Total float is a measure of how long an activity may delay without delaying the entire project. Positive and zero total float are acceptable. Negative float, however, means your schedule is already behind, which is not good if you’re still at the planning stage.
The Defense Contract Management Agency (DCMA) 14-point assessment inspects project schedules to promote their success. Most typically the DCMA is involved with larger government contracts over a value of $20m and these assessment points are tested on an earned value management integrated master schedule; which is the context in which this series of DCMA 14 point assessment articles is written.
The negative float assessment notes the number of incomplete tasks with negative float. The negative float assessment fails if any task has total float less than zero. Tasks that have negative float should have an “explanation and a corrective action plan to mitigate the negative float”. So the DCMA negative float assessment supports negative float monitoring and respective adjustments to eliminate any vestiges of negative total float in the schedule.
Total float, also referred to as total slack, is computed from the forward and backward network passes and its value is the Late dates minus the Early dates. Total float is a property assigned to each task or milestone in the schedule. Total float values can be positive, zero, or negative numbers in days.
A positive total float task may slip according to the value of its positive total float. Yes, positive total float is good. It’s what project managers are hoping for. It is like a built in safety margin. It means you may delay an activity, accordingly, and not affect an activity constraint date or the project completion date.
Zero total float tasks require attention. When a task has a zero total float value, the task cannot slip at all. Any delay on a zero total float task means you will miss either a target activity constraint date or the project completion date. Not good! But the longest path through the schedule network are all connected tasks that have zero total float. So zero total float activities are not necessarily bad; they tell you the duration of the project schedule. However, as noted, zero total float tasks require attention; they do not have a delay safety margin or buffer.
Negative total float tasks are your warning something is amiss in the schedule. Negative total float tasks indicate probable failure to meet one or more schedule target completion goals. Negative total float means you are in danger of delaying an activity constraint date or the entire project. And a negative total float value is generated on every task that is linked in the potential target date failure. This is good, because it tells you which activities require optimization adjustments to realign the schedule in keeping with target dates.
Okay, you have monitored your schedule and found negative total float activities. How do you mitigate this negative float? Well, again, your negative total float tasks are warning you that your schedule duration in light of desired completion dates is too long. And implementation of the schedule as is will result in missing these target dates. There are a number of optimization efforts schedulers can implement, which will shorten the schedule and remove negative float. Below is a list:
- Fast Track – Make sequential activities parallel.
- Fast Track – Make sequential activities partial dependencies.
- Crash – Add resources to respective activities.
- Duration Estimates – Review and look for “padding”.
- Lag Estimates – Review and confirm the needed lag time.
- Long Duration Tasks – Consider breaking up and fast tracking the resulting elements.
- Scope – Remove nonessential scope, and associated tasks.
- Constraints – Review date constraints.
- Buffer – Consume schedule risk buffers or margin.
- Relief – Ask for delivery date contractual relief.
Refer to the blog To Shorten The Critical Path for a detailed explanation on these schedule duration optimizing alternatives.
The normal condition of successful projects are zero or positive float tasks. Again, the zero float tasks reveal your critical activities and longest path. Positive float is great; it’s like having a built in safety margin, which allows for unpredictable delays. Negative float tasks, however, indicate that your schedule is already behind, and target dates cannot be achieved.
The DCMA negative float assessment (which is run against schedules in the late to completed planning stage, fails any schedule that has negative float tasks. The negative float assessment further specifies that negative float activities should have an explanation and a negative float corrective action plan.
The implication here is that the schedule is approved pending implementation of the negative float mitigation action plan. So consider the many ways to optimize your schedule to limit negative float, and develop your negative float mitigation action plan for review.