"How do we build a brand-new aircraft (Modern Application) while the existing runway (Legacy Infrastructure) is riddled with potholes, and the old fleet must keep flying passengers every single second?"

It sounds like an impossible constraint. In practice, it is the most common condition under which large-scale enterprise modernization actually happens. Systems cannot be taken offline. Business operations cannot pause. And yet the architecture holding everything together has become a structural liability that the organization can no longer afford to carry.

Interestingly, almost all major financial institutions found themself at exactly this juncture. Their core banking platform was approaching fifty years old. What began as a maintenance burden had become a systemic risk — not just to IT operations, but to the organization's capacity to compete in a digital economy that no longer waited for nightly batch cycles to complete.

This case became one of the most instructive we discuss in the classroom. The intersection of exceptional technology and profound architectural thinking—a combination that elevated the entire project to success.

THE BASELINE — DIAGNOSING THE ARCHITECTURAL DEBT

Before any transformation strategy can be designed, the current state has to be assessed honestly. Not optimistically, and not comprehensively for its own sake — but with enough clarity to name the specific constraints that are blocking the organization's ability to move.

The diagnosis in this case revealed three structural failure patterns that practitioners will recognize across industries.

The first was temporal coupling. The core platform was built on a batch-processing model from an era when overnight reconciliation was the industry standard. In a 24/7 digital economy, that constraint meant every real-time transaction was ultimately dependent on a nightly cycle. The architecture was not broken — it was doing exactly what it was designed to do. The problem was that the business had grown beyond what it was designed for.

The second was product-centric fragmentation. The system architecture was organized around products, not customers. Data lived in silos. A unified view of any individual customer across their full relationship with the organization was structurally impossible without a complete overhaul. The organization knew its products intimately. It was effectively blind to its customers.

The third was key-person risk. The engineering expertise required to maintain and extend the legacy system was concentrated in a small group of specialists approaching retirement. The risk was not just technical — it was that the business logic embedded in decades of COBOL code existed nowhere else. When those people left, the organization would lose its living documentation.

Incremental patching was not a viable response to this diagnosis. The architectural debt had compounded to the point where the cost of maintaining the existing structure exceeded the cost of designing a path out of it. A target state was needed. The more difficult question was how to reach it without bringing the operation down in the process.

THE STRATEGY — CONSTRUCTING THE ARCHITECTURE RUNWAY

The Fit-for-Purpose concept frames architectural work around a conceptual equation: the value generated by addressing stakeholder concerns and enabling decisions, divided by the granularity and effort required to produce it. The goal is to maximize that ratio — not to build the most comprehensive architecture, but to build the most effective one for the specific context at hand.

In the context of a live enterprise transformation, that equation has a specific implication: you cannot begin migrating a core system until you have a place for the new services to land. The Architecture Runway is that place.

Drawn from the Scaled Agile Framework® and adapted within the TOGAF® enterprise architecture context, the Architecture Runway is a proactive mechanism — building the technical foundations, integration standards, and approved patterns that delivery teams will need, one to two steps ahead of when they need them. It ensures that when implementation teams encounter a design decision, the approved answer already exists. Compliance becomes faster than improvisation.

In this transformation, the runway was established through a modern presentation layer built ahead of the core migration. The strategic logic was deliberate. By decoupling the user experience from the legacy backend first, the organization could deliver a unified customer view — the most urgent business concern — while the deeper structural migration was still in its early stages.

This is the Concern-Driven pillar of the Fit-for-Purpose concept in practice. The architecture team did not begin by documenting the full current state. They began by asking which business decision was currently blocked — and what was the minimum structural change that would unblock it. A modern presentation layer, acting as an enterprise-scale abstraction, answered that question. It delivered immediate business value while creating the stable ground from which the more complex work could proceed.