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EASA Part-66 Module 4 Cats B1 · B2 · B2L · B3

Electronic Fundamentals EASA Part-66 — Module 4 Practice Questions

Module 4 covers the semiconductor devices, integrated circuits, printed circuit boards and servomechanisms that sit underneath every modern avionics box. Below: what's in the syllabus, exam format for each licence category, and seven sample questions in the same style you'll meet on exam day.

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Every question comes with a worked, EASA-grounded explanation — understand why, don't just memorise.
876
Questions in bank
5
Syllabus sections
25 min
Exam time (B1/B2)
75 %
EASA pass mark

Syllabus at a glance

Full Module 4 syllabus
Section 4.1.1
Diodes
  • PN junctions, forward & reverse bias, leakage current
  • Zener, Schottky, varactor, photo & light-emitting diodes
  • Rectifier circuits: half-wave, full-wave, bridge, voltage doublers
Section 4.1.2
Transistors
  • PNP & NPN construction, base / collector / emitter operation
  • Amplifier classes A, B & C and biasing networks
  • Oscillators, multivibrators, flip-flops & field-effect transistors
Section 4.1.3
Integrated Circuits
  • Logic gates & Boolean expressions
  • Op-amps as integrator, differentiator, comparator & voltage follower
  • Positive vs negative feedback and stage coupling methods
Section 4.2
Printed Circuit Boards
  • Construction: fibreglass laminate with etched copper tracks
  • Conformal coating & insulation resistance testing
  • Modular PCB layouts and fault-finding advantages
Section 4.3
Servomechanisms
  • Open vs closed loop, feedback, follow-up & analogue transducers
  • Synchros: control, torque, differential, resolvers & E/I transformers
  • Servo loop gain, bandwidth, hunting & reversal of synchro leads

Three classic exam-day traps

Conventional current vs electron flow

Inside an NPN transistor, electrons leave the emitter — but conventional current flows the other way. Read each question carefully to spot which convention is in use.

Common-emitter vs common-collector phase

Common-emitter inverts the signal (180° phase shift). Common-collector (emitter-follower) keeps input and output in phase. Mixing these up is one of the most-missed amplifier traps.

Synchro power: AC, never DC

Synchros & resolvers run on AC excitation — applying DC will burn out the rotor winding. Candidates sometimes second-guess this because the receiver appears to follow a steady position.

What Module 4 covers — in plain English

Module 4 of the EASA Part-66 syllabus introduces the building blocks of avionics hardware: semiconductor diodes, transistors, integrated circuits, printed circuit boards and servomechanisms. It is the foundation that the avionics modules (4 leads directly into Module 5 Digital Techniques, Module 11 Aeroplane Aerodynamics, Structures & Systems, and Module 13 for B2 candidates) all assume you already understand. Where Module 3 stops at passive components and AC/DC theory, Module 4 starts where the silicon begins — charge carriers, PN junctions, biasing, gain stages and feedback loops.

For the certifying engineer on the line, this is the theory behind every black box you swap. Knowing the difference between a half-wave and a bridge rectifier, why a decoupling capacitor sits right next to a logic chip's power pin, or what a synchro reversal does to an indicated heading, all comes back to Module 4. The exam tests practical recognition more than calculation: most questions ask about behaviour, symbol identification, or the consequence of a single change in a circuit — not about deriving transistor parameters from first principles.

Category A candidates do not sit Module 4. B1 and B3 candidates sit a 20-question paper at knowledge level 2, while B2 and B2L candidates sit the larger 40-question paper at the same knowledge level — reflecting the avionics-heavy nature of the B2 licence. Every sub-section is examinable across all four licences with no level-1 carve-outs. The full per-section breakdown is on our Module 4 syllabus page.

These samples are drawn from our live Module 4 question bank of 876 questions. The full timed practice quiz draws 20 questions per attempt (or 0 for Cat A), scored against the official EASA 75 % pass mark, with weak-area tracking across attempts.

7 free sample questions

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Q1 Diodes · Materials

A silicon diode, when compared to a germanium diode has

  1. A a higher forward bias voltage.
  2. B the same forward bias voltage.
  3. C less forward bias voltage.
Reveal answer + explanation Hide answer
Correct answer: A — a higher forward bias voltage.
A silicon diode needs roughly 0.6–0.7 V of forward bias to conduct, while a germanium diode conducts at around 0.2–0.3 V. Silicon is preferred in modern designs for its temperature stability and lower leakage current despite the higher forward drop.
Q2 Diodes · PN Junctions

In a semiconductor junction diode, electrons are the minority carriers

  1. A within the P region.
  2. B within the N region.
  3. C in both the N and P regions.
Reveal answer + explanation Hide answer
Correct answer: A — within the P region.
In P-type material, holes are the majority carriers and electrons are the minority. In N-type the reverse is true. Minority-carrier behaviour is what gives reverse-biased diodes their (small) leakage current.
Q3 Transistors · Construction

