Finish to Finish isn't Being Enforced - Why?

Question

Hi All,
I'm struggling...I have a task that needs to have a Finish to Finish (FF) relationship to a prior task because the task cannot finish before the first one finishes.  It was working fine until Actual Hours were entered. now the FF isn't being enforced
and I don't understand why.   It is allowing the task to finish months prior to the first task finishing.
Task Inspector doesn't show anything useful I can find, but if I delete the predecessor and then add it again, I get a warning:
but I don't think there's any conflict.  The task has no constraints on it, nor does the predesscor task.  Row 41 is the one I am speaking of specifically, it should have a FF with task 35, but you can see it's not enforced like the other tasks
that also have a FF with 35.  The difference are the Actual Hours on 41, which I understand will effect the Start, but shouldn't effect Finish.
What am I missing?
Thanks!

Answer 1

RichPM,
Yes, that's correct, once a task has started, the predecessor link still exists but it is as I said, null-and-void. Keep in mind that task dependencies define the dynamics of a schedule - how things will play out according to the original plan. The plan
remains dynamic until actual data drives a stake in the ground. Network logic continues to drive the schedule for any tasks that have not actually started.
I was going to use your tasks as an example but you apparently have some custom calendars that make it difficult to replicate your dates so I'll use a simple example. Let's say we have two tasks A and B that are set up with a finish-to-finish dependency.
Task A has a start date of 8/18/14 with a duration of 10 days and task B has a start date of 8/25/14 with a duration of 5 days. The start date of task B is driven by the finish-to-finish predecessor with task A so both tasks have a planned finish date of 8/29/14.
Task A starts on plan (i.e. 8/18/14). The resources were available to go ahead and start task B so an actual start of 8/20/14 is entered for task B. Since there is nothing that changed the duration of task B, it remains at 5 days, and that then pulls the finish
date back to  8/26/14, three days earlier than the finish date of Task A (8/29/14). Oops.
If both tasks must finish together, how do we fix this? There are a few ways, but trying to set up a finish-no-earlier-than constraint isn't one of them. We could simply extend the duration to 8 days but that will increase the work content. If the work content
must remain unchanged, we can edit the work or resource assignment level such that the desired finish date of 8/29/14 is maintained.
Note that if task A has a delayed start date, and task B has not been started, then the schedule dynamics will still be in effect and task B will slide out such that it still shows a finish date the same as task A.
Hope this helps.
John