7.1 Type Certification, TCDS, Major/Minor Changes & Supplemental Type Certificates (STC)

7.1 Type Certification, TCDS, Major/Minor Changes & Supplemental Type Certificates (STC)

Quick Answer: EASA Part-21 (Annex I to Commission Regulation (EU) No 748/2012) governs initial airworthiness, establishing the certification rules for aircraft, engines, propellers, parts, and appliances, as well as design and production organisations. A Type Certificate (TC) certifies that a type design complies with its certification basis, while the Type Certificate Data Sheet (TCDS) defines its certified specifications and operating boundaries. Under rule 21.A.91, changes to type design are classified as Minor (no appreciable effect on mass, balance, structural strength, reliability, operational characteristics, noise, or emissions) or Major. Minor changes and minor repairs can be approved by EASA or by an approved Design Organisation (DOA) under the single privilege at 21.A.263(c)(2), whereas major changes require EASA approval (or a DOA holding the extended privilege at 21.A.263(c)(8)), and a non-TC holder introducing a major change needs a Supplemental Type Certificate (STC) under Subpart E. Major repair designs are approved by EASA or by a DOA holding the 21.A.263(c)(5) privilege.

In European aviation law, airworthiness is divided into two distinct statutory domains: Initial Airworthiness (the design, certification, and manufacture of aeronautical products) and Continuing Airworthiness (the maintenance, management, and inspection of products in operational service). While continuing airworthiness is governed by Regulation (EU) No 1321/2014 (Part-M, Part-ML, Part-145, Part-66), initial airworthiness is governed by Commission Regulation (EU) No 748/2012, whose Annex I is universally known as EASA Part-21.

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Regulatory Framework: Regulation (EU) No 748/2012 and Scope of Part-21

Part-21 establishes the harmonized legal requirements for certifying aeronautical products and the enterprises that design and manufacture them. Its legal scope covers:

1. Product Certification: The issuance of Type Certificates (TC), Restricted Type Certificates (RTC), and Supplemental Type Certificates (STC) for aircraft, engines, and propellers;
2. Parts and Appliances: Certification under European Technical Standard Orders (ETSO);
3. Design Changes & Repairs: Classification and approval of modifications and structural repair schemes;
4. Airworthiness and Environmental Documentation: Issuance of Certificates of Airworthiness, Restricted Certificates of Airworthiness, Noise Certificates, and Permits to Fly;
5. Organizational Approvals: Standards for Design Organisation Approval (DOA - Subpart J) and Production Organisation Approval (POA - Subpart G).

+-----------------------------------------------------------------------------------+
|                     EASA AIRWORTHINESS REGULATORY DIVISION                        |
+-----------------------------------------------------------------------------------+
| INITIAL AIRWORTHINESS:                     CONTINUING AIRWORTHINESS:              |
| Commission Regulation (EU) No 748/2012     Commission Regulation (EU) No 1321/2014|
| - Annex I: Part-21                         - Annex I: Part-M (Commercial/Complex) |
|   * Subpart B: Type Certificates           - Annex II: Part-145 (Maintenance Orgs)|
|   * Subpart D/E: Design Changes & STC      - Annex III: Part-66 (Certifying Staff)|
|   * Subpart G: Production Orgs (POA)       - Annex Vb: Part-ML (Light Aircraft)   |
|   * Subpart J: Design Orgs (DOA)           - Annex Vc: Part-CAMO (Management)     |
|   * Subpart M: Repair Design Approvals     - Annex Vd: Part-CAO (Combined Orgs)   |
+-----------------------------------------------------------------------------------+

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Type Certificates (TC) and Restricted Type Certificates (RTC)

A Type Certificate (TC) issued under 21.A.21 is the document issued by EASA certifying that the type design of an aircraft, engine, or propeller complies with the applicable Certification Basis (Certification Specifications and environmental protection standards). Demonstrating compliance is known as "showing of compliance" and requires extensive flight tests, structural load tests, system safety analyses, and software evaluations.

The Certification Basis

The certification basis of an aircraft is established by EASA and recorded in the TC. It consists of:

• The applicable Certification Specification (CS) established at the date of application (e.g. CS-25 for large jetliners, CS-23 for light aeroplanes);
• Any Special Conditions (SC) issued under 21.A.16B for novel or unusual design features not addressed by existing CS standards (such as full fly-by-wire flight control architectures, composite fuselage barrels, or novel electric propulsion systems);
• Any Equivalent Safety Findings (ESF) under 21.A.21 where compensating safety factors balance technical non-compliances;
• Applicable environmental protection requirements (noise and emissions standards defined in ICAO Annex 16).

Restricted Type Certificate (RTC — Rule 21.A.23)

Where an aircraft model does not satisfy standard airworthiness specifications (for instance, former military jet trainers, specialized agricultural aircraft, or vintage transport aircraft), EASA may issue a Restricted Type Certificate (RTC). The RTC defines specific operational limitations (e.g. carriage of passengers prohibited, restricted operating airspaces) ensuring adequate safety for its specific role. An aircraft holding an RTC can only be issued a Restricted Certificate of Airworthiness.

