In-House Fabrication per EASA Part-145.A.42

Understanding In-House Fabrication under EASA Part-145

In the European aviation maintenance sector, In-House Fabrication (IHF) refers to the limited production of aircraft parts by a Part-145 approved Maintenance, Repair, and Overhaul (MRO) organization for its own maintenance needs. Under the EASA framework, IHF is tightly controlled and is not equivalent to full manufacturing. Instead, it is a privilege that allows an approved maintenance organisation to fabricate certain parts strictly for use in its own facility and during maintenance work. This practice is governed by Section 145.A.42 of the EASA regulations, which outlines how and when an MRO can perform part fabrication internally. The term “fabrication” in this context signifies restricted production under specific limitations, ensuring it supports maintenance tasks without crossing into uncontrolled manufacturing.

Regulatory Basis: EASA Part-145.A.42 and Its Guidance

EASA Part-145.A.42 (often cited as 145.A.42(b)(iii) in the regulation) provides the legal basis for in-house fabrication. While the regulation itself sets the high-level rule, detailed expectations are provided in the Acceptable Means of Compliance (AMC) and Guidance Material (GM). According to AMC1 145.A.42(b)(iii), an organisation must have the explicit agreement of its competent authority (usually the national aviation authority or EASA for foreign approvals) to conduct in-house fabrication. This agreement is formalized by including a detailed fabrication procedure in the Maintenance Organisation Exposition (MOE), which is the company’s approved manual outlining how it complies with Part-145 requirements.

Key regulatory points include:

• Technical Capability: The maintenance organisation must only fabricate parts that lie within its technical and procedural capability. This means the staff, tools, equipment, and processes should be adequate for making the part to the required standards. If a special process (e.g. heat treatment or complex machining) is required that the organisation cannot perform or control, then that part cannot be fabricated in-house without an approved alternative solution.

   

• Approved Design Data: The part must be fabricated strictly in accordance with approved data. Acceptable design data sources include the Type Certificate (TC) holder’s manuals or drawings, Part-21 design organisation data (e.g. STC or repair scheme), or other data approved or accepted by EASA. In practice, this means you cannot just copy a broken part by measuring it (“no fabrication to pattern”) without a proper engineering drawing or spec that is approved. All dimensions, materials, and processes need to be defined in the approved data used.

   

• Authority Oversight: The scope of parts that an organisation is allowed to fabricate, and the procedures to do so, must be accepted by the authority. The MOE procedure for fabrication will usually detail what categories of parts can be made, how they will be made and inspected, and references to the approved data. The competent authority reviews and approves this procedure, effectively licensing the organisation’s fabrication privileges. Any changes to the scope (for example, if the organisation wants to fabricate a new type of part) typically require an MOE amendment and further approval.

   

Permitted Scope and Examples of IHF Parts

EASA’s guidance provides examples of the kinds of parts that Part-145 organisations might fabricate in-house. These are generally ancillary or simple parts that support maintenance or repairs, rather than entire complex assemblies. According to the AMC, examples of permissible in-house fabricated parts include:

• Bushes, sleeves, and shims: Small spacers or alignment components often needed during assembly or repairs.
• Secondary structural elements and skin panels: Non-primary structure parts or patch panels for repairs, made to approved repair scheme dimensions.
• Control cables: Fabrication of control cable assemblies (e.g. for flight controls or door mechanisms) using approved cable specifications and end fittings.
• Flexible and rigid pipes: Manufacturing replacement fluid hoses or tubes, such as hydraulic or fuel lines, to the specs given in maintenance manuals.
• Electrical cable looms and harnesses: Assembling wiring harnesses or looms for avionics or electrical systems in accordance with wiring diagrams and instructions.
• Formed or machined sheet metal parts for repairs: Creating sheet metal parts, like brackets or clips and repair doublers, especially when performing structural repairs as per approved repair data.

These examples are illustrative and not exhaustive. The common thread is that each part is made to support a specific maintenance task (overhaul, repair, or modification) on an aircraft or component that the MRO is working on, and each is backed by approved technical data. Fabrication should never be done on an ad-hoc basis without proper data – for instance, making a part just by copying an old one is not allowed unless you have an engineering drawing for it that the authority finds acceptable.

It's also worth noting that these fabricated parts are typically one-for-one replacements or repair parts used immediately on the job at hand. They are not fabricated in large batches for future stock or sale.

Operational Boundaries: Fabrication vs. Manufacturing

One of the most important compliance considerations is understanding the boundary between in-house fabrication and aircraft part manufacturing. EASA regulations draw a clear line to ensure that Part-145 maintenance organisations do not drift into unauthorized manufacturing:

• Internal Use Only: Any part fabricated under a Part-145 approval may only be used by that same organisation and only on aircraft/components that are in its facility for maintenance. In-house fabricated parts cannot be sold or supplied to third parties, nor can they be transferred to another organisation’s stock. Even within the company, if a locally-fabricated part is left over as surplus, it must be segregated and kept out of any certified inventory shipments. In other words, these parts don’t get an EASA Form 1 and cannot leave the organisation as airworthy certified spares.

