5.3 Out-of-Sequence Logic: Progress Override vs. Retained Logic

5.3 Out-of-Sequence Logic: Progress Override vs. Retained Logic

AACE Professional Context: In a textbook CPM network, construction proceeds in strict chronological order according to baseline logic. In field execution, however, contractors frequently adapt: work commences out of order due to material availability, selective access, or subcontractor expediting. When a successor activity begins before its predecessor finishes, the network encounters Out-of-Sequence (OOS) Progress. How the scheduling engine resolves this conflict—via Retained Logic (RL) or Progress Override (PO)—fundamentally impacts early dates, total float, critical path alignment, and delay claim liabilities. Mastery of these calculation algorithms is a cornerstone of the AACE PSP examination.

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Definition and Causes of Out-of-Sequence Work

An activity is executing out of sequence when it records progress (an Actual Start date or physical percent complete) prior to the satisfaction of its predecessor logic relationships.

                  NORMAL SEQUENCE (Finish-to-Start)
                  [Activity A: Foundations] ──(FS)──► [Activity B: Backfill]
                  (Activity A finishes ──► Then Activity B starts)

                  OUT-OF-SEQUENCE PROGRESS
                  [Activity A: Foundations] ──(FS)──► [Activity B: Backfill]
                             ▲                                  │
                             │          ACTUAL START            │
                             └──────── (Starts early!) ─────────┘
                  (Activity B starts while Activity A is still in progress!)

Primary Root Causes of Out-of-Sequence Work

1. Field Workarounds and Expediting: Site superintendents seize operational opportunities. For example, backfilling around completed pier footings before all foundation walls in the area are poured.
2. Defective Baseline Logic (Preferential Logic): The original baseline incorporated discretionary or soft logic (e.g., an arbitrary Finish-to-Start tie between independent work areas) rather than true physical dependencies.
3. Scope Packaging and Granularity Issues: An activity represents too large a scope. If ACT-100: Install Underground Piping covers 5,000 feet, the electrical contractor may begin ACT-200: Install Duct Bank in Trench Zone 1 while pipe testing continues in Trench Zone 3.
4. Data Entry Errors: The site clerk erroneously records an Actual Start date on Activity B instead of Activity A.

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The Two Primary CPM Calculation Modes

When calculating the forward pass for an updated schedule containing out-of-sequence progress, scheduling software (such as Primavera P6) requires the user to select a calculation mode: Retained Logic, Progress Override, or Actual Dates.

1. Retained Logic (RL)

Under Retained Logic, the software respects the original network relationship, regardless of the progress achieved to date. Although the successor activity has started and accumulated actual duration prior to the Data Date, its Remaining Duration cannot resume until its predecessor finishes.

$\text{Early Start of Successor Remaining Duration (RL)} = \max(\text{Data Date}, \text{Early Finish of Predecessor})$

• Physical Interpretation: The software assumes that whatever portion of the successor work remains is strictly dependent upon the incomplete predecessor work.
• Network Impact: If the predecessor is delayed, the remaining portion of the successor is pushed out into the future, creating a "split activity" or extended duration.
• Float Impact: Preserves logical dependencies, resulting in lower (and often realistic or negative) total float.

2. Progress Override (PO)

Under Progress Override, the software overrides the network relationship. The algorithm assumes that because work on the successor has already begun, the predecessor logic has been broken, invalidated, or bypassed in the field. The Remaining Duration of the successor is permitted to proceed immediately from the Data Date, completely unconstrained by the predecessor's early finish date.

$\text{Early Start of Successor Remaining Duration (PO)} = \text{Data Date}$

• Physical Interpretation: The software assumes the unfinished predecessor work no longer restrains the remaining successor scope.
• Network Impact: The successor finishes much earlier than under Retained Logic, often finishing before its own predecessor finishes!
• Float Impact: Artificially increases total float on the successor path, frequently masking real project delays.

3. Actual Dates Option

Some scheduling software offers an Actual Dates calculation option. Under this setting, backward pass calculations evaluate float based on actual dates where recorded. However, forward pass calculations for remaining durations typically adhere to Retained Logic rules. While theoretically pure, Actual Dates mode can generate erratic negative float on historical activities, making Retained Logic the preferred professional industry standard.

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Comprehensive Comparison: Retained Logic vs. Progress Override

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Mathematical Worked Example: The Concrete Basin vs. Hydrostatic Test

To see the dramatic divergence in mathematical outcomes, examine a two-activity network on an industrial wastewater facility.

