tracking vehicles which may not always be visible on radar when they are behind buildings, so will we need to devise an eVTOL version of the road rules and safety that can work in three dimensions? For example, always arriving at buildings on the north side and leaving from the south side and thinking about different flight levels and what controls would need to be placed around those.” 

Modern flight is augmented by plenty of automated systems to support the pilot, but still requires a large amount of human input. For the new challenges of eVTOL, significantly more automation will be required to ensure its safe operation, and these systems will of course need testing and certification.  

“For the new challenges of eVTOL, significantly more automation will be required to ensure its safe operation” 

Mark continues, “Pilots will need reliable technology that can manage an aircraft in three dimensions amongst buildings; locating and avoiding hazards; managing the systems; and, of course, flying the aircraft! One eVTOL aircraft flying into a city is relatively straightforward, but hundreds operating in the same space, flying at different speeds and heights, is going to be difficult to manage.” 

“The elephant in the room is AI.” says Mark. “There’s a lot of flight control laws and, in an ideal world, we could get AI to design that for us. But of course, safety with software is not that easy. Add an AI learning element into the mix and this becomes very complex indeed.” 

Luke adds, “What many of the eVTOL companies see in future is totally autonomous flight, with no manual pilot, and perhaps with ground station control. So, the next consideration is, do these vehicles talk to each other and would you need, for example, some kind of standardised API protocols and other standardised systems? This of course goes beyond the design of the aircraft, but it’s clear there’s a really broad range of things that need to be considered.” 

The magnitude of the challenges ahead are not fully realised. Simon explains, “We are getting to the point where the overall system and how these aircraft operate is going to be far more complicated than a human can understand – so if a human didn't create it, how can a human say it’s safe? A lot of work need to be done on how you certify an AI system.” 

4. Most of the eVTOL companies are starting their aircraft designs from scratch at the same time as building their company. At what point should they start to think about their safety and certification plans? 

Certification needs to be a consideration as early as possible in an eVTOL design, ideally right from the start.  

Simon says, “If your starting point in design is with a concept, rather than with certification requirements, then in reality this is a harder project to deliver, particularly in aerospace.” 

Luke explains, “A company might put together a demonstrator for the purposes of investment. But once they need to develop a manned prototype that could, for example, fly at an air show, they end up having to start again from scratch.”  

A company that takes more time over the initial design to factor in safety will reap the benefits in the longer term. 

There are benefits to including certification at an early stage – if you incorporate safety into the early design stages, it can make the process quicker and cheaper as you’re not reworking the designs to meet the safety criteria. Mark explains, “You also make the certification process smoother because it’s much harder to make design changes once you reach the certification stage. Sometimes this means you are more constrained in how you can subsequently adjust the design, and you may not have your design changes ready for the stage of the program you’re hoping for, putting your program milestones at risk.”  

“If you incorporate safety at an early stage, it can make the design and certification process quicker and cheaper” 

Luke reflects on other industries who are developing brand new technology, “Unlike the space industry, AAM doesn’t have the same level of tolerance for failure. For example, Space X had a large number of failures when pioneering its reusable rockets, albeit with no crew on board. Had an AAM company experienced that same level of repeated failures, the impact on its reputation would be quite significant – nobody would want to fly on those vehicles and this in turn would likely affect its funding.” 

Simon agrees, “The mantra of fail fast isn’t something that the public will accept for something they actually have to sit inside.” 

5. The regulations from FAA and EASA are broadly similar to each other and have evolved over many decades. How do you see the picture for eVTOL regulations developing over the next few years? 

Luke says, “In terms of regulations, most of these journeys will be micro haul and not necessarily crossing lots of international borders, so you may end up having very different regulators geographically, certainly in the short term. And they each may have different regulations as different regions adjust or relax regulations to encourage take-up." 

Mark draws on his experience in military regulations, “Several years ago we used early versions of Defence Standard (Def Stan) 00-56, which was very prescriptive. Later versions put the onus on the customer to demonstrate their design could meet a particular goal, rather than telling them how to achieve it. It’s hard to predict which way eVTOL will go, but I suspect it may be more be goal-oriented rather than the prescriptive approach because the aircraft, environments, manufacturers, countries, and ethos are so different from one another.”  

Mark considers that, “It would probably be safer for everyone to work to one standard from a single regulator, but I think there will be more onus on the company and the certification bodies to ascertain eVTOL safety.” 

It would be safer to have a single regulator, but the likelihood is there will be several across different geographic regions. 

6. As safety and certification engineers, what are the other main challenges ahead for the AAM industry? What can we collectively do to catch up to what manufacturers are going to do? 

As we’ve established, the AAM industry works in a very different way to traditional aerospace. The majority of companies who are making this brand-new technology are start-ups and scale-ups, which lends itself to a more agile way of working and a much shorter time to market, against a backdrop of funding rounds linked to project milestones.  

“This means we have to think laterally and move more quickly,” Luke explains. “The industry is challenging the conventions of traditional aerospace which ordinarily sees new aircraft designed, certified and operational in around 10 years – for AAM they need this to be more like 2!”  

However, to streamline effectively, this needs a very co-ordinated and collaborative approach. Luke continues, “It’s very easy for different parties to work in silos – to counter this, the Original Equipment Manufacturers (OEMs) and suppliers need to be more open with their information, but this is obviously a challenge with Intellectual Property (IP) and Non-Disclosure Agreements (NDAs).”  

Mark also explains a further challenge, “At the initial design stage manufacturers often use parts that don't come from the aircraft environment, which would make it difficult to certify. As safety experts, we need to make sure the aircraft can meet a hybrid of standards across CS 23, 25, 27 and 29.”  

There’s plenty to learn from this new way of working and it's likely it will influence the methodologies of traditional aerospace, improving lead times for conventional aircraft and helicopter development. 

Some of the developments, particularly in relation to electromechanical actuators which we're developing for many clients, are forming the groundwork for new technology that could go into conventional aircraft. 

In summary

When it comes to certification and safety in eVTOL development, manufacturers can optimise their design and mitigate unnecessary program delays by following a few key principles: 

• Be selective about what elements you want to design from scratch – don't try to do it all.

• Get a safety expert involved from the start. 

• Open the lines of communication with regulators to better understand the technical safety requirements. 

• Adopt a collaborative approach to support the demanding development timeframes, and avoid the temptation to work in silos.

And when looking ahead, it is worth factoring in: 

• That greater automation will be required to ensure safety, and we need to think about the role of AI. 
• The infrastructure requirements for the environment your aircraft will operate in.

To find out more about how Stirling Dynamics could support your AAM programme, please get in touch.