Actuators and Controlled Processes

The factors discussed so far have involved inadequate control. The other case occurs when the control commands maintain the safety constraints, but the controlled process may not implement these commands. One reason might be a failure or flaw in the reference channel, that is, in the transmission of control commands. Another reason might be an actuator or controlled component fault or failure. A third is that 

A waypoint is a set of coordinates that identify a point in physical space. 

In a hierarchical control structure, the actuators and controlled process may themselves be a controller of a lower-level process. In this case, the flaws in executing the control are the same described earlier for a controller. 

Once again, these types of flaws do not simply apply to operations or to the technical system but also to system design and development. For example, a common flaw in system development is that the safety information gathered or created by the system safety engineers (the hazards and the necessary design constraints to control them) is inadequately communicated to the system designers and testers, or that flaws exist in the use of this information in the system development process. 

3 Coordination and Communication among Controllers and Decision Makers 

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Figure 4.8 shows the classification. The causal factors in acddents can be divided into three general categories (1) the controller operation, (2) the behavior of actuators and controlled processes, and (3) communication and coordination among controllers and decision makers. When humans are involved in the control structure, context and behavior-shaping mechanisms also play an important role in causality. 

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