CAA NZ Basic Turbine Knowledge (Aeroplane) key terms

The thermodynamic cycle describing how a gas turbine works: air is compressed, fuel is burned at near-constant pressure, and the hot gas expands through a turbine to produce work. It replaces the piston engine's Otto or Diesel cycle.

The ratio of compressor discharge pressure to inlet pressure. Higher ratios generally raise thermal efficiency but increase compressor exit temperature, affecting material limits and the surge margin.

The proportion of fuel heat energy converted into useful shaft or jet work. It rises with compression ratio and turbine entry temperature and falls with losses such as tip clearance and bleed extraction.

Fuel mass burned per unit of thrust or shaft power per hour. It is a key measure of economy; lower values mean the engine converts fuel into output more efficiently across the operating range.

The forward reaction force produced by accelerating a mass of air and exhaust gas rearward. In a turboprop it is replaced largely by shaft power turning the propeller.

The mass of air flowing through the fan duct divided by the mass flowing through the engine core. High bypass ratios improve propulsive efficiency and reduce noise, typical of modern turbofans.

A standard scheme labelling engine cross-sections, such as inlet, fan, compressor entry and exit, combustor, turbine stages and exhaust, so that pressures and temperatures can be referenced unambiguously.

The rotating module that raises the pressure of incoming air before combustion. It may be axial, centrifugal or a combination, and draws power from the turbine via a shaft.

A violent breakdown of airflow through the compressor, causing a loud bang, airflow reversal and possible flameout or damage. It is often triggered by disrupted inlet air or operation outside the surge margin.

The chamber where fuel is injected and burned with compressed air to raise gas temperature before the turbine. It may be annular, can-annular or can type, and must keep flame stable over the power range.

The module that extracts energy from hot combustion gas to drive the compressor and accessories, and in a turboprop also the propeller. Blades run in a very hot, high-stress environment and need cooling.

The rotational speed of the low-pressure spool, usually the fan or low-pressure compressor. In many engines it is the primary thrust-setting parameter and is displayed as a percentage of a reference speed.

The rotational speed of the high-pressure spool, which drives the high-pressure compressor. It is used for starting limits, monitoring and, on some engines, setting power.

Exhaust gas temperature, measured downstream of the turbine. It indicates turbine thermal loading and is a key limit during start, takeoff and climb, with a defined maximum and start-abort value.

A starting malfunction where EGT rises above the permitted limit, usually from excess fuel, low airflow or slow acceleration. The crew must abort the start and motor the engine to clear fuel.

A start in which the engine lights but fails to accelerate to idle speed, so N1 or N2 stagnates while temperature may climb. Causes include weak starter, low bleed pressure or fuel scheduling faults.

The device that rotates the engine during starting until it can sustain combustion and accelerate. Common types are electric, air-turbine and, historically, cartridge starters, each with its own duty limits.

A spark plug-like device that ignites the fuel-air mixture in the combustor during start and, on some engines, for continuous relight in rain or icing conditions. It is powered by an exciter unit.

The high-energy electrical unit that charges and discharges the igniter plug, producing a high-voltage spark. It is typically mounted on the engine casing and can be a source of radio interference when faulty.

Full Authority Digital Engine Control: a computer system that schedules fuel and controls engine parameters without a mechanical backup, using inputs such as throttle position, pressures, temperatures and speeds.

Electronic Engine Control: a computer that regulates fuel flow and engine limits, sometimes with hydromechanical backup. It may be supervisory or full authority depending on the installation.

The hydromechanical or electronic unit that meters fuel to the combustor in response to throttle and engine parameters, enforcing acceleration schedules and limits to prevent surge, flameout or overtemperature.

The process of delivering the correct fuel mass flow for the demanded power while respecting acceleration, deceleration and temperature limits. It is scheduled by the fuel control unit or FADEC.

The injector that atomises fuel into the combustor for efficient mixing and stable burning. Nozzle fouling or blockage can cause hot spots, uneven temperature and starting difficulties.

Loss of combustion in the engine, causing a rundown in speed and loss of thrust. Causes include fuel starvation, water or ice ingestion, compressor surge and extreme altitude or attitude excursions.

The combination of altitude and airspeed within which an engine can be restarted in flight, either by windmilling or with starter assistance. Outside it, relight may be impossible or damaging.

The system that supplies filtered oil to bearings and gears for lubrication, cooling and corrosion protection, and often provides sealing. It includes tanks, pumps, filters, coolers and chip detectors.

A heat exchanger that removes heat from engine oil, usually using fuel or air as the cooling medium. Fuel-cooled types also warm the fuel, helping prevent ice formation in the fuel system.

A magnetic plug in the oil system that collects ferrous metal particles, warning of internal wear or damage. Findings must be inspected and reported according to maintenance instructions.

The pressure at which oil is delivered to bearings and gears. Low pressure indicates pump failure, leakage, blockage or low quantity and requires prompt crew action and reporting.

Compressed air taken from the compressor for cabin pressurisation, air conditioning, anti-ice and engine starting. Its extraction reduces engine performance and affects the surge margin.

A system that uses hot bleed air or electrical heating to prevent ice build-up on engine inlets and airframe surfaces. Ice ingestion can damage the engine and disturb airflow.

Auxiliary Power Unit: a small gas turbine providing electrical power, bleed air for starting and air conditioning, and sometimes hydraulic power when the main engines are off.

A gear train driven by the engine that turns pumps, generators, the starter and other accessories. Its condition affects multiple systems, so failures can have wide consequences.

A system that redirects fan or exhaust gas forward to decelerate the aircraft after landing. It must only be selected when the aircraft is firmly on the ground and is not used for backing.

Selecting and controlling engine power for each phase of flight, using ratings, derates and autothrust so that the aircraft meets performance while respecting engine limits and noise requirements.

A reduced takeoff or climb thrust setting below maximum rated power, used to extend engine life and reduce maintenance cost while still meeting the required performance for the conditions.

The operating boundaries that must be respected to protect the engine, including maximum EGT, N1 and N2, minimum idle, spool-up times and restrictions on rapid throttle movements.

The formal process of recording and communicating engine faults, exceedances or abnormal indications so maintenance can act. It is a regulatory obligation and supports airworthiness and safety analysis.