Turbine Engines practice questions

Answer: A) A hung start

A hung start has a normal light-off, but RPM hangs below idle and does not accelerate. Insufficient starter power is a common cause, and the engine should be shut down.

• ACorrect. A hung start is a normal light-off where RPM stays at a low value and does not rise to normal idle. A common cause is too little starter power. The engine should be shut down.
• BIncorrect. In a hot start, the engine turns normally but exhaust temperature goes over the prescribed limit. Here EGT stayed within limits.
• CIncorrect. In a no-light (false) start, the fuel-air mixture does not ignite. The scenario says light-off was normal.
• DIncorrect. A wet start is fuel entering the engine without ignition, which can leave fuel pooled in the combustor or tailpipe. Here the engine lit off normally.

Answer: B) To remove blade deposits that reduce compressor efficiency and raise EGT

Field washing removes dirt and salt deposits from the compressor blades. This restores compressor efficiency and airflow, which lowers EGT and brings back lost performance.

• AIncorrect. Compressor washing is not a cooling procedure. Lower EGT after a wash comes from better compressor efficiency, not from cooling hot-section parts.
• BCorrect. Dirt and salt deposits on compressor blades reduce airflow and efficiency, so the engine runs hotter to make the same power. Washing removes these deposits and restores performance.
• CIncorrect. Carbon deposits form in the hot section. A compressor wash is aimed at the compressor blades, not the fuel nozzles or combustor.
• DIncorrect. Cracks are found by inspection methods such as borescope inspection. Washing the compressor is done to recover performance, not to find cracks.

Answer: A) Fuel flow

• ACorrect. There's no throttle valve restricting the air.
• BIncorrect. That's a piston engine.
• CIncorrect. Prop pitch affects load, not the gas generator directly.
• DIncorrect. Turbines don't use magnetos for control.

Answer: A) Loss of combustion

• ACorrect. Combustion stops while fuel or air supply is disrupted.
• BIncorrect. A flameout is unintended.
• CIncorrect. That is a torching or tailpipe fire.
• DIncorrect. This is different.

Answer: B) Ingested object damage

• AIncorrect. This is not FOD.
• BCorrect. Foreign object damage comes from debris drawn into the engine.
• CIncorrect. This is not FOD.
• DIncorrect. This is not FOD.

Answer: C) Adjusting the fuel control unit so the engine meets its dataplate performance

Trimming adjusts the fuel control unit so the engine produces rated thrust. The technician uses the engine dataplate values (such as EPR at a given RPM) as the target.

• AIncorrect. Blending is a repair for blade damage. It does not set the engine's power output.
• BIncorrect. Reverser rigging is an exhaust and reverser system adjustment. It is not engine trimming.
• CCorrect. Trimming adjusts the fuel control unit so the engine produces its rated thrust, such as the dataplate EPR at a specified RPM.
• DIncorrect. Checking the EGT indicating system makes sure the instruments read accurately. It does not adjust fuel scheduling or engine output.

Answer: B) Accelerating a mass of air rearward

• AIncorrect. Thrust comes from momentum change.
• BCorrect. Newton's third law gives the forward reaction.
• CIncorrect. Airflow is essential.
• DIncorrect. The compressor alone doesn't make thrust.

Answer: C) Reduce vibration and tip leakage

• AIncorrect. That isn't the purpose.
• BIncorrect. They don't affect it directly.
• CCorrect. Shrouds form a ring that dampens blades.
• DIncorrect. That isn't the purpose.

Answer: B) Thrust decreases because less dense air reduces the mass airflow

Turbine thrust depends on the mass of air the engine accelerates. Hot air is less dense, so mass airflow and thrust fall as outside air temperature rises.

• AIncorrect. Thrust depends mainly on the mass of air accelerated. Hot inlet air is less dense, so the engine moves less mass, and any extra expansion does not make up for that loss.
• BCorrect. As temperature rises, air density falls, so less air mass enters the engine and thrust drops. Cold, dense air raises mass airflow and thrust.
• CIncorrect. Holding rpm constant does not hold mass airflow constant. At the same rpm, less dense air means less mass flow and therefore less thrust.
• DIncorrect. Compressing warmer air takes more work for a given pressure rise, not less. Warm air also lowers mass flow, so thrust goes down.

Answer: C) Dovetail roots

• AIncorrect. Mechanical roots are used.
• BIncorrect. That would weaken the blade.
• CCorrect. Turbine blades often use fir-tree roots.
• DIncorrect. Blades mount on the disk.