3.1 Part-66 Licence Categories, Scope & Privileges

3.1 Part-66 Licence Categories, Scope & Privileges

Quick Answer: EASA Part-66 (Annex III to Regulation (EU) No 1321/2014) establishes the harmonised European qualification system for aircraft maintenance certifying staff. The primary categories are: Category A (line mechanic: minor scheduled tasks and simple defect rectification personally performed), Category B1 (mechanical technician: airframe, powerplant, mechanical, electrical, and simple avionic LRUs, automatically including Category A privileges), Category B2 (avionic technician: electrical, avionics, instruments, autoflight, and radar, without automatic Category A privileges), Category B2L (modular avionic system ratings for light aircraft), Category B3 (piston non-pressurised aeroplanes ≤2 000 kg MTOM), Category C (base maintenance certifying engineer releasing the entire complex aircraft following heavy maintenance), and Category L (sailplanes, powered sailplanes, balloons, and airships). Crucially, holding a Part-66 licence certifies technical competence but does not grant automatic release authority; certification privileges can only be exercised through an official Certification Authorisation issued by an approved maintenance organisation (Part-145 or Part-CAO).

Under European civil aviation law, aircraft airworthiness hinges on the personal accountability of the certifying personnel who sign the Certificate of Release to Service (CRS). Annex III to Regulation (EU) No 1321/2014, universally designated as EASA Part-66, lays down the harmonised requirements for the application, issuance, scope, and privileges of Aircraft Maintenance Licences (AML). Understanding the precise boundaries between categories, subcategories, system ratings, and operational environments is essential for maintenance engineering and Module 10 examinations.

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Regulatory Architecture: Annex III (Part-66)

Regulation (EU) No 1321/2014 acts as an overarching Commission Regulation detailing the continuing airworthiness of aircraft and aeronautical products, parts, and appliances. Part-66 serves as its third annex, establishing an indivisible tripartite framework alongside:

1. Part-145 (Annex II): The standard for approved maintenance organisations, which employ certifying staff and grant company certification authorisations under rule 145.A.35.
2. Part-66 (Annex III): The individual technical qualification and licensing standard for certifying personnel.
3. Part-147 (Annex IV): The standard for approved maintenance training organisations delivering basic knowledge instruction, examination, and aircraft type rating training.

A foundational tenet of EASA regulations is that a Part-66 licence is a personal qualification document, not an unrestricted release ticket. Holding a Part-66 AML proves that an engineer meets the basic knowledge, practical experience, and type rating standards required by European law. However, to legally release an aircraft to service under Part-145, the licence holder must additionally hold a formal Company Certification Authorisation (CCA) issued by an approved maintenance organisation under rule 145.A.35.

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Category A: Line Maintenance Certifying Mechanic

The Category A licence is designed for line maintenance mechanics operating in fast-paced flight-line environments (ramp operations, transit stops, and overnight line checks).

Subcategories and Operational Scope

Category A is divided into four distinct subcategories based on aircraft architecture and propulsion:

• A1: Aeroplanes Turbine
• A2: Aeroplanes Piston
• A3: Helicopters Turbine
• A4: Helicopters Piston

Under Part-66.A.20(a)(1), a Category A licence permits the holder to issue certificates of release to service and to act as a certifying mechanic following:

1. Minor scheduled line maintenance, such as pre-flight checks, daily inspections, weekly service checks, and routine component lubrications.
2. Simple defect rectification, limited strictly to tasks within the capacity of a line mechanic.

Crucially, the permissible task envelope is not left to technician discretion. The tasks must be explicitly listed in the maintenance organisation exposition (MOE) of the employing Part-145 organisation, guided by the task list published in AMC to 145.A.30(g). Typical tasks include replacing wheels and brake units, renewing engine oil and hydraulic fluids, replacing navigation lights, passenger cabin interior components, wiper blades, and external emergency equipment.

