Critical Chain Project Management - Module 2

How to plan a project with CCPM


In this second episode of a 4-video series about Critical Chain Project Management, Philip Marris explains how to plan projects with CCPM :

  • Dynamic schedules,
  • Critical Chain identification (differences with Critical Path),
  • Reduction of tasks durations,
  • Insertion of project buffers and feeding buffers,
  • Robust and useful schedules.

To enhance your expertise, Marris Consulting organizes Critical Chain training sessions. 

 Training details and Registration


<< See Module 1 : Problem


See Module 3 : Execution >>

After looking at the problems of traditional project management, we will now look at the Critical Chain through its three pillars:

This video is about the first pillar. A case study, in the form of a Gantt chart, will be presented throughout the video. The schedule is composed of three lines of activities followed by a final activity to close the project. It is first represented in a classic way while following a certain number of recommendations:

  • Resources are assigned full-time on tasks, to avoid multitasking we avoid scheduling part-time resources on a task
  • Resources are always identified
  • All interdependencies between tasks are clearly identified

It is a dynamic planning, it is not fixed in time and evolve little by little as it is executed. The critical path is shown in red, which is the longest task sequence that determines the duration of the project. This critical path does not consider resource capacity, for example "Pierre" is assigned to two scheduled tasks in parallel. In addition, the non-critical activities, blue on the Gantt, are planned as early as possible with the logic "to finish his project on time the earlier we start the better".

The critical path is well identified and most software allows, in theory, a leveling of resources (that is to say, taking into account capabilities). By using this feature, the tasks assigned in parallel to the same resource are shifted and a leveled schedule is obtained. The consequence (on MS Project) is the loss of visibility of the critical path.

The first step in getting a Chain Critical schedule is to remove individual margins. Each task, as explained in the previous video, has a safety margin to prevent against possible hazards, in order to ensure that tasks complete all on time.

     You will often see in the literature that by practicing the Critical Chain we will divide the duration of the tasks by two. It is true that it is in certain writing and that you can obtain the Critical Chain like that, but we insist on the fact that this is not our way of doing things. Our method is to train people on the Critical Chain to understand the principles. Then they are not asked to commit to a delivery date of a task but they are asked a focused duration of completion of the task. That is to say, a duration of the task for which the actor has all the necessary information and is in ideal working conditions (no multitasking, no meetings ...). It must be emphasized that the duration requested is in no way a commitment but an average duration. There is therefore a 50% chance of going faster or slower than this duration. It is with this approach that we obtain significantly shorter times than the initially estimated times. It is possible to obtain a focused duration lower than the previously estimated durations because they generally take into account non-value-added operations such as multitasking, project management meetings, waiting of document validation, and so on.

      To succeed in planning in Critical Chain, we must also be able to estimate the variability of a task. Let's take two examples:

  • Stability test of a pharmaceutical product: 12 months in a refrigerator. This duration is not variable, it is a legal obligation.
  • Design of a new mechanical part. The variability is consistent depending on whether the piece looks like something pre-existing, which would require a few hours of plan modification, or on the contrary the specifications are more complex than what has already been done and it will take weeks to finish the design.

We therefore identify the focused durations and the variability associated for each task.

Let's go back to our initial planning, so we reduce the duration of the tasks and take into account the capacity of the resources by leveling the activities. A schedule is obtained without any safety margin taking into account the availability of resources. The next step is identifying the Critical Chain: this is the longest sequence of tasks that takes into account resource dependencies. The difference with the critical path is the consideration of resources. This definition of the Critical Chain is, however, very restricted. It is this task sequence that really determines the duration of the project, it is on it that we must work to improve the performance of a project.

The 4th step is to decide when to start the non critical tasks, the ideal is to plan them just in time, not at the earliest, nor at the latest.

The last stage of Critical Chain planning is fundamental, but only possible if the previous steps have been followed. Focused durations having only a 50% chance of finishing on time, the schedule as we built it has almost no chance of finishing on time if left as is. It is necessary to protect the project against the hazards, the probable delays which can occur on each of the tasks. For this we insert at the end of the project a "buffer". It is there to absorb the problems and delays encountered on the activities of the Critical Chain. It is calculated from the variabilities of the tasks of the Critical Chain. The advantage is the mutualisation of project protections. This is not the only buffer since auxiliary buffers are inserted whose function is to ensure that non-critical tasks do not jeopardize the Critical Chain. They are positioned everywhere where non-critical activities join the Critical Chain.

The Critical Chain plan obtained is both efficient and robust. Efficient because we reduced the duration of the tasks to obtain the focused durations, robust because it did not ignore the variability and protected from it with the buffers. In this way we go fast and we are protected from hazards. We thus have a very high probability of completing all the projects on time or even in advance.

Ta plan a portfolio of projects, if we want the whole to be manageable, it is better that each project is planned with the Critical Chain approach, so they all have a good probability of going well. These different projects can use the same resources, how to plan them together? This amounts to use the Theory of Constraints, and thus identifying the capacity constraint of the system. It is necessary to take into account the capacity of this constraint and to smooth the launch of the projects according to this constraint.

In conclusion if you roll out all these steps on one of your projects it can take time the first time. But planning will become more efficient and more robust.

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