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Sample SACAA AME Engines Practice Questions

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1In a standard four-stroke operating cycle of a reciprocating piston engine (Otto cycle), how many degrees of crankshaft rotation are required to complete one full cycle of events?

A.180 degrees

B.360 degrees

C.720 degrees

D.1080 degrees

Explanation: A four-stroke engine operating on the Otto cycle requires four distinct piston strokes (intake, compression, power, and exhaust). Each stroke corresponds to 180 degrees of crankshaft rotation. Therefore, 4 strokes × 180° = 720° of total crankshaft rotation (or two complete revolutions) to execute the complete thermodynamic cycle.

2What is the primary aerodynamic and thermodynamic purpose of valve overlap in a four-stroke aircraft piston engine?

A.To prevent detonation by reducing peak combustion pressure

B.To utilize the inertia of exiting exhaust gas to scavenge the combustion chamber and draw in fresh intake charge

C.To ensure that both valves remain tightly sealed during the power stroke

D.To advance ignition timing at high engine rotational speeds

Explanation: Valve overlap is the period near Top Dead Center (TDC) end of the exhaust stroke / start of intake stroke when both intake and exhaust valves are open simultaneously. The rapid velocity of exiting exhaust gases creates a low-pressure area in the cylinder, helping scavenge remaining burned gases while pulling in the fresh intake air-fuel mixture, thereby improving volumetric efficiency and cylinder cooling.

3Which surface treatment process is commonly applied to steel aircraft cylinder barrels to produce an extremely hard, wear-resistant interior surface while retaining core toughness?

A.Anodizing

B.Nitriding

C.Alodining

D.Cadmium plating

Explanation: Nitriding is a surface hardening process in which the steel cylinder barrel is heated in an atmosphere of ammonia gas (nitrogen compounds). Nitrogen reacts with alloy elements in the steel to form micro-hard nitrides on the cylinder wall, creating a highly wear-resistant surface while maintaining the ductility and toughness of the underlying steel core.

4What is the primary function of the oil control ring installed on an aircraft engine piston?

A.To seal combustion pressure within the cylinder dome

B.To scrape excess oil from the cylinder wall and regulate the thickness of the oil film

C.To align the gudgeon pin inside the piston bosses

D.To prevent piston slap during cold engine starting

Explanation: The oil control ring is positioned below the compression rings. Its primary duty is to wipe excess lubricating oil from the cylinder walls during piston downstrokes and return it to the crankcase through relief oil holes in the piston ring groove, leaving only a microscopic oil film necessary for lubrication.

5Dynamic counterweights (pendulum dampers) fitted to aircraft engine crankshafts are designed to damp out which specific structural hazard?

A.Piston side-thrust forces

B.Torsional vibrations caused by power impulses

C.Propeller gyroscopic precession

D.Centrifugal oil pressure fluctuations

Explanation: Dynamic counterweights act as unguided pendulums attached to crankshaft crank cheeks. They oscillate at specific frequencies tuned to counter the torsional vibrations produced by power impulses from individual cylinders, preventing crankshaft fatigue failure caused by critical speed resonance.

6In a radial aircraft piston engine, what type of connecting rod assembly is utilized to connect all pistons in a single cylinder bank to the single crankpin?

A.Fork-and-blade connecting rod assembly

B.Master-and-articulated connecting rod assembly

C.Plain plain-type connecting rod assembly

D.Split-journal floating rod assembly

Explanation: Radial engines utilize a master-and-articulated connecting rod assembly. The master rod directly connects one piston (master cylinder) to the single crankpin, while the remaining cylinders' articulated rods connect to knuckle pins installed around the big-end flange of the master rod.

7What is the standard firing order for a typical four-cylinder horizontally opposed aircraft engine (e.g., Lycoming O-360)?

A.1 - 2 - 3 - 4

B.1 - 3 - 2 - 4

C.1 - 4 - 3 - 2

D.1 - 3 - 4 - 2

Explanation: The standard firing order for standard 4-cylinder horizontally opposed Lycoming and Continental aircraft engines is 1 - 3 - 4 - 2. Cylinder 1 is right rear, Cylinder 2 is right front, Cylinder 3 is left rear, and Cylinder 4 is left front (or vice-versa depending on manufacturer layout conventions), ensuring balanced power impulses and minimal vibration.

8What primary operational advantage do hydraulic valve lifters (tappets) provide in aircraft engines over solid mechanical lifters?