Baseline Conditions:

• Activity A (Predecessor): Pour Concrete Basin Walls ($OD = 10 \text{ days}$)
• Activity B (Successor): Install Hydrostatic Test Seals & Fill Basin ($OD = 6 \text{ days}$)
• Network Relationship: Activity A $\xrightarrow{\text{FS}}$ Activity B (Basin walls must be poured before test seals and filling occur)

Month 1 Update Status (Data Date = Day 6):

• Activity A Status: Actual Start = Day 1. Worked 6 days ($AD = 6$). Due to honeycombing and repair work, the remaining duration is evaluated at 8 days ($RD = 8$). $\text{Early Finish of Activity A} = \text{Data Date (6)} + 8 = \text{Day 14}$
• Activity B Status (Out of Sequence!): The piping crew jumped ahead and pre-installed test bulkheads on an adjacent pipe spool on Day 4. Actual Start = Day 4. Worked 2 days ($AD = 2$). Remaining Duration = 4 days ($RD = 4$).

  DAY:        1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18
  Activity A: [=== Actual ===] [======== Remaining Duration =======]
                               ▲                                    ▲
                               DD (Day 6)                           EF = Day 14

Forward Pass Calculation Under Both Modes:

1. Retained Logic (RL) Calculation:

• The Remaining Duration of Activity B ($RD = 4$) cannot start until Activity A finishes.
• $\text{ES of Activity B Remaining} = \max(\text{Data Date 6}, \text{EF of Activity A 14}) = \text{Day 14}$.
• $\text{Early Finish of Activity B} = 14 + 4 = \mathbf{\text{Day 18}}$.
• Result: Activity B is split: worked Days 4–6, paused Days 6–14 while waiting for concrete repairs on Activity A, and completes on Day 18. This accurately reflects that the basin cannot be filled with water until the concrete walls are finished!

2. Progress Override (PO) Calculation:

• The Remaining Duration of Activity B ($RD = 4$) starts immediately at the Data Date.
• $\text{ES of Activity B Remaining} = \text{Data Date} = \text{Day 6}$.
• $\text{Early Finish of Activity B} = 6 + 4 = \mathbf{\text{Day 10}}$.
• Result: Activity B finishes on Day 10, while Activity A is still pouring concrete until Day 14! Progress Override produces a physically absurd schedule: the basin is hydro-tested and filled with water 4 days before the walls are poured!

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AACE Best Practice: Resolving Out-of-Sequence Logic

Core AACE Principle: Neither Retained Logic nor Progress Override is a substitute for proper engineering schedule maintenance. When out-of-sequence progress occurs, investigate the field condition and decide whether the remaining dependency still applies, the logic should be revised, or a calculation option is appropriate under the governing requirements.

                    OUT-OF-SEQUENCE RESOLUTION PROTOCOL
  ┌────────────────────────────────────────────────────────────────────────┐
  │ 1. Run the software schedule update log to identify all OOS tasks.     │
  │ 2. Investigate site reality with superintendents and project engineers. │
  │ 3. Determine if the relationship was discretionary or a true restraint.│
  │ 4. If work is truly concurrent: replace FS with SS/FF or break scope.  │
  │ 5. If true restraint exists: retain logic and enforce the dependency.   │
  │ 6. Document all logic modifications in the Schedule Narrative Report.  │
  └────────────────────────────────────────────────────────────────────────┘

Standard Logic Solutions for OOS Activities

1. Convert to Start-to-Start (SS) / Finish-to-Finish (FF) Ladder Logic: If the successor genuinely did not need the predecessor to finish, replace the Finish-to-Start (FS) tie with a Start-to-Start (SS) tie with appropriate lag, plus a Finish-to-Finish (FF) tie to ensure the predecessor still governs completion.
2. Activity Scope Decomposition (Fragmenting): Decompose the activity into geographic or phase steps. For example, divide ACT-A: Concrete Walls into Area 1 Walls and Area 2 Walls, and link Area 1 Walls $\xrightarrow{\text{FS}}$ Area 1 Backfill.
3. Delete Inapplicable Preferential Logic: If an FS relationship represented merely a contractor preference that has been abandoned, delete the tie and link the successor to its true physical predecessor.

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Forensic Delay & Claims Implications (AACE RP 29R-03)

In forensic schedule delay analysis, out-of-sequence progress is a primary battleground:

• "Gaming" the Critical Path: An unscrupulous contractor facing owner liquidated damages might switch calculation settings from Retained Logic to Progress Override between monthly updates. This instantly eliminates negative float and delays without adding craft labor or re-sequencing in the field.
• Forensic reproducibility: Record calculation options and changes across schedule versions. If retained-logic or progress-override settings changed without explanation, test the material effect and disclose it; do not assume that reversing every change produces one uniquely true path.