The critical chain method comes from the world of manufacturing. You’ll need to know some basics for the PMP Certification Exam. In manufacturing, the rate of production is determined by bottlenecks in the process. If you can clear a bottleneck in production, you can get more product through the production line. In projects, the bottlenecks are usually resources. Thus, the critical chain methodology focuses on resolving resource constraints.
To determine the critical chain, you start with the critical path and then load resources. This usually causes a change to the critical path, based on resource constraints. The resource-constrained critical path is the critical chain.
To account for the uncertainty associated with the critical chain, you add buffers. Buffer at the end of the project — project buffer — is used to protect the delivery date. Along the critical chain are paths that feed into the critical chain. If any path is late, the critical chain is impacted.
Therefore, buffers are put into the schedule at these points: feeder buffers. For critical chain scheduling, you manage the remaining buffer, as opposed to critical path where you manage the float.
Some of the other details associated with the critical chain methodology include
All resources doing work on the critical chain are protected. This means that they are not pulled off their work to do other work, go to unrelated meetings, or are otherwise distracted from the work at hand.
Resources that are in limited supply, or that are the bottlenecks, are exploited. In other words, work is scheduled around their availability to maximize their efficiency.
All duration estimates are aggressive. Team members are asked to give the duration that they have about a 50/50 chance of attaining.
Buffer is used to protect those activities that don’t meet their estimated end date.
Activities are scheduled at the late start and finish dates.
This method can be used to increase the throughput of projects in a portfolio, especially when you have one or only a few resources that are working on many projects. The individual project dates may be sacrificed for the good of the portfolio.