The goal of good project managers is to complete the project in as little time as possible. To help achieve this goal project managers will constrain tasks in forward scheduling to begin As Soon As Possible (ASAP). But there are times when an As Late As Possible (ALAP) constraint on an activity better adheres to the true project situation.
Constraints are additional restrictions placed on tasks to further describe the importance of a particular date in the life of the project. Constraints come in two flavors: soft or hard. Soft constraints can be overridden by network logic and will not generally create negative total float. Hard constraints have the potential to create negative float, and some hard constraints will even violate network logic.
Both ASAP and ALAP are soft constraints. Neither has an associated constraint date. In forward scheduling an ASAP constrains the task to begin the first allowable day, as per network logic. The ALAP constraint burns all available total float before commencing the task. The ASAP constraint gets the work done earlier and has the total float as a buffer for any delays occurring during task execution. The ALAP constraint in forward scheduling is the exception, but may be required to better describe the true schedule situation.
This article describes the insertion of an ALAP constraint in Microsoft Project and below, we have in Figure 1 our demonstration project schedule.
This schedule depicts a gear manufacturing project. The ideal material delivery for this project is just-in-time manufacturing where the material delivery coincides with commencement of manufacturing. After material selection it takes 4 business days for order and delivery of material. The default constraint for tasks in Microsoft Project is ASAP. The material delivery is scheduled to commence immediately after material selection, Figure 1. In this situation the material arrives on site 4 business days earlier than required. Note the gear manufacturing August 20th start date, which is defined with a Must Start On constraint.
Our ideal delivery is for receipt of material on the morning of August 20th, just prior to gear manufacturing. With an ASAP constraint on Material Delivery we have 4-days total float or our material arrives 4 days earlier than ideal. To remove the total float, so material delivery coincides with gear manufacturing change the constraint type of material delivery to ALAP. To do this display the constraint type column in the task table and select “As Late As Possible” from the drop down menu for material delivery, Figure 2.
The resulting schedule is displayed in Figure 3.
Total float has been removed and Material Delivery occurs on Friday evening and manufacturing gears takes place the next working day, Monday morning, August 20th.
The default constraint in Microsoft Project is ASAP. This is the ideal for most forward scheduling situations. There are times, however, when a Project Manager would want to delay a task so that its completion coincides with a successor task, most likely a date constrained task.
The ALAP possible constraint burns total float to align the completion of a predecessor task with the commencement of its constrained successor. And if the successor constraint date changes Microsoft Project automatically updates the commencement of the ALAP predecessor activity, accordingly.