What was missing from MRP for APS toemerge?

We get a lot of questions about APSsoftware — what it is, what it does, and what problems it solves. In thisarticle, we'll walk through how APS came about and the key gaps it fills in MRPand ERP systems.

‍THE ORIGIN

Production planning

For those less familiar with thebackground: MRP calculates net material requirements by taking finished productdemand and breaking it down through every level of the product structure —whether that's an internally manufactured component or a purchased rawmaterial. Each requirement is assigned a date based on standard replenishmentlead times. At its heart, MRP is a series of straightforward, interconnectedcalculations, but in industries with complex bills of materials and multi-levelstructures, it's an enormously useful tool — especially given when it firstappeared. As demand for manufactured goods surged after the 1960s, a newchallenge emerged: capacity. Knowing which materials were needed was no longerenough; manufacturers also needed to know whether they could actually produceor procure those volumes, and what the financial implications would be. Thatneed gave rise to MRPII in the 1980s, which brought resource management intothe picture — factoring in labor, machinery, and materials, and connectingplanning to financial and engineering functions.

From MRPII comes the Master ProductionSchedule (MPS) — the SKU-level plan of what finished goods will be produced ina given period. With that in hand, the full material requirements are thencalculated via MRP. Those requirements are validated against capacity byworking through every operation in the product's Manufacturing Routing andmapping time consumption against each production center — essentially what mostmanufacturers know as machine load analysis. These concepts weren't all inplace from day one; they evolved over time. By the mid-1990s, the growingcomplexity of industrial operations drove the emergence of fully integratedmanagement systems — ERPs (Enterprise Resource Planning) — which connectedevery function of a business: accounting, HR, finance, engineering,manufacturing, and sales. At the same time, the limitations of these systemswhen it came to accurate production scheduling sparked the development ofFinite Capacity Scheduling (FCS), which later evolved into Advanced Planningand Scheduling (APS). Both APS and FCS emerged specifically to address what MRPand ERP couldn't handle well: finite capacity constraints, queue management,routing complexity, and synchronization between production operations. Let'slook at those limitations in detail.

Fixed Lead Time

Like most people in the world, you probably

Batch or Lot Processes

Another area worth highlighting is batch processing — operations like heat treatment,paint booths, galvanizing, dyeing, and abrasive machining that process multipleproducts at once. MRP and MRPII treat these no differently from operationsdefined by time-per-unit or throughput rate, which means their capacity istypically miscalculated and the resulting production plan is difficult toexecute reliably. Some argue these processes aren't always bottlenecks — thatcan be true for heat treatment in metalworking environments — but in the vastmajority of other cases, batch operations tend to become bottlenecks withnotable regularity. Based on hundreds of plant visits over the years, roughlyhalf of all manufacturers we've worked with have at least one of theseprocesses.

Synchronization

When a product requires more than one operation, those operations need to happen in aspecific order — you can't package something before it's been painted orassembled. The Manufacturing Routing defines that sequence. The problem is that CRP (Capacity Requirements Planning) doesn't handle inter-operationsynchronization well. It typically takes one of two approaches: loading alloperations into the same planning period — which causes delays when queues pushlater operations into the next period — or distributing operations sequentiallyacross periods, which avoids some delays but stretches out lead times, reducesthe proportion of actual value-added time, and increases work-in-processinventory. Both approaches come with real trade-offs.

Finite Capacity

This is arguably MRP's most fundamental limitation. Planning what to produce orpurchase without first validating capacity means the output is essentially awish list — internally consistent math with no guarantee of being executable. And capacity isn't a single constraint. It's not just one machine orworkstation: operators, tooling, floor space, and many other factors all imposereal limits. Analyzing capacity only at the primary constraint — or worse, onlyat a single bottleneck — barely scratches the surface. When you layer finitecapacity on top of the synchronization problem described earlier, things geteven more complex. Running a machine load analysis means nothing if it can'taccount for the fact that a product apparently scheduled for delivery can'tmove forward because the tool it needs is in use on another machine. Situationslike that — involving shared tooling and labor — are far more common than mostplanning systems acknowledge.

The Sequence

Looking at Taiichi Ohno's seven wastes of Lean Manufacturing, two of them are directly tied to production sequencing: waiting and overprocessing — the latter largely driven by setups. In some environments, setup times alone can consume up to 50% of available production time. Ask anyone who's changed a loom cylinder orcleaned a tank before switching to an allergen-sensitive food product. Thesequence in which operations are run can dramatically reduce changeover times,mold and tool adjustments, pipe and tank cleaning, color transitions, and evenoperator travel distances. Because MRPII and CRP don't account for operationsequence, they default to average setup times — which can range anywhere from 5 minutes to 3 hours. Using an average introduces errors in completion timeestimates that ripple through downstream operations in a domino effect, quietly undermining the whole plan. Without a defined sequence, one shift may leaveproducts that the next shift simply can't process — because the right setup crewisn't on, or the operation needs more operators than are available. The resultis more waiting between operations, another of Ohno's wastes. The bottom line: systems that ignore these variables trap companies in a cycle of rough-estimatetargets and oversimplified controls. Closing these gaps requires a more capableapproach. That's where APS comes in.

But what exactly is an APS software?

‍APS — Advanced Planning and Scheduling — is a specialized system designed not toreplace ERP, but to complement it and fill its gaps. Working alongside ERP, APSprocesses production and sequencing data while accounting for all relevant constraints: finite capacity, tooling and labor availability, and the synchronization required between operations. The result is a realistic, executable production plan aligned with each company’s unique priorities andconstraints. NEO is the largest APS consulting firm in Latin America. Perform your production sequencing with a specialist in technological solutions.

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