Turbine Engine Air Systems practice questions

Answer: C) Compressor air through them

• AIncorrect. Oil is not sprayed on blades.
• BIncorrect. Fuel is not used to cool blades.
• CCorrect. Cooling air flows through internal passages and out small holes in the blade.
• DIncorrect. This is not blade cooling.

Answer: B) Keep large debris out of the compressor

• AIncorrect. Screens restrict flow slightly.
• BCorrect. They reduce foreign object damage.
• CIncorrect. That's anti-ice.
• DIncorrect. That isn't their purpose.

Answer: A) A leaking compressor bearing seal letting oil into the compressor airflow

Bleed air comes from the compressor, so oil fumes in bleed-supplied cabin air usually mean that engine oil is getting into the compressor airflow, typically through a leaking bearing seal. Faults downstream of the bleed ports cannot contaminate the bleed air.

• ACorrect. Bleed air is taken from the compressor. If a bearing oil seal leaks, lubricating oil enters the compressed air and can be carried into the cabin. Certification rules require that lubrication system failures not cause hazardous contamination of cabin air for this reason.
• BIncorrect. Combustion happens downstream of the compressor bleed ports, so combustion products cannot reach the bleed air. A clogged filter would also tend to reduce fuel flow rather than cause rich combustion.
• CIncorrect. The exhaust is at the back of the engine, well downstream of the bleed ports. An exhaust leak is a nacelle fire and heat hazard, but it does not contaminate compressor bleed air.
• DIncorrect. Fuel collecting in the combustor or turbine section is downstream of where bleed air is extracted, so it would not produce oil fumes in the bleed-supplied cabin air.

Answer: A) Rotating knife edges run very close to a seal land, and a small airflow across them keeps oil in the bearing sump

A labyrinth seal is a non-contact seal. Rotating knife edges run close to a land, and a small airflow through the gap keeps oil from leaking out of the bearing sump.

• ACorrect. The seal's rotating teeth almost touch the land. A small, controlled flow of air through the gap stops oil from moving past the seal.
• BIncorrect. This describes a carbon seal, which is a rubbing contact seal. A labyrinth seal does not touch its land and depends on close clearance plus airflow.
• CIncorrect. This describes active clearance control, which manages blade tip clearance, not bearing sump sealing.
• DIncorrect. This describes a compressor bleed valve, which prevents stall. It has nothing to do with sealing oil in a bearing sump.

Answer: A) Cabin pressurization and air conditioning packs

Bleed air is compressed air taken from the engine compressor. On transport aircraft it is used for pressurization, air conditioning, heating and anti-ice. Landing gear and flight controls are hydraulic, and ignition exciters are electrical.

• ACorrect. Compressor bleed air is ducted to the air conditioning packs and used for cabin pressurization, heating and cooling. It is also used for anti-ice.
• BIncorrect. On transport aircraft, the landing gear is normally moved by hydraulic actuators, not bleed air.
• CIncorrect. On transport aircraft, the primary flight controls are powered by hydraulic systems, or electrohydraulic systems on some designs. They are not powered by bleed air.
• DIncorrect. Ignition exciters are electrical units that take aircraft or engine electrical power and turn it into high-energy sparks.

Answer: A) Cooling the nacelle

• ACorrect. Cowl airflow cools engine accessories and the nacelle area.
• BIncorrect. Core air enters through the inlet.
• CIncorrect. This is not its purpose.
• DIncorrect. This is not its purpose.

Answer: A) Strip oil from vent air

• ACorrect. Bearing-sump air is cleaned before venting, which reduces oil loss.
• BIncorrect. That would contaminate it.
• CIncorrect. That's cooling air.
• DIncorrect. That's bleed air.

Answer: A) It lowers the temperature of compressor bleed air, using fan discharge air, before the air enters the aircraft ducting

The precooler is a heat exchanger in the strut. It uses fan air to cool hot compressor bleed air before that air goes into the aircraft pneumatic ducting.

• ACorrect. The precooler is an air-to-air heat exchanger. Fan air is the heat sink that brings hot compressor bleed air down to a safe temperature for the pneumatic ducts and the systems they feed.
• BIncorrect. Oil is cooled by the engine's air-oil or fuel-oil coolers, not by the strut-mounted pneumatic precooler.
• CIncorrect. Turbofan engines have no intercooler between the fan and the core. The precooler handles air that has already been bled from the compressor.
• DIncorrect. On turbine engines, fuel usually absorbs heat (for example in a fuel-oil cooler) rather than being cooled. The precooler does not handle fuel.

Answer: B) It keeps manifold air from other engines, the APU, or a ground cart from flowing back into that engine

Bleed manifold check valves prevent reverse flow. They keep air from other engines, the APU, or a ground cart from flowing back into an engine's compressor through its bleed port.

• AIncorrect. Bleed temperature is controlled by the precooler and its fan-air control valve. Overheat protection comes from detection systems and shutoff valves, not from a check valve.
• BCorrect. A check valve allows flow in one direction only. It stops higher-pressure air from another source from flowing backward into an engine whose bleed pressure is lower or that is shut down.
• CIncorrect. Keeping bleed pressure at a set value is the job of the pressure-regulating (and shutoff) valve. A check valve does not modulate pressure.
• DIncorrect. Pulling the fire handle isolates bleed air by commanding a powered bleed shutoff valve closed. A check valve only responds to the direction of flow.

Answer: A) Less thrust or shaft power available for the same engine settings

Bleed air is compressed air taken out of the engine cycle, so extracting it reduces the thrust or power the engine can deliver. 14 CFR 33.66 accepts reduced output as the only allowable adverse effect within the bleed limits.

• ACorrect. Air taken out of the compressor no longer passes through the combustor and turbine to produce work. 14 CFR 33.66 allows bleed extraction up to the established limits as long as the only adverse effect on the engine is reduced thrust or power output.
• BIncorrect. The compressor has already done work on the bled air, and that energy is lost to the engine cycle. Extracting bleed air reduces thrust rather than increasing it.
• CIncorrect. With less air passing through the core, the engine has to burn relatively more fuel to hold the same power, so exhaust gas temperature typically rises rather than falls.
• DIncorrect. Bleed air is taken from the compressor stages, not from behind the turbine. Removing it measurably affects engine performance.