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Module 16 Piston engine: 50 practice questions

Real EASA paper: Category A 52 Q / 65 min · B1.2 76 Q / 95 min · B3 76 Q / 95 min. Three options, 75% to pass. Answer key on the last page. From part66exam.com · independent study aid, not an official exam or a past paper.

1. Engine cowlings serve to:
1. A. streamline the engine and guide cooling air
2. B. carry the engine weight to the airframe
3. C. act as the primary fire barrier
2. What is the purpose of ignition harness shielding?
1. A. To increase the spark voltage
2. B. To cool the ignition leads
3. C. To reduce radio interference
3. Why do many turbocharger installations need a scavenge pump in the turbo oil return line?
1. A. Oil often cannot drain back from the turbo by gravity
2. B. To pressurise the turbine housing with oil
3. C. To feed oil into the compressor inlet for sealing
4. Hydraulic valve lifters in an opposed engine are supplied with:
1. A. fuel from the injector lines
2. B. engine oil under pressure
3. C. grease packed at overhaul
5. A light piston engine manual specifies a multigrade ashless dispersant oil. Using a straight mineral oil in normal service would:
1. A. lose its required cleaning and cold-flow benefits
2. B. raise the octane rating of the fuel
3. C. make no difference to the engine
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?
1. A. 92.5 %
2. B. 7.5 %
3. C. 8.11 %
7. Cylinder numbering on horizontally opposed engines:
1. A. varies between manufacturers; the manual must be used
2. B. always starts at the front right cylinder
3. C. is always clockwise viewed from the front
8. A digital engine monitor records an 'exceedance'. This means that:
1. A. the monitor has exceeded its memory capacity
2. B. the pilot pressed the event button only
3. C. a parameter went beyond its limit and was logged
9. During depreservation, the propeller shaft is cleaned and then:
1. A. lightly coated with engine oil
2. B. painted with zinc chromate
3. C. left completely dry
10. Why is a rich mixture used at take-off power?
1. A. A rich mixture gives the highest combustion temperature
2. B. It gives the lowest specific fuel consumption
3. C. The extra fuel cools the cylinders and suppresses detonation
11. Hydraulic valve lifters (tappets) are used because they:
1. A. increase valve lift at high rpm
2. B. eliminate the need for valve springs
3. C. keep valve clearance at zero automatically
12. In an electronically controlled piston engine, fuel is often delivered by:
1. A. a float-type carburettor and venturi
2. B. a single updraft pressure carburettor
3. C. solenoid injectors timed for each cylinder
13. Automotive engines converted for aircraft use often need a crankshaft extension with an extra front bearing. Why?
1. A. To carry propeller bending and gyroscopic loads
2. B. To lower the compression ratio for avgas
3. C. To drive a second magneto
14. Carburettor heat should not be used on the ground in dusty conditions because:
1. A. it stops the engine
2. B. the heated air is unfiltered
3. C. it overheats the oil
15. Wiring looms in the engine compartment must be:
1. A. routed tight against the exhaust for protection
2. B. left unsupported to allow engine movement
3. C. supported by clamps and kept clear of hot parts
16. Magneto coils, distributor rotors and blocks are waxed in order to:
1. A. lubricate the rotating parts inside
2. B. make moisture bead and prevent flashover
3. C. reduce radio interference from sparks
17. A turbocharger shows excessive oil in the compressor outlet and induction. A likely cause is:
1. A. worn seals or a blocked drain
2. B. a stuck-open waste gate valve
3. C. a partly clogged fuel injector
18. Some piston engines have oil jets that spray the underside of the pistons to:
1. A. lubricate the propeller governor
2. B. prime the fuel system
3. C. cool the pistons
19. Ethylene dibromide is added to leaded AVGAS to:
1. A. raise the fuel octane rating directly
2. B. scavenge lead and reduce deposits
3. C. dye the fuel for identification
20. During a ground run, oil temperature rises above the red line while oil pressure falls. A likely cause is:
1. A. a rich mixture at idle
2. B. a correctly operating thermostat
3. C. a blocked cooler or low oil
21. An engine with a supercharger boosting manifold pressure above ambient (e.g. above 30 inHg) may have a volumetric efficiency:
