Part-66 Module 16 is the piston engine module, and for many light aircraft engineers it is the most practical paper in the licence. If you are looking for Part-66 Module 16 questions, you are probably working towards B1.2 or B3, or a category A2 licence. The paper is long, 76 questions under EASA rules, and it rewards people who have actually done a magneto check, a compression test or a carburettor heat check, because so many questions describe a symptom and ask for the cause.
This page gives the paper size for every category under both systems, explains the syllabus differences between EASA and UK rules, walks through all 14 sub-modules with the topics examiners like and the traps that catch people, and ends with a study plan. Part-66 Prep is an independent study aid, not EASA, the UK CAA or a Part-147 organisation. For where Module 16 sits among the 17 modules, see the Part-66 modules guide.
Module 16 paper size by category
| Category | EASA questions / time | UK CAA questions / time |
|---|---|---|
| A2, A4 (site: category A) | 52 / 65 min | 52 / 65 min |
| B1.2, B1.4 | 76 / 95 min | 72 / 90 min |
| B3 | 76 / 95 min | 68 / 85 min |
Every paper is three-option multiple choice, 75 seconds a question, 75% to pass, with no essays and no negative marking. The EASA numbers are from Appendix II as replaced by Regulation (EU) 2023/989; the UK numbers are from the retained text on legislation.gov.uk. Part-66 Prep covers categories A, B1.2 and B3 for this module; B1.4 uses the same EASA paper size as B1.2.
Key fact: Under EASA rules a paper with more than 90 minutes allowed may be split into two partial exams, so a 95-minute Module 16 paper can be sat in two parts at the same organisation, each passed at 75%. UK Part-66 has no general partial-exam rule.
Knowledge levels and the EASA/UK difference
Under EASA rules B1 and B3 share the same knowledge levels: level 2 for almost everything, level 3 for engine monitoring and ground operation, level 2 for storage and preservation, and level 1 for alternative constructions. Category A is level 1 throughout and does not cover storage.
The UK syllabus differs in two ways. It has 13 sub-modules, not 14, because 16.14 alternative piston engine constructions was added to the EU syllabus later. And it sets lower B3 levels in two places: engine monitoring and ground operation at level 2 (B1 stays at 3) and storage and preservation at level 1. That partly explains the shorter UK B3 paper. The CAA's knowledge requirements page links to the current UK text.
Where the marks are
The EASA guidance on question spread (AMC1 to Appendix II) suggests this split for the 76-question B1 and B3 paper. It is a guide, not a fixed blueprint, but our papers follow it.
| Sub-module | Approx. questions (B1.2/B3, EASA) |
|---|---|
| 16.1 Fundamentals | 5 |
| 16.2 Engine performance | 5 |
| 16.3 Engine construction | 8 |
| 16.4 Fuel systems (carburettors, injection, electronic control) | 12 |
| 16.5 Starting and ignition | 5 |
| 16.6 Induction, exhaust and cooling | 4 |
| 16.7 Supercharging and turbocharging | 6 |
| 16.8 Lubricants and fuels | 5 |
| 16.9 Lubrication systems | 4 |
| 16.10 Engine indication | 7 |
| 16.11 Power plant installation | 3 |
| 16.12 Monitoring and ground operation | 5 |
| 16.13 Storage and preservation | 3 |
| 16.14 Alternative constructions | 4 |
Fuel systems, construction and indication together are about a third of the paper.
Sub-modules 16.1 to 16.3: theory, performance and construction
Fundamentals and the Otto cycle
Know the four strokes and what the valves do in each, plus valve lead, lag and overlap and why they improve volumetric efficiency. Know the three efficiencies: thermal (power out over heat in the fuel), mechanical (brake horsepower over indicated horsepower) and volumetric (actual charge over the charge that would fill the swept volume). The syllabus also covers two-stroke, Diesel and, under EASA rules, rotary engines. Aviation diesels compress air alone to a high ratio, burn Jet A-1 and need no ignition system.
Displacement and compression ratio are reliable calculations. A worked example in the style you should expect: a cylinder with a swept volume of 700 cm³ and a clearance volume of 100 cm³ has a compression ratio of (700 + 100) ÷ 100 = 8:1. The trap is to divide swept volume by clearance volume and answer 7:1. Firing order and configuration (horizontally opposed, in-line, V, radial with an odd number of cylinders per row) also appear.
