Quality schedules have a continuous critical path from the project start milestone to the project finish milestone. It may, however, be difficult to perceive that your critical path is truly unbroken when you have a vast number of activities and, possibly, activity constraints.
How can one be certain that their schedule’s critical path forms an unbroken link or chain of tasks from start to finish?
The Defense Contract Management Agency’s (DCMA) 14-point assessment measures a schedule’s potential for successful implementation, but does the assessment help inspect critical path integrity? Yes, the assessment includes a Critical Path Test to inspect the soundness of the schedule’s critical path. The ideal, mentioned above, is for one complete critical path from project start to finish.
This article discusses the DCMA Critical Path Test as a way to gage the soundness of a schedule’s critical path.
The DCMA Critical Path Test assesses the integrity of the overall network logic. Schedule’s should commence at a single point, i.e. a milestone and complete at a single point, preferably a finish milestone.
But in between you may have multiply paths. One of those paths, however, should begin at the schedule start milestone and conclude at the schedule finish milestone. This is your schedule’s critical path. It forms an unbroken link through the entire schedule, and it is the longest path through the schedule logic.
The Critical Path Test is implemented by increasing the remaining duration of an open task on the critical path by a specified amount. This should be an open task nearest the schedule start date. Some guidelines recommend a 600-day increase. The amount is not important, but note the slippage value. If there is one unbroken chain of activities from the start point to the end of the schedule, you will observe that the project early finish date is affected in direct proportion to the inserted test slippage.
Schedules that have project constraint deadlines will show a negative total float increase in direct proportion to the slippage. If you do not observe this change to the total float or finish date it means you have a critical path discontinuity (a gap) somewhere in the schedule, and the schedule is flagged for further review. The critical path test is a Boolean pass/fail metric. If a commensurate amount of schedule slippage occurs on the project finish milestone, the schedule passes the Critical Path Test.
A failed test indicates broken logic, which is usually the result of either missing predecessors or successors. The schedule log file in Primavera P6 Professional lists activities without a predecessor or without a successor. Again, only one activity at the beginning of the schedule should be without a predecessor, and only one activity at the end of the schedule should be without a successor.
Summary
Knowing the critical path or longest path through the schedule is important for schedule optimization efforts and to realistically predict the end date of the project. A schedule’s critical path should form one continuous link from the first to last activities. The Critical Path Test provides a simple and effective way to test for critical path continuity. The Critical Path Test is a binary pass/fail test that flags suspect schedules for further activity logic inspection.
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