What is eVTOL?
VTOL (vertical takeoff and landing aircraft) is an aeronautics vehicle category that includes fixed-wing aircraft (e.g. Harrier and F35 Lightning II), rotorcraft, cyclocopters and tiltrotor aircraft. VTOL aircraft can land and takeoff without needing a runway, and can perform maneuvers that conventional aircraft cannot.
Electric VTOL (eVTOL) is a subcategory of VTOL. eVTOLs use electric power to drive their propulsion mechanisms. To date, eVTOL technology has primarily been developed for unmanned applications, however, the technology is now being more widely applied for use in personal aerial vehicles (PAVs).
Why use eVTOL technology?
One use case for eVTOL is to reduce traffic volumes in many major cities and increase the speed of journeys in these environments. One of the well-known initiatives in this sector is Uber Elevate which is being developed by the ride-hailing company Uber. They are working towards large-scale aerial ridesharing, which is set to launch in 2023. Another use case is for ‘last mile’ delivery solutions, where packages can be flown by an eVTOL from a warehouse to a residential destination. This technology is currently being tested by Amazon.
eVTOLs are cheaper and quieter compared to jet-propulsion or piston engine planes and are more environmentally friendly as they contribute no emissions within their area of operation, improving air quality.
Need for regulations and certification
For traditional passenger-carrying commercial aircraft, DO-178C is the primary document by which certification authorities such as FAA, EASA and CAA approve aerospace software systems. Complying with DO-178C guidelines requires significant testing of software to ensure that the probability of software failure is extremely remote.
Some manufacturers have avoided conforming with the rigors of DO-178C certification by classifying their aircraft as ultralight vehicles as the FAA has a certification section for these. However, eVTOLs have developed significantly and need to be classified on their own. Some can’t fall under UAV regulation as they are designed to carry passengers, some will be heavier than the set allowable weight for ultralight vehicles, and some will be autonomous.
If this new mode of transportation is to be adopted, passenger safety as well as safety of people near the aerial vehicles area of operation needs to be addressed by appropriate certification. eVTOL technology is developing at a rapid rate and certification approaches are only catching up reactively. The major regulatory bodies have not yet developed the complete regulatory framework required for the increasingly ambitious eVTOL systems that are in development.
The road to eVTOL certification
EASA recently released the Special Condition for small VTOL aircraft(SC-VTOL-01), the first document listing regulations that must be met for eVTOLs to be classified as air worthy. SC-VTOL-01 includes flight requirements (flying qualities, stability and control regulations), structural regulations and lift/thrust system regulations. It does not, however, include any regulations addressing certification of the avionics software used to operate eVTOLs.
No explicit guidance is currently available on how to certify eVTOLs, and each applicant pursuing certification currently negotiates directly with certification authorities on how best to address their certification needs. In the future, we can expect updates to certification guidelines.
The current approach is that system designers demonstrate that they’ve done tests appropriate to address risks (presenting test & review evidence, traceability results, system design information) and certifying authorities can test to see if this is true. CAST papers are then written to show how a certain attribute will affect guidance and future applicants can follow the new recommended procedures rather than having to do the explicit assurance that other manufacturers did already each time. This is highly dependent on empirical evidence not just theoretical or conceptual standards and until there is a lot of data to play with, there’s a long way to go.
How Rapita fits into the picture
Currently, the most rigorous certification standard in the aerospace industry is DO-178C, which is used in the development and testing of safety critical avionics software. DO-178 was developed by industry professionals with practicality and cost in mind for the aerospace manufacturers. It was designed to be flexible in that it can be applied to virtually any development model, and to make avionics software as reliable as can be reasonably explained. The safest way for eVTOL software to be certified is to develop to DO-178C.
As leaders in aerospace certification, Rapita have developed a flexible approach to proactively tackle the challenges of certifying unconventional aircraft. We are working with some of the biggest names in the eVTOL industry as a trusted partner assisting with verification and validation of software for DO-178 certification. We provide training for our tools and guidance throughout the certification process.