This paper addresses the challenge of enforcing ethical behaviors at runtime in autonomous systems through a structured ethics assurance process. At the core of this process is a subsystem that rigorously operationalizes ethical rules, specifically social, legal, ethical, empathetic, and cultural (SLEEC) requirements. This subsystem enables the dynamic evaluation, adaptation, and enforcement of ethically compliant behavior within a formally defined runtime model. The proposed approach, named SLEEC@run.time, is demonstrated through a running example involving firefighter-uncrewed aerial vehicles. In addition, by leveraging its flexible runtime model, SLEEC@run.time accommodates changes such as the addition or removal of SLEEC rules, ensuring a robust and evolvable approach to ethical assurance in autonomous systems.