Certifying Staff vs Support Staff In EASA Part - 145

EASA Part-145 (EU Reg. 1321/2014 Annex II) sets strict rules for approved maintenance organizations. A key question many ask is “What is a certifying staff?” In this context, certifying staff are Part-66 licensed maintenance personnel authorized to release an aircraft to service. In contrast, support staff assist in maintenance but do not issue the final release. Understanding the difference is vital for an EASA Part-145 maintenance organisation to operate correctly. We first define Line Maintenance and Base Maintenance, then explain Part-66 license categories (A, B1, B2, C) and how these tie into the roles of certifying and support staff under Part-145.

Line Maintenance vs Base Maintenance

Line maintenance refers to routine tasks performed to keep an aircraft airworthy before flight. It includes daily or transit checks, troubleshooting, and minor repairs. EASA guidance (AMC 145.A.10) defines line maintenance as “any maintenance carried out before flight to ensure the aircraft is fit for the intended flight”. Common line tasks include: troubleshooting and defect rectification, component replacements (even engines or props if equipped for quick change), and scheduled inspections (e.g. daily checks or simple A-check items) that do not require extensive disassembly. For example, replacing a faulty indicator lamp, changing a tire, or correcting a minor electrical fault on the ramp are line maintenance tasks. Minor repairs or simple on-ramp engine runs also fall under line maintenance.

The tasks outside these criteria are considered Base Maintenance. Base maintenance involves more in-depth work, usually in a hangar, requiring significant disassembly or specialized equipment. Examples include any scheduled check or modification that requires extensive teardown or inspection of the airframe or engines. EASA provides examples: tasks involving “maintenance or replacement of major components requiring a hangar, special GSE such as a docking structure and complex planning (e.g. full landing gear replacement, simultaneous replacement of two engines)”; any scheduled inspection needing extensive disassembly; and major repairs or modifications. In short, if a task cannot be done quickly on the line with basic tools and access, it is base maintenance. For instance, a C‑check such as a 2 year check or higher requiring deep structural inspection, performance of wing structural repairs, or overhauling a hydraulic system are all base maintenance tasks.

EASA Part-66 License Categories (A, B1, B2, C)

EASA Part-66 (EU Reg. 1321/2014 Annex III) defines the Aircraft Maintenance License categories. These licenses qualify who can certify maintenance work:

• Category A – Line Maintenance Certifying Mechanic. Permits release-to-service after minor scheduled line maintenance and simple defect rectification. The license is subdivided by aircraft type (A1 turbofan airplane, A2 piston airplane, A3 turboprop helicopter, A4 piston helicopter). An A-license holder may only certify tasks listed on their Part-145 authorization.
• Category B1 – Mechanical Maintenance Certifying Technician. Covers aircraft structures, powerplant, and mechanical/electrical systems. A B1 licensee can certify both minor and major maintenance on these systems. B1 includes all privileges of A (so B1 can also do the A tasks). For example, a B1 engineer with a Boeing 737 rating can sign off engine removals, landing gear overhauls, airframe repairs, and any routine tasks within that scope.
• Category B2 – Avionics Maintenance Certifying Engineer. Covers avionic and electrical systems. A B2 licensee can certify maintenance on avionics/avionic systems and perform certain electrical/mechanical tasks (simple tests, minor line checks). B2 does not include the broader A tasks (no inherent A privileges), but the holder can sign minor line tasks on their authorization. For instance, a B2 with a 737 rating can certify aircraft radios, instruments, and flight controls diagnostics.
• Category C – Base Maintenance Certifying Engineer. Allows the holder to issue a Certificate of Release to Service (CRS) after base maintenance of the entire aircraft. Category C licenses are obtained through experience (e.g. 3 years as B1/B2) and entail only certifying duties. A Category C holder supervises and signs off any heavy maintenance event, but typically does not perform individual tasks. Notably, a C license can also be obtained through the academic route whereas a B1/B2 cannot be obtained through an academic route.

Note: There are further licence categories per EASA Part-66 but for the context of this Article the A, B1, B2 and C licence categories are mentioned.

Each Part-145 maintenance organisation must ensure that its certifying (and support) staff hold the appropriate Part-66 license and are authorized within its scope. Any limitation on a Part-66 license (e.g. type ratings or subcategory) must be reflected in the person’s Part-145 authorization.

Certifying Staff in Line Maintenance

In line maintenance, the certifying staff are those mechanics licensed in categories A, B1, or B2 who have been given authorisation to sign for release-to-service on line tasks. By definition, certifying staff (C/S) are “staff authorised by a maintenance organisation to release an aircraft to service… following line or base maintenance”. In practice:

• A-license holders act as line certifying staff for the simplest tasks. For example, an A licensed technician might handle a daily check or a quick wheel change. They can only certify work they personally performed, as defined in their authorization.
• B1 and B2 license holders can also be certifying staff in line maintenance, each signing off work in their specialty. A B1 might certify the completion of a scheduled engine check or structural repair, and a B2 might certify avionics troubleshooting or recalibration. Part-145 requires that each line certifying staff be listed in the organisation’s exposition with the scope of aircraft types/subtypes they are authorised for.

Certifying staff must meet experience and training requirements, and the organisation must grant them an individual authorisation (per 145.A.30). Essentially, any suitably rated A, B1 or B2 licensed engineer can be certifying staff for line maintenance, provided they are properly trained on company procedures and their particular aircraft. In summary, line maintenance certifiers are Part-66 license holders (A, B1 or B2) working within their licence scope, signing the Techlog, jobcards, work orders or equivalent for line work they do.

