Phantom Float

This paper presents a resource-constrained critical path method (RCPM) technique that capitalizes on and improves the existing critical path method (CPM) and resource-constrained scheduling (RCS) techniques. A traditional CPM schedule is not realistic, because it assumes unlimited resources, some of which are highly limited in practice. Although traditional RCS techniques can consider resource limitations, they do not provide the correct floats and critical path, as the CPM does. The difference between the theoretical remaining total float and the real remaining total float is referred to as “phantom float” in this study. Work sequence in a resource-constrained schedule could also be considerably changed with a schedule update, resulting in high costs to reorganize it. This is because in addition to technological relationships, a resource-constrained schedule contains resource dependencies between activities that are neglected in traditional RCS techniques. This study proposes a step-by-step RCPM procedure to consider those resource-constrained relationships. Hence, the method can identify real floats and correct critical paths considering both technological and resource relationships, making late start and late finish times more meaningful. In addition, because of identified resource relationships, the RCPM also provides a certain level of stability with a schedule update.