HKSM

A schedule analysis technique that models activity dependencies and durations to calculate the longest path through the network. It identifies early and late dates, total float, and the activities that drive the shortest possible project duration.

Definition

Definition is provided above.

Key Points

• The critical path is the longest path through the network and determines the shortest possible project duration.
• Activities on the critical path typically have zero total float; any delay on them delays the project finish.
• Forward and backward passes compute early and late dates and total and free float.
• Basic CPM assumes unlimited resources; resource leveling can change the critical path and finish date.
• Negative float usually signals infeasible dates or hard constraints that require action.
• Multiple critical or near-critical paths increase schedule risk and require closer monitoring.

Scheduling Objective

Determine the project end date by identifying the longest path of dependent activities, and reveal where schedule flexibility exists. Use this insight to focus control on critical and near-critical work and to evaluate options to compress the schedule when needed.

Method Steps

• List activities and define logical relationships, including leads and lags.
• Estimate activity durations and apply appropriate calendars and working time.
• Build the network diagram showing nodes and dependencies.
• Perform a forward pass to calculate early start and early finish dates.
• Perform a backward pass to calculate late start and late finish dates.
• Compute total and free float; identify the critical path(s) with zero total float.
• Review near-critical paths and consider schedule compression options such as fast-tracking or crashing if needed.
• Update and re-run CPM when estimates, sequencing, or actual progress change.

Inputs Needed

• WBS, activity list, and activity attributes with defined predecessors and successors.
• Duration estimates and basis of estimates, including assumptions and uncertainties.
• Project and resource calendars, working time, and any leads or lags.
• Constraints and target dates such as deadlines and milestones.
• Risk information that may affect durations or sequencing.
• Resource availability data if you plan to level or limit resources after CPM.

Outputs Produced

• Schedule network diagram with calculated early and late dates.
• Total and free float for each activity.
• Identified critical path(s) and near-critical paths.
• Projected project duration and finish date under current assumptions.
• Schedule data that can feed bar charts, milestone lists, and reports.
• What-if analysis results for potential compression or sequencing changes.

Constraints

• Accuracy depends on realistic activity definitions, logic, and duration estimates.
• CPM uses single-point durations; variability is better handled with techniques like PERT or simulation.
• Resource limits are not resolved by CPM alone; leveling may alter the critical path and duration.
• Hard date constraints and calendars can produce negative float and override logical dates.
• Networks with many merges or parallel paths can create multiple or shifting critical paths.

Example

Activities and durations (days): A 2d (start), then B 4d after A, C 3d after A, and D 2d after both B and C.

• Path A-B-D = 2 + 4 + 2 = 8 days.
• Path A-C-D = 2 + 3 + 2 = 7 days.
• Critical path is A-B-D with duration 8 days; A, B, and D have zero total float.
• C has 1 day of total float because its path is 1 day shorter than the critical path.

Pitfalls

• Ignoring resource limitations and assuming the CPM result is executable without leveling.
• Using optimistic or unvalidated duration estimates, leading to unreliable paths.
• Failing to re-run CPM after scope changes or progress updates.
• Overlooking calendars, leads, and lags that materially affect dates and float.
• Focusing only on the critical path and neglecting near-critical paths that can become critical.
• Misinterpreting total float as free time without checking impacts on successors and constraints.

PMP Example Question

During schedule analysis, you find a path with -5 days of total float due to a fixed finish date. What should you do next?

1. Add resources randomly to activities on the path to eliminate the negative float.
2. Switch to a different estimating method such as PERT to remove the constraint.
3. Evaluate schedule compression options on the constrained path or negotiate the finish date with stakeholders.
4. Ignore the result because it is likely a tool error.

Correct Answer: C — Evaluate schedule compression options on the constrained path or negotiate the finish date with stakeholders.

Explanation: Negative float indicates an infeasible date given current logic and durations. Address it by compressing the constrained path or by revising the constraint through stakeholder discussion.