14 CFR Part 23 Certification

14 CFR Part 23 is the regulation that establishes the airworthiness standards for normal-category airplanes — the general aviation fleet, from single-engine pistons to smaller multi-engine aircraft. Like Part 25 for transport-category aircraft, Part 23 is a broad regulation covering the whole airplane: structures, flight characteristics, systems, and equipment. And like Part 25, it has one portion that sits directly alongside the engine work most propulsion certification involves — the powerplant installation.

Part 23 is where the powerplant installation lives for normal-category aircraft. The engine itself is certified under 14 CFR Part 33 — but how that engine is installed in and integrated with a normal-category airplane is a Part 23 question. That division is the key to understanding how Part 23 fits into propulsion certification work.

What Part 23 Covers

Part 23 sets the standards a normal-category airplane must meet to be airworthy. In scope it spans the whole aircraft — structural strength, flight performance and handling, systems and equipment, and the requirements that protect the people aboard. It's the airworthiness backbone for general aviation airplanes, the same way Part 25 serves transport-category aircraft and Part 33 serves engines.

For propulsion work, the section that matters most is the powerplant installation portion of the regulation. That's the part of Part 23 governing how the engine, propeller, and associated components are installed and integrated into the airframe — along with the fuel system, induction system, and exhaust system that serve them. It's a distinct body of requirements from the engine's own type certification.

The Part 23 / Part 33 Division: Installation vs. Engine

This is the distinction worth being precise about, because it determines which regulation a given piece of work answers to.

Part 33 is the engine. The engine's design, performance, durability, and the test program that proves it — that's Part 33. The engine earns its own type certificate against those standards, independent of any particular aircraft.

Part 23 is the installation. Once that engine is going into a normal-category airplane, a different set of questions opens up: how it's mounted and supported, how the fuel and induction and exhaust systems interface with it, how the installation behaves in normal and failure conditions, how controls and instruments and markings are handled, how it's accounted for in the airplane's overall airworthiness. Those are Part 23 powerplant installation questions, not Part 33 engine questions.

The same physical engine sits at the intersection of two regulations — certified under Part 33 as an engine, and integrated under Part 23 as an installation in a normal-category airplane. Work that touches the powerplant on a Part 23 aircraft almost always has to account for both.

How Part 23 Connects to PMA and STC Work

For most manufacturers, the practical encounter with Part 23 isn't certifying a new airplane — it's PMA or modification work that touches the powerplant installation on an aircraft that's already type-certified.

A PMA for a powerplant-installation component on a normal-category airplane still has to show the part meets the applicable airworthiness standards — and for installation components, those standards live in Part 23. An STC that changes a powerplant installation — a different engine, a modification to the fuel or exhaust system, a change to how an installed engine operates — has to demonstrate the modified installation still complies with the applicable Part 23 standards. And because those changes often reach the engine too, they can pull in Part 33 at the same time.

The common thread with the rest of propulsion certification holds: Part 23 is the standard for the installation side on normal-category aircraft. What varies is how much of it applies to a given project, and how the compliance case is built.

Where Prime Propulsion Fits

Part 23 powerplant installation work rewards the same thing the rest of propulsion certification does — getting the compliance approach scoped right early, before the wrong assumption becomes an expensive problem. The installation-versus-engine division, and the way a single project can reach into both Part 23 and Part 33, is exactly the kind of thing that's clearer with experience behind it.

Our in-house DER has propulsion certification experience from inside the FAA and in private industry, with delegation across Parts 23, 25, and 33. We help manufacturers work through powerplant installation, PMA, and modification projects on normal-category airplanes — scoping which standards apply, coordinating the Part 23 and Part 33 sides of a project, and building substantiation the FAA will accept.

If you have a project that touches the powerplant installation on a normal-category airplane and want to talk through how Part 23 applies, contact us — there's no cost to scope it out. You can also learn more about our FAA PMA certification services and STC certification 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.