From Signal to Evidence: Establishing the Evidentiary Threshold for System Reliance

This paper examines a structural limitation present across safety-critical systems: the absence of a mechanism to evidence system condition at the moment of reliance.Current safety frameworks rely on certification, inspection, and maintenance processes to demonstrate compliance at defined points in time. These mechanisms establish that systems have met required standards, but they do not provide contemporaneous evidence of operational condition when those systems are depended upon.Through a cross-domain comparison, this paper analyses aviation data recording systems as a reference model for continuous evidencing. Aviation systems capture time-stamped operational data, enabling the reconstruction of system condition at any given moment. This evidencing capability is contrasted with the prevailing assurance model in the built environment, where system condition is verified periodically and assumed to persist between verification events.The analysis demonstrates that the absence of present-state evidencing is not a technical limitation. Continuous evidencing is demonstrably achievable and already implemented in other safety-critical domains. The gap identified is therefore structural, arising from the absence of design and governance requirements to evidence system condition in real time.The paper concludes that where system condition is not recorded as it exists, reliance remains assumed. This creates an evidentiary gap between verified compliance and actual system performance at the moment of reliance, with implications for risk management, accountability, and incident investigation.