Performance
Power calculations use torque and rpm or the PLANK formula, with factors that reduce power: lower air density from altitude, heat or humidity, intake restrictions and carburettor heat. Mixture questions are common: the chemically correct ratio is about 15:1, best power is slightly rich of that, best economy is leaner, and full rich at take-off cools the cylinders and suppresses detonation. Know the difference between detonation (explosive burning after the spark) and pre-ignition (ignition before the spark from a hot spot).
Construction
Expect questions on the crankcase, crankshaft and dynamic dampers, the camshaft turning at half crankshaft speed in an opposed engine, hydraulic lifters, double valve springs wound in opposite directions to prevent surge, sodium-filled exhaust valves, choke-bored cylinder barrels, piston rings and full-floating gudgeon pins, connecting rod types (plain, fork-and-blade, master and articulating) and reduction gearboxes. A spur reduction gear turns the propeller opposite to the crankshaft; a planetary set can keep the same direction.
Sub-modules 16.4 and 16.5: fuel, starting and ignition
Carburettors, injection and electronic control
The float carburettor is examined system by system: float and needle valve, main metering jet and air bleed, idle system, accelerating pump, economiser, mixture control with idle cut-off, and throttle valve. Carburettor icing is a favourite. Know the three types (fuel evaporation ice, throttle ice and impact ice), that icing can occur in warm humid air, and the classic symptom sequence when carburettor heat is applied: rpm drops first, because hot air is less dense, then rises as the ice melts. Carburettor heat is not used for take-off because it reduces power and the air is unfiltered.
Continuous-flow fuel injection brings in the fuel servo or fuel-air control unit, the flow divider and the injector nozzles. One trap appears often: on many injected engines the fuel flow gauge actually measures pressure at the flow divider, so a blocked nozzle gives a higher flow reading while real flow falls. Electronic engine control (piston FADEC) uses dual channels with crank position, manifold pressure and temperature, CHT and EGT sensors. The fuel systems note and the Pro fuel systems drill cover this in depth.
Starting and ignition
Know the starter, solenoid, Bendix drive and starter duty cycle, then the magneto in detail: rotating magnet, primary and secondary coils, contact breaker, capacitor and distributor, and the E-gap, where the points must open for the strongest spark. The impulse coupling retards the spark and spins the magnet quickly at cranking speed; the click you hear when turning a propeller by hand means the magneto can fire. The P-lead switches the magneto off by earthing its primary circuit, so a broken P-lead means a live magneto. Spark plug heat range is a reliable question: a hot plug for a cold-running engine, a cold plug for a hot-running one. The starting and ignition note has the full magneto check fault table.
Exam tip: On a magneto check, no rpm drop when one magneto is selected off is not a good result. It suggests an open P-lead or switch fault, which means that magneto cannot be switched off.
Sub-modules 16.6 to 16.9: air, boost, fuel grades and oil
Induction, exhaust and cooling. Alternate air doors open automatically if the filter blocks; exhaust heat exchangers supply cabin and carburettor heat, so a cracked muffler can put carbon monoxide into the cabin. Air cooling relies on fins, baffles, pressure cooling and cowl flaps (open for ground running and climb, closed in cruise).
Supercharging and turbocharging. This sub-module carries about six questions. Know the wastegate logic (open means less boost), the controllers (absolute pressure, variable absolute pressure, density and differential pressure controllers), deck pressure, critical altitude, ground-boosted versus normalised engines, bootstrapping, overboost protection and intercoolers.
Lubricants and fuels. Avgas grades and colours (100LL blue, 100 green, 80 red), anti-knock rating and performance numbers, volatility and vapour lock, tetraethyl lead, alternate and drop-in unleaded fuels, and oil types: straight mineral oil for running in, ashless dispersant oil afterwards.
Lubrication systems. Wet and dry sump, pressure relief valve, filter bypass, the oil cooler's thermostatic valve, breathers that must not ice up, and why oil filters and screens are inspected for metal.
Sub-modules 16.10 to 16.14: indication, installation and ground running
Indication carries about seven questions: tachometers (mechanical drag-cup, tacho-generator, electronic), CHT and EGT thermocouples, resistance bulbs for oil temperature, Bourdon tube oil pressure gauges with restrictors, absolute manifold pressure and fuel flow. Instrument markings (green arc, yellow arc, red line) appear too.
Installation covers firewalls and fireproof penetrations, cowlings and fasteners, engine mounts and dynafocal anti-vibration mounts, fire-resistant hoses, wiring looms, and control rods and cables with full travel and cushion at the stops.