1. A. greater than 100 %
2. B. always below 70 %
3. C. exactly 100 % at all powers
22. Oil pressure on a piston engine is sensed at:
1. A. the oil pump outlet
2. B. the scavenge line to the tank
3. C. the oil tank vent
23. During engine preservation, the cylinders are typically treated by:
1. A. filling them completely with engine oil
2. B. spraying corrosion-preventive mixture into each cylinder
3. C. leaving the spark plugs out and cylinders open
24. Best power mixture is often set at about:
1. A. 100 °F rich of peak EGT
2. B. exactly at peak EGT
3. C. 100 °F lean of peak EGT
25. How is piston ring side clearance checked?
1. A. By fitting the ring in the cylinder and measuring the gap
2. B. By weighing the ring on a balance
3. C. With a feeler gauge between the ring and its groove land
26. How does the RSA system shut off fuel to the nozzles at idle cut-off?
1. A. The flow divider valve closes
2. B. The throttle valve closes fully
3. C. The boost pump is switched off
27. Why are many light-sport engines geared?
1. A. To run at high engine rpm with slower propeller rpm
2. B. To reverse the propeller for braking
3. C. To eliminate the need for a propeller governor
28. The principal hazard of a cracked exhaust system inside the engine compartment is:
1. A. reduced engine oil pressure
2. B. carburettor ice formation
3. C. fire and carbon monoxide
29. Most light aircraft reciprocating engine mounts are made of:
1. A. cast magnesium alloy
2. B. laminated wood
3. C. welded steel tubing
30. Most modern light piston engines are started by:
1. A. a direct-cranking electric starter
2. B. an inertia starter with a flywheel
3. C. a cartridge starter
31. The three main parts of a typical turbocharger are the:
1. A. compressor, turbine wheel and floating bearing assembly
2. B. impeller, carburettor and waste gate controller
3. C. supercharger gear train, clutch and diffuser
32. Turning the oil pressure relief valve adjusting screw clockwise normally:
1. A. decreases the oil pressure
2. B. changes the oil temperature
3. C. increases the oil pressure
33. The cloud point of an oil is the temperature at which:
1. A. its vapour flashes when a flame is applied
2. B. it stops flowing when cooled further
3. C. wax crystals start to separate and make it cloudy
34. A cold cylinder check is used to locate:
1. A. the hottest cylinder for the CHT probe
2. B. oil leaks at the rocker covers
3. C. dead or intermittently firing cylinders
35. Volumetric efficiency of a piston engine is the ratio of:
1. A. brake horsepower to indicated horsepower
2. B. useful work to the heat energy in the fuel
3. C. the charge actually inducted to the swept volume
36. If a manifold pressure gauge reads higher than ambient with a normally aspirated engine stopped, the likely cause is:
