Gas Turbine Engine Management

A set of Q&A flashcards covering key concepts in gas turbine engine management, including EPR, RPM, spool terminology, health monitoring, start procedures, and common start and in-flight issues.

What does EPR stand for and how is it calculated?

Engine Pressure Ratio; it is the ratio of exhaust pressure to intake pressure (exhaust pressure divided by intake pressure).

What is EPR used for in gas turbine engines?

A primary means of setting thrust by measuring thrust output through the EPR ratio.

If an engine does not provide EPR, what is commonly used as the primary thrust reference?

Engine RPM (spool speed) expressed as a percentage of the maximum normal RPM.

In a two-spool engine, what does N1 refer to?

The speed of the fan/low-pressure compressor and the low-pressure turbine.

In a two-spool engine, what does N2 refer to?

The speed of the high-pressure compressor and the high-pressure turbine.

In a three-spool engine, what is N3?

The high-pressure spool; N2 is the intermediate spool and N1 is the fan/low-pressure spool.

How is engine RPM typically expressed in gas turbine engines?

As a percentage of the maximum normal operating RPM.

What does a torquemeter measure and why is it useful?

Engine torque (twisting force); it is proportional to horsepower and provides a useful indication of engine output.

Why is Exhaust Gas Temperature (EGT) important for engine health monitoring?

EGT indicates the exhaust temperature; if it gets too hot, it can damage the turbine and exhaust, especially during start.

What are the alternative names for EGT readings?

Turbine Inlet Temperature (TIT), Turbine Entry Temperature (TET), Turbine Outlet Temperature (TOT).

What role does a vibration indicator play in gas turbine engines?

It helps assess engine health; small vibrations can signal issues, while larger vibrations can indicate a problem or failure.

What is a hot start in starting a gas turbine engine?

An start where the EGT rises too high due to insufficient air flow or a weak starter/APU, risking damage.

What are common causes of a hot start?

Insufficient air flow (weak starter or inadequate APU air), or starting with a strong tailwind.

What action is typically taken during a hot start?

Shut the engine down promptly to prevent damage.

What is a hung start?

An engine fail to accelerate to self-sustaining speeds after ignition, often requiring a starter or cross-bleed restart.

What is a tailpipe fire in the context of engine starts?

Unburnt fuel ignites and flames exit the back of the engine after a failed start.

What is a blowout cycle?

Engaging the starter but not the igniters to blow out excess fuel with airflow through the engine.

What is a compressor stall?

Disruption of airflow through the compressor blades caused by an excessive blade angle of attack (AoA).

Under which two conditions can a compressor stall occur?

Air flowing slowly with high RPM, or air flowing fast with low RPM.

What is compressor surge?

A breakdown in airflow over a portion of the compressor; often used interchangeably with stall and reduces thrust.

What is flameout?

The flame in the combustion chamber goes out due to causes such as incorrect fuel-air mixture, insufficient air, icing, or fuel exhaustion.

What is a relight envelope?

The set of conditions (altitude and speed) under which an inflight restart is permissible.

What is a windmill start?

Starting the engine by using only ambient air to rotate the core, without the starter.