Why You Should Work With A Designated Engineering Representative (DER)

If you're pursuing a PMA, STC, or any certification project that requires engineering data approval, at some point the question comes up: do you work with a Designated Engineering Representative, or route everything through the FAA directly?

The short answer is that a DER doesn't just speed things up — a DER changes how the project runs from the beginning. And that difference shows up in the timeline, the number of FAA review cycles, and whether problems get found early enough to fix cheaply or late enough to be expensive.

What a DER Actually Is

A DER is an engineer appointed by the FAA to act on the agency's behalf for specific types of engineering approvals. The FAA doesn't hand this out casually — the requirements include an engineering degree, at least eight years of advanced engineering experience, and demonstrated expertise in the relevant discipline. DERs are typically specialized: powerplant, structures, systems, flight test.

The authority that matters is Form 8110-3 — the approved data sheet. A DER can review and approve engineering data and issue an 8110-3, which the FAA accepts as an approved finding. That's not a recommendation or a preliminary review. It's an approval that carries the FAA's authority. When a DER signs off on your data, that data is approved — it doesn't sit in an FAA queue waiting for someone to get to it.

Why That Changes a Certification Project

The value of a DER isn't just that approvals happen faster, though they do. It's that working with a DER changes the structure of your project in ways that prevent problems rather than just reacting to them.

The project gets built right from the start. A DER who's involved early helps you scope the compliance path, define what data you actually need, and organize the package the way the FAA expects to see it — before you've committed engineering resources to the wrong approach. That front-end scoping is where the real time savings come from. A project that's structured properly from the beginning doesn't generate the kind of FAA comments that send you back to rework something you thought was finished.

Problems get found before the FAA finds them. This is the part most people underestimate. When your DER reviews the data package before submission, they're looking at it with the same eyes the FAA would — because they hold the FAA's authority and they know what generates comments. Issues that would surface as formal FAA findings weeks or months into a review cycle get caught and resolved during the development phase instead. Every problem found early is a comment cycle you never have to go through.

Review time compresses. When a DER issues an 8110-3, the FAA receives a package with approved findings already in place. The agency's review is lighter because the detailed engineering review has already been done by someone they've authorized to do it. Compare that to submitting without DER findings, where the FAA has to do the full engineering review internally — on their timeline, at their capacity, with whatever backlog they're carrying. The difference in turnaround is real and it's usually measured in months, not days.

What This Looks Like in Practice

Consider a typical PMA project. The data package includes drawings, material and dimensional analysis, substantiation data, and a compliance matrix — all of which has to be reviewed and found acceptable. Without a DER, that entire package goes to the FAA for engineering review. With a DER, the engineering data is reviewed, approved, and the 8110-3 is issued before the package ever reaches the FAA. The FAA still reviews the submission, but the engineering approval is already done.

The same logic applies to STC projects, test cell correlations, repair specifications, and any certification effort where engineering data needs to be substantiated and approved. The DER's role is the same in each: review the data, find the problems before the FAA does, approve what's ready, and make sure the package that reaches the agency is clean.

The Difference Between a DER on Staff and a DER You Coordinate With

Not all DER arrangements are the same, and the distinction matters.

Some firms use external DERs — an independent engineer engaged for the approval step, often late in the project, who reviews a package someone else assembled. That works, but it limits how much value the DER can add. If they're only seeing the data at the end, the front-end scoping benefit — the part that prevents problems — is mostly lost.

Working with a firm that has a DER on staff is a different relationship. The DER is involved from the scoping conversation through final approval. They're shaping the compliance approach, reviewing data as it's developed, and catching issues in real time rather than at the finish line. The project doesn't have a handoff between "the team that builds the package" and "the DER who reviews it" — it's the same team, the same conversation, the whole way through.

That's the model we run at Prime Propulsion, and it's why "DER-led" isn't a marketing phrase for us — it describes how the project is actually structured.

Where Prime Propulsion Fits

Our in-house DER has propulsion certification experience from both inside the FAA and in private industry, with delegation across Parts 23, 25, and 33. We work with small to mid-size manufacturers who need senior DER attention without large-firm overhead — the kind of companies where a certification project's timeline and budget can't absorb unnecessary FAA comment cycles.

If you have a certification project and want to understand how working with a DER would change the timeline, contact us — there's no cost to talk it through. You can also learn more about our FAA PMA certification services, STC services, and test cell correlation services.

Prime Propulsion delivers expert FAA certification solutions for small to medium-sized aerospace firms. Our DER-led team specializes in PMA, STC, Test Cell Correlations, and Repair Specification support.