1. A. an instrument error
2. B. a leaking intake pipe
3. C. a clogged air filter
37. When a piston engine is preserved, the wax-like protective coating applied to its metal surfaces is typically:
1. A. petroleum-based, wax-like films
2. B. water-based paint coatings
3. C. acid-etch primer coatings
38. The mixture that gives maximum power from a given airflow is approximately:
1. A. 15:1 air-fuel (0.067 fuel/air)
2. B. 17:1 air-fuel (0.060 fuel/air)
3. C. 12:1 air-fuel (0.0725-0.080 fuel/air)
39. A 'choked' cylinder barrel is:
1. A. blocked by carbon in the exhaust port
2. B. one whose cooling fins are clogged
3. C. smaller in diameter at the top than at the bottom
40. How is power lever (throttle) position usually signalled to a piston FADEC?
1. A. By a pneumatic line from the throttle valve
2. B. By a throttle position sensor, such as a potentiometer
3. C. By a Bourdon tube in the air box
41. Why must the two carburettors of a twin-carburettor light-sport engine be synchronised?
1. A. So one carburettor can act as a standby unit
2. B. So the choke works equally on both sides
3. C. So both sides get equal airflow for smooth running
42. Shock cooling of an air-cooled engine is caused by:
1. A. a slow, steady descent with power on
2. B. running the engine at idle on the ground
3. C. a rapid power reduction at high speed
43. The primary purpose of the engine firewall is to:
1. A. confine an engine fire to the nacelle
2. B. support the weight of the engine
3. C. act as the main oil cooler baffle
44. Spark plug heat range is a measure of its ability to:
1. A. transfer heat from the tip to the cylinder head
2. B. withstand high voltage without flashover
3. C. operate over a wide rpm range
45. Supercharging affects the engine parameters by increasing:
1. A. manifold pressure and charge temperature
2. B. compression ratio and valve overlap
3. C. the octane rating of the fuel
46. On a dry-sump system, why is the oil tank vented to the engine crankcase?
1. A. To pressurise the tank for the pump inlet
2. B. To cool the oil in the tank
3. C. To prevent oil loss through the vent
47. At what outside temperature does the FAA state engine and oil preheat is normally required, regardless of oil type?
1. A. Below 50 °F (10 °C)
2. B. Below -40 °F (-40 °C)
3. C. Below about 20 °F (-7 °C)
48. During a compression test, air escaping from the exhaust stack indicates leakage past the:
1. A. exhaust valve
2. B. intake valve
3. C. piston rings
49. Which reciprocating engine type is used predominantly in modern light aircraft?
1. A. Single-row radial, air-cooled
2. B. Horizontally opposed, air-cooled
3. C. V-12, liquid-cooled
50. A sudden sustained rise on the CAT gauge during operation may indicate:
1. A. carburettor ice forming
2. B. an induction system fire
3. C. a lean mixture at cruise

Answer key

1. A — Cowlings reduce drag and, with baffles and cowl flaps, control cooling airflow. They are inspected for cracks, loose fasteners and chafing.
2. C — The braided metal shielding grounds stray radiation from the high-voltage leads, reducing interference with radios and other electronic equipment.
3. A — 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. B — Pressurised engine oil fills the hydraulic lifter, keeping zero clearance in the valve train during operation.
5. A — Ashless dispersant oils hold contaminants in suspension and multigrades flow better at low temperatures; straight mineral oil is normally only for break-in.
6. B — Loss % = (80 - 74) ÷ 80 × 100 = 7.5 %.
7. A — 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. C — Engine monitors log parameters exceeding set limits (e.g. CHT, rpm, MP) with time and value, for maintenance investigation.
9. A — Corrosion-preventive compounds are washed from the propeller shaft, which is then lightly coated with engine oil before the propeller is fitted.
10. C — 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. C — Hydraulic (zero-lash) lifters use engine oil to take up clearance automatically, eliminating routine valve clearance adjustment. They are quieter and better lubricated.
12. C — The ECU calculates fuel quantity and opens solenoid injectors at the right time.
13. A — 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. B — Carburettor heat air bypasses the air filter, so dust can enter the engine.
15. C — Wiring is routed and clamped to avoid chafing, excessive heat and fluid contamination, with slack only where needed to allow engine movement.
16. B — Waxing causes moisture to bead so it cannot form a continuous conducting path, reducing flashover and carbon tracking.
17. A — 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. C — Directing oil at the piston crown underside removes heat from highly loaded pistons.
19. B — Ethylene dibromide combines with lead during combustion to form volatile compounds that leave in the exhaust, reducing lead deposits and plug fouling.
20. C — 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.
21. A — Because charge density is referred to standard conditions, an engine with true supercharging can induct more than its swept volume of standard-density charge, giving volumetric efficiency above 100 %.
22. A — The main oil pressure reading is taken at the pump outlet (pressure side), showing the pressure at which oil is supplied to the bearings.
23. B — With the piston at BDC, corrosion-preventive compound is sprayed into each cylinder through the plug holes; then dehydrator plugs are fitted and openings sealed.
