Critical Path Planning and Scheduling: An Introduction and Example

Critical Path Planning and Scheduling is a labour management aid considerably in advance of those previously available. First devised for the U.S. Navy in 1958, it divides project programming into two phases planning, and scheduling. In the planning phase a graphic representation of all activity relations is obtained by constructing an arrow network diagram. In the scheduling phase, duration times are assigned to activities and the three floats (spare time) available to each are computed. This allows the determination of the critical path of the project. Variable activity duration times and associated costs can also be handled. The techniques of Critical Path Planning and Scheduling are described in Section 3. The discussion, however, is confined to project timing, and cost scheduling is left over to an appendix. This does not detract from the argument but makes it easier to prepare for a practical example of how CPPS may be applied in farming. The planning and scheduling of some eleven activities required to describe the land preparation and sowing of 250 acres of wheat reveals that, with the assumed precedential ordering, there is spare time available when ordering the seed; and some delays completing the first scarifying and harrowing do not prevent the entire operation being completed in 42 man-days. With a five and half day working week, it therefore takes between seven and eight weeks to complete the planting. This means that to sow no later than the first week in July, the plough must be put into the ground before the second week in May. The conclusion is that CPPS could have some use in farm management. Its significance, however, may be less than that of other O-R techniques and its application will be heavily dependent on the gathering of more labour requirements.