Gas Turbine Engines
Construction and sections
Know the layout: intake, compressor, combustion chamber, turbine and exhaust. Compressors may be axial or centrifugal, and the turbine extracts energy to drive the compressor and accessories. Traps include the difference between a turbojet, turboprop and turbofan, and the fact that the turbine drives the compressor on the same shaft in a single-spool engine.
Lubrication and starting
Lubrication uses a dry-sump system with a pressure pump, scavenge pumps and an oil cooler. Starting uses an starter, ignition and fuel, with a start sequence that must be followed. Traps include the question of why the starter is disengaged after light-up, and the role of the igniter during a relight.
Thrust augmentation
Thrust augmentation may use an afterburner, water injection or a higher bypass ratio. Know that an afterburner adds thrust by burning fuel in the exhaust, at high fuel consumption. Traps include the fact that thrust augmentation is not the same as increasing compressor speed beyond limits.
Worked example
If exhaust gas temperature rises above limits during start, abort the start and investigate. Rule of thumb: monitor EGT, RPM and oil pressure during start; any exceedance means abort.