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EASA Part-66 Module 15 Cats A1 · A3 · B1.1 · B1.3

Gas Turbine Engine EASA Part-66 — Module 15 Practice Questions

Module 15 covers the gas turbine engine end-to-end — Brayton cycle theory, intake and compressor behaviour, combustion, the hot section, fuel and oil systems, indications, and ground operation. Below: what's examinable, exam format, 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.
1 377
Questions in bank
5
Syllabus sections
115 min
Exam time (B1/B2)
75 %
EASA pass mark

Syllabus at a glance

Full Module 15 syllabus
Section 15.1 / 15.2
Fundamentals & Performance
  • Brayton cycle, Newton's laws & energy conversion
  • Turbojet, turbofan, turboprop & turboshaft layouts
  • Gross/net thrust, EPR, bypass ratio & SFC (B1 only)
  • Flat rating, altitude & hot-day limitations (B1 only)
Section 15.3 / 15.4
Intake & Compressor
  • Inlet duct configurations & ice protection
  • Axial vs centrifugal compressors
  • Stall & surge — causes, indications, recovery
  • Bleed valves, VIGVs & variable stator vanes
Section 15.5
Combustion Section
  • Annular, can & cannular chamber layouts
  • Primary, secondary & dilution airflow split
  • Swirl vanes, flame-tube cooling & hot-spots
Section 15.6 / 15.7
Turbine & Exhaust
  • Impulse, reaction & impulse-reaction blading
  • Nozzle guide vanes, blade root attachment
  • Creep, stress & shrouded rotor tips
  • Convergent & convergent-divergent nozzles, thrust reversers
Section 15.14 / 15.21
Indications, Monitoring & FOD
  • EGT/ITT, EPR, N1/N2, oil & fuel parameters
  • Trend monitoring, oil analysis & vibration
  • Borescope inspection & FOD assessment (level 3 for B1)
  • Compressor wash & ground run-up procedures

Three classic exam-day traps

Brayton: constant-pressure, not constant-volume

The Otto cycle (piston engines) is constant-volume; the Brayton cycle (gas turbines) is constant-pressure. Many candidates swap them under exam pressure and lose easy fundamentals marks.

Subsonic vs supersonic nozzle behaviour

Subsonic air speeds up in a convergent duct and slows in a divergent one. Supersonic flow does the opposite. Mix the regimes and every exhaust-section question becomes a coin-flip.

N1 indicates LP — but the LP turbine drives it

In a twin-spool engine, the front fan and LP compressor share the N1 shaft, but that shaft is turned by the rear LP turbine — not the HP turbine. Twin-spool spool-up questions hinge on this.

What Module 15 covers — in plain English

Module 15 is the dedicated gas-turbine paper sat by Category A1, A3, B1.1 and B1.3 candidates — the aeroplane-turbine and helicopter-turbine licence streams. Candidates working towards a piston licence (A2, A4, B1.2, B1.4) sit Module 16 instead, and B2 avionics candidates skip both. The syllabus walks the engine from intake to tailpipe: Brayton-cycle fundamentals, inlet aerodynamics, axial and centrifugal compressors, combustion, the hot section, bearings and seals, fuel and oil systems, air and anti-ice systems, ignition and starting, indications, alternate constructions, turboprop and turboshaft variants, APUs, the powerplant installation, fire protection, ground operation and storage. B1 candidates also cover engine performance — gross and net thrust, EPR, SFC, bypass ratio, flat rating — and the newer 15.15 section on geared turbofans, open-rotor and hybrid-electric concepts introduced by EU 2023/989 in June 2024.

