Integrating for Safety – A Proposed Approach to the Integration of Propulsion Battery Systems in Hybrid Electric Aviation

In the last year we have witnessed a notable surge in the designs and in the guidance material for electric and hybrid aircraft. FAA and EASA have continued to evaluate the safety of Propulsion Battery Systems (PBS), with a focus on thermal runaway containment testing. As a result, a harmonization white paper was issued to provide a certification path for Thermal Runaway (TR) Hazards, followed by an EASA certification memorandum on the acceptable approaches for the certification of Electric/Hybrid Propulsion Systems (EHPS). And just recently, an FAA Advisory Circular (draft) was issued for the “powered-lift” aircraft that feature these propulsion battery systems. In spite of the advances made by electric/hybrid aircraft manufacturers and the aviation authorities, there is still a missing piece of the puzzle. Mainly, we are still not confident in our ability to properly integrate the PBS into the EHPS architecture, in such a way where safety is never compromised, no matter the hazard. The burden is still on systems engineering to transcend the lethargic pace of the authorities in issuing a standard that addresses the novelties and integration complexities of EHPS. In our previous paper, we outlined the necessary approach for the hazard analysis of the battery system, with an emphasis on TR hazards [3]. In this paper, we will build upon this approach by outlining a methodology that serves to guide the system architectural development in addressing the complexities of the interdependence of the PBS, amongst the other systems of the EHPS. This approach is designed to evaluate the robustness of the architecture in achieving the safety objectives for every potential hazard scenario. With this approach, we can be certain that a correct and complete set of design safety requirements can be derived for the EHPS, no matter the aircraft configuration. With this “designing for safety” approach, or in this case: “integrating for safety”, we can be assured a clear pathway to certification.