As-Built vs. As-Maintained: The Configuration Gap That Costs Aerospace Real Money

A customer asked for spare parts for a fuel pump. Engineering shipped them. The response: “These are for a gasoline engine. We converted to diesel about ten years ago.”

Ten years. Nobody at headquarters knew.

That’s not a story about incompetence. Every individual in that chain did something reasonable. It’s a story about what happens when the configuration in the field stops matching the configuration in your system, and nothing in your process is designed to notice.

Three configurations, not one

Most people think of a product as having a configuration. In long-life products there are at least three, and they diverge over time.

As-designed — what engineering specified. Lives in your PLM system. Clean.

As-built — what actually came off the line. This is already different. Deviations get approved during manufacturing, substitutions get made, a supplier ships a functionally equivalent part. If you didn’t capture those against the specific unit, you’ve lost the thread on day one.

As-maintained — what’s installed right now, after years of service, repairs, overhauls, and field changes. This is the one that matters when a customer calls, and it’s the one almost nobody has.

The fuel pump story is a gap between as-designed and as-maintained that went unnoticed for a decade.

How the gap opens

It usually isn’t one dramatic failure. It’s ordinary work.

• Emergency field changes. Something fails somewhere inconvenient. A technician does exactly the right thing and gets the unit running. The paperwork is the last priority, correctly, and sometimes it never gets written.

• Documentation that doesn’t come home. Sometimes the change is recorded — on a form, in a local system, in a maintenance log at the site. It just never makes it back to the organization that maintains the master record.

• Fleet drift. Ten units built identically diverge over fifteen years of independent service histories. At some point “what configuration is unit 7?” has no answer anyone can give you from a system.

• Overhaul decisions made blind. When a customer decides a major overhaul beats buying new — often the right economic call — you need to know the current configuration to scope it. If you don’t, you’re quoting a job against a guess.

Why this is worse in aerospace, defense, and med device

The gap exists everywhere. It’s expensive specifically where products stay in service for decades and where regulators care.

Aerospace, defense, industrial equipment, and medical devices share a profile: long service life, high consequence of error, and a regulatory expectation that you can produce traceable records on demand. An airframe may be in service longer than the engineers who designed it stay at the company. Institutional memory is not a configuration management strategy.

These are hard use cases to solve. They’re also where the returns are largest, for a reason most people miss.

The upside nobody talks about

Everything above is downside — cost avoidance, embarrassment avoidance, compliance. That framing undersells it.

Consider what happens when you do have accurate as-maintained data across your installed base.

A customer needs a custom upgrade. You design and deliver it. Now you can ask a question you previously couldn’t answer: how many other units in the field are similar enough to take this same upgrade?

Suddenly a one-off engineering job becomes a product. You go to those customers with something specific: here’s a kit, here’s what it costs, here’s what it does for your operating economics. And frequently the response is “I didn’t know I wanted this — now I do.”

That’s not cost avoidance. That’s revenue you could not previously see, sitting inside data you already technically own.

It also builds something harder to quantify: customers learn that you know their equipment better than they do. That’s the difference between being a parts supplier and being the company they call first.

What closing the loop actually requires

• Capture as-built against the unit, not the design. Deviations and substitutions have to be recorded against the specific serialized unit — otherwise you have a design record, not a build record.

• Give the field a path home for data. If reporting a field change is harder than making it, the data will not come back. This is a process and tooling problem, not a discipline problem.

• Connect the systems. The service organization and the engineering organization typically run different systems for legitimate reasons. The question is whether they exchange data automatically or whether someone emails a spreadsheet. If it’s the spreadsheet, you already know how this ends.

• Feed it back to engineering. As-maintained data is the highest-quality product feedback you will ever get — real failure modes on real units in real conditions. Most organizations let it die in the service system.

The short version

• Long-life products have three configurations — as-designed, as-built, as-maintained — and they drift apart.

• The gap opens through ordinary work: emergency repairs, documentation that never comes home, decades of independent service history.

• It’s most expensive in aerospace, defense, industrial equipment, and med device — long life, high stakes, regulatory traceability.

• Downside: shipping the wrong parts, scoping overhauls blind, losing customer confidence.

• Upside, and the bigger one: knowing your installed base lets you resell upgrades you’ve already engineered.

If you can’t answer “what’s actually installed in unit 7 right now” from a system, that’s the gap. It’s worth knowing how wide it is before a customer tells you.

Element Consulting implements PLM and digital-thread systems for aerospace & defense, medical device, and industrial manufacturers — including the configuration management that keeps as-built and as-maintained data connected. Related reading: Aerospace & Defense and What is Windchill PLM. Talk to a Windchill expert →