100+ Free Module 15 Gas Turbine Engine Practice Questions

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Sample Module 15 Gas Turbine Engine Practice Questions

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1Which of the following correctly describes the thermodynamic stages of the Brayton cycle in a gas turbine engine?

A.Constant volume combustion followed by constant temperature expansion

B.Adiabatic compression, isobaric combustion, adiabatic expansion, isobaric heat rejection

C.Isochoric compression, isothermal expansion, isobaric combustion, adiabatic exhaust

D.Isothermal compression, isobaric combustion, isothermal expansion, isochoric exhaust

Explanation: The Brayton cycle, which represents the ideal thermodynamic cycle of a gas turbine engine, consists of four continuous processes: adiabatic (isentropic) compression in the compressor, isobaric (constant pressure) combustion in the combustor, adiabatic (isentropic) expansion in the turbine, and isobaric (constant pressure) heat rejection in the atmosphere.

2In gas turbine engine performance, what is the mathematical relationship between net thrust (Fn) and gross thrust (Fg)?

A.Net thrust is equal to gross thrust plus the momentum drag of the fuel

B.Net thrust is equal to gross thrust minus ram drag

C.Net thrust is gross thrust multiplied by the compressor pressure ratio

D.Net thrust is gross thrust divided by the exhaust gas velocity ratio

Explanation: Net thrust (Fn) represents the actual usable thrust developed by the engine during flight. It is calculated by subtracting ram drag (the force required to accelerate the incoming air mass flow to the aircraft flight speed) from the gross thrust (Fg) produced by the exhaust jet nozzle.

3Which of the following design modifications will directly increase the thermal efficiency of a gas turbine engine?

A.Decreasing the turbine inlet temperature to reduce blade thermal stress

B.Increasing the compressor pressure ratio and increasing the turbine inlet temperature

C.Decreasing the compressor stage efficiency to increase compressor outlet temperature

D.Reducing the bypass ratio of the engine to increase jet velocity

Explanation: Thermal efficiency is defined as the ratio of work produced to heat energy supplied. According to Brayton cycle thermodynamics, increasing the compressor pressure ratio and the turbine inlet temperature (TET) directly increases the cycle's peak temperature and pressure, thereby maximizing the thermal efficiency.

4How does the speed of sound vary with altitude within the troposphere, and what is its effect on the engine's Mach number?

A.The speed of sound increases with altitude, increasing the engine Mach number for a constant flight speed

B.The speed of sound decreases with altitude, increasing the engine Mach number for a constant flight speed

C.The speed of sound remains constant, having no effect on the engine Mach number

D.The speed of sound decreases with altitude, decreasing the engine Mach number for a constant flight speed

Explanation: The speed of sound is directly proportional to the square root of the absolute temperature of the air. Since ambient temperature decreases with altitude in the troposphere, the speed of sound also decreases. Consequently, for a constant true airspeed (TAS), the flight Mach number (M = TAS / speed of sound) increases as altitude increases.

5According to Bernoulli's theorem, what happens to subsonic air as it flows through a divergent duct?

A.Velocity increases, static pressure decreases, and temperature decreases

B.Velocity decreases, static pressure increases, and temperature increases

C.Velocity increases, static pressure increases, and temperature remains constant

D.Velocity remains constant, while static pressure and temperature decrease

Explanation: Bernoulli's theorem states that for an incompressible, steady flow of fluid, the sum of static pressure and dynamic pressure is constant along a streamline. In a subsonic divergent duct, the cross-sectional area increases, causing the air velocity to decrease. As velocity (dynamic pressure) decreases, static pressure and temperature increase due to energy conservation.

6What is meant by the term 'ram recovery' in a gas turbine engine inlet duct?

A.The recovery of structural integrity after an inlet bird strike

B.The recovery of static pressure from the kinetic energy of the incoming air stream

C.The redirection of bypass air into the compressor to prevent compressor stall

D.The cooling of bleed air using ram air in the secondary heat exchanger

Explanation: Ram recovery (or ram pressure recovery) is the process by which an engine inlet duct slows down the incoming air stream (converting dynamic pressure/kinetic energy into static pressure) before it reaches the compressor face. Good ram recovery ensures high inlet total pressure, which maximizes engine thrust and efficiency.

7Calculate the net thrust (Fn) produced by a gas turbine engine if the air mass flow is 80 kg/s, the exhaust gas jet velocity is 600 m/s, and the aircraft is flying at a true airspeed of 250 m/s (neglect fuel mass flow).

A.48,000 N (48 kN)

B.28,000 N (28 kN)

C.20,000 N (20 kN)

D.68,000 N (68 kN)

Explanation: Net thrust (Fn) is calculated using the equation Fn = m_dot * (V_j - V_a), where m_dot is the air mass flow, V_j is the jet velocity, and V_a is the aircraft speed. Substituting the given values: Fn = 80 kg/s * (600 m/s - 250 m/s) = 80 * 350 = 28,000 N (or 28 kN).

