The Critical Path That Is Not the Longest Path
At a monthly review, the contractor reports the project 35 days behind and states the critical path runs through mechanical completion. The owner's analyst finds that the longest path actually runs through electrical commissioning, but that path carries 18 days of total float because of a finish-to-finish relationship and a 10-day lag. The contractor's report lists only zero-float activities as critical. Three calendars are in use: 5-day office, 6-day construction, and 7-day commissioning. A 12-day owner-caused review delay occurred on an activity that the contractor's report shows with 5 days of float. The steering committee wants to know whether the delay is on the critical path and what to report.
1. How should the analyst determine the true driving path and evaluate the 12-day delay claim?
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The zero-float filter is not a reliable definition of criticality when calendars and lags differ. The analyst should run a longest-path analysis, not a total-float filter, and trace the path with the greatest duration from the data date to completion. Then examine the finish-to-finish relationship and the 10-day lag: a lag can make a path appear to have float while still driving a successor's finish. Convert float into calendar days per calendar; 18 days of float on a 5-day calendar is not 18 calendar days on a 7-day commissioning calendar.
For the delay, insert a 12-day fragnet representing the owner review at the correct point, with the correct calendar, and rerun the schedule. If the review lies on the driving path in the relevant window, it may consume float and extend completion; if the path has genuine float after calendar conversion, the delay may be absorbed. The claim should be assessed with a contemporaneous time impact analysis, not by comparing total float on a summary report.
2. What should the report show to avoid misleading the steering committee?
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Report the driving path by name, with its activities, relationship types, lags, calendars, and float in calendar days. Show the near-critical paths, say those within 10 days of the longest path, because the 18-day float path may become critical after the delay. Separate the baseline, current plan, and forecast, and explain the 35-day variance by cause rather than a single number. Present a path table or time-scaled logic diagram and include a sensitivity check: what happens if commissioning slips or the review delay repeats.
Avoid labeling only zero-float activities as critical; define critical as the longest path and state that definition. The committee should see the delay's effect on the forecast and remaining float, not just a claim that the critical path runs through mechanical completion. This prevents the report from steering decisions toward the wrong trade.