Part-66 licence categories: privileges, modules and experience
1,038 words · checked 2026-10-03 · Free
A Part-66 aircraft maintenance licence (AML) lets you certify maintenance once your employer (a Part-145 or Part-CAMO/CAO organisation) also gives you a certification authorisation. The licence category decides what you may certify; the type ratings or group ratings decide on which aircraft.
Categories and subcategories (66.A.3)
| Category | Subcategories | Aircraft |
|---|---|---|
| A | A1 aeroplanes turbine, A2 aeroplanes piston, A3 helicopters turbine, A4 helicopters piston | as named |
| B1 | B1.1 aeroplanes turbine, B1.2 aeroplanes piston, B1.3 helicopters turbine, B1.4 helicopters piston | as named |
| B2 | none (avionics) | all aircraft |
| B2L | system ratings: com/nav, instruments, autoflight, surveillance, airframe systems (at least one) | all aircraft except Group 1 |
| B3 | none | piston-engine non-pressurised aeroplanes of 2 000 kg MTOM and below |
| C | none (base maintenance) | aeroplanes and helicopters |
| L | L1C ... L5 (sailplanes, balloons, airships, ELA1 aeroplanes) | light aircraft; separate syllabus (Appendix VII), not covered by this app |
Privileges in plain words (66.A.20)
| Category | What you may release |
|---|---|
| A | Minor scheduled line maintenance and simple defect rectification, limited to tasks listed on your certification authorisation and to work you personally performed. |
| B1 | Maintenance on structure, powerplant, mechanical and electrical systems, plus avionic work needing only simple tests (no troubleshooting). You may also act as B1 support staff in base maintenance. B1 includes the matching A subcategory. |
| B2 | Maintenance on avionic and electrical systems, and electrical/avionic tasks within powerplant and mechanical systems needing only simple tests. Also minor scheduled line maintenance and simple defect rectification within the ratings held. B2 does not include an A subcategory. |
| B2L | Electrical systems; avionic systems within the system ratings endorsed; with the airframe systems rating, electrical/avionic tasks in powerplant and mechanical systems needing simple tests. |
| B3 | Like B1, but only for piston non-pressurised aeroplanes of 2 000 kg MTOM or less. |
| C | Release of the whole aircraft after base maintenance. |
Key fact: Category A certifies only work you did yourself, and only tasks on your authorisation. B1 and B2 support staff ensure all tasks are completed in base maintenance; the C certifier releases the aircraft as a whole.
To use your privileges you also need (66.A.20(b)): 6 months of relevant maintenance experience in the preceding 2 years, adequate competence for the aircraft, and the language skills to read the maintenance data. The licence document becomes invalid 5 years after its last issue or change unless you send it in for renewal (66.A.40); this is an administrative renewal, not a new exam.
Aircraft groups (66.A.5)
- Group 1: complex motor-powered aircraft, multi-engine helicopters, aeroplanes certified above FL290 (except piston aeroplanes), fly-by-wire aircraft, gas airships other than ELA2 - individual type ratings needed.
- Group 2: 2a single turboprop aeroplanes; 2b single turbine helicopters; 2c single piston helicopters.
- Group 3: piston-engine aeroplanes not in Group 1.
- Group 4: sailplanes, powered sailplanes, balloons, airships not in Group 1.
Which modules you must pass
EASA Appendix I §2 (Reg. 2023/989). "X" = required.
| Module | A1 / B1.1 | A2 / B1.2 | A3 / B1.3 | A4 / B1.4 | B3 | B2 / B2L |
|---|---|---|---|---|---|---|
| 1 Mathematics | X | X | X | X | X | X |
| 2 Physics | X | X | X | X | X | X |
| 3 Electrical fundamentals | X | X | X | X | X | X |
| 4 Electronic fundamentals | B1.1 only | B1.2 only | B1.3 only | B1.4 only | X | X |
| 5 Digital techniques / EIS | X | X | X | X | X | X |
| 6 Materials and hardware | X | X | X | X | X | X |
| 7 Maintenance practices | X | X | X | X | X | X |
| 8 Basic aerodynamics | X | X | X | X | X | X |
| 9 Human factors | X | X | X | X | X | X |
| 10 Aviation legislation | X | X | X | X | X | X |
| 11 Aeroplane aerodynamics, structures and systems | X | X | — | — | X | — |
| 12 Helicopter aerodynamics, structures and systems | — | — | X | X | — | — |
| 13 Aircraft aerodynamics, structures and systems | — | — | — | — | — | X |
| 14 Propulsion | — | — | — | — | — | X |
| 15 Gas turbine engine | X | — | X | — | — | — |
| 16 Piston engine | — | X | — | X | X | — |
| 17 Propeller | X | X | — | — | X | — |
- Module 4 is not required for category A.
- In the UK the split modules apply: A1/B1.1 take 11A and 17A; A2/B1.2 take 11B and 17A; B3 takes 7B, 9B, 11C, 17B; everyone else takes 7A and 9A.
- Category C applicants must meet either the B1 or the B2 knowledge levels (a degree route is also possible, see 66.A.30(a)(3)-(4)).
- B2L needs Modules 1-10, Module 13 parts for each system rating, and Module 14 only for the instruments and airframe systems ratings.
Basic experience before the licence is issued (66.A.30)
Practical maintenance experience on operating aircraft:
| Category | No relevant technical training | Skilled worker in a technical trade | Part-147 basic course |
|---|---|---|---|
| A, B1.2, B1.4, B3 | 3 years | 2 years | 1 year |
| B2, B1.1, B1.3 | 5 years | 3 years | 2 years |
| B2L | 3 years | 2 years | 1 year (+3 months per added system rating) |
- At least 1 year of the experience must be recent and on the category/subcategory you apply for.
- Experience must be practical, cover a representative cross section of tasks and fall within the 10 years before the application.
- Category C: e.g. 3 years exercising B1.1, B1.3 or B2 privileges on complex aircraft (incl. 12 months as base maintenance support staff), or a relevant academic degree route.
- The UK rule text (66.A.30) has the same durations; the CAA adds that it does not currently recognise any course as meeting the "skilled worker" reduction.
Key fact: The Part-147 approved basic course is the fastest route: 1 year experience for A/B1.2/B1.4/B3 and 2 years for B1.1/B1.3/B2, instead of 3 and 5 years.
Typical study order
- Modules 1, 2 and 3 (maths, physics, electrical) build the base for everything else.
- Modules 8, 9 and 10 are short and largely independent - good early wins.
- Modules 4, 5, 6 and 7 next; Module 7 includes the essays.
- Finish with the aircraft and engine modules for your category (11/12/13, 14/15/16, 17).
Remember: each module pass is valid for the licence application for 10 years, so plan the sequence within that window.