In an NPN transistor the P is the

  1. A collector.
  2. B emitter.
  3. C base.
Reveal answer + explanation Hide answer
Correct answer: C — base.
NPN names the layers in order: N (emitter) – P (base) – N (collector). The thin P-type base sits between two N-type regions and controls the flow of electrons from emitter to collector. PNP is the mirror image.
Q4 Transistors · Operation

With an NPN transistor electrons leave the

  1. A Base.
  2. B Collector.
  3. C Emitter.
Reveal answer + explanation Hide answer
Correct answer: C — Emitter.
The emitter emits the charge carriers — electrons in an NPN, holes in a PNP. Conventional current flows the opposite way (into the collector, out of the emitter terminal), so watch for questions that flip between the two conventions.
Q5 Integrated Circuits · Op-Amps

What is the average gain of an Op Amp?

  1. A 20
  2. B 200,000.
  3. C 200.
Reveal answer + explanation Hide answer
Correct answer: B — 200,000.
A typical op-amp has an open-loop gain of around 10⁵ (100,000–200,000). In practical circuits this is tamed down to a useful value by negative feedback — the closed-loop gain is set by the external resistor ratio, not the op-amp itself.
Q6 Printed Circuit Boards · Protection

How is a PCB protected after manufacture?

  1. A By conformal coating.
  2. B With non-conductive varnish.
  3. C With wax.
Reveal answer + explanation Hide answer
Correct answer: A — By conformal coating.
Conformal coating — typically acrylic, silicone or polyurethane — is sprayed or dipped over a finished board to seal it against moisture, dust and vibration. It is removable for repair using the right solvent, unlike a hard varnish or potting compound.
Q7 Servomechanisms · Control Synchros

The "null" point on a control synchro is when the two rotors are

  1. A wired in series.
  2. B at 90degrees to each other.
  3. C parallel to each other.
Reveal answer + explanation Hide answer
Correct answer: B — at 90degrees to each other.
In a control synchro (CT), the output is at its null — zero error voltage — when the rotor of the control transformer sits at 90° to the rotor of the control transmitter. Any deviation produces an error signal proportional to the angular difference.
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Module 4 — frequently asked questions

How many questions are in the EASA Part-66 Module 4 exam?
Module 4 is not part of the Category A syllabus, so Cat A candidates do not sit it at all. For B1, B2, B2L and B3 the paper is 20 multiple-choice questions. Every question is a single-best-answer item drawn from the diodes, transistors, integrated circuits, printed circuit boards and servomechanisms sections.
What is the pass mark for EASA Part-66 Module 4?
The pass mark is 75%, the same threshold that applies to every EASA Part-66 module. On the 20-question paper that means you need at least 15 correct answers. There is no negative marking, so it is always worth attempting every question rather than leaving blanks.
How long is the Module 4 exam?
For B1, B2, B2L and B3 candidates the Module 4 exam lasts 25 minutes for its 20 questions, which works out to roughly 75 seconds per question. Module 4 is not part of the Category A syllabus, so there is no Cat A allowance.
Which EASA licence categories require Module 4?
Module 4 is required for B1, B2, B2L and B3 candidates. It is not part of the Category A syllabus, so aircraft mechanics on the A licence do not study it. The electronic fundamentals here underpin all four of these categories.
What does Module 4 cover, and what do students find hardest?
Module 4 (Electronic Fundamentals) covers semiconductor diodes (PN junctions, biasing and rectifier circuits), transistors (PNP/NPN construction, amplifier classes and oscillators), integrated circuits (logic gates, op-amps and feedback), printed circuit boards and servomechanisms including synchros and resolvers. Students most often trip up on the difference between conventional current and electron flow — in an NPN transistor electrons leave the emitter, but conventional current flows the other way. Two other classic traps are confusing common-emitter (which inverts the signal by 180°) with common-collector (which stays in phase), and forgetting that synchros and resolvers run on AC excitation, since applying DC will burn out the rotor winding.
How should I revise for Module 4?
Focus on recognition and behaviour rather than heavy calculation — most questions ask what a component does, how to read its symbol, or the consequence of a single change in a circuit. Drill the traps that catch people out: current-flow convention in an NPN transistor, the phase difference between common-emitter and common-collector stages, and the fact that synchros need AC excitation. Working through practice questions in the same single-best-answer style as the real paper is the fastest way to lock in those distinctions before exam day.

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Module 4 study resources

Module 4 detailed syllabus
Per Commission Regulation (EU) 2023/989
Module 4 study notes
Topic-by-topic explanations
Q&A forum
Ask about tricky Module 4 questions
EASA licence categories
A · B1 · B2 · B2L · B3 overview

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