If your logic in Primavera P6 is correct negative float is a good thing. It actively reflects the true nature of the job. If however you feel, with consultation from construction that the logic is not correct then the correct approach is to change the logic. The old saying ”pay me now or pay me later” applies wherby if the logic is not fixed it will come back to haunt you.Group your schedule by Total Float, then Sort by Start for the correct flow of the logic.
Your top section of float will be your lowest float and you can trace it from the first activity down through the logic. If you have milestones or just one or two activities in your top path(s) look a bit further down in float paths to find the driver.
To adjust float you need to have correct status (in relation to the project) and then you may need to look at the possibility of overlapping activities (logic) due to out of sequence logic (from status).
Do this in steps:
1- Highlight if you’ve any hard constraints in place. Look for logic and get rid of them. (Hint: Filter is the best option to use)
2- Check if your project has Finish date set in its settings. Get rid of it, if it has and set it to about 6 months after you expect your project will likely to finish.
Surely negative float comes about because there is a restraint or restraints somewhere in a schedule that prevent or restrain the “correct” finish dates being shown and therefore generate negative float on the backward pass.
So the simple and correct answer is to go through the schedule in Primavera P6 and remove any finish restraints. This will generate an extended completion date or sectional dates but using these dates the critical items will have zero TF and all other non-critical activities should have a positive number for float.
I personally dislike negative float because it is the devil to explain to non-planning people. I prefer to let the end-date go out and record the variance.
Step by Step to analyze your most negative total float path (I do not use P6 “Longest Path” for large networks):
1. Remove or change any “Hard constraints” that prevent the logical float calculation from flowing, i.e. ON’s -Sta or Fin, ON OR BEFORE’s Sta or Fin and Mandatory Sta or Fins –You should maintain only one (1) major or interim L1 or L2 project milestone at the end of your path (to maintain the float negativity). All float calculations should be derived from this 1 project milestone. All other constraints should be “Soft constraints” Sta/Fin on or AFTERS or Expected Finishes
2. Verify all in-progressed activities in the negative path are accurate – Remaining Dur or Expected Fins, downstream logic relationships, interface constraint dates, etc.
3. Verify the non-progress schedule forecast negative path makes sense, i.e. the Activities, OD, Calendars, Logic relationships, interface relationships and constraints (if any).
4. Review the critical path with the project stakeholders who own/manage the tasks that reside within the negative path. Discuss your analysis with them and ask them to verify the PLANNED — activity tasks, durations logic and relationships (FS, SS, FF,) as well as any interface activities (engineering, material or other hand-offs) for accuracy.
Do not assume your Stakeholder understand schedule management. You can assist your stakeholder by making these suggestions:
a). Can any work task on the path and be performed on multiple or extended hours/shifts or weekends” (allows to edit the calendar for that task)
b). Can any work task on the path and be performed more efficiently by adding resources? (allows to reduce the duration)
c). Can any work task on the path performed in series be worked in parallel? ? (allows to change the logic sequence)
d). Can any interfaces pre-requisites be expedited? (allows for a change to a Start or Finish On or After date)
5. After Stakeholder response, perform corrections to the schedule network and re-calculate the project to determine the change to the refreshed negative float value.
NOTE: Iteration may be necessary — Go back thru steps 1-5 if possible.
6. If this does NOT solve your negative path issue then:
a). Perform a formal Risk analysis and mitigation plan with assumptions / actions clearly identified. Document ALL RISK ASSUMPTIONS/OPPORTUNITIES, i.e. expedite engineering, material, additional craft or critical resources, additional work hours, parallel work, etc.
b) Document all risks as a “Schedule Analysis and Risk Mitigation Plan” document. Review with them with your management and obtain agreementment. Then track the approved Risk Mitigation Plan until any recovery to the schedule is achieved.
c) Finally document any actions taken on from your Risk Mitigation Plan on a Schedule Risk Mitigation Log (if you have) for use in your future rebaseline or contract adjustments.
7. If steps above do not resolve the negativity then, you should formally document such to your project management. It is their responsibility to mitigate or accept the delay. Once a management decision is made, a new baseline should be established at an appropriate time.