In an ideal world, activities in a schedule should progress according to the activity network logic. However, activities are sometimes performed out-of-order and in a way that violates these activity relationships. No matter how good the schedule logic might be, when the work gets started all manner of unforeseen variables come into play and it becomes necessary to do things in a different sequence in order to keep the project moving forward. The question is how do we handle these out-of-sequence activities in Primavera P6 as we progress the schedule?
When activities are performed out-of-Sequence the fundamental relationships that define the schedule are ignored. An out-of-sequence activity may have a negative impact on the quality of the deliverable, i.e. the end product.
This article discusses procedures for handling out-of-sequence activity schedule progression using Primavera P6.
We have in Figure 1 our demonstration schedule.
Figure 1
This is a basic underground pipe installation project schedule. This schedule has three main activities excavate trench, lay pipe, and insulate pipe. The relationship between each activity is finish-to-start (FS), which stipulates that the predecessor activity must completely finish before beginning the successor activity.
When we schedule our project we have three options for how we want Primavera P6 Professional to handle out-of-sequence activities: retained logic, progress override, and actual dates.
Retained Logic
In retained logic the successor activity maintains its adherence to the predecessor-to-successor relationship in the precedence diagram even though the successor commencement violated this logic. Without going into great detail we want to set the schedule options to retained logic, so at least the remainder of the successor activity holds true to the predecessor-to-successor relationship. Refer to the following blog Options for Handling Out-of-Sequence Progress in Primavera P6 for a more in-depth discussion on the out-of-sequence activity schedule options.
In Figure 2 we progress the schedule one week.
Figure 2
Both Dig Trench and Lay Piping start in week one. Note that even though Dig Trench is an incomplete predecessor to Lay Piping in a FS relationship, Lay Piping has begun. Lay Piping has begun out-of-sequence. The schedule log file, Figure 3, warns of this out-of-sequence Lay Piping activity.
Figure 3
Its remaining duration though honors the FS relationship with the predecessor Dig Trench.
We progress the schedule another week in Figure 4.
Figure 4
No progress is logged on Dig Trench and Lay Piping is complete. This makes no sense. You absolutely must finish Dig Trench before you can complete Lay Piping. This is a real problem. But notice also that Insulate Piping does not commence immediately after the completion of Lay Piping. Insulate Piping has a FS relationship with Lay Piping and should commence on the completion of Lay Piping. However, Insulate Piping is pushed back by the unsatisfied FS relationship between Dig Trench and Lay Piping. So the out-of-sequence Lay Piping activity negatively effects both its predecessor and successor activities. Well, our schedule progression has turned into a real mess, and the integrity of the entire project schedule is now in jeopardy.
How do we remedy this out out-of-sequence activity situation? Well, we have to go back to before our first week of progress when the out-of-sequence event occurred, Figure 1. We need to reassess our FS relationship between Dig Trench and Lay Piping. It is apparent from our schedule progression that the true relationship between Dig Trench and Lay Piping is not FS; it is start-to-start (SS). Redefine the relationship between Dig Trench and Lay Piping to include a SS and 2-day lag, Figure 5.
Figure 5
We also include a FF relationship between Dig Trench and Lay Piping, so any delay in Dig Trench delays the completion of Lay Piping, again, Figure 5.
Let’s now progress the schedule again one week, Figure 6.
Figure 6
We clearly see on the Gantt chart that no relationships are violated after progressing the schedule one week. We also note in the log file that there no out-of-sequence activities, none, Figure 7.
Figure 7
Great! We have a progressed schedule with no relationship violations. Further, our log file documents that no activities are out-of-sequence. We now have a progressed schedule we can have confidence in.
Summary
Progressing the schedule Primavera P6 in a way that stays true to the schedule situation may become a tedious process. Follow these steps to update the schedule
- Progress the schedule with the stipulated updates
- Examine the log file for any out-of-sequence activities
- If out-of-sequence activities are present in the schedule return to the non-progressed schedule
- Reassess the relationship where the out-of-sequence activity occurs. Your schedule adjustment may be as simple as replacing a FS relationship with a SS and Lag
You will need to review the respective relationships with a stakeholder intimately involved in the project and schedule creation. Yes, this process requires meticulous attention to detail and good communication, but it results in a schedule that is certified and conformed to the true project schedule situation.
So, progressing your Primavera P6 schedule in a way that stays true to the schedule situation may require more effort than at first anticipated. Making these logic adjustments is also good for the historic record as it may be true that a more efficient way of working has been worked out on site – and as a scheduler you’ll probably want to model that method again in the future.