Monitoring and ground operation is level 3 for B1 under both systems, and for B3 under EASA rules. Expect practical questions: hydraulic lock in radial and inverted engines and how to clear it (remove lower plugs, never force the propeller), oil pressure within the specified time after start, run-up checks, the idle mixture check, static rpm on a fixed-pitch propeller, and the differential compression test at TDC on the compression stroke, including where you hear air for each leak path.
Storage and preservation covers inhibiting oil, desiccant plugs and depreservation. Alternative constructions (EASA only, level 1) introduces hybrid piston-electric systems and electric power augmentation.
Module 16 and the rest of your licence
Module 16 pairs with Module 17 propellers for B1.2 and B3: governors, constant-speed operation and propeller run-up checks link straight back to engine handling. It also pairs with the airframe module, Module 11B or 11C, which covers the fuel, electrical and instrument systems on the aircraft side of the firewall.
For B3 candidates, Module 16 is one of the three longest papers under EASA rules, after Modules 6 and 7, and the clearest example of the UK/EASA size gap. The B3 licence guide sets out every paper. For B1.2, the Part-66 B1 licence guide covers the full module set and experience requirements.
EASA now has 18 modules: Regulation (EU) 2025/111, applicable from 13 February 2026, added a B1.E subcategory for electric aeroplanes and Module 18 on electric power plants. Module 16 itself is unchanged by that, apart from the hybrid concepts already in 16.14. Part-66 Prep covers Modules 1 to 17 and has no Module 18 questions yet.
Background reading: the FAA's Aviation Maintenance Technician Handbook – Powerplant has excellent chapters on reciprocating engines, induction, ignition and lubrication. It uses US terminology and rules, so take the technology from it and the regulation from Part-66.
Practising Module 16
Part-66 Prep has 739 original Module 16 questions. Choose EASA or UK CAA rules on the start screen and the paper takes the right size for your category.
- B1.2: Module 16 paper 1 and free quick practice
- B3: Module 16 paper 1 for B3
- Category A: Module 16 for category A
- Printable: the Module 16 question sheet, 50 questions with an answer key
These are exam-style papers written for the app and site. Neither EASA nor the CAA publishes past papers, and we never use recalled exam questions.
Your study plan
- Confirm your category and system, and note whether your paper is 52, 68, 72 or 76 questions.
- Read the free fundamentals and performance note and work its calculations by hand.
- Take the free B1.2 quick practice to find your weak sub-modules.
- Sit the full timed Module 16 paper 1 (or the B3 version) in one go.
- Work through fuel systems, ignition and turbocharging first, since they carry the most marks, then sit papers 2 to 10 with Pro.
- Book when you score 85% or more on three different papers. New to the licence? Start with the free B1.2 diagnostic or B3 diagnostic.
20 free Part-66 Module 16 Piston engine practice questions with answers
Try each one, then open the answer. For the timed experience use the free exam-style paper or the printable version.
1. Engine cowlings serve to:
- A. streamline the engine and guide cooling air
- B. carry the engine weight to the airframe
- C. act as the primary fire barrier
Show answer
A. streamline the engine and guide cooling air
Cowlings reduce drag and, with baffles and cowl flaps, control cooling airflow. They are inspected for cracks, loose fasteners and chafing.
2. What is the purpose of ignition harness shielding?
- A. To increase the spark voltage
- B. To cool the ignition leads
- C. To reduce radio interference
Show answer
C. To reduce radio interference
The braided metal shielding grounds stray radiation from the high-voltage leads, reducing interference with radios and other electronic equipment.
3. Why do many turbocharger installations need a scavenge pump in the turbo oil return line?
- A. Oil often cannot drain back from the turbo by gravity
- B. To pressurise the turbine housing with oil
- C. To feed oil into the compressor inlet for sealing
Show answer
A. Oil often cannot drain back from the turbo by gravity
Oil that has lubricated and cooled the turbo bearings must return to the engine. Where the turbo is mounted low or the drain path is poor, a scavenge pump returns the oil so it does not collect and leak past the seals.
4. Hydraulic valve lifters in an opposed engine are supplied with:
- A. fuel from the injector lines
- B. engine oil under pressure
- C. grease packed at overhaul
Show answer
B. engine oil under pressure
Pressurised engine oil fills the hydraulic lifter, keeping zero clearance in the valve train during operation.
