PNG CASA Basic Gas Turbine cheat sheet

Brayton (open) cycle stages: intake compression, constant-pressure combustion heat addition, expansion through the turbine, exhaust heat rejection to atmosphere.

Ideal thermal efficiency depends only on pressure ratio: η = 1 − 1/(PR)^((γ−1)/γ); raising PR or turbine inlet temperature raises efficiency and specific output.

Isentropic relations: T2/T1 = (P2/P1)^((γ−1)/γ) and P2/P1 = (T2/T1)^(γ/(γ−1)); γ ≈ 1.4 for air, ≈ 1.33 in the hot section.

Compressor work = m·cp·(T2 − T1); turbine work = m·cp·(T3 − T4); useful shaft work is the difference, minus accessory and bleed losses.

Specific fuel consumption (SFC) = fuel mass flow ÷ net thrust (or ÷ shaft power); lower SFC means better fuel economy at a given rating.

Compression is split into LP and HP sections with interstage cooling in some designs; overall pressure ratio is the product of stage pressure ratios.

Combustion is essentially constant pressure; pressure loss across the combustor (typically a few percent) is a direct performance penalty.

Turbine expansion drives the compressor plus output shaft; a free-power turbine on a turboshaft is aerodynamically independent of the gas generator.

Surge and choke bound the compressor map: surge is low-flow/high-pressure-ratio instability, choke is flow limited to sonic velocity at the throat.

Axial compressor: alternating rotor blades and stator vanes; stators convert velocity into pressure, rotors add kinetic energy; blade count and stagger set the flow and pressure rise.

Centrifugal compressor: impeller accelerates air radially, diffuser converts velocity to pressure; robust to foreign object damage but limited to lower pressure ratios per stage.

Combustor types: can (multiple cans), can-annular (cans within an annular casing), and annular (single continuous liner); annular gives the most uniform exit temperature profile.

Turbine blades are cooled by compressor bleed air through internal passages and film cooling holes; cooling air is a performance cost because it bypasses the combustor.

Materials: titanium alloys for compressor and fan (high strength-to-weight), nickel-based superalloys with thermal barrier coatings for turbine blades and vanes.

Turbine discs are usually forged nickel or steel alloys; blade roots are fir-tree or dovetail, retained by centrifugal load and locking features.

Bearings: ball and roller (rolling element) types carry radial and some axial load; thrust is taken by a dedicated thrust bearing with a defined load path.

Accessory gearbox is driven from the HP spool and drives fuel pump, oil pump, hydraulic pump, starter/generator and tachometer generators.

Casings provide the air/fuel containment, blade tip clearance control and mounting points; tip clearance directly affects efficiency and EGT margin.

Oil functions: lubrication, cooling, cleaning, corrosion protection and sealing; a dry-sump system uses a pressure pump plus scavenge pumps returning oil to the tank.

Oil pressure is regulated by a pressure relief valve; low oil pressure with normal quantity indicates pump wear, blockage, or a leaking/blocked filter bypass.

Oil filter differential pressure indicates a clogged element; the bypass valve opens to keep oil flowing, but unfiltered oil then reaches the bearings.

Fuel system: tank/boost pump, LP fuel filter, HP fuel pump (gear or plunger type), fuel control unit/metering unit, fuel shut-off valve, flow divider and nozzles.

Fuel is metered by the fuel control unit using inputs of N1/N2, compressor inlet temperature/pressure, throttle position and EGT; the hydro-mechanical or FADEC unit schedules acceleration and deceleration limits.

Fuel nozzles: simplex (single orifice), duplex (primary and secondary), and air-blast/air-spray types; carbon build-up on the tip distorts spray pattern and causes hot starts or EGT spread.

Ignition: high-energy capacitor discharge exciter feeds igniter plugs; typically two igniters used for starting and one (or both) for relight and anti-ice/continuous ignition.

Ignition exciter output is a high-voltage pulse (thousands of volts) at low energy per spark; a weak spark shows as difficult light-off and slow EGT rise.

Fuel contamination checks: water drain from sumps, microbial growth, particulate; incorrect fuel grade or water ingress can cause flameout or fuel control malfunction.

Start sequence: motoring by starter, ignition on, fuel on at minimum N2 (or N1) threshold, light-off confirmed by EGT rise, acceleration to idle, starter cut-out.

Hung start: engine lights but fails to accelerate to idle, usually low starter power, low fuel flow, or high EGT - abort before exceeding start EGT limit.

Hot start: EGT exceeds the start limit due to excess fuel, weak ignition or low airflow; shut off fuel and continue motoring to purge before attempting a restart.

Wet start (no light-off): fuel is introduced but no ignition; fuel must be purged by motoring before another start attempt to avoid a fire or hot start.

Typical instrumentation: N1/N2 (% rpm), EGT (°C), fuel flow, oil pressure and temperature, torque (turboprop/turboshaft), and inlet/compressor discharge pressure and temperature.

EGT is measured by thermocouples in the turbine exhaust; a spread between probes indicates a faulty probe or a distorted fuel spray pattern.

Torque is measured by a torquemeter (e.g. a hydraulic or strain-gauge type) on turboprop/turboshaft engines; it is the primary power indication for those types.

Overspeed protection: a governor or electronic overspeed protection trips fuel shut-off; N1/N2 limits are the primary structural protection for the rotating assemblies.

Instrumentation errors: a slow or lagging EGT or N1 indication during acceleration can mask a hot start; cross-check against fuel flow and oil pressure.

