EASA & UK CAA PART-66 · TERMS AND ABBREVIATIONS

The Part-66 glossary

This page defines 31 Part-66 terms in plain English: the annexes and appendices, the licence categories, the exam machinery and the application paperwork. Each definition is one or two sentences, names its regime where the two texts differ, and links the page that answers its subject in full. The official texts write Part-66 with the hyphen; everyday searches mostly type Part 66; both mean the same annex, and both belong here.

Checked against the current regulations on 3 August 2026. Sources: Regulation (EU) No 1321/2014, consolidated (EUR-Lex) · UK assimilated Regulation 1321/2014 (legislation.gov.uk) · UK Part-66 licensing (UK CAA).

01 THE LAW AND THE AUTHORITIESREG (EU) 1321/2014 · ANNEX III

Whose rules are these?

Nine terms cover the legal machinery. The two texts started as one and have moved apart since Brexit; how far apart has a page of its own.

Part-66: Annex III to Regulation (EU) No 1321/2014: the aircraft maintenance licence, its categories, the knowledge syllabus and the examination standard. The official texts hyphenate the name; everyday writing and most searches type Part 66, and both mean this annex.
Regulation (EU) No 1321/2014: The continuing airworthiness regulation Part-66 is an annex of. EASA reads it as consolidated to 22 February 2026; Great Britain reads its own assimilated copy of the same regulation.
Assimilated legislation: The UK’s name for retained EU law. EU aviation safety law ceased to apply to the UK on 31 December 2020, and the text kept that day is the one the UK CAA still examines against.
Appendix I: Part-66’s knowledge syllabus: the module tables, their numbered sub-topics, and the knowledge level each licence category needs on every one.
Appendix II: Part-66’s examination standard. Question format, pass mark, timing, essays, resit waits and attempt limits all come from it.
AMC: Acceptable Means of Compliance: the authority’s published way of meeting a rule. Guidance rather than law, and this site says so wherever it leans on one.
EASA: The European Union Aviation Safety Agency, which writes the EU side of Part-66 and has amended it twice since Brexit. It issues no licences itself; a Member State authority does.
UK CAA: The United Kingdom Civil Aviation Authority. It issues the UK Part-66 licence, runs its own computer-based examinations, and examines to the older module set, which EASA has since rewritten.
Competent authority: The national body a regime’s rules put in charge: it issues the licence and may run examinations, which in the UK means the CAA. EASA is an agency rather than a competent authority for issue, so an EASA licence comes through a Member State.

02 THE LICENCEPART-66 · 66.A.20

What do the letters on the licence mean?

The licence carries its privileges as letters and numbers. What each one permits, and the whole route to holding one, is the licence guide’s job; these entries give you the words.

AML: Aircraft maintenance licence: the document Part-66 defines, held by a licensed aircraft maintenance engineer and applied for on Form 19 once the exams and the experience are in place.
Category B1: The mechanical certifying category: aircraft structure, powerplant, mechanical and electrical systems, and avionic work limited to simple serviceability tests (66.A.20(a)(2)). A B1 licence includes the matching A subcategory.
Subcategory B1.1: The aeroplanes turbine subcategory of B1, and the one this site prepares readers for. What B1.1 covers, in full.
Certificate of release to service: The signature that returns an aircraft to service after maintenance, and the privilege the whole licence exists to grant.
Certifying staff: The rule text’s collective name for the people entitled to issue a certificate of release to service, licensed engineers included.
Type rating: An entry on the licence for one aircraft type, added under 66.A.45 after the licence exists. Module passes alone certify no particular aircraft.

03 THE EXAMINATIONAPPX I + II

What do the exam terms mean?

Everything the papers are built from. The exam format page owns the detail; a definition here is deliberately the short version.