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Obligations of the Type Certificate Holder (Rule 21.A.44)

Holding a Type Certificate confers significant commercial rights, but it also imposes binding, long-term statutory obligations under 21.A.44:

1. Continued Airworthiness Support: The TC holder must maintain continuous technical capability to monitor and support the fleet throughout its operational lifespan;
2. Instructions for Continued Airworthiness (ICA): The TC holder must prepare, publish, and distribute complete maintenance documentation (Aircraft Maintenance Manual - AMM, Illustrated Parts Catalogue - IPC, Wiring Diagram Manual - WDM, Structural Repair Manual - SRM) to all operators;
3. Airworthiness Limitations Section (ALS): The TC holder must publish mandatory life limits, fatigue replacement thresholds, and Certification Maintenance Requirements (CMR) within the ALS of the ICA. These limits cannot be deviated from by operators;
4. Occurrence Monitoring & Investigation (21.A.3A): The TC holder must maintain an occurrence reporting system, investigate in-service accidents and structural failures, and report any unsafe condition to EASA within 72 hours;
5. Corrective Actions & Service Bulletins: When an unsafe condition is identified, the TC holder must develop corrective engineering solutions, issue Service Bulletins (SBs), and submit proposed corrective data to EASA for mandatory Airworthiness Directive (AD) rulemaking.

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The Type Certificate Data Sheet (TCDS)

The Type Certificate Data Sheet (TCDS) is the official legal appendix to the Type Certificate published by EASA. It serves as the definitive reference manual defining the exact boundary of the certified product. For licensed maintenance engineers, the TCDS is the ultimate authority when verifying aircraft configuration and installed equipment.

Essential Contents of a TCDS

• Model Designations: All approved sub-variants (e.g. Airbus A320-214, A320-232, A320-271N);
• Certification Basis: Applicable CS amendment level, Special Conditions, and exemptions;
• Approved Powerplants: Exact engine model variants, thrust/power ratings, and operating limits;
• Propellers (if applicable): Approved blade and hub assemblies, diameter ranges, and pitch limits;
• Airspeed Limitations: Certified indicated airspeeds including $V_{NE}$ (never-exceed speed), $V_{NO}$ (normal operating limit), $V_A$ (manoeuvring speed), $V_{MO}/M_{MO}$ (maximum operating limit speed/Mach), and $V_{FE}$ (flaps-extended speed);
• Mass and Center of Gravity Limits: Maximum Take-Off Mass (MTOM), Maximum Landing Mass (MLM), Maximum Zero Fuel Mass (MZFW), datum reference location, and fore/aft center of gravity envelopes;
• Fuel and Fluid Capacities: Total and usable fuel volume per tank, approved fuel specifications (e.g. Jet A-1, AVGAS 100LL), and approved engine lubricating oils;
• Cabin & Crew Configurations: Minimum required flight crew (e.g. two pilots) and maximum passenger seating capacity;
• Kinds of Operations Equipment: Mandatory instrument and avionics lists for Day VFR, Night VFR, IFR, Category III all-weather autoland, and ETOPS approval.

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Classification of Changes to Type Design (Rule 21.A.91)

Once an aircraft is certified, modifications are inevitable. Under rule 21.A.91, every change to a type design must be classified as either Minor or Major prior to approval:

"A 'minor change' is one that has no appreciable effect on the mass, balance, structural strength, reliability, operational characteristics, noise, fuel venting, exhaust emission, or other characteristics affecting the airworthiness of the product. All other changes are 'major changes'."

Major vs Minor Change Classification Criteria

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Approval of Changes: EASA vs DOA vs Supplemental Type Certificates (STC)

The approval pathway depends directly on the classification of the change and the identity of the applicant:

+-----------------------------------------------------------------------------------+
|                         TYPE DESIGN CHANGE APPROVAL PATHWAYS                      |
+-----------------------------------------------------------------------------------+
|                                                                                   |
| 1. MINOR CHANGE (21.A.95):                                                        |
|    - Approved directly by EASA; OR                                                |
|    - Approved internally by an approved Design Organisation (DOA) under          |
|      privilege 21.A.263(c)(2), which covers minor changes AND minor repairs,
|      without Agency involvement.                         |
|                                                                                   |
| 2. MAJOR CHANGE BY TC HOLDER (21.A.97):                                           |
|    - Approved directly by EASA as an amendment to the Type Certificate or as a    |
|      standard Major Change Approval.                                              |
|                                                                                   |
| 3. MAJOR CHANGE BY NON-TC HOLDER (Subpart E - 21.A.111):                         |
|    - Must be approved by EASA as a SUPPLEMENTAL TYPE CERTIFICATE (STC).           |
|    - Applicant must demonstrate compliance with the applicable certification basis|
|      and assume ongoing continuing airworthiness responsibilities for the STC.   |
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Supplemental Type Certificates (STC — Subpart E)

An STC is issued under 21.A.115 exclusively by EASA. It certifies a major modification developed by an engineering organisation that does not own the original Type Certificate (for example, an avionics company retrofitting modern glass cockpits into older transport aircraft, or a cargo conversion specialist converting passenger airframes to freighters).