The exam is one of the larger Part-66 papers — 92 questions in 115 minutes for B1.1/B1.3, or 60 questions in 75 minutes for A1/A3. Time per question is roughly 75 seconds, so the paper rewards candidates who can recognise a stem (e.g. "the working fluid of a gas turbine is …") and lock the answer in without re-deriving it. The hot-section topics — combustion airflow split, NGV function, turbine creep, EGT limits — and the FADEC/fuel-control questions are where most marks are lost. The performance section also catches B1 candidates who memorise formulas but mix up which efficiency applies (thermal, propulsive, or overall) for a given stem, or who confuse N1 and N2 spool attribution on twin-spool engines.

Knowledge levels run mostly at level 2 for B1 across the syllabus, with level 3 on 15.21 — Engine Monitoring and Ground Operation, reflecting that B1 engineers actually carry out ground runs, borescope inspections and trend interpretation on the line. Cat A1/A3 candidates sit a smaller subset, mostly at level 1, and skip 15.2 Performance, 15.8 Bearings and Seals, 15.15 Alternate Constructions and 15.22 Storage entirely. Section 15.6 Turbine and 15.3 Inlet are level 2 even at A-licence, because line maintenance on those sections is part of an A-engineer's scope. The full per-section breakdown — including which paragraphs you can safely skim and which need full level-2 recall — is on our Module 15 syllabus page.

These samples are drawn from our live Module 15 question bank of 1 377 questions. The full timed practice quiz draws 92 questions per attempt (or 60 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 Fundamentals · Thermodynamic cycle

The Brayton cycle is known as the constant

  1. A temperature cycle.
  2. B mass cycle.
  3. C pressure cycle.
Reveal answer + explanation Hide answer
Correct answer: C — pressure cycle.
The Brayton (gas-turbine) cycle is the constant-pressure cycle: combustion adds heat at essentially constant chamber pressure while the gas accelerates through the engine. Piston engines run the constant-volume Otto cycle — a common swap in exam stems.
Q2 Performance · Bypass ratio

A high bypass engine results in

  1. A overall slower airflow and greater propulsive efficiency.
  2. B overall faster airflow.
  3. C greater propulsive efficiency.
Reveal answer + explanation Hide answer
Correct answer: A — overall slower airflow and greater propulsive efficiency.
A high bypass ratio moves a larger mass of air at a lower velocity, which raises propulsive efficiency (smaller jet/aircraft velocity gap) and cuts SFC and noise. The "faster airflow" distractor describes a low-bypass turbojet, not a modern high-bypass turbofan.
Q3 Compressor · Gas-path pressures

At what point in an axial flow turbojet engine will the highest gas pressures occur?

  1. A At the compressor outlet.
  2. B At the turbine entrance.
  3. C Within the burner section.
Reveal answer + explanation Hide answer
Correct answer: A — At the compressor outlet.
Pressure peaks at the compressor outlet (P3/CDP), just before combustion. The Brayton cycle is constant-pressure, but small losses through the diffuser and flame tube mean turbine entry pressure is fractionally lower than compressor discharge.
Q4 Combustion · Flame stabilisation

What component creates a vortex in a gas turbine flame tube?

  1. A Tertiary hole.
  2. B Swirl vanes.
  3. C Cascade vanes.
Reveal answer + explanation Hide answer
Correct answer: B — Swirl vanes.
Swirl vanes sit around the fuel nozzle and impart rotation to the primary airflow, creating the low-velocity recirculation zone that anchors the flame. Without that vortex the flame would be blown downstream and the chamber would weak-extinguish.
Q5 Exhaust · Subsonic flow

As subsonic air flows through a convergent nozzle the velocity

  1. A decreases.
  2. B increases.
  3. C remains constant.
Reveal answer + explanation Hide answer
Correct answer: B — increases.
For subsonic flow, a converging duct accelerates the gas (and pressure falls) — continuity plus Bernoulli. Most exhaust nozzles on civil turbofans are simple convergent designs because they only need to reach Mach 1 at the throat for choked operation.
Q6 Indications · EGT limits