24. A — Manufacturers commonly quote best power at about 100 °F rich of peak EGT, with best economy at or near peak.
25. C — Side clearance is checked with the ring in its groove, using a feeler gauge between ring and land. End gap is checked separately by placing the ring squarely in the cylinder bore.
26. A — When the mixture is placed in idle cut-off, metered pressure falls and the flow divider spring closes the valve, shutting off the individual nozzle lines for a clean stop.
27. A — Small high-revving engines produce power at high rpm; a reduction gearbox lowers propeller speed to an efficient value with acceptable tip speed.
28. C — Exhaust leaks can ignite fuel or oil and allow carbon monoxide into the cabin, especially through the cabin heater muff. Exhaust systems require careful inspection at each inspection.
29. C — Most reciprocating engine mounts are welded steel tube structures, attached to the firewall/fuselage and carrying the engine via rubber vibration isolators.
30. A — Direct-cranking electric starters are used on almost all light piston aircraft; they crank the engine immediately when energised through a starter solenoid.
31. A — The turbocharger comprises the compressor assembly, the turbine wheel assembly and a full-floating shaft bearing assembly in the centre housing.
32. C — On most engines, turning the screw clockwise increases spring tension on the relief valve, raising the pressure; counterclockwise lowers it.
33. C — As oil is cooled, waxes begin to crystallise at the cloud point. Further cooling reaches the pour point, where it no longer flows.
34. C — After running the engine on each magneto, cylinder temperatures are compared (e.g. with a temperature probe or grease pencil marks). A cold cylinder indicates it was not firing on that magneto.
35. C — Volumetric efficiency compares the volume of charge inducted (corrected to standard temperature and pressure) with the piston displacement. A naturally aspirated engine is below 100 %; a supercharged engine may exceed it.
36. A — With the engine stopped, manifold pressure equals ambient. A higher reading indicates the gauge or its line/transducer is faulty or needs calibration.
37. A — Corrosion-preventive compounds form a wax-like film over the metal. Heavy compounds are applied by dipping/brushing; light ones by spraying, often mixed with oil for the engine interior.
38. C — Best power mixtures lie between 0.0725 and 0.080 fuel/air (about 12:1 to 13.8:1). The excess fuel increases the working mass and speeds combustion.
39. C — Some barrels are ground smaller at the top (head end). As the hotter top expands more in operation, the bore becomes nearly parallel.
40. B — A throttle position sensor (commonly a potentiometer, often duplicated) gives the control an electrical signal proportional to lever or throttle-plate position.
41. C — Each carburettor feeds one side of the engine. Mechanical synchronisation (cables) and then pneumatic synchronisation (vacuum gauges) make both deliver the same airflow, giving smooth idling and even running.
42. C — A rapid drop in cylinder head temperature, e.g. a sudden power reduction in a fast descent, causes uneven contraction that can crack cylinder heads. Gradual power changes are recommended.
43. A — The firewall is usually the foremost bulkhead of the nacelle and is made of stainless steel or another fire-resistant material. It also provides mounting and a disconnect point for lines, linkages and wiring.
44. A — The plug must run hot enough to burn off carbon deposits but cool enough to avoid pre-ignition. Heat range depends mainly on the length of the insulator nose.
45. A — Compressing the charge raises manifold pressure and temperature; power rises but so do cylinder pressures and detonation tendency. Aftercooling and limits on MP and temperature manage this.
46. C — Tank vent lines connect to the crankcase so any oil carried over is returned rather than lost; the tank is indirectly vented through the crankcase breather.
47. C — At temperatures below 20 °F, preheating of the engine and oil supply is normally required regardless of the type of oil used.
48. A — Listening at the exhaust, intake and breather locates the leak: exhaust stack = exhaust valve, air intake = intake valve, breather = piston rings.
49. B — Small general aviation aircraft use mostly horizontally opposed engines, which have a low weight-to-power ratio, a narrow silhouette and low vibration.
50. B — A momentary rise indicates a backfire; a continuous increase indicates a sustained induction system fire.

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