Part-21 (Design and Production Organisations)

Part-21 is the airworthiness certification code for the design and manufacture side of European aviation, set out in Annex I to Commission Regulation (EU) No 748/2012. Where Part-M and Part-ML keep an aircraft airworthy over its life, Part-21 is about how the aircraft, and every part and appliance on it, becomes airworthy in the first place: how a design is certified, how a part is manufactured to that design, and how the organizations that do this work are approved.

The design side runs through the type certificate. A new aircraft type is granted a type certificate on the basis of a certification programme demonstrating compliance with the applicable certification specifications. Changes to that approved design are classified under 21.A.91 as either minor or major: a minor change has no appreciable effect on mass, balance, structural strength, reliability, operational characteristics or other airworthiness characteristics, and everything else is major. Major changes to type design that are significant enough to be handled separately are approved as supplemental type certificates (STCs). Repairs are classified on a parallel basis, with the criteria for repairs set out around 21.A.435. Major design work generally has to be carried out or blessed by an organization holding a Design Organisation Approval under Part-21 Subpart J, which lets the organization approve certain minor changes and repairs within its privileges rather than routing everything through EASA.

The production side runs through the Production Organisation Approval under Part-21 Subpart G. A POA demonstrates it can consistently manufacture products, parts and appliances that conform to the approved design and are in condition for safe operation. The tangible output of that system is the authorized release certificate — the EASA Form 1 — which accompanies a part and attests conformity to design data and safe-operation condition. Under 21.A.307 a part is generally only eligible for installation on a type-certificated product when released on an EASA Form 1 or when it is a qualifying standard part. The DOA-versus-POA distinction is fundamental: the DOA owns the design and its changes, the POA owns making things to that design, and the two functions are approved and audited separately even when one company holds both.

Part-21 sits directly beneath the EASA Basic Regulation (Regulation (EU) 2018/1139) and connects to the rest of the airworthiness framework — it is the type-design approval that a Certificate of Airworthiness certifies conformity to, and airworthiness directives issued against a type flow from problems identified in the certified design. The FAA equivalent is its own 14 CFR Part 21, which likewise governs certification procedures for products and parts and issues its own authorized release document, the FAA Form 8130-3; STCs carry the same meaning and broadly parallel approval process on both sides of the Atlantic.

Most flight schools and aeroclubs are consumers of Part-21 rather than holders of its approvals, but the regulation shapes their day-to-day maintenance and modification decisions. When a school wants to fit a new avionics package, a glass cockpit or a modified interior to a trainer, whether that change is minor or major under 21.A.91 — and whether it needs an STC — determines the cost, the paperwork and how long the aircraft is on the ground. A change that looks trivial operationally can still be a major change in Part-21 terms.

Part-21 also governs the parts pipeline that keeps a fleet flying. Every serviceable component fitted to a certificated trainer should arrive with an EASA Form 1, and a school's maintenance provider is expected to reject parts without proper release documentation. For an operator that tracks parts inventory and installations, the Form 1 is the evidence that a component was legitimately produced to an approved design — the initial-airworthiness proof that continuing-airworthiness records then build on.

Aviatize's Maintenance Execution and Digital Data & Records modules capture the initial-airworthiness evidence that Part-21 generates — the EASA Form 1 authorized release certificate for each installed component, the modification or STC embodied, and the classification of the change — and tie that evidence to the specific airframe. That keeps the design-approval paperwork attached to the aircraft it belongs to rather than scattered across paper files.

When a school embodies a modification or fits a serialized part, Maintenance Control links the change to the aircraft's configuration and continuing-airworthiness record, so the audit trail runs cleanly from the Part-21 design approval through to the release to service and the next airworthiness review.