The great variety of turbine engines makes it impractical to cover specific operational procedures, but there are certain operational considerations common to all turbine engines. They are engine temperature limits, foreign object damage, hot start, compressor stall, and flameout.
Engine Temperature Limitations
The highest temperature in any turbine engine occurs at the turbine inlet. Turbine inlet temperature is therefore usually the limiting factor in turbine engine operation.
Turbine engine thrust varies directly with air density. As air density decreases, so does thrust. Additionally, because air density decreases with an increase in temperature, increased temperatures will also result in decreased thrust. While both turbine and reciprocating powered engines are affected to some degree by high relative humidity, turbine engines will experience a negligible loss of thrust, while reciprocating engines a significant loss of brake horsepower.
Foreign Object Damage (FOD)
Due to the design and function of a turbine engine’s air inlet, the possibility of ingestion of debris always exists. This causes significant damage, particularly to the compressor and turbine sections. When ingestion of debris occurs, it is called foreign object damage (FOD). Typical FOD consists of small nicks and dents caused by ingestion of small objects from the ramp, taxiway, or runway, but FOD damage caused by bird strikes or ice ingestion also occur. Sometimes FOD results in total destruction of an engine.
Prevention of FOD is a high priority. Some engine inlets have a tendency to form a vortex between the ground and the inlet during ground operations. A vortex dissipater may be installed on these engines. Other devices, such as screens and/or deflectors, may also be utilized. Preflight procedures include a visual inspection for any sign of FOD.
Turbine Engine Hot/Hung Start
When the EGT exceeds the safe limit of an aircraft, it experiences a “hot start.” It is caused by too much fuel entering the combustion chamber, or insufficient turbine rpm. Any time an engine has a hot start, refer to the AFM/POH or an appropriate maintenance manual for inspection requirements.
If the engine fails to accelerate to the proper speed after ignition or does not accelerate to idle rpm, a hung or false start has occurred. A hung start may be caused by an insufficient starting power source or fuel control malfunction.
Learn more about aircraft and their systems with A Pilot’s Guide to Aircraft and Their Systems by ASA. Pilot-oriented rather than mechanic-oriented, this guide to aircraft systems is designed specifically to help general aviation pilots understand how aircraft systems work so that they can better use them in flight.