14 CFR Part 27 Certification

14 CFR Part 27 is the regulation that establishes the airworthiness standards for normal-category rotorcraft — the smaller helicopters used across commercial, utility, and private operations. Like its fixed-wing counterparts Part 23 and Part 25, Part 27 covers the full aircraft. But the portion that intersects with propulsion certification work is specific to rotorcraft in a way that sets it apart from the fixed-wing regulations.

In a fixed-wing aircraft, the engine turns a propeller or produces thrust. In a rotorcraft, the engine drives a transmission and rotor system — and the mechanical chain between the engine and the rotor is a significant, safety-critical system with its own certification requirements. That difference shapes what Part 27 demands and where PMA opportunities exist.

What Part 27 Covers

Part 27 sets the standards a normal-category rotorcraft must meet to be airworthy. In scope it spans the entire aircraft — structural strength, flight characteristics, systems and equipment, and the requirements that protect the people aboard.

The powerplant installation portion of Part 27 is broad, covering how the engine and all associated systems are installed and integrated into the rotorcraft. That includes the engine installation itself, fuel and oil systems, engine controls and instruments, exhaust systems, fire protection, cooling, and — unique to rotorcraft — the drive and transmission systems that transfer engine power to the main and tail rotors.

That last piece is what makes rotorcraft powerplant certification genuinely different from fixed-wing. A transmission, a freewheeling unit, drive shafts, and the associated lubrication and monitoring systems are all safety-critical components with no fixed-wing equivalent. They carry their own design, test, and substantiation requirements under Part 27.

The Part 27 / Part 33 Division

This is the same installation-versus-engine distinction that runs through all of propulsion certification, but with an added layer for rotorcraft.

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, whether it ends up in a fixed-wing aircraft or a rotorcraft.

Part 27 is the installation and the drivetrain. Once that engine goes into a normal-category rotorcraft, Part 27 governs how it's installed and how the power it produces gets to the rotor. The full scope of powerplant installation requirements applies — from the engine mount to fire protection to the transmission — and each of those systems has its own substantiation demands distinct from the engine's Part 33 certification.

How Part 27 Connects to PMA

For most manufacturers, the practical encounter with Part 27 isn't certifying a new rotorcraft — it's PMA work on components that go into the powerplant installation of rotorcraft already in service.

A Parts Manufacturer Approval for a component in any of these systems still has to show that the part meets the applicable airworthiness standards — and for a normal-category rotorcraft, those standards live in Part 27. Whether the compliance path is identicality or test and computations, the substantiation has to close against the relevant Part 27 requirements.

The PMA opportunity in rotorcraft drivetrain and transmission components is worth noting specifically. These are high-value, maintenance-intensive parts on aircraft that stay in service for decades — the same demand pattern that makes piston engine PMA attractive in fixed-wing general aviation. OEM support narrows as platforms age, lead times stretch, and operators look for approved alternatives. Every one of those parts is a potential PMA candidate.

Where Prime Propulsion Fits

Our in-house DER holds Part 27 delegation specifically scoped to engine installations, fuel and oil systems, and drive and transmission systems — the propulsion and drivetrain core of the rotorcraft powerplant. Those are the areas where we can review and approve the engineering data in your PMA submission via Form 8110-3.

That delegation scope covers much of where rotorcraft PMA demand actually concentrates. Transmission components, drive system hardware, fuel system parts, oil system components, and engine installation fittings are all high-maintenance, high-value items on platforms that stay in service for decades. Scoping which Part 27 requirements apply to a given component, and how they interact with Part 33 on the engine side, is the kind of work that goes more efficiently with someone who's done it before.

If you have a rotorcraft component in any of those areas and want to talk through whether it's a viable PMA candidate, contact us — there's no cost to scope it out. You can also learn more about our FAA PMA 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.