Protection In A Critical Chain Project

In a Critical Chain project, management accepts that task times are not deterministic. This means that during planning, a person cannot state that the task will take exactly 3.2 days, for example. Task times are guesses. Therefore, it is perfectly normal for task times to take longer than estimated.

Management does not worry about whether or not a task finishes on time. They focus on finishing the project on time. In Critical Chain environments, organizations quote annual project on-time percentages typically above 95 percent. This section examines the way in which projects are protected to achieve these results.

W. Edwards Deming taught management the importance of having a system that stays in control. By this, Deming refers to the "predictability" of a system, relative to its goals. In describing such a system, Deming refers to two types of "problems" that any system can encounter. He calls these problems "variations."6 Every system is subject to a type of problem called "common cause" variation. These types of problems are absolutely normal, and management should do nothing about them. In fact, if a manager tries to do something about a common cause variation, it often causes the system to go into chaos.

For example, in any organization, it is perfectly natural and expected that some people occasionally will not show up to work on time or will report in sick. It is perfectly natural for machines to break down from time to time. A person, designing the procedures for an organization, should expect these "common cause variations." Deming insists that the correct procedure, when a common cause variation is encountered, is to do nothing.

In any system, "common cause" variation (in which managers should expect the variations and take no action) and "special cause" variation (in which managers always take action) must be defined.

To arrive at a project plan that will stay in control throughout the entire execution, the following steps are necessary:

• Take all forms of padding out of the task estimates. This can be done through moving from "elapsed time estimates" to "dedicated time estimates." Another way to remove padding is to educate the organization on the Critical Chain methodology, and give this task to the project managers. This step removes any chance of "Student Syndrome."

• Resource level the project. Do not schedule the project assuming that resource contention will magically take care of itself. In Critical Chain, resource contention is resolved up front.

• Don't measure people on completing their tasks on time or on the accuracy of their estimates. If management wants to reward team members, the reward should be based on finishing the project on time or early.

• Allow people to work on a Critical Chain task in a "dedicated" manner. This is part of the second focusing step, "Exploit the system's constraint." Dedicated behavior implies that once a person begins to work on a task, he will work only on that task until either it is complete, or he has progressed far enough on the task to turn it over to the next resource to work on it. Further, dedicated behavior implies that if the task is turned over to the next resource, but will be returned to the current

6. An excellent explanation is contained in Donald J. Wheeler, Understanding Variation, The Key to Managing Chaos, 2nd ed. (Knoxville, TN: SPC Press, 2000).

resource within a very short period of time for more work, the current resource will wait for the return of the task, rather than begin work on a new task. This is true if the new tasks will take up substantially more time than waiting for the current task to be returned.

• Change the organization's resource management approach to implement the paradigm that resources on the Critical Chain have more flexibility to accept work earlier than expected. This is usually accomplished through an early warning system, called the resource buffer. The resource buffer does not take up any time on a schedule. It simply acts as an alarm clock, warning resources that they are X days away from receiving a new task.

• Implement a project buffer to protect the project's Critical Chain. It sits at the end of a project and is calculated as a percentage of the length of the Critical Chain, typically 30-50 percent. This buffer is protecting the collection of tasks on the Critical Chain from any common cause variation.

• Implement feeding buffers on each feeding path, to protect the Critical Chain from variances on any feeding path.

We will use the same example as shown in Figure 22-1 to illustrate how this works.

Figure 22-4 shows what the project looks like, after the protection has been removed from each task. For example, the first task, "Modify Standard Parts," was changed from the sixteen-day estimate shown in Figure 22-1 to a ten-day estimate. The task "Design Custom Parts" was changed from a forty-day estimate to a fifteen-day estimate.

The next step is to perform resource leveling. Since the same resources from the Engineering Drawings area and the Procurement area will be working on all of these tasks, we will not allow them to do two tasks at the same time.

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Project Management Made Easy

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