2.6 Schedule Freeze Windows + Change Control

A supply chain cannot execute a moving target. If the production schedule changes daily, or if Engineering changes part numbers while the line is running, the result is "System Nervousness." This phenomenon causes MRP to generate erratic expedite and de-expedite signals, flooding suppliers with noise until they stop listening. To stabilize the signal, you must enforce rigid time fences.

The Time Fence Architecture

Divide the planning horizon into three distinct zones based on the cost of change.

Zone 1: The Frozen Zone (0 – 2 Weeks)

• Definition: The "Clear to Build" (CTB) window. Materials are staged, lines are staffed, and machines are programmed.
• Rule: Total Lock.
  • No Schedule Changes (Quantity or Date).
  • No Engineering Changes (ECOs).
• Exception: Requires Plant Manager sign-off + payment of expedited freight/scrap costs.

Zone 2: The Slush Zone (2 – 6 Weeks)

• Definition: The "Material Drive" window. POs are placed, but materials are in transit or at the distributor.
• Rule: Trade-off Logic.
  • Volume changes ±10% allowed.
  • Date shifts allowed if material is available.
  • ECOs allowed only if "Effectivity Date" aligns with material arrival.

Zone 3: The Liquid Zone (> 6 Weeks)

• Definition: The "Forecast" window.
• Rule: Open.
  • Planning can adjust mix and volume freely to align with Sales demand.

Engineering Change Control (ECO) Discipline

An Engineering Change Order (ECO) is a supply chain destructor if not synchronized with procurement reality. You must define how the change enters the system.

The Cut-In Strategy

• Running Change (Soft Transition):
  • Logic: "Use Up Old Revision first."
  • Impact: Zero Scrap. Lowest Risk. Preferred method.
• Hard Cut (Hard Transition):
  • Logic: "Stop immediately. Build New Revision only."
  • Impact: Immediate obsolescence of Old Rev stock.
  • Constraint: Forbidden inside the Frozen Zone without a "Scrap Authorization."

The Blocked Stock Rule

• Trigger: When an ECO is released pending approval.
• Action: Place existing inventory on Quality Hold (Status Q).
• Why: Prevents the warehouse from picking obsolete parts for a new build while the paperwork is being signed.

Inventory Disposition Logic

When a change happens, the old material does not vanish. It becomes a liability on the balance sheet. You must assign a disposition immediately to clear the warehouse and stop the bleeding.

If ECO = Hard Cut (Immediate Obsolescence):

Check 1: Rework?

• Question: Can the Old Rev be modified to meet the New Rev spec? (e.g., Firmware re-flash, add jumper wire).
• Decision:
  • Yes: Issue Rework Order. (Cost = Labor).
  • No: Move to Check 2.

Check 2: Return to Vendor (RTV)?

• Question: Will the original supplier accept a return for credit?
• Decision:
  • Yes: Execute RTV. (Recovery ≈ 80–100% minus restocking fee).
  • No: Move to Check 3.

Check 3: Liquidation (Sell)?

• Question: Is there market demand for this component? Can we sell to a broker or surplus aggregator?
• Decision:
  • Yes: Execute Asset Recovery Sale. (Recovery ≈ 5–20%).
  • No: Move to Check 4.
  • Constraint: Ensure you are not selling proprietary/custom silicon or parts with IP restrictions.

Check 4: Scrap (Write-Off)

• Question: Is the part toxic inventory?
• Action: Finance must write off the value. Physical destruction is required to prevent the parts from re-entering the supply chain as "counterfeit/pulled" stock later.
  • Cost: Negative (you pay for disposal).

The Change Request Template

Standardize the request to force stakeholders to acknowledge the cost of their instability.

Change Request Form (CRF)

• Requestor: [Sales / Engineering]
• Change Type: [Schedule Pull-in / Push-out / ECO]
• Constraint: Request falls inside Frozen Zone (T-10 Days).

Impact Analysis (Supply Chain to Complete):

1. Material Cost: $ [Expedite Fees]
2. Scrap Cost: $ [Obsolete Inventory]
3. Line Down Risk: [High / Med / Low]
4. Feasibility: [Possible / Impossible]

Approval Authority:

• [ ] Accepted (Cost center charged)
• [ ] Rejected (Adhere to original plan)

Approval Matrix

The signature required depends on the Zone and the Impact.

Horizon	Change Type	Financial Impact	Required Approver
Liquid (>6w)	Any	N/A	Master Scheduler
Slush (2-6w)	Qty > 10%	< $1k	Supply Chain Mgr
Slush (2-6w)	ECO	> $1k	PM + SCM Mgr
Frozen (<2w)	ANY	Any	VP Ops + Plant Mgr

Final Checklist

Control Point	Requirement	Critical Threshold
Freeze Zone	Duration Defined	Fixed (e.g., 14 Days)
ECO Phase-In	Use-Up logic applied	Default = Yes
Disposition	Old Rev Inventory	Cleared < 48 Hours
Approvals	Inside Freeze Window	Executive Sign-off
Cost Allocation	Expedite fees charged to Requestor	Mandatory
MRP Integrity	Old POs Cancelled	Immediate