Certifying Staff in Base Maintenance (Category C)

In a base maintenance environment, only Category C license holders serve as certifying staff. The C license grants authority to issue the CRS for the entire aircraft after a base maintenance event. These C certifying staff typically do not perform the hands-on work; instead, they oversee the base maintenance process. EASA guidance makes this clear: “the principal function of category C certifying staff is to ensure that all required maintenance has been called up and signed off by category B1, B2… support staff, as appropriate, before issue of the certificate of release to service.”.

In other words, the C certifying staff have final technical responsibility. They check that every maintenance task (from structural checks to avionics repairs) was done to standard. Only when all work and inspections are completed and signed by the support staff can the C certifier sign the CRS on behalf of the maintenance organisation authorising them for this role. Often, but not mandatory, a C license holder also holds a B1 or B2 rating, so they understand the work. Crucially, Part-66 C license alone does not empower one to perform maintenance; it only empowers one to sign the release after base maintenance. In summary, in base maintenance the certifying staff are specifically the Category C engineers who supervise the process and issue the final sign-off.

Support Staff in Base Maintenance

Support staff in base maintenance are experienced technicians (typically B1 or B2 licensed) who assist the Category C certifying staff. They are authorised by the Part-145 organisation to carry out and sign off maintenance tasks but do not hold release-to-service privileges. By regulation, “support staff” are defined as holders of B1, B2, B2L, B3 or L Part-66 licenses working in a base maintenance environment, not necessarily with certification rights.

In practice, B1 support staff handle mechanical/structural work and B2 support staff handle avionics/electrical work. They perform tasks (e.g. engine overhauls, avionics bench tests), sign the task cards, and ensure each piece of maintenance meets standards. They effectively verify to the C certifying staff that “their part” of the work is done correctly. For example, after a major engine swap, a B1 support engineer will sign that the engine install and tests are complete. The C certifying staff then uses these signatures to confirm all items are done. As one EASA guide notes, support staff “ensure that all relevant tasks or inspections have been carried out to the required standard before the Category C certifying staff issues the certificate of release to service.”.

The Part-145 organisation’s Maintenance Organisation Exposition (MOE) will specify which B1/B2 individuals are support staff and their responsibilities. Support staff must also meet experience and training criteria similar to certifiers (regular checks, human factors training, etc.). They effectively coordinate and oversee the maintenance flow at base: assigning tasks, supervising unlicensed helpers, and maintaining maintenance records. Although they cannot issue the final CRS, their role is crucial. Support staff act as the “eyes and hands” of the certifying staff during complex maintenance, ensuring the B1/B2 teams execute work correctly so the Category C engineer can confidently complete the release.

Unlicensed Personnel in Base Maintenance

Many base maintenance organisations employ unlicensed personnel (e.g. apprentices or assistants) to perform certain tasks under supervision. EASA rules require that unlicensed mechanics always work under the direct oversight of authorised staff. A non-licensed worker may replace parts or assist in inspections, but cannot certify any work. Importantly, EASA guidance clarifies that a signing mechanic can only supervise an unlicensed helper on the same specific task they are doing. An authorised mechanic may not oversee multiple helpers across different jobs simultaneously – that broader coordination is the responsibility of the certifying/support staff.

In effect, certifying and support staff must identify any unlicensed helpers in the maintenance team and supervise them carefully. The MOE typically requires listing these helpers and defining who oversees them. Before a Category C certifier signs off base maintenance, they must be assured that any work done by unlicensed personnel was properly checked by the licensed staff. This hierarchy of supervision helps maintain safety: even though unlicensed personnel can contribute, every action must be backed up by a qualified certifying or support engineer.

Conclusion

In summary, EASA Part-145 clearly distinguishes certifying staff from support staff. Certifying staff are the licensed engineers who legally sign an aircraft back into service. In line maintenance, this role is filled by Category A, B1 or B2 license holders, each certifying tasks within their scope. In base maintenance, only a Category C license holder serves as the certifying staff, overseeing all work and issuing the final release. Support staff, on the other hand, are B1/B2 (or similar) licensed technicians in a base environment who execute and sign off individual maintenance tasks. They ensure every task is completed correctly under company procedures, but do not issue the CRS themselves. Unlicensed personnel may assist under direct supervision, but ultimate responsibility lies with the licensed staff.

Understanding “what is a certifying staff” versus support staff removes confusion: it is simply a matter of who releases to service under Part-145. Every Part-145 maintenance organisation must have an approved scope (part 145 maintenance organisation certificate) and ensure each certifier’s Part-66 licence covers the work they sign off. To answer “what is part 145 certification?”: it refers to the organisation’s EASA approval and the associated requirement to use properly licensed certifying staff. Likewise, an “aircraft maintenance license” means the EASA Part-66 license (A, B1, B2, C, etc.) that qualifies the engineer.

By summarizing the roles:

• Line maintenance certifying staff: Part-66 A/B1/B2 licensed, sign off line tasks.
• Base maintenance certifying staff: Part-66 C licensed, oversee entire base check and sign CRS.
• Support staff (base): Part-66 B1/B2 (etc) licensed, perform and sign off tasks, assist C-staff.
• Unlicensed: Assist only under supervision, no certification privileges.

Maintaining clear procedures and authorisations in line with EASA Part-145 and Part-66 ensures all staff know their duties. This comprehensive view resolves confusion: the license category and the Part-145 role (line or base) together determine who can certify and who supports. Auditors and maintenance managers should document these distinctions in the MOE so that every “EASA license” holder’s role – and every “support staff” versus “certifying staff” – is explicit, ensuring compliance and safety under EASA 145 regulations.