The Personal Execution Mandate

The defining legal constraint of Category A privileges is the personal performance rule: Category A certifying mechanics may only issue a CRS for tasks that they have personally carried out in the maintenance organisation that issued the certification authorisation. A Category A mechanic cannot supervise an uncertified technician, inspect the completed work, and then sign the release. If a Category A mechanic did not physically turn the wrenches, inspect the torque, and conduct the functional check themselves, they cannot sign the CRS.

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Category B1: Maintenance Certifying Technician (Mechanical)

The Category B1 licence represents the primary mechanical certification role in European aviation. It is a comprehensive qualification covering systems engineering, mechanical troubleshooting, structural integrity, and powerplant management.

Technical Scope and Systems Depth

Category B1 is partitioned into the same four propulsion and airframe subcategories:

• B1.1: Aeroplanes Turbine (e.g., Airbus A350, Boeing 787, ATR 72)
• B1.2: Aeroplanes Piston (e.g., Cessna 172, Piper PA-34 Seneca)
• B1.3: Helicopters Turbine (e.g., Airbus H145, Leonardo AW139)
• B1.4: Helicopters Piston (e.g., Robinson R44)

Under Part-66.A.20(a)(2), a Category B1 licence holder is privileged to issue certificates of release to service and to act as support staff following:

• Maintenance performed on aircraft structure (fuselage, empennage, wings, nacelles).
• Powerplant and auxiliary power units (APUs), including fuel, oil, ignition, and thrust reverser systems.
• Mechanical and hydraulic systems (landing gear, flight controls, pneumatic and environmental control systems).
• Electrical systems (power distribution, generation, batteries, and lighting).
• Replacement of avionic Line Replaceable Units (LRUs), provided the replacement requires only a simple test to prove its serviceability.

The Simple Avionic Test Boundary: A B1 technician can replace a flight management guidance computer (FMGC) or a VHF communication transceiver if verification requires only initiating an onboard Built-In Test Equipment (BITE) check or a basic operational self-test. If the installation requires external avionic test sets, complex pin-out measurements, or specialized diagnostic software, the task falls exclusively into Category B2.

Automatic Privileges: The Built-in Category A Rule

A major efficiency within Part-66 is the automatic subcategory privilege inheritance: Holding a Category B1 licence automatically confers the certification privileges of the corresponding Category A subcategory. For example, an engineer holding a Category B1.1 licence automatically possesses full Category A1 privileges. This allows the B1 technician to perform and release minor line maintenance tasks under Category A procedures when operating in a line maintenance role, without requiring an additional Category A licence document.

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Category B2: Maintenance Certifying Technician (Avionic)

The Category B2 licence covers electronic, electrical, and data systems across all aircraft. Unlike Category B1, Category B2 is not divided into subcategories; a single B2 licence applies to aeroplanes and helicopters alike, though aircraft type ratings are endorsed individually.

Avionic Scope and System Boundaries

Under Part-66.A.20(a)(3), Category B2 certification privileges encompass:

• Aircraft electrical power generation, bus switching, and wiring interconnection systems (EWIS).
• Avionics, including communication (VHF, HF, SATCOM), navigation (ILS, VOR, GPS, DME), and surveillance (weather radar, TCAS, ADS-B, transponders).
• Flight control electronic architectures, autopilot, autoflight, and flight guidance computers.
• Electronic instruments, electronic flight displays (EFIS), engine indication and crew alerting systems (EICAS), and central maintenance computers.
• Electrical and avionic tasks within powerplant and mechanical systems that require only simple tests to verify serviceability.

No Category A Subcategory — but a Separate Line Privilege Exists

Candidates frequently misunderstand the relationship between B2 and Category A. The regulation is explicit: "The category B2 licence does not include any A subcategory." However, that is not the same as saying a B2 holder can never sign minor line tasks.

