chain scheduling is a process of planning and managing projects that emphasizes
the resources. These resources are people, equipment or physical space required
to accomplish a project. The process was developed by Eliyahu M. Goldratt. A study by the Standish group in their Chaos
report says that 31.1% of projects are cancelled before they are finished and
above 52% of projects after completion will cost 189% of their original
estimated cost. “According to Dr.
Eliyahu M Goldratt, projects fail to execute within the committed time and
budget despite the fact that the commitments themselves contain significant
contingencies because the existence of such contingencies leads to specific
behaviors by members of the project team” (Robinson
& Richards, 2009). Dr.
Goldratt developed a management philosophy call the Theory of Constraints (TOC)
that will help improve these statistics.
The TOC suggests that any complex systems has a constraint that will
limit its ability to complete its goal and that constraint must be identified
and managed with that in mind (Schwalbe, 2014). “Critical chain scheduling is a method of
scheduling that considers limited resources when creating a project schedule
and includes buffers to protect the project completion date” (Schwalbe, 2014).
chain scheduling looks to eliminate various scheduling issues such as, student
syndrome, Parkinson’s Law, and multi-tasking that is plaguing projects. Student syndrome is the classic case of a
student who waits until the semester is almost over to start working on their
term paper. (Robinson & Richards, 2009)
Parkinson’s Law states that work expands to fill the time allowed to complete
the task. Multi-tasking occurs when a resource works on more than one task at a
time. Critical chain scheduling manages
these issues by first determining precedence for all the project tasks. It first identifies the critical chain of
the project, aggregates uncertainty allowances into feeding buffers and keeps
the schedule fixed during project execution.
It requires early reporting of completion of task and uses buffers as a
warning mechanism during project execution.
chain scheduling uses two types of buffers to manage a project’s schedule. They
are feeding and project buffers. The
default procedure to figure out the project buffer is to use 50% of the
projected project duration. The feeding
buffer is half the duration as the longest non-critical chain path leading into
it. Feeding buffers are inserted into
the critical chain whenever a noncritical activity joins the critical
chain. The project buffer is added to
the end of the project to protect promised due date. As tasks in the project are being executed,
the project is managed by using the buffers as a proactive warning sign. Project managers should keep track of buffer
consumption as tasks are completed. As
long as a predetermined portion of the buffer remains buffer consumption is
only in the green everything is assumed to be going well. Once the buffer moves past a certain point, you
begin to plan contingencies to get the project back on track. If the buffer consumption gets past a
critical point, you put your contingency plan into operation to get the project
back on track. (Herroelen, Leus, &
fundamental merits of critical chain scheduling are that it explicitly
recognizes interactions between activity durations, precedence relations,
resource requirements, and resource availabilities that determines the project
duration (Herroelen, Leus, & Demeulemeester,
2002). Critical chain scheduling is a powerful tool that helps to
eliminate or at least minimize the negative outcomes that plagues the project
execution. It allows project managers to
achieve their goals regardless of the project levels of complexity,
interdependency, or uncertainty of the environment. If use correctly, critical chain scheduling
will result in reducing the number of project failures and improve a project
schedule, budget, and scope.
Herroelen, W., Leus, R., & Demeulemeester, E. (2002).
Critical Chain Project Scheduling: Do Not Oversimplify. Project Management
Robinson, H., & Richards, R. (2009). An Introduction to
Critical Change Project Management. AACE interanational Transactions,
Schwalbe, K. (2014). Information Technology Project
Management. Boston: Course Technology Cengage Learning.