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66.A.25 specifies the basic knowledge standards and examination requirements that applicants must satisfy for each licence category, covering subjects such as mathematics, physics, electrical fundamentals, and aircraft-specific technology modules.
What it means in practice
Before you can obtain a Part 66 licence, you must demonstrate by examination a level of knowledge in the subject modules of Appendix I to Part 66 — or, for the L licence categories, Appendix VII. The subjects are organised into numbered modules, from Module 1 (Mathematics) through to Module 17 (Propeller), with different modules required depending on the licence category. For example, a Category B1.1 applicant must pass modules covering turbine engine technology, while a Category A applicant faces a reduced syllabus with less depth.
Regulation (EU) 2023/989 substantially revised the basic knowledge framework: the syllabus in Appendix I was restructured to reflect current aircraft technology, with the module and sub-module titles and knowledge levels retained at regulation level while the detailed descriptive content of each module moved to AMC level — so training organisations and self-study candidates must now work from both the regulation and the associated AMC to see the full examinable content.
The knowledge level required varies by category. Category A examinations test knowledge at a lower level than Category B1 or B2. Each module has defined knowledge levels (Level 1, 2, or 3) that specify how deeply the applicant must understand each topic. Examinations are conducted by appropriately approved Part 147 training organisations or by the competent authority.
Key requirements
Examinations must be conducted under controlled conditions, with multi-choice questions forming the standard format. The pass mark is 75%. Examination results are valid for 10 years from the date of the examination, meaning if you do not apply for your licence within that period, you may need to re-sit expired modules.
Applicants who complete an approved basic training course at a Part 147 organisation benefit from the course being designed to meet the full syllabus requirements. Those taking the direct examination route with the competent authority must ensure they have studied the complete Appendix I (or Appendix VII) syllabus for their category. Credit may be given for previous examinations and for other technical qualifications assessed as equivalent, in accordance with 66.A.25(c) and the credit report process of the competent authority.
Common compliance gaps
A frequent issue is applicants not realising that examination passes expire after 10 years. If there is a long gap between passing examinations and submitting a licence application, some module passes may have lapsed. Another common problem is applicants studying the syllabus for the wrong category level, particularly when upgrading from Category A to Category B1, where additional modules and higher knowledge levels are required. Since the Regulation (EU) 2023/989 syllabus restructure, candidates preparing from older course notes should also confirm their material reflects the current Appendix I module content as detailed in the AMC.
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