Schedules are critical to planning, coordinating, and managing a successful project. A reliable schedule equips a team to align performance goals and milestones. It also allows them to evaluate alternatives and make better-informed decisions. A schedule that integrates essential data such as budgets, costs, resources, and risks can support a comprehensive project control system. The benefits extend beyond coordination and planning, giving owners a valuable tool to document progress and support payment applications. A reliable schedule is critical in legal contexts, often providing evidence in claims for equitable adjustments.
However, a schedule is only as useful as it is reliable. A schedule that appears sound may, in fact, be manipulated to obscure float. Surface-level alignment of activities with the owner’s critical path may not hold up under scrutiny. Owner project managers must be aware of these risks, but analyzing them can require specialized tools and knowledge. Engaging professional schedulers to audit their schedules can help to identify and resolve unreliability before it derails a schedule.In this article, we’ll discuss factors that affect reliability in Critical Path Method (CPM) scheduling.
Key Areas for Schedule Review
Schedule Logic
Critical Path Method (CPM) scheduling determines the project completion date according to the relationships between activities. The “path” in CPM represents the sequence of activities from the project start to its finish, with the longest potential sequence, or path, used as the timeline for project completion. Disruptions that affect path continuity create an unreliable completion date. Float, or the buffer surrounding a given activity, is inherently variable and is a necessary part of project scheduling. This variability creates opportunities for manipulation in a variety of ways, as described below. Since float is typically owned jointly, it becomes critical that the owner check the schedule to protect against float manipulation in these otherwise innocuous scheduling techniques:
- Lags and Leads: Lag and leads are intentional delays inserted between tasks in a project schedule. These are an inherent part of the work process to accommodate activities such as the curing time for concrete. Lags can also be misused to suppress activity float and artificially place tasks on the critical path. This is particularly concerning when it affects owner activities. For instance, an owner activity could be manipulated onto the critical path, making its delay appear to threaten substantial completion—and shifting responsibility unfairly to the owner. Lags are hidden within the schedule, making them challenging to identify in large projects without specialized tools. To locate lags, one must examine every relationship in the schedule—an impractical task without software assistance. Scheduling tools like Primavera P6 can generate lag reports, though these reports are often not user-friendly or well-formatted. Owners must utilize such tools or request detailed lag reports to ensure transparency.
- Constraints: Date constraints impose fixed limits on activity start or finish dates, restricting the natural flow of the schedule and potentially disrupting the critical path. While constraints may be appropriate for contractually fixed dates, they should never replace proper logic. Excessive use of constraints can create gaps in the schedule flow, generate negative float, and distort the critical path. Constraints are visible in schedules, often marked with an asterisk (*) in the date column. However, reviewing their details requires examining specific tabs or adding relevant columns to the schedule report. Owners should ensure constraints are only used where required and do not undermine the schedule’s integrity.
- Open-Ended Activities: The sequence of activities forms the foundation of CPM scheduling. If an activity lacks a predecessor, it can start at any time, making it immune to delays in preceding tasks. Similarly, if an activity lacks a successor, it can finish without impacting subsequent tasks. Both scenarios disrupt the critical path and compromise the accuracy of completion forecasts. Identifying open-ended activities requires detailed schedule reports. Owners can request contractors to add specific columns to highlight such activities or provide the schedule’s native file for analysis. These issues are not visible in typical PDF printouts, so it is important to have native file access.
- Out-of-Sequence Progress: During execution, activities may progress differently than planned. While changes like these are common, the schedule must be revised to reflect the actual sequence. Failure to revise can produce inaccurate projections for the remaining work and project completion. Out-of-sequence progress is relatively easy to identify (at least in Primavera P6). Owners can use the native file to calculate the schedule using the contractor’s original data date, and review the schedule log to check whether there are any out-of-sequence instances. If out-of-sequence activities are present, contractors should revise the logic and resubmit the schedule. If the native file is unavailable, the contractor should provide a printout of the schedule log to verify that all progress aligns with the current logic.
Schedule Progress
Monitoring schedule progress throughout a project’s duration allows owners to keep track of the critical path to completion. Not all delays affect the project completion date—only delays to critical activities do. Regular reviews of a progress schedule can reveal potential impacts to contractor performance. Slower production on critical activities can lead the contractor to compress remaining activities to maintain deadlines on the schedule. This compression, while seemingly effective, may increase the risk of delays and compromise reliability if the revised durations and logic are unrealistic.
Progress schedules also reveal how float is being consumed, and they can alert owners to potential delays. Reviews can highlight stalled activities or underperforming tasks, providing invaluable insights to manage the project schedule. Assessing the float consumption and responding accordingly, with schedules revisions if necessary, can mitigate risk and cascading disruptions to the critical path.
Schedule Changes
Throughout a project, contractors often make changes to the schedule, such as adjusting sequences, durations, calendars, or activity lists. These modifications are usually necessary to reflect actual site conditions and progress. Certain characteristics, such as weather, labor market fluctuations, or other site nuances, are difficult to predict in advance. Some changes are virtually inevitable and are acceptable as long as contractors provide a clear explanation.
Owners should carefully review narrative reports to ensure changes are justified and assess their impact on the critical path. However, some changes may reduce a schedule’s transparency, complicating performance tracking and comparisons. Tracking changes in the actual dates or activity descriptions often requires professional tools and expertise. Engaging a professional scheduler can help owners leverage this expertise.
Schedule Submission Requirements
To fully utilize schedule progress reports, owners must ensure that contractors submit comprehensive documentation at the end of each update period. Key components include:
- Schedule Printouts: These provide basic details, such as activities, planned and actual dates, and total float. While printouts are a necessary component, they offer limited insight without accompanying documentation.
- Native Schedule Files: Native files allow owners to identify schedule logic, errors, and quality issues—and ensure schedules are accurate and reliable. Owners should require native files with every schedule submission.
- Narrative Reports: A narrative report is an integral, yet often overlooked, component of the progress submission. It should describe schedule risks, delays, changes, and recovery plans while explaining critical path performance. Any shifts in the critical path must be identified and justified in the report. Narrative reports enhance transparency and serve as crucial records for claims and disputes.
Owners must specify these submission requirements in contract technical documents. Without clear contractual mandates, owners may face challenges obtaining the necessary information or enforcing compliance.
Final Thoughts
Timely project delivery is a top priority for every construction project, and a reliable schedule is essential to achieving this goal. Owners must prioritize schedule management from the earliest stages, starting with detailed requirements in RFPs and contracts. During execution, they must enforce these requirements and ensure contractors adhere to them. Each schedule submission should be rigorously audited. In case of deficiencies, contractors must be required to make corrections and resubmit.
By maintaining a disciplined approach to schedule management, owners can strengthen project records, enhance transparency, and lower their risk if claims and disputes arise.
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