Calculating and Executing the Forward Pass
The forward pass is an important part in creating the project’s schedule and constitutes the first step in constructing the network diagram and determining the critical path of the project, Calculating the critical path involves three sets of calculations: the forward pass, the backward pass, and the float calculations. The forward pass can be considered as the first chapter of the project manager's playbook for establishing a schedule. It is the most optimistic but realistic projection of the project's completion date and takes into account the time requirements of each task. A forward pass is used to determine the early start and the early finish for the project. The early start is the earliest point in time when a task can be started and is determined by resource constraints, including equipment and personnel availability. The early finish is the earliest point in time that a task can be finish. Calculating the forward pass is relatively easy and doesn't require any special math skills, but a project manager needs to have a farily good estimate of the time requirements for each task. A well-executed forward pass requires:
1. Determining the earliest time a task can start.
2. Adding the duration to the early start to calculate the early finish.
3. If there is more than one predecessor for a task, selecting the latest early finish as the early start for the successor task.
Here are a few illustrations that show how the forward pass works. In the first example of short forward passes, each task has a duration of five days and the critical path includes all five tasks. Task 1 kicks off the start of the project and is assigned the start time of Day 0. You can think of the Day 0 as the equivalent of a kickoff that results in a touchback so that the offense begins their possession of the project on the 20 yard line. In driving the ball through the schedule, the quarterback manager throws a series of forward passes moving from one task without delay making a first down on each drive. In this example, the quarterback manager reaches the end zone and scores on Day 25 with the completion of the project.
In this second example, the forward pass includes one instance where there are two predecessor tasks to Task 5. In order to calculate the early start for Task 5, the quarterback manager must determine the latest finish of the two predecessor tasks. In this schedule, the early finish of Task 4 must be used because it has the latest early finish date. When there are two predecessor tasks, it may be helpful to think of the forward pass as taking two plays to reach the first down marker.
If everything goes according the game plan, the quarterback manager can then shift into the role of spectator and watch the well-executed forward pass play out to the project's completion.