INFO6007 Chap.4 Schedule Networks, PERT and Critical Path
Schedule Networks, PERT and Critical Path
This chapter turns WBS work into activities, dependencies, duration estimates and a controlled schedule. Network analysis comes before visual presentation because it reveals the path that determines completion. PERT represents uncertainty, forward and backward passes determine timing, float identifies flexibility, and compression decisions focus on critical work rather than simply busy work.
Activities must follow logical predecessors and use realistic calendars, resources and external approval lead times. The longest valid path controls the earliest finish, even when another path contains more activities. Forward and backward passes reveal early and late timing, while total float shows flexibility under the current logic.
PERT weights optimistic, most likely and pessimistic durations without pretending uncertainty disappears. A Gantt chart communicates the resulting plan but cannot repair a faulty network. Crashing spends cost or capacity on critical work; fast tracking overlaps work and can increase rework.
Schedule control keeps the approved baseline distinct from the current forecast and uses authorised change when the controlling logic, scope or milestone commitment must move.
What this chapter covers
- 01
Activity definition from the WBS
- 02
Dependency sequencing
- 03
Network diagrams
- 04
PERT expected duration
- 05
Forward and backward passes
- 06
Critical path and total float
- 07
Crashing and fast tracking
- 08
Build dependency logic before calculating early dates, late dates, total float and the controlling path through the network
- 09
Apply one consistent activity convention and recalculate every affected path after duration, logic or resource assumptions change
- 10
Interpret PERT expected duration and variance as uncertainty summaries rather than guarantees about the actual completion date
- 11
Check resource capacity because a mathematically feasible network may require the same specialist in simultaneous activities
- 12
Compare crashing cost with fast-tracking rework risk and target only activities capable of changing the completion forecast
- 13
Preserve the approved schedule baseline separately from the current forecast and any proposed corrective scenario
Worked example · free
Find the controlling path
- +1List path A B D E as 2 + 4 + 3 + 1.
- +1Calculate that path as 10 weeks.
- +1List path A C D E as 2 + 2 + 3 + 1.
- +1Calculate that path as 8 weeks.
- +1Name A B D E critical and C branch float as 2 weeks.
Key terms
- PERT estimate
- The weighted expected duration calculated as optimistic plus four times most likely plus pessimistic, divided by six.
- Critical path
- The longest duration path through the network and the path determining the earliest finish.
- Fast tracking
- Overlapping work that was sequential to shorten time, usually with increased coordination or rework risk.
Schedule Networks, PERT and Critical Path FAQ
How do I identify the critical path?
Build a valid dependency network, calculate the duration of every complete path and select the longest. Confirm timing with forward and backward passes when networks become more complex.
What does total float mean?
Total float is the time an activity may move without delaying the current project finish. Resource constraints or later changes can alter the network and its float.
When should I crash a schedule?
Crash only activities on the controlling critical path where added cost or resources can reduce duration. Assess quality, risk and resource consequences before approving compression.
Exam move
Build schedule skill in a fixed sequence. Start from WBS work packages and define activities needed to create each deliverable. Sequence them using real logical dependencies, not preferred dates. Draw an activity network before drawing a Gantt chart so hidden logic remains visible. For small networks, list every complete start to finish path and add durations. The longest valid path controls the earliest completion.
Then practise forward and backward passes so early and late dates, total float and criticality come from the same network. Remember that a path with fewer activities may still be longer, and that resource constraints can make a logically valid network infeasible. Use PERT only with estimates in the same unit: expected duration equals optimistic plus four times most likely plus pessimistic, divided by six.
Explain what the estimate represents and keep the uncertainty visible rather than presenting the result as certainty. For every float result, state what can move, by how much and under the current logic. Review the schedule against the WBS for missing work, against resources for over allocation and against milestones for strategic meaning. Distinguish the approved baseline from the current forecast.
Actual slippage changes the forecast; only an authorised decision changes the baseline. Practise compression as a decision rather than a vocabulary question. Crashing adds cost or resources to selected critical work. Fast tracking overlaps activities and can increase coordination and rework risk. Applying either technique to noncritical work will not shorten the project while the controlling path remains unchanged.
Use original numbers and recompute them from scratch, then finish each calculation with the management consequence: which activity needs attention, which option could protect the milestone and who can approve its cost or risk. Put the PERT formula, path rule, float meaning and compression caution on the notes sheet. The high value habit is to move from dependency logic to numbers to a controlled decision.
Working through Schedule Networks, PERT and Critical Path in INFO6007? Sia is AskSia’s AI Project Management tutor — ask any INFO6007 Schedule Networks, PERT and Critical Path question and get a clear, step-by-step explanation grounded in how INFO6007 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.