Free UK CAA Part-66 Module 16 Piston Engine — B1.2 Practice Questions

Sample Practice Questions

Try these 10 sample questions from the UK CAA Part-66 Module 16 Piston Engine — B1.2 practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1An engine cylinder has a volume of 480 cm³ at bottom dead centre and 60 cm³ at top dead centre. What is its compression ratio?

   1. A.7:1
   2. B.8:1Correct answer: B
   3. C.9:1
   4. D.1:8

   Explanation: The handbook defines compression ratio as "a comparison of the volume of space in a cylinder when the piston is at the bottom of the stroke to the volume of space when the piston is at the top of the stroke." Thus 480 cm³ ÷ 60 cm³ = 8, giving 8:1; units cancel and no rounding is needed. 7:1 incorrectly subtracts clearance volume first; 9:1 adds it to an already total volume; 1:8 reverses the ratio.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 1, Compression Ratio

2. 2Which power measurement represents the useful power delivered to the propeller shaft?

   1. A.Indicated horsepower
   2. B.Brake horsepowerCorrect answer: B
   3. C.Friction horsepower
   4. D.Heat input per second

   Explanation: The handbook states: "The power delivered to the propeller for useful work is known as brake horsepower (bhp)." Indicated power precedes internal losses; friction power is consumed by losses; fuel heat input has not all become shaft work.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 1, Brake Horsepower

3. 3What maintains a nearly constant fuel level in a float-type carburettor bowl?

   1. A.The throttle butterfly and its stop
   2. B.The accelerator pump and linkage
   3. C.The float-operated needle valve and seatCorrect answer: C
   4. D.The main air bleed and discharge nozzle

   Explanation: The handbook states: "The level of fuel in the float chamber is kept nearly constant by means of a float-operated needle valve and a seat." The float positions the inlet valve as fuel is used; the other systems control airflow, transient enrichment or metering characteristics.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 2, Float Chamber Mechanism System

4. 4What provides the basic magnetic field in an aircraft engine-driven magneto?

   1. A.The aircraft battery
   2. B.A permanent magnetCorrect answer: B
   3. C.The starter-generator field coil
   4. D.The spark plug's centre electrode

   Explanation: The handbook states: "The magneto, a special type of engine-driven alternating current (AC) generator, uses a permanent magnet as a source of energy." A rotating permanent-magnet field enables self-generated ignition; battery, starter field and plug electrode are not its basic field source.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 4, Magneto-Ignition System Operating Principles

5. 5What is the purpose of a spring-loaded alternate-air door that opens under induction suction?

   1. A.To admit induction air when the normal intake is blockedCorrect answer: A
   2. B.To bleed induction pressure when the throttle is fully open
   3. C.To maintain the same fuel flow with the throttle closed
   4. D.To direct heated air through the intake filter in every condition

   Explanation: The handbook states: "An alternate air door can be opened by engine suction if the normal route of airflow should be blocked by something." The door provides a bypass air path after normal intake obstruction. It is not a pressure-relief valve, fuel metering device or permanently selected filtered-heating route.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 3, Basic Carburetor Induction System

6. 6What does an engine oil's SAE viscosity-grade number establish?

   1. A.Its complete approval for every aircraft engine
   2. B.Its relative viscosity grade rather than overall qualityCorrect answer: B
   3. C.Its ash content as a percentage of oil mass
   4. D.Its maximum permissible service interval

   Explanation: The handbook states: "An SAE number indicates only the viscosity grade or relative viscosity; it does not indicate quality or other essential characteristics." Grade alone is not an engine approval, ash measurement or service interval.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 6, Viscosity

7. 7What difference in oil storage distinguishes a dry-sump engine lubrication system from a wet-sump system?

   1. A.Dry-sump engines keep the main supply in the crankcase
   2. B.Dry-sump engines keep the main supply in a separate tankCorrect answer: B
   3. C.Wet-sump engines keep the main supply in a separate tank
   4. D.Both types keep the main supply in a separate tank

   Explanation: The handbook states: "The oil supply in this type of system is carried in a tank." The reservoir location distinguishes the systems. Dry sump uses a supply tank and scavenge return; wet sump carries its supply in the engine sump.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 6, Dry Sump Oil Systems

8. 8What does a conventional piston-engine manifold-pressure gauge indicate?

   1. A.Peak combustion pressure after the spark
   2. B.Oil pressure delivered to the propeller governor
   3. C.Induction-mixture pressure before the cylindersCorrect answer: C
   4. D.Exhaust pressure downstream of the muffler

   Explanation: The handbook states: "The manifold pressure gauge measures the pressure of the air-fuel mixture before it enters the cylinders." It senses the induction manifold, not combustion peaks, governor oil or exhaust.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 3, Internally Driven Supercharger System

9. 9During the prescribed ignition-switch check, selecting OFF does not stop combustion. What condition should be investigated?

   1. A.A failed high-tension lead on every spark plug
   2. B.An excessive gap at both magnetos' breaker points
   3. C.A faulty connection in a magneto grounding circuitCorrect answer: C
   4. D.A shorted ignition condenser preventing all sparks

   Explanation: The handbook states: "failure of the engine to cut out while switching to off, indicates that one or both ground connections are faulty." Continued combustion after OFF indicates that ignition has not been grounded. Failures preventing all sparks would stop combustion rather than keep a magneto live.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 10, Ignition Switch Check

10. 10What is the purpose of silica-gel desiccant in a stored engine?

    1. A.To coat metal surfaces with a wax-like protective film
    2. B.To absorb moisture from the surrounding atmosphereCorrect answer: B
    3. C.To keep the surrounding air humid by releasing stored moisture
    4. D.To provide a moisture-tight physical seal at each opening

    Explanation: The handbook states: "There are a number of substances (referred to as desiccants) that can absorb moisture from the atmosphere in sufficient quantities to be useful as dehydrators. One of these is silica gel." Silica gel absorbs moisture rather than deliberately humidifying the stored engine. Preservative compounds coat metal, while covers provide physical seals.

    Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Chapter 8, Dehydrating Agents