Forum Discussion
Finish-to-Finish constraint not allowing representation of early start.
That's better, or at least it now makes more sense.
As set up the predecessors for 'Task A' effectively determine when 'Task A' can start. The driving dependency is the finish-to-finish with 'Task D'. A finish-to-finish dependency means that 'Task A' CANNOT be completed until, in this case, 'Task D' is complete. There is no conflict with the finish-to-start relationship with 'Task B' since that dependency means that 'Task A' cannot start until 'Task B' is complete. It does NOT mean that 'Task A' will start immediately after 'Task B' finishes.
I note that tasks 'C' and 'D' have start-no-earlier than constraints but the start of 'Task B' is apparently defined by the Project Start date. If there is some flexibility in when 'Task B' starts then this dependency configuration will get what you want.
If that doesn't work in your situation, then the only way to have 'Task A' start immediately after 'Task B' finishes is to remove the finish-to-finish relationships.
John
You have not asked a question, but you seem to expect that MS Project's scheduling algorithm will treat task durations as elastic. It does not. While task duration can be made to automatically respond to resource assignments, it is rigid for the schedule calculations. Consequently, the ES-EF and LS-LF intervals must equal the duration. As a result, the ES of your task A is pushed out as needed for the EF date to satisfy the more stringent FF restraint from tasks C and D.
Elastic durations were allowed in early CPM scheduling software, but the introduction of non-FS relationships and extensive resource-loading makes for a lot of complications.
Most importantly, elastic durations are anathema for efficient resource use. E.g. assume your task A's optimal duration has been estimated on the basis of a large machine and crew working for two weeks, but task B finishes four weeks before the finish of either C or D. You may start work on Task A immediately after B finishes (your expected early start), but the crew will soon need to slow down or interrupt work to avoid violating the later constraints. Productivity suffers. MS Project (like other modern scheduling tools), delays the early start of Task A until a clear path of uninterrupted progress to its completion exists - i.e. two weeks before the completion of tasks C and D.