The Part-66 B2 licence is the avionics category of the aircraft maintenance licence (AML). B2 engineers look after everything electrical and electronic on an aircraft: power generation, radios, navigation aids, autopilots, instruments, displays and the computers that tie them together. This guide explains what a B2 engineer may certify, which modules you sit and how long each paper is under EASA and UK CAA rules, how much experience you need, and the realistic routes into the job.
Part-66 Prep is an independent study aid, not an authority or a Part-147 organisation. The rule text is Part-66 in Regulation (EU) No 1321/2014 for EASA licences and the retained UK Part-66 for UK licences. B2 is one of several categories; the Part-66 licence categories guide compares them all.
What a Part-66 B2 engineer can certify
Privileges are set out in 66.A.20. In plain terms, a B2 licence allows you to issue a certificate of release to service (CRS), and to act as B2 support staff, for:
- maintenance on avionic and electrical systems, the core of the job
- electrical and avionic tasks within powerplant and mechanical systems that need only simple tests to prove they are serviceable, for example replacing an engine indication sensor
- minor scheduled line maintenance and simple defect rectification, within the aircraft type ratings on your licence
B2 does not include a category A subcategory, unlike B1, and B2 privileges do not extend to structural or mechanical work beyond the electrical and avionic tasks above.
Key fact: A licence on its own does not let you sign anything. You also need a certification authorisation from the approved maintenance organisation you work for, which sets out exactly what you may release, plus six months of relevant experience in the preceding two years (66.A.20(b)).
Where type ratings come in
For group 1 aircraft (complex motor-powered aircraft, multi-engine helicopters, aircraft certified above FL290 and fly-by-wire aircraft), a B2 needs an individual type rating for each type, gained through approved type training. For other aircraft groups, the B2 licence can be endorsed with group ratings. The Part-66 type ratings guide explains how this works.
The B2 modules and paper sizes
B2 candidates sit 12 modules. The table shows multiple-choice questions and time for each, under both systems. Every paper is three-option multiple choice with a 75% pass mark; Module 7 adds two essays in both systems, and the UK adds one essay each to Modules 9 and 10.
| Module | EASA | UK CAA | Practice page |
|---|---|---|---|
| 1 Mathematics | 32 / 40 min | 32 / 40 min | Module 1 questions |
| 2 Physics | 52 / 65 min | 52 / 65 min | Module 2 questions |
| 3 Electrical fundamentals | 52 / 65 min | 52 / 65 min | Module 3 questions |
| 4 Electronic fundamentals | 40 / 50 min | 40 / 50 min | Module 4 questions |
| 5 Digital techniques and electronic instrument systems | 72 / 90 min | 72 / 90 min | Module 5 questions |
| 6 Materials and hardware | 60 / 75 min | 60 / 75 min | Module 6 questions |
| 7 Maintenance practices | 60 / 75 min + 2 essays | 60 / 75 min + 2 essays (7A) | Module 7 questions |
| 8 Basic aerodynamics | 24 / 30 min | 20 / 25 min | Module 8 questions |
| 9 Human factors | 28 / 35 min | 20 / 25 min + 1 essay (9A) | Module 9 questions |
| 10 Aviation legislation | 44 / 55 min | 40 / 50 min + 1 essay | Module 10 questions |
| 13 Aircraft aerodynamics, structures and systems | 188 / 235 min | 180 / 225 min | Module 13 questions |
| 14 Propulsion | 32 / 40 min | 24 / 30 min | Module 14 questions |
| Total | 684 questions, 2 essays | 652 questions, 4 essays |
What the numbers tell you
- The electronics load is heavy. Modules 3, 4 and 5 together are 164 questions for B2, against 112 for B1. Module 5 alone is 72 questions for B2 and 40 for B1.1.
- Module 13 is the centrepiece. At 188 questions under EASA rules it is the longest Part-66 paper in either system. EASA allows it to be split into up to three partial exams; the UK text says it may be split into two.
- Mechanical content is lighter. Module 6 is 60 questions for B2 against 80 (EASA) or 72 (UK) for B1, and Module 7 is 60 against 80.
- EASA and UK differ on four papers. Modules 8, 9, 10 and 14 are shorter under UK rules, but UK candidates write two extra essays in Modules 9 and 10.
The EASA vs UK CAA guide explains why the two systems now differ.
