What do MRO capability ratings mean (EASA Part-145 A/B/C/D vs FAA repair station ratings) when sourcing a maintenance provider?

When you source a maintenance, repair and overhaul (MRO) provider, the single most important thing to read is their capability rating — the formal list of what their approval actually permits them to work on. A shop is…

When you source a maintenance, repair and overhaul (MRO) provider, the single most important thing to read is their capability rating — the formal list of what their approval actually permits them to work on. A shop is only legally allowed to release work that falls inside its rated scope. This brief decodes the two dominant rating systems — EASA Part-145 (Class A/B/C/D) and FAA 14 CFR Part 145 repair station ratings — so a buyer can match a provider's scope to the job before signing.

Why the rating, not the brochure, is the source of truth

Marketing copy says "full-service MRO." The approval certificate says exactly which aircraft types, engines, and component classes the shop can sign off. If a task falls outside the rating, the provider cannot legally issue the release for it, regardless of how capable they say they are. Always source against the rating and its associated capability list, not the sales deck.

EASA Part-145 class ratings

EASA Part-145 organises capability into four classes, each subdivided.

Class	Covers	Examples of sub-ratings
A — Aircraft	Complete aircraft (base/line maintenance)	A1 aeroplanes above 5,700 kg; A2 aeroplanes 5,700 kg and below; A3 helicopters; A4 other aircraft (e.g. balloons, sailplanes)
B — Engines	Complete engines and APUs	B1 turbine; B2 piston; B3 APU
C — Components	Components other than complete engines, organised by ATA chapter	e.g. C1 air conditioning & pressurisation; C2 auto flight; C3 communications & navigation; through to the higher ATA-chapter categories
D — Specialised services	Discrete specialist processes	Predominantly non-destructive testing (NDT): penetrant, magnetic particle, eddy current, ultrasonic, radiographic

For an aircraft-class (A) rating, EASA also distinguishes base maintenance from line maintenance privileges, and the rating is tied to specific type ratings on the capability list — an A1 shop approved for one widebody family is not automatically approved for another.

FAA 14 CFR Part 145 repair station ratings

The FAA system (14 CFR §145.59) uses a different vocabulary but answers the same question. The rating categories are:

Airframe — four classes, split by aircraft size (small vs large) and construction (composite vs all-metal): Class 1 composite small, Class 2 composite large, Class 3 all-metal small, Class 4 all-metal large.
Powerplant — Class 1 reciprocating engines of 400 hp or less; Class 2 reciprocating engines over 400 hp; Class 3 turbine engines.
Propeller — Class 1 fixed-pitch and ground-adjustable; Class 2 other propellers.
Radio, Instrument, and Accessory ratings — each with their own classes.
Limited ratings — issued for specific makes and models, or for a specific specialised task (including specialised services not covered by other ratings) where particular equipment and skills are required.

Like EASA, FAA repair stations operate to a capability list / operations specifications that names the specific articles they may work on.

Mapping the two systems

There is no clean one-to-one equivalence, but the rough correspondence helps a buyer translate:

Job	EASA Part-145	FAA Part 145
Heavy/base maintenance on a widebody	Class A1 (base) + type rating	Airframe rating (heavy class) + capability list
Engine overhaul (turbine)	Class B1	Powerplant Class 3
Avionics/component shop work	Class C3 (and related C categories)	Radio / Instrument / Accessory ratings
NDT / special process	Class D1	Limited rating (specialised service)

Many GCC and global providers hold both EASA and FAA approvals (often plus their national authority's, e.g. GCAA), because Gulf fleets carry a mix of EASA-, FAA- and locally registered aircraft. Dual approval widens the registrations a shop can release for — which is exactly why you check the rating against the registration of your aircraft.

How a buyer should use ratings when sourcing

Match the rating to the task and the registration. Confirm the provider's class/rating covers your aircraft type, engine, or component category — and that it is valid for the registration state of your asset.
Read the capability list, not just the class. A C-class component rating still has to name the specific article; an A-class rating still has to name the specific type.
Check currency and scope limits. Ratings carry limitations and expiry; a lapsed or restricted rating is not a release authority.
For special processes, look for the D / limited rating plus underlying accreditation. NDT and other special processes are often also backed by Nadcap accreditation.
Confirm the release document. The output of approved work is an authorised release certificate (EASA Form 1 / FAA 8130-3 / the local authority's equivalent) — that paper is what makes the work installable.

Bottom line

A maintenance provider's capability rating is a precise legal statement of what they can sign off, expressed as EASA Part-145 classes (A aircraft, B engines, C components, D specialised) or FAA repair-station ratings (airframe, powerplant, propeller, radio, instrument, accessory, plus limited ratings). Source against the rating and its capability list, matched to your aircraft's type and registration — that is the difference between a release you can use and one you cannot.