EASA’s Proposed Special Condition for VTOL Certification notice is the result of the realization that VTOL certification standards are not, and never were, specifically constructed for the purposes of certifying the VTOL aircraft that are being designed, manufactured, and tested today. While the mechanics of flight have not changed for these aircraft, the traditional certification guidelines that supported either fixed-wing or rotorcraft certification do not wholly apply to current VTOL configurations. VTOL designs from 2010 onward will have two key differences from traditional aircraft designed before 2010. They may not be able to auto rotate as a rotorcraft would in emergency power failure situations, and their distributed propulsion systems have new failure modes that have not been completely explored to the point where certification guidelines can encompass the vast majority of VTOL propulsion configurations.
EASA’s special condition was established in a similar spirit as recent amendments to EASA’s code of regulations have been established, such as CS-23, Amendment 5, which describes performance or objective based technical specifications.
EASA specifies VTOL certification for small (5 passengers or less, with MTOW < 2,000 kg) aircraft in this special condition issuance, meaning that other aircraft that exceed either the maximum takeoff weight and/or the passenger count criteria are excluded from certification under this special condition.
Here are some of the criteria of note from the special condition document:
- Certification of Small-Category VTOL Aircraft VTOL.2005: Two categories exist for certification of light aircraft:
- Category Enhanced: aircraft that intend to be operated as commercial air transports (CAT) over congested areas and are capable of flight and safe landing after critical malfunction/failure of thrust/lift system
- Category Basic: aircraft capable of an emergency landing after critical malfunction of thrust/lift.
- Note: all air taxi operations will thus be certified under the Enhanced Category per this proposed regulation. In general, the enhanced category has requirements for safety of flight during all phases of a typical mission while a “thrust/lift unit” has critically malfunctioned.
- Flotation VTOL.2310: If certification for intended operations on water is requested, then the VTOL must provide buoyancy 80% in excess of the maximum required to support the vehicle in freshwater.
- Thrust/Lift System Operational Characteristics, VTOL.2425: If the safety benefit outweighs the hazard, the design must allow the shutdown and restart of a thrust/lift unit in flight within an established envelope.
- Thrust/Lift System Installation, Energy Storage and Distribution Systems, VTOL.2430: No fire of one system shall affect another system, energy storage system must not suffer critical failure during a survivable emergency landing.
- Thrust/Lift Installation Support Systems VTOL.2435: Any likely failures of the thrust/lift system that result in a critical malfunction of thrust/lift must be mitigated.
- Installation of Recorders VTOL.2555: specifies that a recorder must be installed that provides “accurate and intelligible recording and safe gaurding of the data supportive for accident investigation, considering the conditions encountered during the crash…” Nowhere included are the specific requirements other than this data.
- High Intensity Radio Frequency (HIRF) Protection Provisions, VTOL.2520: General requirements for lack of critical systems malfunction while exposed to HIRF, and suitable restart time delay should HIRF be encountered in higher-than expected volumes.
This special condition notice has not been confirmed or finalized, and EASA is still collecting feedback on their proposed regulations. The feedback form, along with the native version of the Special Condition notice are available on EASA’s website here.
Why it’s important: The approach that EASA is adopting for UAM certification is fundamentally different than some other regulatory bodies, including the FAA. While CFR Part 23 should not require significant restructuring to allow for the certification of eVTOL’s, EASA is indicating with the issuance of their special conditions that a more tailed approach to certification may be more advantageous, despite the additional effort required to stand up this regulatory framework.