In support of completing a project on time, project managers will normally schedule activities to commence as soon as possible (ASAP). However, there are times when project sequencing and timing dictates that a particular activity commence as late as possible (ALAP). Let’s investigate this situation.
Both ASAP and ALAP are soft or tendency constraints. Soft constraints do not have a date restriction associated with them, and, therefore, allow the greatest flexibility. Even though they do not have a constraint date, soft constraints may have a tremendous constraining impact on the schedule.
If you are using forward scheduling where you schedule from the project start date you will want to have ASAP as your default task constraint type. This ensures that the majority of your tasks will start ASAP, and minimize the risk of schedule slippage. You may, however, have exceptions where it just makes more sense for a task to commence ALAP. So in forward scheduling ALAP constraints are the exception, but, never-the-less, may have a positive constraining impact on the schedule.
Important Note: Although not everyone resource levels, it is worth noting that the ALAP constraint is ignored when resource leveling.
This article describes why and how to insert an ALAP constraint in Primavera P6 Professional.
As mentioned above, there are situations in forward scheduling where an ALAP project constraint makes good sense. This is the case for lighting a birthday cake. In this simple example, logic says your guests have arrived so you can light the candles. However, you really want to delay lighting the birthday cake candles until later. To keep the candle flames from burning down to the frosting you would schedule lighting the birthday cake ALAP, perhaps, to just before opening the presents.
Another example is a moving project where you schedule computer equipment packing ALAP to put it just before the move. Just-in-time manufacturing is another example where you do not stock inventory, but parts are manufactured as material arrives on site. Here the delivery of manufacturing material is delayed ALAP. Ideally you would want the delivery date to coincide with the commencement of manufacturing, which is not always a realistic goal in reality. If these examples are not sufficient one more says to delay training ALAP until just before the students apply the training to their work, so they do not forget the training in the down time between training and implementation.
Let’s proceed with a demonstration project, Figure 1.
Here we have a Gear manufacturing project. Again, the ideal is for the material delivery to coincide with commencement of manufacturing in just-in-time practice. After Gear Material selection the material is ordered. It takes four days for material delivery.
Note that the default for Primavera P6 Professional is ASAP, which they refer to as none, so our Material Delivery commences immediately after material selection, Figure 1. We see from our schedule that this causes the material onsite delivery to occur several days before manufacturing begins. Note that the Manufacturing Gears has a ‘Start On’ primary constraint set for March 14th.
We want our manufacturing material to arrive just before commencement of manufacturing. Because with an ASAP primary constraint the material delivery has free float and comes in too soon we want to switch the primary constraint of material delivery to ALAP. This can be done two ways. One way is to highlight Material Delivery in the activities table and select the Status tab in the bottom details, Figure 2.
In the constraints section select ‘As Late AS Possible’ from the drop down menu. Another way selects ‘As Late As Possible’ directly from the Material Delivery Primary Constraint drop down menu in the activities table, Figure 3.
Either way works. Recalculate the schedule and the ALAP constraint removes the total float and/or free float, so that the material delivery occurs on Friday evening and the Manufacturing Gears takes place on the next business day, Monday morning, Figure 4.
Although the default in Primavera P6 Professional is no primary constraint the reality is that the default actually is an ASAP primary constraint. This works well for most situations in forward scheduling.
However, there are times when a project manager wants to actually delay an activity until the last possible moment, logic permitting. This is when the ALAP primary constraint comes in handy.
Though the ALAP primary constraint is a soft constraint and rather flexible it will remove total float and/or free float to better align the completion of a predecessor activity with the commencement of a successor activity. The ALAP primary constraint is helpful and definitely has its place in the toolkit of Primavera P6 Professional constraints.