HKSM

A schedule technique that accounts for resource limits and uncertainty by identifying the resource-constrained longest path and protecting it with buffers. It replaces individual task padding with project, feeding, and resource buffers to stabilize delivery dates. Teams then monitor buffer consumption to control the schedule.

Key Points

• Focuses on resource constraints, not just task logic, to find the longest chain of dependent work.
• Removes excessive safety from individual tasks and centralizes protection in buffers.
• Uses project, feeding, and resource buffers to absorb variability and protect the final milestone.
• Discourages multitasking and encourages tasks to start as soon as predecessors and resources are ready.
• Controls schedule performance by tracking buffer consumption rather than task float.

Purpose of Analysis

Build a realistic, resource-feasible schedule that can withstand variation without frequent replanning. Provide an early-warning mechanism through buffer usage so the team can act before the finish date is threatened.

Method Steps

• Create the activity network and preliminary critical path from dependencies.
• Estimate task durations with reduced safety (e.g., aggressive but achievable durations).
• Add resource dependencies and perform resource leveling to identify the critical chain.
• Insert a project buffer at the end of the critical chain sized by an agreed rule (e.g., 50% of total cut safety or statistical aggregation).
• Insert feeding buffers where noncritical paths feed into the critical chain.
• Add resource buffers or alerts ahead of critical chain tasks that need scarce skills.
• Baseline the schedule model and establish buffer tracking (e.g., fever chart).
• Execute and manage by buffer consumption, escalating when thresholds are crossed.

Inputs Needed

• Activity list, attributes, and dependency relationships.
• Duration estimates and uncertainty assumptions.
• Resource requirements, skills, and availability calendars.
• Organizational policies or heuristics for buffer sizing.
• Risk register entries affecting schedule variability.
• Historical data or team performance metrics to calibrate durations.

Outputs Produced

• Resource-feasible schedule model with the critical chain identified.
• Project buffer size and placement protecting the final delivery date.
• Feeding buffers on paths that merge into the chain.
• Resource buffers or notifications for key skill availability.
• Baseline schedule data and buffer tracking artifacts (e.g., fever chart).
• Updates or change requests if resource limits force sequence changes.

Interpretation Tips

• Green/Yellow/Red buffer zones indicate how much contingency remains before the delivery date is at risk.
• Rapid feeding buffer consumption signals potential impacts to the chain and the need to expedite or resequence.
• The chain may differ from the critical path because it includes resource constraints; do not rely on float alone.
• Use buffer trends to trigger action plans, not to penalize teams for variability.

Example

A data migration project has sequential extract, transform, and load tasks that all require the same database engineer. After leveling for that resource, those tasks form the critical chain. The team removes task padding and adds a 10-day project buffer at the end, plus 4-day feeding buffers on reporting and cleanup paths that merge into the chain. During execution, the feeding buffer begins to shrink quickly, so the manager brings in a second analyst temporarily to protect the project buffer.

Pitfalls

• Leaving safety inside tasks and adding buffers, which double pads the schedule.
• Oversizing or undersizing buffers due to arbitrary rules without data.
• Ignoring resource calendars and skill overlaps, producing an infeasible chain.
• Allowing multitasking that delays flow across the chain.
• Treating buffers as slack to be consumed rather than shared protection.
• Not tracking buffer trends, losing the early-warning benefit.

PMP Example Question

A project team removed individual task padding and then observed that noncritical work merging into the resource-constrained sequence is causing delays. What should the project manager do next using the critical chain method?

1. Increase durations of all upstream tasks.
2. Add or adjust feeding buffers where the paths merge into the chain.
3. Recalculate only the critical path without resources.
4. Insert additional float on the final milestone.

Correct Answer: B — Add or adjust feeding buffers where the paths merge into the chain.

Explanation: In critical chain, variability from noncritical paths is absorbed by feeding buffers before they affect the chain. Extending task durations or adding float to milestones defeats the method and may not be resource-feasible.