Chapter 4 Turbine engine operation, instruments, Maintenance, and overhaul

Why are compressor washes performed?

To remove contaminants from the compressor section and improve engine performance.

What methods are commonly used for compressor washes?

Fluid wash and abrasive grit wash.

How can you tell if a turbofan or turbojet engine is out of trim?

There will be a high exhaust gas temperature at the target engine pressure ratio for takeoff power.

What types of compressor blade damage may be found during inspection?

Dents, cracks, galling, pitting, scratches, burrs, burns, gouges.

What kind of markers can be used to mark parts in hot and cold sections during repair?

Layout dye, felt tip marker, chalk.

How does relative humidity affect turbine engines?

Negligible effect.

What criteria determines the replacement of life-limited turbine engine components?

Cycles, hours and/or calendar time.

Why should turbine blades be re-installed in the same location on a turbine disc?

To maintain the balance of the turbine wheel.

How are gas turbine engine tachometers calibrated?

They are calibrated in percent r.p.m.

What is the engine pressure ratio on a turbine engine?

It is the ratio between the total inlet pressure and total turbine exhaust pressure.

What does the engine pressure ratio indicate?

It indicates the thrust developed by the engine.

What does exhaust gas temperature (EGT) indicate on a turbine engine?

EGT is the average temperature of the turbine discharge gases.

How is exhaust gas temperature (EGT) obtained?

EGT is obtained by thermocouples placed near the turbine exit.

Can the EGT system on a turbine engine be checked without running the engine?

Yes, by checking the resistance of the thermocouples and circuits.