   

• No Commercial Production: EASA explicitly prohibits fabrication of parts or modification kits for onward supply or sale by a Part-145 organisation. Such activity would be considered manufacturing, which falls under Part-21 (Production Organisation Approval) regulations. If there is a business need to produce parts for sale or use outside your own maintenance activities, the company must obtain a Part-21 production approval.

   

• One-off Maintenance Purpose: Fabrication under Part-145 is intended for one-off or limited scope needs as part of maintenance. As summarized by industry experts, fabricated components are created for specific maintenance or modification activities, have no Form 1 certificate, and are not made for mass production or broad distribution. By contrast, manufactured parts (under Part-21) are produced under a regulated production system with a Form 1 and often intended for general use or sale. This distinction ensures that any part entering the supply chain with a Form 1 has been made under the more stringent production oversight, whereas parts made under Part-145 stay tied to the maintenance task they were needed for.

In essence, fabrication serves immediate maintenance needs, whereas manufacturing addresses commercial supply. Part-145 in-house fabrication is a tightly controlled subset of activities, always linked to a repair or modification on hand, and ceases once that need is fulfilled.

Compliance Requirements and Demonstrating Conformity

For a maintenance organisation to exercise in-house fabrication privileges, it must demonstrate compliance with EASA’s requirements both in documentation and in practice. Key compliance elements include:

• Maintenance Organisation Exposition (MOE) Procedures: The MOE is required to contain a dedicated procedure detailing how parts fabrication is managed. This procedure typically covers the approval scope (what can be fabricated), responsibilities (who can authorize and perform fabrication tasks), process steps (from design data verification, material sourcing, fabrication method, to inspection), and record-keeping. The competent authority must approve this procedure, and any fabrication activity must strictly follow it.

   

• Approved Design Data for Each Part: Before fabrication begins, ensure you have the correct, approved design data for the part. This could be a reference in the aircraft’s maintenance or repair manual, a service bulletin, or a specific engineering drawing or repair scheme provided by a Design Organisation (e.g. an EASA Part-21J DOA). The data should specify the part number, material, dimensions, and processes. Using approved data means the final fabricated part meets an established aerospace design standard. If only incomplete data exist (e.g. a rough sketch or just an old sample part), fabrication should not proceed until proper approved data is in hand or an alternative solution is approved by the authority.

   

• Capability and Resources: The organisation’s capability list and workshops must align with the fabrication work. If the MOE procedure allows making control cables, for example, the shop should have proper swaging tools, test rigs, and trained personnel for cable assemblies. EASA expects that fabrication and any required testing are within the organisation’s proven capabilities. Auditors will look for evidence like special process approvals (for welding, plating, etc.), technician training records, and calibrated tooling to verify this.

   

• Independent Inspection: After fabricating a part, it must undergo an inspection prior to installation. This inspection step should ideally be done by someone other than the person who made the part (an independent inspector or quality control staff) to verify the part fully conforms to the approved data. The inspection should check dimensions, material certification, and any functional tests as applicable. This ensures an objective quality gate before the part is used on the aircraft.

   

• Documentation and Records: All steps of fabrication need to be traceable. Maintain a fabrication work order or shop traveller that links to the work order for the aircraft/component, references the approved data used, records material batch numbers and any process like heat treatment, and includes the results of inspections and tests. These records should be retained as part of the maintenance records. They demonstrate that the part was made correctly and provide traceability. During compliance audits, such records are reviewed to ensure the procedure was followed and the part can be traced from raw material to installation.

   

• Part Marking: Every fabricated part should be clearly identified. The AMC guidance requires that, where practical, the part is stamped or labeled with a part number that ties back to the design/data, and also marked with the organisation’s identity (such as a company code or maintenance organisation approval number). For example, an MRO might assign an internal part number or use the original part number with a suffix, and add its EASA approval reference or a unique code and date (e.g., MOE-ABC-2024/05) to identify it as locally fabricated. This traceability marking is important if the part is ever inspected or removed later – it shows it was an in-house fabricated item and not an uncertified spare from elsewhere. Marking also helps segregate these parts from commercial inventory.

By adhering to these requirements, an organisation demonstrates that its in-house fabrication is under control, aligns with regulatory standards, and that safety is not compromised.

