Critical Chain Method/CCM of Project Planning and Control
By Dr.Russell Archibald
The critical chain method has emerged in the past few years and is embraced by some practitioners as a significant advance in the state of the art of project planning, scheduling and control. Others take the position that it is not significantly different from the critical path method/CPM, when that method is effectively used. CCM builds on the familiar CPM network planning technique in the following ways:
- Resources and ‘Resource Buffers’: CCM focuses more intensively on resource constraints in creating the network plan logic. It identifies quantified resource buffers to assure that critical resources will be available when required to avoid project delays. Quantified resource buffers are certainly a new addition to project planning and control practices, although some would argue that they are basically the same as the ‘management reserves’ that have long been used in the application of CPM.
- Duration Estimates: CCM uses range estimates for activity durations, but its use of a ‘mean value’ is disputed by Piney (2000) as inferior to the original PERT approach to range estimates of duration. Many practitioners use range estimates with CPM as well, although this is not a formal requirement with CPM.
- Critical Chain Buffers: These are sized in CCM based on the uncertainty in the protected group of activities, and CCM proponents claim that these are different from CPM float or slack. Arguments by practitioners continue about these and related points concerning the differences between CCM and CPM. (See Archibald 2003, pp 274-275, Piney 2000, and Leach 2000 for more detail on these points.)
Reported Benefits of CCM: As an example, the U. S. Navy recently reported significant improvements when they switched from using CPM to CCM in 2002 at the Pearl Harbor Naval Shipyard for its Fleet Maintenance Availability Project for Submarines. These include:
- Better schedule performance, with the last 13 submarines finishing on time.
- 11% more jobs done for each submarine turnaround while using 5% fewer people hours.
- 13% increase in job completions.
- Average length of repair time reduced by 5.6 days (PMI PMNetwork 2003 p 10).
The Navy says that main reason the switch to CCM produced these improvements is because with CCM if a job finishes early the next job will start immediately, whereas with CPM the next job would not start until its original scheduled date, since the needed resource would not be available to start earlier. CCM encourages a ‘relay race’ behavior, they say, with workers finishing a job as quickly as possible and passing the baton without delay to the next in line. Others would argue that this type of behavior is not dependent on the planning method used.
Dr. Russell D. Archibald, PhD (Hon), MSc, Fellow PMI and APM/IPMA, PMP, is one of the six founding members of the Project Management Institute. Now semi-retired, he has many years of management experience in engineering and operations with a variety of major US corporations in Europe and South America as well as the US. He has made major contributions to the understanding of project management, is author of the best selling 2003 book “Managing High-Technology Programs and Projects” (published also in Russian, Chinese, and Italian), has trained more than a thousand program and project managers and project specialists around the world, and has consulted in project management to clients in 14 countries on 4 continents. E-mail: firstname.lastname@example.org. Website: www.russarchibald.com.