Chapter 10: Gas Turbine Engine Support Systems

Flashcards covering ignition, fuel control, lubrication and cooling, bleed air, ice protection, reverse thrust, and related safety considerations from the lecture notes.

Why is the ignition system in a gas turbine engine generally simpler than in a piston engine?

Because once the engine is running it is self-sustaining, so a continuous spark is not required and the spark does not need to be accurately timed to a specific point in the engine cycle.

How is a very powerful spark produced in the gas turbine ignition system?

Low voltage from the aircraft (APU or battery) is converted into high voltage and stored so energy can be released all at once.

What component delivers the high voltage spark to the combustion chamber in a gas turbine engine?

The ignitor plug, connected by high voltage ignition leads.

Why do most engines have two independent ignition systems?

For redundancy in case of a failure of one ignition unit; typically two ignitor plugs in different positions.

When is continuous ignition typically activated and why?

During critical phases like take-off and approach, in icing conditions or severe turbulence, and when anti-icing or stall warning is active; it helps relight quickly if airflow is interrupted.

What is flameout in a gas turbine engine?

When the fuel–air mixture is extinguished due to disruption of airflow through the engine.

What conditions can disrupt airflow and increase the risk of flameout?

Sudden changes in aircraft pitch, icing conditions, or ingestion of ice or water into the engine.

What is the Fuel Control Unit (FCU) and what does it do?

The FCU monitors mass air flow, changes in temperature and pressure, and automatically adjusts fuel delivery based on the pilot’s thrust setting (or autothrottle setting).

Where is the FCU located in the fuel system?

Between the fuel tank and the engine.

What are the start-up and rapid acceleration responsibilities of the FCU?

During start, it carefully delivers fuel to ignite; during rapid acceleration/deceleration, it quickly adapts to changes in air flow to maintain the desired thrust.

What is the fuel spray nozzle’s function in the combustion process?

To mix the fuel with incoming air to ensure rapid and efficient burning; some designs include a swirl chamber to create tiny droplets.

What are the two main recirculatory oil system configurations and how do they differ?

Pressure relief valve system (controls flow with a relief valve, opening at preset pressure) and full-flow system (delivers oil directly to bearings via a pump; used in engines with high bearing chamber pressure).

Why do turboprop and turboshaft engines often have a separate oil system for the reduction gearbox?

Because the reduction gearbox operates under heavy loads and benefits from using a higher viscosity (thicker) oil.

What additional components are typically part of the lubrication system?

Oil filter and oil cooler; some aircraft integrate a Fuel Oil Heater Exchange (FOHE) to heat fuel and cool oil.

What does FOHE stand for and what does it do?

Fuel Oil Heater Exchange; it runs fuel through a tube surrounded by hot oil, heating the fuel and cooling the oil.

What incident at Heathrow highlighted fuel temperature and water-in-fuel concerns?

The January 17, 2008 Heathrow incident where very cold conditions led to ice forming from water in the fuel, restricting fuel flow and causing engine problems on a BA 777.

How are high turbine temperatures managed in the engine?

Cooler air is directed through internal passages to cool turbine blades and nozzle guide vanes, allowing higher temperatures and thrust.

What is bleed air used for in aircraft systems?

Bleed air from the compressor powers systems such as pressurized cabins and ice protection, and is heated or cooled as needed before use.

What is a major downside of using bleed air?

Less air remains for thrust, with up to around 20% of intake air potentially diverted to non-thrust systems; may require valve adjustments during certain phases.

How is reverse thrust achieved in a turboprop engine?

By turning the propeller blades to a negative angle to create backward thrust (drag).

What are clamshell reversers and how do they work?

Two large plates rotate within the exhaust to block the normal exit and deflect exhaust gases through a side duct when reverse thrust is selected.

What are bucket reversers?

Outside-exhaust plates that rotate to block flow just beyond the normal exhaust, deflecting exhaust gases when reverse thrust is selected.

What is a cold stream reverser and when is it used?

Used in high bypass engines; translates the engine cowl to expose cascade vanes and uses a blocker door to deflect bypass air; cooler air provides limited thrust with lighter components.

What safety issues have occurred with thrust reversers deployed in flight?

Electrical faults have caused unintended in-flight deployment, such as the Bangkok 1991 incident and the 1996 Fokker 100 incident, highlighting the importance of safety interlocks and alarms.

What is the difference between anti-icing and de-icing in engine operation?

Anti-icing is activated before icing conditions to prevent ice buildup; de-icing is activated after ice has formed.

How do engineers monitor engine health and why is it important?

A range of instruments provide health data to pilots, enabling early intervention if something is wrong, improving safety and reliability.