Troubleshooting Unexpected MxAPS Schedule Results

Use this article when an MxAPS schedule does not appear to follow the expected order, or when production orders are not scheduled.

Operations Appear Out of Rank Order

The most common reason operations appear out of rank order on a machine center is that a higher-ranked operation is waiting for a predecessor operation to finish.

MxAPS must respect operation sequence. A later operation cannot start until its predecessor operation has completed.

Example

Machine 1:
Order 1, Operation 10, Rank 1000

Machine 2:
Order 2, Operation 10, Rank 3000
Order 1, Operation 20, Rank 2000

At first, Machine 2 appears to be scheduled out of rank order because Order 2, Operation 10 has rank 3000 and is scheduled before Order 1, Operation 20 with rank 2000.

However, Order 1, Operation 20 cannot start until Order 1, Operation 10 has finished.

MxAPS can use the available gap on Machine 2 for Order 2, Operation 10 if doing so does not delay Order 1, Operation 20.

What to Check

When operations appear out of sequence, check:

1. Predecessor operations.
2. Operation sequence on the routing.
3. Machine availability.
4. Material availability.
5. Allow Holes setup.
6. Hole On setup on the scheduling rule.
7. Hole Total Duration and Hole Idle Duration on the work center or machine center.
8. Manual moves or locked operations.
9. Order sets.

Unscheduled Production Orders

Production orders may remain unscheduled for several reasons.

Common causes include:

1. Missing or incomplete routing.
2. Insufficient work center or machine center capacity.
3. Very long setup time or run time.
4. Machine center calendar not calculated far enough into the future.
5. Schedule duration is too short.
6. Insufficient quantity of constrained items.
7. Start After DateTime is later than the scheduling horizon.
8. A subcontracting purchase order has an expected receipt date later than the scheduling horizon.

Check the Routing

1. Open the production order.
2. Select the production order line.
3. Choose Line > Routing.
4. Confirm the routing operations exist.
5. Confirm each operation has a valid work center or machine center.
6. Confirm setup and run times are reasonable.

A missing routing, incomplete routing, or excessive operation duration can prevent the order from fitting into the schedule.

Check Capacity

Review the work center or machine center used by the unscheduled operation.

Check:

1. The work center or machine center calendar is calculated far enough out.
2. Capacity exists during the scheduling horizon.
3. Shop calendars and downtime are not blocking the required time.
4. The schedule duration is long enough to include the operation.

If the operation requires more capacity than exists in the scheduling window, MxAPS may leave it unscheduled.

Check Constrained Items

If constrained material is not available, MxAPS may be unable to schedule the operation.

To test whether constrained material is the cause:

1. Open the item setup for the constrained item.
2. Temporarily change the item from constrained behavior to tracking behavior.
3. Regenerate the schedule.
4. If the production order schedules, the constrained item was likely preventing scheduling.

Use this as a diagnostic test only. Restore the correct constraint setup after testing.

Check Start Dates and Subcontracting Dates

An operation may be blocked by a future start condition.

Check:

1. Start After DateTime on the Prod. Order Routing line.
2. Expected receipt dates on subcontracting purchase orders.
3. Whether those dates fall outside the schedule duration.

If the operation cannot start until after the schedule horizon, it will not schedule within the current run.

Troubleshooting Unexpected Gaps in the Schedule

If an MxAPS schedule contains an unexpected period where no work is scheduled, start with the first operation scheduled after the gap. A gap is often caused by that operation, or one of its required resources, being unavailable until the later date.

Review the operation and determine what must be available before it can start. Check the assigned work center or machine center, predecessor operations, constrained items, secondary constraints, and any alternate groups configured for the operation.

For each required resource, also review its calendar. In particular, check Shop Calendar Exceptions. A Shop Calendar Exception can make a machine, skill, labor resource, tooling constraint, or other calendar-controlled resource unavailable even when its normal Shop Calendar would otherwise show working capacity.

For example, if an operation requires a labor skill configured as a secondary constraint and that skill’s Shop Calendar contains an exception covering the apparent gap, MxAPS cannot schedule the operation until the skill becomes available. Operations that depend on that operation may consequently also be scheduled later.

If the required resource is unavailable, also check whether the routing operation has an Alternate Group that provides another valid resource. Without a configured alternate, MxAPS must wait until the required resource becomes available.

When investigating a gap:

1. Locate the first operation after the gap.
2. Review its predecessor operation and routing sequence.
3. Identify its primary and secondary resource requirements.
4. Check the Shop Calendars and Shop Calendar Exceptions for those resources.
5. Review constrained item availability and any applicable start conditions.
6. Check whether alternate groups are configured and available.
7. Regenerate the schedule after correcting any unintended configuration.

This approach helps identify the resource or condition that establishes the earliest time the affected operation can be scheduled.

Best Practices

1. Start troubleshooting with predecessor operations before assuming rank is wrong.
2. Review the Machine Schedule Summary together with the production order routing.
3. Confirm the production order was included in the schedule filters.
4. Confirm calendars and schedule duration cover the required horizon.
5. Test constrained material carefully by switching to tracking only as a diagnostic step.
6. Regenerate the schedule after each setup change.

Summary

Unexpected schedule results are usually caused by constraints, not by MxAPS ignoring rank.

Before changing scheduling rules, check operation sequence, predecessor operations, capacity, calendars, material constraints, start-after dates, and subcontracting receipt dates.