Exam tip: Module 5 for B2 is longer than most people expect. Treat it as a major module, not a foundation one, and give it as much time as Module 3.
Knowledge level: B2 depth vs B1 depth
The syllabus in Appendix I gives each topic a knowledge level from 1 (familiarisation) to 3 (detailed knowledge). B2 and B1 share the same foundation levels in Modules 1 to 3, but in Modules 4 and 5 B2 goes deeper. Transistors, integrated circuits, printed circuit boards and servomechanisms are level 2 for B2 and level 1 for B1, and several topics are B2 only: diode and transistor operation, servomechanism construction, logic diagram interpretation, computer operation, microprocessors, integrated circuits and multiplexing in Module 5. In Module 13, autoflight, communications, navigation and instruments are at level 3 for B2, while a B1 learns them at level 1 or 2 in Module 11. The B1 vs B2 comparison sets the two side by side.
B2 experience requirements (66.A.30)
You need practical maintenance experience on operating aircraft before the licence is issued. For B2 the minimum is:
| Your background | Minimum experience |
|---|---|
| No previous relevant technical training | 5 years |
| Skilled worker in a relevant technical trade (as accepted by the authority) | 3 years |
| Completed a Part-147 approved B2 basic training course | 2 years |
At least one year must be recent experience in the category you are applying for, and the experience has to be within the 10 years before your application. In the UK, the CAA currently recognises no course that qualifies for the skilled worker reduction, so in practice UK candidates use the five-year or two-year figures. The Part-66 experience requirements guide explains what counts and how to record it, usually in a logbook such as the CAA's CAP 741.
B2 is the same in this respect as B1.1 and B1.3, which also need five, three or two years. B2L, the limited avionics licence, needs three, two or one year plus three months for each extra system rating; see the B2L licence guide.
How to become a B2 engineer
There are three common routes. Which suits you depends on your age, where you live and whether you are already working in aviation.
1. Apprenticeship or Part-147 basic course
Airlines and maintenance organisations run apprenticeships that combine a Part-147 approved basic training course with paid work experience. Full-time Part-147 courses are also open to self-funding students. The Part-147 route has two advantages: the shortest experience requirement (two years for B2) and module exams taken at the school as part of the course. Places are competitive and courses are a significant cost if you fund yourself.
2. Working your way up with self-study
Many B2 engineers start as avionics or electrical mechanics, often with an electrical trade background, and sit their modules one at a time while working. Without approved training the experience requirement is five years, but you earn throughout, and modules can be sat at a Part-147 organisation that accepts external candidates or, in the UK, at a CAA exam venue. The self-study guide covers how to plan this.
3. Moving from another background
People from military avionics, electronics engineering or a B1 licence sometimes move into B2. Military experience may be partly credited, and an existing licence category can give module credits; ask your authority what applies to your case. A B1 holder adding B2 sits the B2-level papers in Modules 4, 5, 13 and 14, and any foundation papers where the B2 level is higher.
The step-by-step path
- Decide whether you need an EASA or a UK licence, based on where you will work.
- Sit the 12 modules, in any order. Most people start with Modules 1, 2 and 3 and finish with 13 and 14.
- Build and record your maintenance experience in a logbook, countersigned by supervisors.
- Apply to your competent authority for the licence once you have all module passes (each valid for 10 years) and enough experience. The licence application guide walks through it.
- Add type ratings as your employer sends you on type courses.
- Receive a certification authorisation from your employer, and start signing.
B2, B2L or B1: choosing your category
If you are deciding which licence to aim for, think about the work you want to do and the aircraft you want to work on.
- Choose B2 if you enjoy fault-finding with wiring diagrams, test sets and maintenance computers, and want to work on airliners, business jets or large helicopters. B2 covers all aircraft groups, including group 1, with the right type ratings.
- Choose B2L if you will work on smaller aircraft outside group 1, such as piston aeroplanes, single-engine turboprops and single-engine helicopters, and want a shorter route. B2L is endorsed with system ratings (communication and navigation, instruments, autoflight, surveillance, airframe systems), and you sit only the Module 13 papers for the ratings you want. Experience is shorter too.
- Choose B1 if you prefer engines, structures and mechanical systems. B1 also brings category A privileges for line tasks, which B2 does not.
Many engineers end up holding more than one category. A B1 who adds B2, or the other way round, is valuable to smaller operators and on night shifts where one engineer covers most defects. Module passes from Modules 1 to 10 can count towards both, as long as you passed them at the higher level needed and within the 10-year window.
