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66.A.3 establishes the aircraft maintenance licence categories (A, B1, B2, B2L, B3, and C), each defining the scope of maintenance certification privileges available to the licence holder.
What it means in practice
The licence categories determine what type of maintenance you are authorised to certify. Category A covers line maintenance certifying mechanics who can release minor scheduled maintenance and simple defect rectification. Category B1 covers line maintenance certifying technicians for mechanical, structural, powerplant, and electrical systems on aircraft. Category B2 covers avionics line maintenance certifying technicians.
Category B2L is a more limited avionics licence for specific systems. Category B3 applies to non-pressurised aeroplanes with piston engines of up to 2000 kg MTOM. Category C authorises the holder to issue certificates of release to service following base maintenance on aircraft. Each category has its own subcategories that further define the aircraft types covered, such as B1.1 for aeroplanes with turbine engines and B1.2 for aeroplanes with piston engines.
Key requirements
Each licence category has distinct knowledge, training, and experience prerequisites. Category A licence holders work under the supervision of B1 or B2 certifying staff and may only certify work they have personally performed. Category B1 and B2 holders can certify line maintenance within their discipline and may direct the work of Category A staff.
Category C licence holders can certify base maintenance but do not need to be personally involved in the physical tasks. They must, however, be satisfied that all work has been completed to the required standard. A Category C licence can be obtained either through the B1/B2 route with additional experience or through an academic degree route with specified practical experience.
Common compliance gaps
One of the most common errors is misunderstanding the boundary between line and base maintenance privileges. A Category B1 or B2 holder cannot certify base maintenance tasks, and a Category C holder cannot certify line maintenance unless they also hold a B1 or B2 licence. Additionally, staff sometimes confuse the subcategories, for example certifying work on turbine-powered aircraft when they only hold a B1.2 (piston engine) subcategory.
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