Why might my critical path be disappearing

Home Forums Microsoft Project Discussion Forum Why might my critical path be disappearing


Viewing 7 reply threads
  • Author
    • #454910
      dan schaeffer

      I’m looking at my critical path (which, does not extend all the way back to the start of the project, but it does run from Aug 2020 – July 2021) using the Critical filter and everything looks reasonable; I see a chain of Total Slack = 0 tasks going to the end of the project. When I use the ‘Update Tasks’ dialog to extend the ‘remaining duration’ of one of those critical tasks (which is in progress), most of the tasks in the critical path fall off (i.e. their total slack becomes non-zero).

      What are some reasons this might be happening? Everything in my critical path is ASAP constraint type.


    • #454961
      Daryl Deffler

      I don’t know that I can provide an answer yet but here are a few questions that might help anyone wishing to chime in.
      1) Is your schedule set up to automatically reschedule tasks when a change is made?
      2) Did you re-level the schedule after the change?
      3) Did you make any other schedule changes at the same time, for example shifting work from one resource to another, increasing assignment units, etc.
      4) Are you scheduling current date to end of project (forward) and not end of schedule to current date (backward)?
      5) Did the critical path re-route to another task sequence or simply disappear?
      6) Did you break any dependency links between tasks on the critical path?
      Some of these question may also hint at something to look at in the schedule and indirectly provide an answer.
      hope this helps start the discussion

    • #455096
      dan schaeffer

      I ‘solved’ my problem but I’m really having a hard time wrapping my head around the explanation. I have some fundamental misconceptions about Task Type which has caused me a lot of grief.

      I have 2 tasks assigned to different resources both nominally of 2 wks duration with task type of Fixed Units- One was 80 hrs and the other 16 hrs. Both have identical predecessors. Though they are nominally 2 weeks in duration the 16hr task appears a tiny bit longer on the gantt chart and has zero days of slack. It’s doppleganger has 1 day of slack.

      Five predecessors upstream in the critical path I extended the duration of a fixed duration, critical, task by a single day and everything between that extended task and the 16 hr task gained a non-zero slack and, thereby, was dropped from the critical path. Everything in that chain had an ASAP constraint type.

      I’m struggling to understand why the intervening 4 tasks gained non-zero Total Slack values. Converting both tasks to fixed duration restored the Total Slack values for those 4 tasks to zero.

      I would love it if someone would do a deep-dive webinar on critical path puzzles like this.


    • #455097
      Thomas Boyle

      Hi Dan, Care to share your schedule? It sounds pretty interesting. Based on a quick read-through, I’d suspect issues with variable calendars. I remember being a fan of fixed-duration tasks when I started using MP for hard project scheduling, having had some years of P3 experience prior. Over time, however, the love faded. Fixed duration tasks in MP seem to be made using a collection of exceptions to the default rules; they constantly surprise me.

      For most people, critical path analysis in MP is a hostage to the total slack calculation, which itself is a hostage to early and late date calculations that may not be carried out the way you expect…. Progress reporting, resource leveling, and variable application of calendars certainly complicate things…. Good luck tom

      • #455484
        dan schaeffer


        Apologies if this is a duplicate post. I’d swear I replied earlier but I see no trace of it.

        >>I remember being a fan of fixed-duration tasks when I started using MP for hard project scheduling, having had some years of P3 experience prior. Over time, however, the love faded.

        I was originally a fan of fixed unit tasks but Oliver Gildersleeve’s https://www.mpug.com/webnlearn-update-better/ webinar convinced me to favor fixed duration. Should I conclude from your comment above you’re now a fixed-units fan?

    • #455122
      dan schaeffer

      I’d be happy to. What’s the mechanism for sharing?

    • #455161
      Thomas Boyle

      I’m not a member here. Check for an email from me with contact info – hoping I parsed your address correctly from your profile.

    • #455787

      Hi Dan, There are exactly 7 possible causes of an incomplete Critical Path:
      1) Incomplete Network Logic
      2) Constraint Dates
      3) Elapsed Durations or elapsed lags
      4) Resource Calendars
      5) Task Calendars
      6) External Predecessors
      7) Workload leveling
      Or any combination of these. If you are interested in a detailed explanation of why these features in Microsoft Project can ‘break’ your Critical Path and how you cna repair a broken Critical Path, please order a copy of my textbook ‘Forecast Scheduling’ on http://www.projectprocorp.com

    • #455834
      Thomas Boyle

      Hi Eric,
      It was number 4. Personal vacations delayed the starts of a couple critical-path tasks, and that pushed out the late finishes of their predecessors. The result was 1 and 2 days positive total slack along the first 2/3 of the driving path to project completion. BR, tom

Viewing 7 reply threads
  • You must be logged in to reply to this topic.