Key fact: Under both EASA and UK rules, module passes count towards a licence application for 10 years. If you plan to add a second category later, keep every certificate of recognition.
Where B2 engineers work
B2 engineers are needed wherever modern aircraft are maintained:
- Line maintenance at airports, where B2 engineers troubleshoot avionics defects between flights and work alongside B1 colleagues.
- Base maintenance in hangars during scheduled checks, as B2 support staff.
- Component and avionics workshops, though shop work is certified under a different release system.
- Helicopter operators (offshore, emergency medical and police), where B2 covers rotorcraft avionics.
- Business aviation, where small teams often value engineers with both B1 and B2.
Salaries vary widely by employer, country and type ratings, and no official figures are published; check current job adverts for your area. Demand for avionics skills has grown with glass cockpits, data link and integrated modular avionics.
Practising for the B2 modules
Our question bank has 7,253 original three-option questions for the B2 modules, each paper sized for B2 under EASA or UK CAA rules (chosen on the start screen). The B2 practice hub lists every module. Free, without an account:
- the 20-question B2 diagnostic across all B2 modules
- paper 1 of every module at full length, for example Module 13 paper 1 and Module 5 paper 1
- a 20-question quick practice per module and a printable 50-question sheet per module
Papers 2 to 10 for every module, the 60-question mixed paper, sub-module drills and all study notes come with Pro, which covers every category. Neither EASA nor the CAA publishes past papers, so all our papers are exam-style papers written for the app.
Your study plan
- Take the free B2 diagnostic to see where you stand across the 12 modules.
- Start with Modules 1, 2 and 3, then the shorter Modules 8, 9 and 10 for early passes.
- Give Modules 4 and 5 real time; they carry far more weight for B2 than for B1.
- Finish with Module 13 and Module 14, sitting full-length papers before you book.
- Book each module when you score 85% or more on three different papers, and keep your experience logbook up to date as you go.
10 free Part-66 B2 practice questions with answers
Try each one, then open the answer. For the timed experience use the free diagnostic.
1. Backups of maintenance data are kept to:
- A. allow staff to access data from home
- B. satisfy the record retention period alone
- C. allow recovery after loss, failure or attack
Show answer
C. allow recovery after loss, failure or attack
Backups, kept separate and tested, let the organisation restore records after ransomware or hardware failure.
2. In an ideal inductor on AC, the average power consumed is
- A. I² × X_L watts
- B. zero watts
- C. V × I watts
Show answer
B. zero watts
With current 90° out of phase, energy taken during one quarter cycle is returned in the next, so the true power is zero. Real inductors dissipate a little power in their resistance.
3. Why do turboprop engines usually have more than one stage of reduction gearing?
- A. Their output shaft speeds are very high
- B. Their propellers turn faster than the turbine
- C. To reverse the propeller for braking
Show answer
A. Their output shaft speeds are very high
Because of the high output speed of gas turbines, turboprop engines use more than one stage of reduction gearing to bring the propeller to an efficient speed.
4. On a mode control panel, 'armed' modes are usually shown in a different colour (often white) from 'engaged' modes (often green). This means an armed mode:
- A. has failed its power-up self-test
- B. engages when its capture conditions are met
- C. is the mode now controlling the aircraft
Show answer
B. engages when its capture conditions are met
Flight mode annunciation shows the active modes in one colour and armed modes in another. An armed mode (for example LOC or G/S) is waiting for its capture criteria and will then become active, replacing the current mode.
5. According to widely quoted accident statistics, approximately what proportion of aviation accidents involve human error as a cause or contributing factor?
- A. 20–25 %
- B. 40–45 %
- C. 75–80 %
Show answer
C. 75–80 %
The FAA AMT handbook states that approximately 75–80 % of aviation accidents result from human error, and illustrates the 80/20 split between human factors and machine failure. This is the main reason human factors training is mandatory for maintenance staff.
6. The gradient of a curve at a particular point is found from:
- A. the chord from the origin
- B. the area under the curve
- C. the tangent drawn at that point
Show answer
C. the tangent drawn at that point
The slope of the tangent at a point gives the instantaneous rate of change there.
