The CAA has reviewed the reference proposed airworthiness criteria and would offer a number of high-level comments on the FAA approach. The CAA has decided to not submit detailed comments on the draft criteria, as there is a fundamentally different safety approach that FAA is proposing, relative to that which the CAA considers appropriate, for this new class of aircraft and its intended operations.
The CAA agrees that the Joby model JAS4-1 represents a new class of aircraft with powered lift capability, that incorporates characteristics from both conventional and rotary wing flight, but also introduces new flight and handling characteristics. As such the CAA agrees that the existing airworthiness standards are not adequate and new standards are needed, which may draw on existing material, but which will also incorporate new material. In this regard, the CAA decided to adopt the SC.VTOL standards published by EASA, and which CAA helped to develop prior to the UK exit from the EU. The CAA has continued to support the application of SC.VTOL and is an active part of the subsequent development of Means of Compliance (MoC) and industry standards through the Eurocae collaborative effort. The CAA considers
that the intended operational model as described by not just Joby, but all the leading designers, to provide paid for passenger flights over densely populated urban environments, constitutes a new risk to third parties which needs to be recognised in the safety performance of the vehicle.
The FAA makes a number of statements about the unique flight and handling characteristics of the powered lift category, as well as expressing that there are concerns in respect to how these aircraft will perform following loss of power or thrust. It also states that these aircraft have highly integrated lift/thrust systems which provide flight directional control. These are all factors with which the CAA agrees. That said, it is not clear why the FAA has chosen to not apply Class 4 (from Pt-23) as the safety target. The rationale is not discussed, and the decision appears to be linked to structural considerations, rather than the wider systems safety and functional hazards issues. The CAA considers that for powered lift vehicles
undertaking commercial passenger operations over densely populated urban areas, Class 4 would be an appropriate certification category. This aligns broadly with the category Enhanced under SC.VTOL.
The FAA states that the JAS4-1 will be used in Pt-135 operations. It is understood that this would be the basis for commercial (hire and reward) operation and that in the USA Pt-135 permits a lower level of safety than for commercial air transport. These factors may be relevant to the FAA determination to not make Class 4 applicable.
However, Pt-135 does not exist in the UK and as such CAA considers that the intended type of operation would fall under Commercial Air Transport (Pt-121 equivalent). This aligns with category Enhanced under SC.VTOL.
JS4.2000 definitions of Continued Safe Flight & Landing (CSF&L), and Controlled Emergency Landing (CEL). The definitions proposed by the FAA are different from those in SC.VTOL. It is unclear if the FAA definition for CSF&L would take into account, the limited options for a safe alternate landing site in an urban operational situation. This concern is specifically recognised within the definition of CSF&L in SC.VTOL. The FAA definition for CEL implies limited control by the flight crew of the aircraft, other than directing it toward a landing site.
Recognising there will be a need to transition the aircraft from wing-borne to thrust-borne to achieve a touchdown, further details are needed from FAA to understand what level of “touchdown impact severity” might be considered acceptable. The CAA supports the CEL definition and guidance on compliance contained in SC VTOL.2000 and MOC VTOL.2000.
JS4.2320(b) Bird Strike. The CAA agrees that this category of aircraft and its intended operations will place it at increased risk from bird strike, so the inclusion of modified criteria based on the output of the RBSWG is supported. However, following a review of the ref ARAC report, it is unclear what safety benefit FAA expects from the inclusion of bird deterrence technology. The ref report recognises that the evidence base is limited and that there is variability between bird species as regards light frequencies and their effectiveness in scaring birds. Of further concern is that FAA has not included criteria for the evaluation of the effects of a multiple-bird strike as described in MOC to SC.VTOL.2250(f). While it is noted that the ref ARAC RBSWG report did not recommend multiple bird strike evaluation criteria for classic rotorcraft, the intended operational environment and low noise signature of these new aircraft, means that the historic data for rotorcraft bird strikes may not be directly applicable.
It is noted that because the criteria described in the draft G-1 IP are performance-based, there remains a large degree of uncertainty as to exactly what will need to be done by the applicant in order to satisfy the FAA that compliance has been demonstrated. To this end, it will not be possible for the CAA to indicate its detailed position in regard to the acceptability or not, of the proposed airworthiness criteria for the Joby JAS4-1, without a detailed review of the means of compliance yet to be assessed and dispositioned by the FAA Administrator under the issue paper process.