THEA: Human Error Analysis for Requirements Definition Bob Fields, Michael Harrison, Peter Wright Human-Computer Interaction Group Department of Computer Science University of York York, YO1 5DD bob, mdh, pcw @cs.york.ac.uk Abstract THEA is a technique developed to help designers in interactive systems (originally in the aviation domain, but hopefully applicable in other contexts) to anticipate interaction failures or “human errors” that may be problematic once their designs become operational. The techniques is intended for use early in the development lifecycle, as design concepts and requirements concerned with safety and usability, as well functionality are emerging. This report uses examples from two flight deck based case studies to illustrate how to use the THEA technique for carrying out a human error analysis during early design. The aim is that this document should accompany a one day tutorial and should be sufficient to capture the essence of the design method. This document introduces material that is an evolution of the THEA techniques and includes some new material and is intended to preserve the flavour of the earlier document that gave a “how to do it” guide to techniques developed both in the Dependable Computing Systems Centre at York, and elsewhere, aimed at practitioners.