7. A propeller de-icing timer cycles power:
- A. between blades or sections, in sequence
- B. continuously to all blades at once
- C. only when the aircraft is on the ground
Show answer
A. between blades or sections, in sequence
Cycling heats sections in sequence, reducing electrical load and allowing ice to be thrown off.
8. A memory is organised as 16 K words of 16 bits. What is its capacity in kilobytes?
- A. 32 KB
- B. 256 KB
- C. 8 KB
Show answer
A. 32 KB
Capacity = 16 K × 16 bits / 8 = 32 KB. 256 is the kilobit value; 8 KB inverts the ratio.
9. Before maintenance starts, Part-145 requires a clear agreement on:
- A. the work order or contract for the work
- B. the colour scheme of the aircraft
- C. the name of the next pilot
Show answer
A. the work order or contract for the work
145.A.65(b)(1): a clear work order or contract is agreed between the organisation and the customer so the maintenance to be done and released is clearly established.
10. Masses of 130 kg and 480 kg sit 1 m and 4 m aft of a datum. Where is their combined centre of gravity?
- A. 2.5 m aft of datum
- B. 1.64 m aft of datum
- C. 3.36 m aft of datum
Show answer
C. 3.36 m aft of datum
CG = total moment ÷ total mass = (130 × 1 + 480 × 4) ÷ (130 + 480) = 3.36 m aft of the datum.
Frequently asked questions
+What is a B2 licence?
It is the avionics category of the Part-66 aircraft maintenance licence. A B2 engineer certifies work on avionic and electrical systems, such as radios, navigation, autopilots, instruments and electrical power, once their employer also issues a certification authorisation.
+What can a B2 engineer certify?
Maintenance on avionic and electrical systems, electrical and avionic tasks within powerplant and mechanical systems that need only simple tests to prove serviceability, and minor scheduled line maintenance and simple defect rectification within the type ratings held. On group 1 aircraft a type rating is needed for each type.
+Which modules do I need for a B2 licence?
Modules 1 to 10, plus Module 13 (aircraft aerodynamics, structures and systems) and Module 14 (propulsion). That is 12 module exams. Under UK rules Modules 7 and 9 are taken as 7A and 9A.
+How long does it take to become a B2 engineer?
The minimum experience is two years after a Part-147 approved basic course, or five years with no relevant technical training. Studying for the 12 modules usually runs alongside that experience, so most people take several years from starting out to holding the licence.
+Is B2 harder than B1?
Neither is officially harder; they are different. B2 has longer papers in Modules 4, 5 and 13 and a lot of electronics, while B1 has more mechanical content and longer papers in Module 6. People with an electrical background usually find B2 more natural.
+Does B2 include a category A?
No. Each B1 subcategory includes the matching category A privileges, but B2 does not include an A subcategory. B2 does include minor scheduled line maintenance and simple defect rectification within its ratings.
+How many questions are in the B2 Module 13 exam?
188 questions in 235 minutes under EASA rules and 180 questions in 225 minutes under UK CAA rules. It is the longest Part-66 paper and may be split: into up to three parts under EASA rules or two under UK rules.
Study offline on your phone too
The Part-66 Prep: EASA & UK CAA app has the same questions plus a module board, essay coach, units drill and an attempt tracker for resit dates.
Keep reading
- Part-66 Licence Categories ExplainedEvery Part-66 licence category explained: A, B1.1 to B1.4, B2, B2L, B3 and C privileges, aircraft groups, modules per category and experience required.
- The Part-66 B2L Licence and Its System RatingsThe Part-66 B2L licence explained: the five system ratings, which modules each needs, EASA and UK CAA paper sizes, experience and the upgrade to B2.
- B1 vs B2: Comparing the Part-66 Mechanical and Avionics LicencesB1 vs B2 licence compared: privileges, the modules and paper sizes that differ, experience, adding the other category and which suits your career.
- Part-66 Module 13 Questions for B2 and B2LPart-66 Module 13 questions for B2 and B2L: 188 EASA or 180 UK questions, partial exams, B2L system rating papers and every sub-module explained.
- Part-66 Module 5 Digital Techniques QuestionsPart-66 Module 5 questions with a free timed paper: EASA and UK paper sizes for every category, all 15 sub-modules, data buses and number systems.
- Part-66 Module 4 Electronic Fundamentals QuestionsPart-66 Module 4 electronic fundamentals: paper sizes per category under EASA and UK CAA rules, every sub-module explained, and free timed practice.