Identification and assessment of zonal hazards emerging in highly integrated Distributed Electrified Propulsion Systems in aviation

The increasing complexity of modern aircraft systems and in particular, concepts of novel highly integrated and Distributed Electrified Hybrid Propulsion Systems (DEHPS), introduce a variety of novel safety challenges in comparison to conventional aircraft engines. Those legacy propulsion systems are designed to be compact with all subsystems of the system typically being located within the physical system boundaries of the engine nacelle. A high degree of integration of individual DEHPS subsystems into the aircraft architecture and the introduction of new technologies lead to novel hazards and an increased effort for the assessment of the system safety. This study identifies physical hazards associated with the integrated architecture of a specific hydrogen powered DEHPS. Particular attention is paid to the assessment of hazards whose effects can propagate across system and zonal boundaries, affecting adjacent subsystems throughout the aircraft. The identification and assessment of said hazards is based on the Zonal Safety Assessment (ZSA). The ZSA methodology is defined in the Aerospace Recommended Practice - ARP 4761A by the SAE International. The DEHPS under consideration consists of multiple propulsion units distributed along the wingspan of an electrified aircraft with fuselage-integrated energy storage and conversion systems. This architecture leads to a spatial separation and a placement of the DEHPS subsystems in several different aircraft zones. The identification and evaluation of hazards show, that the integration of novel DEHPS poses risks for the safety of adjacent novel and legacy systems, aircraft zones and subsequently the entire aircraft. Aiming at the certifiability of this and similar novel propulsion systems, means of mitigation of the assessed hazards and failure conditions are developed and can be considered for the definition of future design and installation requirements.

Keywords: Aircraft safety, Zonal Safety Assessment (ZSA), Physical hazard, Mitigation, Airworthiness, Hydrogen Electric Propulsion