Module: One examined subject with its own paper. Category B1.1 needs 13 of them under either authority; EASA numbers them without letter suffixes, while the UK still writes 7A, 9A, 11A, 17A.
Sub-topic: One numbered row inside a module’s Appendix I table, carrying its own knowledge level, or no level at all where the row is not required for the category in question.
Knowledge level: The depth a sub-topic is examined to: level 1 is familiarisation, level 2 is general theoretical and practical knowledge you can apply, level 3 is detailed knowledge you can combine across subjects (Annex III (Part-66), Appendix I, point 1).
Multi-choice question: The regulation’s own spelling of multiple choice. Every question carries 3 alternative answers with one of them correct, under both authorities.
Essay element: Written questions on top of the multi-choice paper, each given 20 minutes: 2 for B1.1 under EASA, both in Module 7, and 4 under the UK CAA, in Modules 7A, 9A, 10.
Pass mark: 75% of the multi-choice part of every module and sub-module, the same under EASA and the UK CAA. How the marking actually works.
Penalty marking: Docking marks for wrong answers to decide a fail. Part-66 does not use it to decide whether you pass, so a guess costs no more than a blank.
Partial exam: An EASA option, with no UK equivalent, to sit one long module paper as two shorter complementary papers.
Resit: A retake after failing. The wait is 90 days, and a shorter wait of 30 days exists only after tailored retraining at a Part-147 approved organisation.

04 APPLYING66.A.10 · 66.A.25 · 66.A.30

Which terms turn up when you apply?

The paperwork between passing the papers and holding the licence. The conditions behind these terms live on the experience page, and every figure they rest on is on the facts and figures page with its regulation beside it.

Form 19: The licence application form under both regimes: EASA Form 19 goes to a Member State authority, CAA Form 19 to the UK CAA, each with evidence of knowledge, training and experience.
Experience requirement: 5, 3 or 2 years of practical maintenance experience for B1.1, depending on the training that came with it. The three routes in full.
Recency: The rule that at least one of the required years must be recent experience, on the category of aircraft the licence is sought for.
The ten-year rule: Two separate windows of 10 years, both counted backwards from the licence application: module passes must sit inside one, and all required experience inside the other.
Examination credit report: The approved report an authority requires before granting discretionary credit for module passes older than the 10 year window. Credit may be applied for; it is never automatic.
Part-147: A maintenance training organisation approved under Annex IV. Its approved basic course shortens the experience requirement to 2 years, it may conduct examinations, and its tailored retraining is the one thing that shortens a resit wait. Prep66 is not one.
Part-145: The approval a maintenance organisation itself holds for the maintenance it performs. In Part-66 it appears where EASA tests whether non-standard experience counts.

05 QUESTIONS PEOPLE ASKFAQ

Part-66 vocabulary questions

Q.01

Is it Part-66 or Part 66?

Both name the same thing. The regulations style it Part-66, as in Annex III (Part-66), and official documents keep that form, which is why this site does. Everyday writing, forum posts and most searches drop the hyphen and type Part 66. Use either; they mean the same annex.

Q.02

What is the difference between Part-66, Part-145 and Part-147?

They are different annexes of the same regulation doing different jobs. Part-66 defines the licence a person holds. Part-145 is the approval a maintenance organisation holds. Part-147 is the approval a maintenance training organisation holds, and the route to the shorter 2 year experience requirement and the reduced resit wait. A person, a hangar, a school.

Q.03

What does AML stand for in aviation?

Aircraft maintenance licence, the Part-66 licence itself. The regulation writes about the applicant for an aircraft maintenance licence, and the industry shortens it to AML. The categories written on it say what the holder may certify, and the licence guide on this site walks the whole route to holding one.

Q.04

What is a knowledge level in Part-66?

The depth Appendix I assigns to every sub-topic of every module. Level 1 is familiarisation with the principal elements, level 2 is general theoretical and practical knowledge you can apply, and level 3 is detailed knowledge you can combine and apply across subjects. A sub-topic can also carry no level for your category, meaning it is not examined at all. Each module page here shows the level beside every sub-topic, for both regimes.

Q.05

Is Prep66 a Part-147 organisation?

No. Prep66 is not a Part-147 approved maintenance training organisation. It does not conduct examinations and nothing bought here has regulatory standing. Your examination must be sat with a Part-147 approved organisation or the competent authority.

06 WHERE TO GO NEXTRELATED

Put the vocabulary in front of real questions.

The free plan opens all thirteen modules, with 25 new questions a day in each one. Every question has three options, the Part-66 format, and an explanation behind every answer. It’s a plan, not a trial, and it needs no card.

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