5. A light piston engine manual specifies a multigrade ashless dispersant oil. Using a straight mineral oil in normal service would:
- A. lose its required cleaning and cold-flow benefits
- B. raise the octane rating of the fuel
- C. make no difference to the engine
Show answer
A. lose its required cleaning and cold-flow benefits
Ashless dispersant oils hold contaminants in suspension and multigrades flow better at low temperatures; straight mineral oil is normally only for break-in.
6. In a differential compression test, 80 psi is applied and the cylinder retains 74 psi. What is the pressure loss as a percentage of the applied pressure?
- A. 92.5 %
- B. 7.5 %
- C. 8.11 %
Show answer
B. 7.5 %
Loss % = (80 - 74) ÷ 80 × 100 = 7.5 %.
7. Cylinder numbering on horizontally opposed engines:
- A. varies between manufacturers; the manual must be used
- B. always starts at the front right cylinder
- C. is always clockwise viewed from the front
Show answer
A. varies between manufacturers; the manual must be used
The numbering of opposed engine cylinders is not standard; some manufacturers number from the rear and others from the front. Always refer to the engine manual.
8. A digital engine monitor records an 'exceedance'. This means that:
- A. the monitor has exceeded its memory capacity
- B. the pilot pressed the event button only
- C. a parameter went beyond its limit and was logged
Show answer
C. a parameter went beyond its limit and was logged
Engine monitors log parameters exceeding set limits (e.g. CHT, rpm, MP) with time and value, for maintenance investigation.
9. During depreservation, the propeller shaft is cleaned and then:
- A. lightly coated with engine oil
- B. painted with zinc chromate
- C. left completely dry
Show answer
A. lightly coated with engine oil
Corrosion-preventive compounds are washed from the propeller shaft, which is then lightly coated with engine oil before the propeller is fitted.
10. Why is a rich mixture used at take-off power?
- A. A rich mixture gives the highest combustion temperature
- B. It gives the lowest specific fuel consumption
- C. The extra fuel cools the cylinders and suppresses detonation
Show answer
C. The extra fuel cools the cylinders and suppresses detonation
Near full power a rich mixture is needed to prevent overheating and detonation. Since full power is used only briefly, the high fuel consumption is acceptable.
11. Hydraulic valve lifters (tappets) are used because they:
- A. increase valve lift at high rpm
- B. eliminate the need for valve springs
- C. keep valve clearance at zero automatically
Show answer
C. keep valve clearance at zero automatically
Hydraulic (zero-lash) lifters use engine oil to take up clearance automatically, eliminating routine valve clearance adjustment. They are quieter and better lubricated.
12. In an electronically controlled piston engine, fuel is often delivered by:
- A. a float-type carburettor and venturi
- B. a single updraft pressure carburettor
- C. solenoid injectors timed for each cylinder
Show answer
C. solenoid injectors timed for each cylinder
The ECU calculates fuel quantity and opens solenoid injectors at the right time.
13. Automotive engines converted for aircraft use often need a crankshaft extension with an extra front bearing. Why?
- A. To carry propeller bending and gyroscopic loads
- B. To lower the compression ratio for avgas
- C. To drive a second magneto
Show answer
A. To carry propeller bending and gyroscopic loads
Car engines are not designed for the bending, thrust and gyroscopic loads a propeller puts on the crankshaft nose. A crankshaft extension supported by a large front bearing takes these loads.
14. Carburettor heat should not be used on the ground in dusty conditions because:
- A. it stops the engine
- B. the heated air is unfiltered
- C. it overheats the oil
Show answer
B. the heated air is unfiltered
Carburettor heat air bypasses the air filter, so dust can enter the engine.
15. Wiring looms in the engine compartment must be:
- A. routed tight against the exhaust for protection
- B. left unsupported to allow engine movement
- C. supported by clamps and kept clear of hot parts
Show answer
C. supported by clamps and kept clear of hot parts
Wiring is routed and clamped to avoid chafing, excessive heat and fluid contamination, with slack only where needed to allow engine movement.
16. Magneto coils, distributor rotors and blocks are waxed in order to:
- A. lubricate the rotating parts inside
- B. make moisture bead and prevent flashover
- C. reduce radio interference from sparks
Show answer
B. make moisture bead and prevent flashover
Waxing causes moisture to bead so it cannot form a continuous conducting path, reducing flashover and carbon tracking.
