Error management (EM) has two components: error reduction and error containment. Error reduction comprises measures designed to limit the occurrence of errors. Since this will never be wholly successful, we also need error containment measures designed to limit the adverse consequences of those errors that still occur. Tripod-Delta has instruments for measuring these disruptive processes termed General Failure Types (GFTs) that does not depend upon incident statistics. Why we are so ready to blame people rather than situation it is because fundamental attribution error so basic to human nature. Human behaviour is governed by the interplay between psychological and situational factors. Free will is an illusion because our range of actions is always limited by the local circumstances. Then The Influence Diagram Approach (IDA) provides the tools for modelling qualitatively the influences, existing at various organizational levels. The Maintenance Error Decision Aid (MEDA) is a tool, devised by Boeing in collaboration with the Galaxy Scientific Corporation, for investigating maintenance errors.