Documentation and Distinguishing IHF in Practice

Documentation plays a crucial role in compliance. Internally, the fabrication process should be documented step-by-step – from the engineering justification to the final inspection release:

• The fabrication request often originates in the maintenance job card or work order, indicating a needed part that is not readily available or needs to be made per a repair procedure.
• The engineering or technical office should verify the approved data. If the data comes from the aircraft’s maintenance documents or an STC/repair scheme, a reference to that document is made. If the data isn’t explicit, engineering might need to produce a drawing and get it approved by the type certificate holder or authority before proceeding.
• A dedicated fabrication work order is opened, and materials are issued from stores (which themselves should conform to required standards and have traceability).
• During fabrication, technicians follow the approved process (e.g. machining a bushing to specified dimensions, or assembling a cable per the manual). Any special process like welding or heat treatment must be done per approved specs and by qualified staff.
• After the part is made, the quality control inspection is performed (dimensional checks, non-destructive testing if applicable, etc.). Results are recorded, and the inspector signs off that the part conforms to the approved data.
• The part is then tagged or marked with the part number and the organisation’s ID, and it’s cleared for installation on the aircraft under maintenance. Importantly, no EASA Form 1 is issued – instead, the installation of the part is released as part of the overall maintenance release or component certificate for the bigger assembly.
• The maintenance records (e.g. the aircraft logbook entry or component release paperwork) should mention that an in-house fabricated part was installed, referencing the internal work order or procedure. This transparency ensures that anyone reviewing the records knows the origin of the part and can follow the trail back to how it was made.

Throughout this process, it’s critical for the MRO to distinguish IHF parts from standard or purchased parts. Good practice is to have unique part number identifiers or prefixes for fabricated parts and to store any spares separately as unapproved for outside use. In an audit, regulators will check that the MRO hasn’t issued any Form 1 or vendor invoice for such parts, and that they remain within the usage scope.

Best Practices for Compliance and Audit Readiness

To excel in compliance and be always audit-ready regarding in-house fabrication, MROs should adopt several best practices:

• Define Clear Boundaries in the MOE: Be very specific in your MOE about what parts your organisation is allowed to fabricate. This can include listing broad categories (like those EASA examples) or even specific part numbers if applicable. Clear scope definition prevents accidental overreach.

   

• Training and Competence: Ensure that personnel involved in fabrication (technicians and inspectors) are trained on the fabrication procedure and understand the regulatory implications. They should be aware, for instance, that a part they make can’t be used on another customer’s job or sold. Regular training refreshers and competency assessments (especially for any special processes like welding or composite repairs) are advisable.

   

• Quality Control and Independence: Incorporate an independent check in the workflow. The person inspecting the fabricated part should ideally not be the same person who made it. This separation adds objectivity and is often looked upon favorably by auditors. It’s a demonstration of the “four-eyes principle” for quality in fabrication.

   

• Materials and Traceability: Source all materials for fabrication with the same diligence as any other aviation part. Use aerospace-grade materials and keep material certificates on file. Traceability of raw material to the finished part is crucial in case of future findings or inquiries.

   

• Internal Audits and Reviews: Your compliance monitoring (internal audit) program should periodically review the fabrication activities. An internal auditor might check a sample of fabricated part records to ensure procedures were followed, or verify that markings and segregation of these parts are being maintained. Regular internal audits will catch any procedural drift early and demonstrate proactive compliance.

   

• Stay Within Your Limits: If a maintenance task seems to require a part that is beyond your approved fabrication scope or capability, resist the temptation to fabricate without authorization. Instead, seek external help – either procure the part from an approved source or engage a Part-21 design/production organisation to make it. Alternatively, approach your authority to see if an expansion of scope can be approved (backed by evidence that you have the necessary capability). It’s better to go through proper channels than to risk a non-compliance by overstepping your approval.

   

• Documentation Readiness: Keep a well-organized file (physical or digital) for each fabrication activity. Include copies of the approved data, material certs, work orders, inspection reports, and photos if taken. In an authority audit, being able to quickly produce this file for a fabricated part will inspire confidence in your control of the process. It shows that you treat fabricated parts with the same rigor as any certified component.

By following these best practices, MROs not only comply with EASA Part-145.A.42 requirements but also ensure safety and quality. In-house fabrication, when done correctly, provides flexibility to solve maintenance issues (like making a rare or long lead-time part) without compromising regulatory compliance or airworthiness.

Conclusion

In-house fabrication under EASA Part-145 is a valuable capability for maintenance organisations, enabling them to fabricate certain parts on the spot to facilitate repairs or modifications. It operates under a strict regulatory framework: the parts made are for maintenance use only within the organisation, must be built to approved data, and are controlled through approved procedures with authority oversight. By clearly distinguishing fabrication from true manufacturing, EASA ensures that safety is upheld – fabricated parts fill immediate maintenance needs but are not injected into the general supply chain.

For aviation compliance personnel and engineers, the focus should be on meticulous adherence to the rules: have the right data, document every step, and stay within the authorised scope. When properly managed, in-house fabrication can greatly enhance an MRO’s effectiveness (for example, reducing downtime by making a needed part in-house) while remaining fully compliant. As with all aspects of Part-145, robust internal processes and a culture of quality are the keys to audit-readiness and safe operations. By following EASA’s guidelines and the best practices above, maintenance organisations can confidently use in-house fabrication to support continued airworthiness without crossing the line into unapproved production.