A factor that limits EGT is the

  1. A jet pipe.
  2. B compressors.
  3. C turbine.
Reveal answer + explanation Hide answer
Correct answer: C — turbine.
EGT redlines are set by the turbine — specifically the NGV and HP turbine blade material limits. Beyond the limit, creep accelerates dramatically. EGT is measured downstream of the turbine precisely because the upstream turbine-inlet temperature is too hot to instrument directly.
Q7 Monitoring · Borescope inspection

When carrying out a borescope the damage on turbine blades that would indicate a failure is

  1. A speckling.
  2. B tip curl.
  3. C colour changes.
Reveal answer + explanation Hide answer
Correct answer: B — tip curl.
Tip curl indicates the blade has crept under combined centrifugal and thermal stress beyond its plastic limit — a reject finding. Speckling and discolouration are normal hot-section signatures and only become reject conditions when they coincide with cracking or material loss.
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Module 15 — frequently asked questions

How many questions are in the EASA Part-66 Module 15 exam?
The Module 15 (Gas Turbine Engine) exam has 92 multiple-choice questions for Category B1.1/B1.3 and 60 questions for Category A1/A3. The counts differ because the B1 syllabus covers more depth — including engine performance (thrust, EPR, SFC, bypass ratio) that Cat A candidates skip.
What is the pass mark for EASA Part-66 Module 15?
The pass mark is 75%, the same across every EASA Part-66 module. For a 92-question B1 paper that means at least 69 correct answers, and for a 60-question A paper at least 45 correct. Aim comfortably above 75% in practice so exam-day nerves do not drop you below the line.
How long is the Module 15 exam?
Category A1/A3 candidates get 75 minutes for 60 questions, and Category B1.1/B1.3 candidates get 115 minutes for 92 questions. That works out to roughly 75 seconds per question, so the paper rewards recognising a stem and locking in the answer rather than re-deriving it each time.
Which EASA licence categories require Module 15?
Module 15 is required for Cats A1, A3, B1.1 and B1.3 — the aeroplane-turbine and helicopter-turbine licence streams. Candidates on a piston-engine licence (A2, A4, B1.2, B1.4) sit Module 16 instead, and B2 avionics candidates skip both engine modules.
What does Module 15 cover, and what do students find hardest?
Module 15 walks the gas turbine from intake to tailpipe: Brayton-cycle fundamentals, intake and compressor behaviour (including stall and surge), the combustion section, the turbine and exhaust, and indications, monitoring and FOD assessment. B1 candidates also cover engine performance. The hardest areas are the hot-section topics and the classic exam traps: confusing the constant-pressure Brayton cycle with the constant-volume Otto cycle, mixing up subsonic and supersonic nozzle behaviour, and misattributing which turbine drives the N1 spool on a twin-spool engine.
How should I revise for Module 15?
Nail the fundamentals first — if you can instantly state that the Brayton cycle is constant-pressure and that subsonic air speeds up in a convergent duct, you protect a block of easy marks. Then drill the hot section (combustion airflow split, NGV function, turbine creep and EGT limits) where most candidates lose points. Working timed sets of practice questions in the real exam style is the fastest way to build the recognition speed the 75-seconds-per-question pace demands.

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1. Mathematics
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2. Physics
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3. Electrical fundamentals
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4. Electronic fundamentals
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5. Digital techniques / Electronic instrument systems
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6. Materials & hardware
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7. Maintenance practices
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8. Basic aerodynamics
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9. Human factors
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10. Aviation legislation
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11. Aeroplane aerodynamics, structures and systems
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12. Helicopter aerodynamics, structures and systems
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13. Aircraft aerodynamics, structures and systems
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14. Propulsion
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16. Piston engine
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17. Propeller

Module 15 study resources

Module 15 detailed syllabus
Per Commission Regulation (EU) 2023/989
Module 15 study notes
Topic-by-topic explanations
Q&A Forum
Ask about tricky Module 15 questions
EASA licence categories
A · B1 · B2 · B2L · B3 overview

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