We received a question from a scheduler who was having difficulty specifying Terminal Float without the associated activity constraint inducing critical path discontinuities. Let’s take a look at what’s going on.
What Is Terminal Float?
Terminal Float has been defined as the difference between the current project end date and the Contract Completion Date (CCD). Our inquiring schedulers project sponsor apparently wanted a separate line item for the CCD, so the Terminal Float is clearly displayed in the schedule. The problem: when the CCD is inserted as an activity constrained line item, it causes critical path fragmentation. The scheduler wanted a way to compute the Terminal Float and retain a continuous longest path from project start to conclusion.
This article demonstrates insertion of a CCD line item and constrained activity in a way that avoids critical path fragmentation and computes the Terminal Float.
Below in Figure 1, we have our demonstration project schedule in Primavera P6.
The conclusion of the project is the ‘Project Complete’ finish milestone. We want a separate line item for the CCD. Proceeding we rename ‘Project Complete’ as ‘Current Project Completion’. Then we add an activity after ‘Project Complete’ named CCD, Figure 2.
To hold the milestone at the proper contract completion date we constrain it with a 16-Apr-2024 activity constraint. See Figure 2. Unfortunately, when the CCD activity is constrained, we lose the critical path, Figure 3.
To recover our critical path, we insert an FF relationship between ‘Project Complete’ and CCD. This by itself does not regain the critical path but when we insert a relationship lag on the FF equivalent to the Total Float separating ‘Project Complete’ and CCD, Figure 3, the critical path is retrieved. Proceeding we insert a 6-day Lag between ‘Project Complete’ and CCD, Figure 4, which was the Total Float of ‘Project Complete’ in Figure 3.
The Total Float of ‘Current Project Complete’ becomes zero. As displayed in Figure 5, we have a continuous critical path and constrained CCD activity finish milestone.
The Terminal Float is equivalent to the 6-day Lag separating ‘Current Project Completion’ and CCD, Figure 5. What happens when a critical activity in the schedule is extended 4-days? Well, that delays ‘Current Project Completion’ by 4-days generating 4-days negative Total Float on ‘Current Project Completion’, Figure 6.
We adjust the Lag between ‘Current Project Completion’ and CCD until the Total Float becomes zero, Figure 7.
The resulting Lag separating ‘Current Project Complete’ and CCD is 2-days, which again, is equivalent to the Terminal Float. The schedule updates therefore result in 4-days Terminal Float erosion. The final Terminal Float, again, is 2-days.
It is possible to insert a constrained Contract Completion Date in a way that does not create discontinuities in the schedule. The remedy is the insertion of Lag equivalent to the separation between the Current Project Completion milestone and Contract Completion Date milestone.
This Lag is also equal to the Terminal Float.
When duration estimates are modified and/or progress scheduled, the Total Float of the Project Completion Date activity skews from zero. Adjust the Current Project Completion FF Lag to reset its Total Float to zero. Then the resulting Current Project Completion FF Lag is the updated Terminal Float, as per the schedule updates.