A fail-safe decision-support framework for onboard greywater reuse in commercial aircraft water systems

Abstract

This paper aims to develop and apply a model-based decision-support framework for pre-adoption screening of onboard greywater reuse as a non-potable flushing option in commercial aircraft water systems. This study uses framework-development research based on publicly available scientific, institutional and industry sources. Evidence from greywater reuse, aircraft lavatory hygiene, aircraft water and waste systems, fault detection, fail-safe operation and airline sustainability management is mapped into mandatory gates informed by failure mode and effects analysis (FMEA), weighted scoring dimensions and case-based directional validation. The Fail-Safe Greywater Reuse Adoption Algorithm separates non-compensatory safety requirements from scored operational and sustainability factors. A publicly reported Boeing 777 long-haul evaluation falls within the adoption-consideration band with a Fail-Safe Greywater Reuse Adoption Algorithm score of 4.050, while an Airbus A320 short-haul scenario falls below the adoption threshold with a score of 2.275. Sensitivity checks retain the same directional separation. The framework is intended as a pre-adoption screening tool rather than a certification, design approval or operational validation instrument. The scoring weights, decision bands and preliminary FMEA values are literature-informed and require refinement through expert elicitation, prototype testing, airline maintenance records, route-level modelling and empirical case studies. The framework helps airlines, manufacturers and maintenance stakeholders identify aircraft-route contexts where onboard greywater reuse may be operationally meaningful before committing to costly engineering or certification work. It supports early screening of hygiene, isolation, fallback, maintainability and sustainability-accounting risks, preventing water-saving claims from overriding safety and service-continuity requirements. Onboard greywater reuse may support more resource-conscious aviation by reducing potable-water carriage and enabling circular use of non-potable water within aircraft service systems. However, its social value depends on passenger trust, hygiene assurance, transparent communication, reliable fallback operation, operational reliability and safety expectations. This paper reframes onboard greywater reuse as an aircraft-system adoption decision rather than a stand-alone water-saving measure. This paper combines aviation management, hygiene control, maintenance exposure, sustainability accounting and mechatronic fail-safe logic in one traceable screening model.