Under 66.A.20(a)(3)(ii), a category B2 licence permits the holder to issue certificates of release to service following minor scheduled line maintenance and simple defect rectification, within the limits of tasks specifically endorsed on the certification authorisation, restricted to work the holder has personally performed in the organisation that issued the authorisation, and limited to the ratings already endorsed on the B2 licence.

Before that privilege can be exercised, 145.A.35(n) requires the B2 holder to complete:

1. the relevant category A aircraft task training (practical hands-on plus theoretical, demonstrated by examination or workplace assessment); and
2. 6 months of documented practical experience covering the scope of the authorisation to be issued.

Both the task training and the experience must be obtained within the maintenance organisation issuing the certifying-staff authorisation. So the B2 engineer does not need a separate Category A licence endorsement — but the privilege is not automatic either.

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Category B2L: Light Aircraft Avionic Certifying Technician

Introduced under Regulation (EU) 2018/1142, Category B2L provides a flexible, modular avionic licensing standard for non-complex aircraft (aircraft other than Group 1). Rather than forcing general aviation avionic technicians to study the entire transport-category avionic syllabus, Category B2L is divided into system ratings:

1. Communication / Navigation (com/nav)
2. Instruments
3. Autoflight
4. Surveillance
5. Airframe Systems

A Category B2L licence is endorsed with one or more of these system ratings. The holder is privileged to issue certificates of release to service following maintenance on electrical systems and avionics falling strictly within the endorsed system ratings, as well as simple electrical and avionic tasks on mechanical systems. Crucially, a Category B2L licence endorsed with all five system ratings can be converted to a full Category B2 licence once the remaining theoretical and practical bridging requirements are completed.

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Category B3: Light Piston Aeroplanes (≤2 000 kg MTOM)

Introduced to support general aviation without the burdensome overhead of large transport aircraft standards, Category B3 applies specifically to:

• Piston-engine aeroplanes.
• Non-pressurised airframes.
• Maximum Take-off Mass (MTOM) of 2 000 kg and below.

Category B3 certifying technicians hold combined privileges covering aeroplane structures, piston powerplants, mechanical systems, electrical systems, and the replacement of avionic LRUs requiring simple tests. However, Category B3 strictly excludes pressurised aeroplanes, turbine engines, multi-engine aeroplanes exceeding 2 000 kg MTOM, and all rotorcraft. Furthermore, Category B3 does not automatically include any Category A subcategory.

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Category C: Base Maintenance Certifying Engineer

Base maintenance (scheduled heavy checks such as C-checks, D-checks, structural overhauls, and major cabin modifications) involves stripping aircraft systems, extensive structural inspections, and prolonged hangar stays. The regulatory philosophy for base maintenance of complex motor-powered aircraft departs significantly from flight-line operations.

The Base Maintenance Release Concept

Under Part-66.A.20(a)(7), a Category C licence holder is privileged to issue a single Certificate of Release to Service following base maintenance of the aircraft; the privileges apply to the aircraft in its entirety. (Since Regulation (EU) 2023/989, a Category C licence issued for complex motor-powered aircraft also carries category C privileges for other-than-complex motor-powered aircraft.) Rather than requiring dozens of individual B1 and B2 technicians to sign customer-facing release forms for each modified valve or harness, European law mandates that a single Category C engineer certifies that the complete maintenance package ordered by the operator or CAMO has been fully satisfied.

The Interface Between Category C and B1/B2 Support Staff

A single Category C engineer cannot personally inspect every rivet, hydraulic seal, and avionics bus across a wide-body aircraft. Therefore, Part-145.A.30(h) and 145.A.35 establish a rigorous symbiotic relationship between the Category C engineer and base maintenance support staff:

1. Role of Support Staff: Category B1 and Category B2 qualified personnel act as support staff in the hangar environment. They do not issue the final CRS to the aircraft. Instead, they personally inspect, verify, and sign off the internal task cards, job cards, and work orders within their respective mechanical and avionic trades.
2. Support Staff Confirmation: The B1 and B2 support staff ensure that all maintenance tasks, non-destructive tests, and defect rectifications have been carried out to the approved standard specified in the Aircraft Maintenance Manual (AMM) and Structural Repair Manual (SRM).
3. Category C Final Determination: The Category C engineer verifies that all work packs are complete, all work cards have been signed by authorised B1 and B2 support staff, all deferred defects are legally addressed per the Minimum Equipment List (MEL) or approved data, and no open discrepancies remain. Only then does the Category C engineer sign the single base maintenance CRS.