17. A turbocharger shows excessive oil in the compressor outlet and induction. A likely cause is:
- A. worn seals or a blocked drain
- B. a stuck-open waste gate valve
- C. a partly clogged fuel injector
Show answer
A. worn seals or a blocked drain
Failed shaft seals, or a restricted scavenge/drain line causing oil to back up in the centre housing, let oil pass into the compressor or turbine housings.
18. Some piston engines have oil jets that spray the underside of the pistons to:
- A. lubricate the propeller governor
- B. prime the fuel system
- C. cool the pistons
Show answer
C. cool the pistons
Directing oil at the piston crown underside removes heat from highly loaded pistons.
19. Ethylene dibromide is added to leaded AVGAS to:
- A. raise the fuel octane rating directly
- B. scavenge lead and reduce deposits
- C. dye the fuel for identification
Show answer
B. scavenge lead and reduce deposits
Ethylene dibromide combines with lead during combustion to form volatile compounds that leave in the exhaust, reducing lead deposits and plug fouling.
20. During a ground run, oil temperature rises above the red line while oil pressure falls. A likely cause is:
- A. a rich mixture at idle
- B. a correctly operating thermostat
- C. a blocked cooler or low oil
Show answer
C. a blocked cooler or low oil
High temperature with falling pressure suggests poor oil cooling (blocked cooler, stuck thermostat, low airflow) or insufficient oil. The engine should be stopped and investigated.
Frequently asked questions
+How many questions are in Part-66 Module 16?
Under EASA rules, 52 questions in 65 minutes for category A2 and A4, and 76 questions in 95 minutes for B1.2, B1.4 and B3. Under UK CAA rules category A is also 52, B1.2 is 72 questions in 90 minutes and B3 is 68 questions in 85 minutes.
+Who needs Module 16?
Anyone working towards a piston-engine licence: category A2 and A4, subcategories B1.2 (piston aeroplanes) and B1.4 (piston helicopters), and category B3. Turbine candidates sit Module 15 instead, and B2 candidates cover engines in Module 14.
+What is in Module 16 piston engine?
Under EASA rules there are 14 sub-modules: fundamentals, performance, construction, fuel systems, starting and ignition, induction, exhaust and cooling, supercharging and turbocharging, lubricants and fuels, lubrication, indication, installation, monitoring and ground operation, storage and preservation, and alternative constructions such as hybrid concepts.
+Is Module 16 different for B3 under UK rules?
Yes. The UK B3 paper has 68 questions in 85 minutes, against 76 under EASA rules. The UK syllabus also sets lower knowledge levels for B3 in ground operation and storage, and has no sub-module on alternative piston engine constructions.
+What causes carburettor icing?
Mainly the cooling effect of fuel evaporating in the carburettor and the drop in air temperature as air speeds up through the venturi and past a partly closed throttle. Ice can form in warm, humid air well above freezing. Impact ice from supercooled water is a third type.
+What is the difference between supercharging and turbocharging?
Both compress the induction air to raise manifold pressure. A supercharger is driven mechanically from the crankshaft and takes engine power to do so; a turbocharger is driven by an exhaust gas turbine, using energy that would otherwise be wasted, and is controlled by a wastegate.
+How long should I study for Module 16?
There is no official figure. It is a long paper with a lot of practical detail, so candidates without piston engine experience usually need longer than those who have done engine work on light aircraft. Plan by sub-module and practise until you score 85% on full papers.
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 Modules 1 to 17: The Complete GuideAll 17 Part-66 modules explained: what each covers, which categories sit it, EASA and UK CAA question counts and times, and free practice papers.
- Part-66 Module 17 Propeller QuestionsPart-66 Module 17 propeller: 17A and 17B paper sizes under EASA and UK CAA rules, every sub-module from blade theory to balancing, and free practice.
- Part-66 Module 11 Questions: Aeroplane Structures and SystemsPart-66 Module 11 questions for 11A, 11B and 11C: paper sizes per category, partial exams, every ATA sub-module explained and free timed papers.
- The Part-66 B3 Licence for Light Piston AeroplanesThe Part-66 B3 licence for piston aeroplanes up to 2,000 kg: privileges, all 13 papers under EASA and UK CAA rules, experience, limitations and B3 vs B1.2.
- The Part-66 B1 Licence: Modules, Exams and ExperienceThe Part-66 B1 licence explained: B1.1, B1.2 and B1.3 privileges, modules and paper sizes under EASA and UK CAA rules, experience, costs and timescales.