“I feel the need; the need for Leads!”
Leads (Negative Lags) are generally regarded as a bad thing when it comes to “Best practice” scheduling. So if you feel the need for leads, get over it. The Defense Contract Management Agency (DCMA) 14 point assessment documentation states that Leads “distort float and may cause resource conflicts and distort the critical path”.
However, as schedulers we often see situations where a “Lead” would appear to be a good option to model the situation on the ground.
This article discusses the situation where a “Lead” would appear to be the answer, and explore alternatives to using them to stay within generally accepted scheduling guidelines.
The need to use a Lead is typically felt when something has to happen at some given time prior to the completion of an activity. However, it’s another one of those best practice conundrums: I shouldn’t use Leads: long Lags are also not good, and a constraint is also discouraged. So how do I model something that’s really happening on the ground when I’m being hobbled by such guidelines? On the face of it this appears to be a fair question, but there is nearly always a way forward that will keep everyone happy – including the DCMA.
In the following example the contract states that the Turnover Package (TOP) be issued 30 days prior to the completion of construction. Therefore a Finish to Finish or Finish to Start relationship with a 30 day negative lag would appear to be a good option. We can’t be sure of the completion date of construction, but whenever that might be, we need to issue the TOP 30 days before it does finish.
Above: with a negative lag of 30 days, the Issue TOP milestone is tied to the back of the Construction activity using a Finish to Finish relationship. While it works, it’s considered bad practice.
Some guidelines offer the suggestion of using a Start to Start relationship with a lag as an alternative to the Lead option. While this may work for some situations, and is definitely a better option, it is still not ideal for our situation. Because we don’t know exactly how long construction will take, we may find ourselves having to maintain the lag to keep the TOP milestone within 30 days of the construction end date; we now have to manage the variable with this lag option.
Above: the variable in activity duration will mean the need to maintain and update the Lag value to keep within 30 days of the end of construction.
Best Practice Example
So how do we lock down the 30 day delivery of the turnover package if neither a negative or positive lag is an option?
The answer is to introduce a 30 day duration activity and tie that in to the schedule between the end of construction with a Finish to Finish relationship, and the Issue TOP Milestone with a Start to Start.
You might be tempted to call this a “dummy” activity, but really it isn’t, nor should it be. During this time in our example, the 30 days is needed to populate the turnover package with all the pertinent data items, so we’ve called it Populate TOP.
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