A.They advance valve timing automatically as engine speed increases

B.They eliminate valve clearance (lash) automatically under all thermal expansion conditions

C.They increase valve lift height beyond the camshaft lobe height

D.They allow intake valves to open twice per cycle

Explanation: Hydraulic valve lifters use pressurized engine oil inside a plunger mechanism to automatically adjust for thermal expansion and wear, maintaining zero valve clearance (zero lash) throughout engine operating temperatures. This reduces valve train wear, eliminates manual clearance adjustments, and ensures consistent valve timing.

9Which of the following conditions distinguishes detonation from pre-ignition in a reciprocating engine?

A.Detonation occurs before the normal spark; pre-ignition is instantaneous uncontrolled explosion after normal spark

B.Detonation is unburned fuel-air mixture auto-igniting uncontrollably after normal spark ignition; pre-ignition is ignition prior to spark plug firing

C.Detonation causes no structural damage; pre-ignition always destroys spark plugs only

D.Detonation occurs only in low-compression engines using high-octane fuel

Explanation: Detonation is the rapid, explosive uncontrolled burning of the end-gas (unburned fuel-air mixture) after normal spark ignition has occurred. Pre-ignition occurs when the fuel-air charge is ignited by a localized hot spot (e.g., incandescent carbon deposit or hot valve) prior to the timed spark plug discharge.

10An aircraft cylinder has a swept volume (piston displacement) of 90 cubic inches and a clearance volume of 15 cubic inches. What is the compression ratio of this cylinder?

A.5:1

B.6:1

C.7:1

D.8:1

Explanation: Compression ratio is defined as the total cylinder volume at BDC divided by the clearance volume at TDC: CR = (Swept Volume + Clearance Volume) / Clearance Volume CR = (90 cu in + 15 cu in) / 15 cu in = 105 / 15 = 7:1.

About the SACAA AME Engines Exam

The SACAA AME Engines examination is a theoretical knowledge paper covering piston engine operations (Otto cycle, magnetos, carburetors, turbochargers), gas turbine engine principles (Brayton cycle, compressors, turbines, thrust calculation), FADEC engine controls, and propeller governors for licensing (CAT C & D).

Exam sponsor: South African Civil Aviation Authority (SACAA). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

Question count not published by the exam provider

Time Limit

75 minutes

Passing Score

75%

Exam / Certification Fees

~R425–R450 per subject (confirm current SACAA Part 187 fee)

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Official sources

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

25%

Reciprocating Piston Engines

Four-stroke Otto cycle, cylinders, pistons, crankshafts, valve timing, firing order, induction systems, supercharging, and turbocharging.

25%

Gas Turbine Engine Fundamentals

Brayton cycle, jet propulsion principles, axial and centrifugal compressors, combustion chambers, turbines, exhaust nozzles, and turboprop/turboshaft configurations.

20%

Fuel Metering, Control & FADEC

Float carburetors, fuel injection systems, hydromechanical fuel control units (FCU), Full Authority Digital Engine Control (FADEC), and fuel nozzles.

15%

Propellers & Governors

Fixed-pitch and constant-speed propellers, governor operation, blade angle, feathering, pitch change mechanisms, and propeller synchronization.

15%

Engine Lubrication, Ignition & Cooling

Engine oils, dry-sump vs wet-sump lubrication, oil coolers, dual magneto ignition, turbine spark igniters, air cooling, and cowl flaps.

Preparing for the SACAA AME Engines Exam

What You Need to Know

Passing score: 75%
Assessment: Question count not published by the exam provider
Time limit: 75 minutes
Exam / certification fees: ~R425–R450 per subject (confirm current SACAA Part 187 fee) Official sources

Using Our Practice Resources

Work through all 100 available questions
Review every answer and explanation
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SACAA AME Engines: Suggested Study Strategy

1Memorise four-stroke engine cycle events: intake, compression, power, exhaust, and valve overlap.

2Understand gas turbine station numbering (Station 1 inlet, 2 compressor entry, 3 compressor exit, 4 turbine entry, 5 exhaust).

3Practice thrust calculations: Thrust = Mass Airflow x (Vexit - Vinlet) + (Pexit - Pambient) x Area.

4Review propeller governor forces: flyweight centrifugal force vs speeder spring pressure.

Frequently Asked Questions

What is the pass mark for SACAA AME Engines?

The pass mark is 75%, tested centrally via SACAA PEXO multiple-choice exam.

Does this exam combine piston engines and gas turbines?

Yes, SACAA General Exam syllabus includes both Piston Engine General (CAT C/D) and Gas Turbine General (CAT C/D) engine theory.

Are thrust calculations and engine performance metrics included?

Yes, calculating net thrust, brake horsepower (BHP), thermal efficiency, and specific fuel consumption (SFC) are standard quantitative questions.

Free Practice Questions for SACAA AME Engines

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