Part-66 Knowledge Levels 1, 2 and 3 Explained by Category

Part-66 knowledge levels are the three depths, 1, 2 and 3, that Appendix I to Part-66 assigns to every syllabus item for every licence category. The same sub-module can be level 1 for a category A mechanic, level 2 for a B1 and level 3 for a B2, so two people sitting "Module 5" are not revising the same thing. The Part-66 modules by category guide lists which modules each category sits; this post explains how deep each one goes.

The levels below are quoted from Appendix I as published on legislation.gov.uk and the EASA Easy Access Rules for Continuing Airworthiness. The level counts come from our syllabus file, built from the EASA AMC1 to Appendix I.

What do Part-66 knowledge levels 1, 2 and 3 mean?

Level 1 is familiarisation, level 2 is general knowledge you can apply, and level 3 is detailed knowledge you can use with manufacturer's instructions. Appendix I defines each one with a short list of objectives.

Level	Appendix I definition	What you must be able to do
1	A familiarisation with the principal elements of the subject	Give a simple description using common words and examples; use typical terms
2	A general knowledge of the theoretical and practical aspects of the subject and an ability to apply that knowledge	Understand the theory; use formulae with physical laws; read sketches, drawings and schematics; apply knowledge using detailed procedures
3	A detailed knowledge of the theoretical and practical aspects of the subject	Know the theory and how it links to other subjects; give a detailed description; prepare simple drawings and schematics; apply knowledge using manufacturer's instructions; interpret results from various sources and measurements

The jump that matters most in the exam is from 1 to 2. At level 1 a question asks what something is. At level 2 it asks you to calculate, read a schematic or predict what happens when a condition changes.

Key fact: A dash in the syllabus table means the item does not apply to that category. A B2 does not study wooden structures (6.3.2) at all, and a B1 does not study microprocessors (5.7).

How knowledge levels differ by licence category

Knowledge levels follow the category's privileges: the deeper you certify, the deeper you study. The table counts the syllabus items at each level in the core modules for four categories.

Module	Category A (L1 / L2 / L3)	B1.1 (L1 / L2 / L3)	B2 (L1 / L2 / L3)	B3 (L1 / L2 / L3)
3 Electrical fundamentals	7 / 0 / 0	4 / 16 / 0	4 / 16 / 0	17 / 1 / 0
4 Electronic fundamentals	not sat	4 / 1 / 0	0 / 9 / 0	4 / 1 / 0
5 Digital techniques	5 / 0 / 0	5 / 7 / 0	2 / 15 / 0	7 / 0 / 0
6 Materials and hardware	11 / 6 / 0	5 / 18 / 1	12 / 9 / 0	5 / 18 / 1
7 Maintenance practices	12 / 5 / 3	1 / 21 / 5	3 / 8 / 5	1 / 21 / 5
8 Basic aerodynamics	5 / 0 / 0	0 / 5 / 0	0 / 5 / 0	5 / 0 / 0
10 Aviation legislation	4 / 4 / 0	5 / 4 / 1	5 / 4 / 1	5 / 4 / 1

Read it as a revision map. Category A sits mostly level 1, so its papers are shorter (Module 3 is 20 questions for A against 52 for B1 and B2). B3 matches B1 in Modules 6 and 7, because a B3 certifies the structure and engine of a light piston aeroplane, but drops to level 1 in electrics.

Level 3 in the core modules

Level 3 is rare in Modules 1 to 10. For B1 it appears in only a handful of items:

• 6.4(b) types of corrosion (level 3 for B1 and B3, level 2 for A and B2);
• 7.1 safety precautions, 7.2 workshop practices and 7.3 tools (level 3 for every category);
• 7.7 EWIS and 7.18(a) types of defects and visual inspection (level 3 for B1, B2 and B3);
• 10.4 independent certifying staff (level 3 for B1, B2 and B3).

Level 3 is concentrated in the aircraft modules instead: 32 items in Module 11A for B1.1 and 24 in Module 13 for B2.

Where B1 and B2 depth differ

B1 and B2 share the same levels in Modules 1, 2, 3, 8, 9 and 10, then split in two directions. B2 goes deeper in electronics; B1 goes deeper in structures and mechanical practice.

Area	B2 deeper than B1	B1 deeper than B2
Module 4	Transistors, integrated circuits, printed circuit boards and servomechanism principles (level 2 against level 1); diode operation, filters and servo construction (B2 only)	none
Module 5	Numbering systems, data conversion and fibre optics (level 2 against 1); logic diagrams, computer operation, microprocessors, integrated circuits and multiplexing (B2 only)	none
Module 6	none	Alloy steels, non-ferrous materials, rivets, springs, control cables, standard unions (level 2 against 1); corrosion types (3 against 2); composite defect detection, wood and fabric (B1 only)
Module 7	none	Fits and clearances (2 against 1); riveting, pipes and hoses, bearings, transmissions, control cables, sheet metal, composites, weighing and structural repair (B1 only)

This is why the papers differ in size even for shared modules: under EASA rules Module 5 is 40 questions for B1 and 72 for B2, and Module 6 is 80 for B1 and 60 for B2. The B1 vs B2 licence guide compares the two categories as careers.

How should knowledge levels change the way you revise?

Revise each item to its level and no further: depth beyond your level costs time you need elsewhere. In practice that means three different study styles.

1. Level 1 items: learn definitions, names and what each component is for. Flashcards and short quizzes work well.
2. Level 2 items: add the why. Work the formulae by hand, trace a schematic, and explain what happens when one value changes. Most of Modules 2, 3 and 8 for B1 and B2 is level 2.
3. Level 3 items: add the detail and the links between systems. Expect questions that combine two facts or ask you to interpret an indication. For B1 that is most of Module 11A; for B2, most of Module 13.

Exam tip: Use the level to judge an unfamiliar question. If a topic is level 1 for your category and the question needs a calculation, reread it: you have probably misread what it is asking.

Our module guides show each module's depth by category, for example Part-66 Module 4 questions, Part-66 Module 5 questions and Part-66 Module 6 questions. A full mock at the real size is the best test of whether you have revised to the right depth; Part-66 mock exams explains how to sit one.

Levels when you add a category

Your module passes count only at the level you sat them. Adding a category means making up the difference wherever the new category needs a higher level or an item you never studied. The UK CAA describes this as a gap analysis between the knowledge you hold and the new category's requirements on its page on adding a category to a UK Part-66 licence.

For example, a B1.1 adding B2 has to cover the B2-only and higher-level items in Modules 4 and 5 above, plus the B2 aircraft systems module. A category A holder moving to B1 has the opposite problem: most core modules jump from level 1 to level 2. The Part-66 licence categories guide explains the upgrade paths.

Next step

Find out where your depth is weakest with the free B1.1 diagnostic or the free B2 diagnostic. Then sit a full free paper for a module where B1 and B2 differ, such as Module 5 paper 1 for B2, and read the free study note on electronic instrument systems and displays. Sub-module drills for the level 2 and level 3 items come with Pro.