ABSTRACTIn civil air transport, at least 70% of accident causal factors are attributed to crew error, so technical reliability is not enough to guarantee safety. There is currently a great deal of discussion about ‘human factors’ in system design. There are text books written on how to create good ‘human centred’ designs; performance failures and accidents are frequently blamed on its shortfalls. This paper will argue that human performance should be considered in system safety assessment, and offers practical suggestions on how to achieve it.Specific techniques will be presented for: Risk identification: a systematic method for the identification of risk areas, and the acceptability of the proposed design. User Involvement: concrete advice on how and when to involve users, what specifically to ask them, and how to collate the results into a single design solution.