8How does high ambient humidity affect the thrust output of a gas turbine engine?

A.It significantly increases thrust because water vapor has a higher density than dry air

B.It causes a small decrease in thrust because water vapor is less dense than dry air

C.It has absolutely no effect because the fuel control unit compensates completely

D.It increases thrust by acting as a water-injection power augmentation system

Explanation: Water vapor is less dense than dry air at the same temperature and pressure. High humidity reduces the density of the air entering the engine, which reduces the total air mass flow. Because thrust is directly proportional to air mass flow, high humidity results in a slight decrease in engine thrust output (typically 1% to 3%).

9What is the primary operational purpose of flat rating a gas turbine engine?

A.To ensure the engine produces the same maximum thrust regardless of altitude

B.To provide a constant maximum thrust up to a specified ambient temperature limit to protect the engine structurally and thermally

C.To maintain constant RPM across all flight phases by using variable pitch fan blades

D.To limit fuel consumption to a constant rate during all takeoffs

Explanation: Flat rating involves designing the engine to produce a constant maximum thrust up to a predetermined ambient temperature (the flat-rate cut-off point, e.g., ISA + 15°C). Below this temperature, thrust is restricted (held constant) to prevent exceeding structural limits of the gearbox or casing. Above this temperature, thrust must be reduced (de-rated) to avoid exceeding turbine entry temperature (EGT) limits.

10In a turboprop engine, how is the Equivalent Shaft Horsepower (ESHP) calculated at takeoff under standard conditions?

A.ESHP = Shaft Horsepower (SHP) + (Jet Thrust in pounds / 2.5)

B.ESHP = Shaft Horsepower (SHP) * Propeller Efficiency

C.ESHP = Shaft Horsepower (SHP) - (Jet Thrust in pounds * 2.5)

D.ESHP = Shaft Horsepower (SHP) + (Jet Thrust in pounds / Propeller Efficiency)

Explanation: At takeoff under static conditions, one pound of jet thrust is approximately equivalent to 0.4 shaft horsepower. To express the residual jet thrust of a turboprop in terms of shaft horsepower, the jet thrust (in pounds) is divided by 2.5 (since 1 / 2.5 = 0.4). This value is added to the engine's shaft horsepower (SHP) to obtain the Equivalent Shaft Horsepower (ESHP).

About the Module 15 Gas Turbine Engine Exam

The CAASL AML Category B Module 15: Gas Turbine Engine examination is structured according to the Sri Lanka Implementing Standard 066 (IS-066), which adopts the EASA Part-66 syllabus. It covers gas turbine fundamentals, engine performance, inlets, compressors, combustion chambers, turbine stages, exhaust systems, and ancillary systems such as fuel, lubrication, starting, ignition, indication, and thrust reversers. It also includes turboprop/turboshaft variants, APUs, powerplant installations, and fire protection systems. The examination is administered by the Civil Aviation Authority of Sri Lanka (CAASL) at the Katunayake examination center. It consists of 92 multiple-choice questions to be completed in 1 hour and 55 minutes, with a passing score of 75%. Candidates are advised to register via the CAASL licensing portal and schedule their exam date in advance. Study should focus on detailed mechanical construction, system operation, and maintenance procedures.

Questions

92 scored questions

Time Limit

115 minutes

Passing Score

75%

Exam Fee

See SLCAP 7100 (CAASL fees schedule) (Civil Aviation Authority of Sri Lanka (CAASL) Examination Center)

Module 15 Gas Turbine Engine Exam Content Outline

20%

Fundamentals and Performance

Brayton cycle, thrust, efficiency, and engine performance factors.

25%

Inlet, Compressor, Combustor, Turbine, Exhaust

Core gas-path sections and construction.

25%

Fuel, Oil, Air, Ignition Systems

Engine systems supporting continuous operation.

30%

Indicating, Starting, FADEC, Maintenance

Indications, starting/ignition, controls, and ground operation.

How to Pass the Module 15 Gas Turbine Engine Exam

What You Need to Know

Passing score: 75%
Exam length: 92 questions
Time limit: 115 minutes
Exam fee: See SLCAP 7100 (CAASL fees schedule)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

Frequently Asked Questions

What is the pass mark for the CAASL AML Module 15 exam?

The CAASL theoretical knowledge pass mark is 75%, with no negative marking for incorrect answers.

How many questions are on the official CAASL AML Module 15 paper?

The official paper is published as 92 questions with a duration of 115 minutes (see SLCAP 3080 / IS-66 / CAASL Examination Center).

Who administers the CAASL AML Module 15 examination?

The Civil Aviation Authority of Sri Lanka (CAASL) conducts knowledge examinations at the CAASL Examination Center.

Where can I confirm fees?

Examination fees are published in CAASL SLCAP 7100 (Fees and Charges). Confirm the current per-subject fee before booking.