For other-than-complex motor-powered aircraft (light general aviation), base maintenance release privileges do not require a Category C engineer; Category B1, B2, B2L, or B3 staff can release base maintenance directly.

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Category L: Light Aircraft Certifying Staff

Annex III (Part-66) also includes Category L, created under Regulation (EU) 2018/1142 to provide a proportional licensing system tailored to light aircraft, gliders, and lighter-than-air craft governed by Part-ML and Part-CAO. Category L is subdivided into:

• L1C: Composite sailplanes / L1: Sailplanes (all structural types).
• L2C: Composite powered sailplanes and ELA1 aeroplanes / L2: Powered sailplanes and ELA1 aeroplanes.
• L3H: Hot-air balloons / L3G: Gas balloons.
• L4H: Hot-air airships / L4G: ELA2 gas airships.
• L5: Gas airships other than ELA2.

Category L enables technicians to qualify through modular, lightweight examinations without sitting the heavy commercial transport syllabus of Category B1 or B2.

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Comprehensive Part-66 Licence Categories Matrix

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Practical Maintenance Scenario: Line Defect Rectification on an A320

An Airbus A320 arrives at a line transit station with two recorded flight crew logbook defects:

1. Defect 1: Right main landing gear outboard tyre exhibits tread wear exceeding maintenance manual limits, requiring a wheel assembly replacement.
2. Defect 2: Weather radar display fails to initiate, accompanied by an electronic centralized aircraft monitoring (ECAM) fault message identifying a transceiver communication failure.

Operational Division of Privileges:

• Category A Mechanic Action: The Category A1 line mechanic can replace the right main wheel assembly, torque the axle nut, install the retention pin, and sign the CRS for that specific task, provided the mechanic personally performed the complete replacement and wheel changes are listed on their company authorisation.
• Category B1 Technician Action: A Category B1.1 engineer can perform or supervise the wheel replacement. Regarding Defect 2, the B1.1 technician can pull the radar receiver/transmitter LRU from the avionics bay, install a replacement unit, and initiate the automatic onboard BITE self-test. If the BITE self-test passes, proving serviceability without external test apparatus, the B1.1 technician can issue the CRS.
• Category B2 Technician Action: If the radar replacement requires coaxial cable time-domain reflectometer testing, RF waveguide attenuation analysis, or custom databus troubleshooting, the task exceeds B1 scope and must be diagnosed, tested, and released by a Category B2 avionic certifying technician.

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Exam Tips & Regulatory Traps

• The Category B1 Automatic Cat A Rule: Exam questions frequently test whether a B1.1 engineer needs a Category A1 licence to sign minor line checks. They do not—B1 automatically includes the corresponding Category A subcategory.
• The Category B2 Trap: The B2 licence includes no A subcategory. But 66.A.20(a)(3)(ii) still lets a B2 holder release minor scheduled line maintenance and simple defect rectification on personally performed work, once the Category A task training and 6 months of documented experience under 145.A.35(n) are complete. Distinguish "no A subcategory on the licence" from "no line privilege at all".
• Category C Isolation: A Category C engineer who holds only Category C cannot sign line maintenance releases, nor can they sign off B1/B2 base maintenance support staff task cards. Category C is strictly for releasing the whole aircraft after base maintenance.
• Personal Work Restriction: Category A mechanics can never certify work performed by apprentices, contractors, or fellow mechanics. If asked: "Can a Category A mechanic certify a brake change performed by an assistant?" The answer is an absolute no.