• Legal Obligations of the STC Holder: The STC holder assumes full "TC-holder-like" statutory obligations for the modified area. They must publish ICA supplements (e.g. Flight Manual Supplements - AFM-S, Maintenance Manual Supplements - AMM-S), report occurrences to EASA under 21.A.3A, and develop corrective Service Bulletins if their modification causes in-service safety issues.

Comparison: Type Certificate (TC) vs Supplemental Type Certificate (STC)

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Repair Design Approvals under Part-21 Subpart M (Rule 21.A.431)

Damage sustained by an aircraft in service (e.g. bird strikes, lightning strikes, ground vehicle collisions, corrosion) requires an approved repair. In European aviation, repairs are governed by Subpart M of Part-21.

Minor Repairs vs Major Repairs (21.A.435)

Repairs are classified as Minor or Major using the identical criteria defined in 21.A.91:

• Minor Repair: A repair that does not appreciably affect mass, balance, structural strength, reliability, operational characteristics, or emissions. Approved by EASA or by an approved DOA under privilege 21.A.263(c)(2), which covers minor changes and minor repairs;
• Major Repair: A repair that appreciably affects structural integrity or flight safety (e.g. a major composite skin splice on a wing torque box or cutting a pressurized fuselage frame). Major repair designs are approved by EASA, or by a DOA that holds the specific privilege at 21.A.263(c)(5) — note that (c)(5) is the major repair privilege, not the minor one.

Design Approval vs Embodiment

Module 10 candidates must strictly distinguish between design approval and embodiment:

• Repair Design Approval (Part-21): The engineering process certifying that the proposed repair drawing and stress analysis satisfy structural CS standards. Conducted under Part-21 by EASA or an approved DOA;
• Repair Embodiment (Part-145 / Part-CAO / Part-ML): The physical maintenance execution of the repair on the aircraft by licensed certifying staff and issuing a Certificate of Release to Service (CRS). Maintenance organisations cannot invent repair designs; they must execute designs approved under Part-21.

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Practical Maintenance Scenario: Classification & Repair Embodiment

Operational Context

During a turnaround inspection of an Airbus A320, a technician discovers a 15-centimeter puncture in the upper wing skin caused by an airport catering truck hoist. The damage penetrates the upper skin into the wing integral fuel tank and damages an underlying structural rib.

Regulatory Assessment under Part-21:

1. Technical Manual Review: The engineer consults the Airbus Structural Repair Manual (SRM). The SRM contains pre-approved repair schemes designed by Airbus under its DOA privileges.
2. Beyond SRM Limits: The structural damage exceeds the maximum dimensional limits published in the SRM. The repair cannot be classified as an approved standard repair.
3. Classification under 21.A.91: Because the damage affects primary load-carrying structure and integral fuel containment, the repair design is classified as a Major Repair under 21.A.435.
4. Design Approval: The airline requests an engineering repair scheme. The scheme is designed by an approved Part-21 Subpart J DOA (Airbus or an independent approved DOA). Because it is a major repair, the engineering package must be approved by EASA (or by the DOA if granted specific extended major repair approval privileges).
5. Embodiment and CRS: Once the approved Part-21 repair design documentation is received, a Part-145 maintenance organisation carries out the physical riveting, sealing, and testing, issuing a Certificate of Release to Service (CRS) referencing the specific Part-21 repair approval number.

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EASA Module 10 Examination Tips & Regulatory Traps

• Regulation Number: Remember that initial airworthiness is governed by Regulation (EU) No 748/2012 (Part-21), whereas continuing airworthiness is governed by Regulation (EU) No 1321/2014.
• Appreciable Effect: Memorize the exact wording of 21.A.91: A minor change has no appreciable effect on mass, balance, structural strength, reliability, operational characteristics, noise, fuel venting, or emissions.
• Who Approves STCs? EASA approves Supplemental Type Certificates. A Part-145 maintenance organisation never approves an STC—it only embodies it.
• DOA Privileges: An approved DOA can approve minor changes and minor repairs under the single privilege 21.A.263(c)(2). Major repair designs need 21.A.263(c)(5) and certain major changes need 21.A.263(c)(8). A DOA can never issue an initial Type Certificate.
• Design vs Embodiment: Repair design approval falls under Part-21 (Subpart M); repair embodiment and release fall under Part-145 (145.A.50) or Part-ML (ML.A.801).