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66.A.20 defines the specific certification privileges granted to each licence category, establishing what maintenance work a licence holder is authorised to certify as complete.
What it means in practice
Your licence category directly determines what you can sign off. A Category A licence holder may issue certificates of release to service following minor scheduled line maintenance and simple defect rectification, but only within the scope of work specifically authorised by the approved maintenance organisation. A Category B1 holder can certify line maintenance on aircraft structure, powerplant, and mechanical and electrical systems. A Category B2 holder covers avionics systems for line maintenance.
A Category C licence holder can issue certificates of release to service after base maintenance on the complete aircraft. Importantly, Category C holders do not need to physically carry out any of the maintenance tasks, but they must be satisfied that all work has been completed satisfactorily. All privileges are exercised only within the scope of the type ratings endorsed on the licence and only when the holder is authorised by an approved maintenance organisation.
Key requirements
The privileges are conditional on several factors. The licence holder must have a valid licence with the appropriate category and type ratings. They must be authorised by an approved maintenance organisation (Part 145 or Part M Subpart F). They must have remained current in accordance with 66.A.40, meaning they can demonstrate recent maintenance experience or have undertaken refresher training.
Category A holders can only certify work they have personally performed. Category B1 and B2 holders can certify work performed by others under their supervision. Category C holders can certify the completion of base maintenance packages. Additionally, the B3 licence grants line maintenance privileges on non-pressurised piston-engine aeroplanes with a maximum take-off mass of 2000 kg or less.
Common compliance gaps
A persistent compliance issue is the exercise of privileges beyond the scope of the organisational authorisation. Even if a licence holder has the correct category and type rating, they cannot certify maintenance unless the approved organisation has specifically authorised them to do so. Another common gap is Category A holders certifying work they did not personally perform, or B1/B2 holders attempting to sign off base maintenance tasks that require Category C authority.
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