ABSTRACT
Plans in HTA indicate how subordinate operations are organised in order to meet their common goal. Plans comprise a limited number of timing and sequencing relationships. For example, in some plans suboperations are carried out in sequence, while in others they may need to be carried out together. In other plans operations are contingent upon certain system events occurring. These timing and sequencing elements may be combined in different ways in actual tasks to account for different sorts of operator performance. Plans also combine to create apparently conplex performance - the apparent complexities of human performance can often be accounted for by describing sitnple plans in combination with one another.
