A Scalable Framework for the Management of STPA Requirements: a Case Study on eVTOL Operations

TL;DR

This paper presents a scalable, automated framework for managing and prioritising safety requirements derived from STPA in complex, safety-critical systems like eVTOL operations, validated through a real-world case study.

Contribution

It introduces a structured, automated framework incorporating Monte-Carlo Simulation for stabilising requirement rankings, specifically tailored for managing STPA outputs in safety-critical system development.

Findings

Framework effectively prioritises requirements in eVTOL case study

Supports decision-making with dynamic visualisation tools

Enhances traceability across development stages

Abstract

System-Theoretic Process Analysis (STPA) is a recommended method for analysing complex systems, capable of identifying thousands of safety requirements often missed by traditional techniques such as Failure Mode and Effects Analysis (FMEA) and Fault Tree Analysis (FTA). However, the absence of a structured framework for managing and prioritising these requirements presents challenges, particularly in fast-paced development environments. This paper introduces a scalable framework for prioritising STPA-derived requirements. The framework integrates outputs from each STPA step and incorporates expert evaluations based on four key factors: implementation time, cost, requirement type, and regulatory coverage. To reduce subjectivity, Monte-Carlo Simulation (MCS) is employed to calculate and stabilise requirement rankings. An automation toolchain supports the framework, enabling dynamic mapping of prioritised requirements in a scaling matrix. This visualisation aids decision-making and ensures traceability across development phases. The framework is applicable from early conceptualisation to more advanced stages, enhancing its utility in iterative system development. The framework was validated through a real-world case study focused on Electric Vertical Take-off and Landing (eVTOL) operations, conducted in collaboration with the UK Civil Aviation Authority. The findings contributed directly to CAP3141, a Civil Aviation Publication that identifies systemic operational risks and safety mitigations for regulators, operators, and vertiports. The prioritisation process supported decision-making by helping stakeholders identify and manage high-impact requirements efficiently. This work contributes a practical solution for managing STPA outputs, bridging gaps in requirement prioritisation and supporting safety-critical development in emerging technologies.