Thrust or shaft power falls with increasing altitude and outside air temperature because air density and mass flow decrease.

Flat-rated engines hold a constant power output up to a defined temperature (the flat-rating break), then output decreases above it.

Take-off rating is time-limited (commonly 5 minutes) at maximum thrust/power; maximum continuous and cruise ratings are unrestricted within limits.

EGT margin is the difference between the observed take-off EGT and the EGT limit; it is a key indicator of engine deterioration and remaining life.

Specific fuel consumption and thrust-specific fuel consumption relate fuel flow to output; deterioration raises SFC and reduces EGT margin together.

Bleed air extraction for cabin pressurization and anti-ice reduces available thrust/power and raises EGT at a given rating.

Power/thrust setting is normally referenced to N1 or torque, not N2; N2 is used mainly for starting and accessory/gearbox limits.

Ratings and limits are published in the engine flight/maintenance manual and type certificate data sheet; the operator applies them through the aircraft flight manual.

Maintenance is performed under an approved maintenance organization (AMO) or equivalent approval; personnel must hold the appropriate licence/authorization for the task.

Documentation: engine logbook, work order/job card, maintenance release, service bulletins, airworthiness directives (ADs) and manufacturer service letters.

ADs are mandatory; service bulletins are usually recommended unless made mandatory by an AD or the operator's approved maintenance programme.

A maintenance release certifies that the work has been completed in accordance with approved data and that the engine is fit for return to service.

Life-limited parts (LLPs) are tracked by cycles or hours; a part that reaches its limit must be removed from service regardless of condition.

Borescope inspection allows internal inspection of compressor and turbine blades without disassembly; findings are recorded with location and stage number.

Torque values, clearances, and limits must come from the current approved manual revision; superseded data must not be used.

After maintenance, an engine run (ground run or test cell) verifies parameters against the manual; results are recorded in the logbook.

Configuration control: part numbers, serial numbers and modification status must be recorded so the engine is traceable to its approved configuration.

High EGT with normal or reduced thrust/power points to compressor fouling, hot-section deterioration, or a bleed leak; wash or borescope confirms.

High fuel flow with low EGT and poor acceleration suggests a fuel control or nozzle fault, or a compressor bleed/leak problem.

Vibration rising with N1 or N2 indicates imbalance, bearing wear, blade damage or a foreign object; trend against speed to isolate the spool.

Low oil pressure with high oil temperature suggests pump wear, a blockage, or excessive bearing clearance; stop the engine if pressure falls below the limit.

Metallic particles in the oil filter or chip detector indicate bearing or gear wear; the debris type and quantity guide the inspection scope.

Slow acceleration or a hung start is typically low starter power, low fuel flow, or a misrigged fuel control; check starter, fuel pressure and rigging.

No light-off with fuel flow present: check igniter condition, exciter output, and fuel nozzle spray; verify the correct fuel grade.

Troubleshooting follows a logical sequence: confirm the indication (cross-check instruments), isolate the system, then verify the fix by run-up and trend data.

Danger zones: intake suction and exhaust blast; never stand in the intake or exhaust plane, and secure loose items before start.

Before start: confirm fire extinguishing equipment, chocks, intake/exhaust area clear, and that personnel are clear of the propeller/rotor disc.

Fuel and ignition safety: no fuel or ignition source near the engine during maintenance; bond/ground the aircraft before refuelling.

Human factors: fatigue, complacency, distraction, and pressure to dispatch are common causes of maintenance error; use checklists and independent inspection.

Regulatory framework: the engine is approved as part of the aircraft type certificate or as a separate engine type certificate; ICAO Annex 8 and national regulations (e.g. EASA Part-66/145, FAA Part 43/145) apply.

Maintenance error reporting and a just culture encourage reporting; the aim is to fix the system, not to blame the individual.

Hearing protection is mandatory near running engines; noise levels exceed safe exposure limits within the ground-running area.

Fire drill: know the location of fire bottles, the fuel shut-off and fire handle; the fire handle closes the fuel and bleed valves and arms the extinguisher.

Compressor pressure ratio (PR) is the ratio of discharge total pressure to inlet total pressure; it is the main driver of cycle efficiency.

Turbine inlet temperature (TIT) is limited by blade material and cooling; higher TIT raises specific work but shortens hot-section life.

Isentropic efficiency accounts for real losses: compression and expansion are not isentropic, so actual work differs from ideal.

Mass flow through the engine is set by the compressor and turbine nozzle areas; a restriction raises back pressure and reduces surge margin.

Thermal efficiency is the ratio of net work to heat added; propulsive efficiency is the ratio of thrust power to jet power.

Overall efficiency = thermal efficiency × propulsive efficiency; a high-bypass turbofan improves propulsive efficiency by moving more air at lower velocity.

Combustor pressure loss is kept low (a few percent) because any loss reduces turbine work and net output.

Engine deterioration shows as reduced EGT margin, higher SFC and lower thrust/power at a given N1 or torque setting.

Fan blades are usually wide-chord titanium or composite; they are the first line of defence against bird strike and FOD.

Compressor variable stator vanes (VSVs) and bleed valves modulate airflow at low speed to maintain surge margin.

Combustor liners use film cooling and thermal barrier coatings; hot spots appear as local discolouration or cracking.

Turbine nozzle guide vanes (NGVs) turn and accelerate the gas onto the rotor blades; they are usually the hottest static parts.

Active clearance control uses cooling air on the casing to shrink tip clearance at cruise for better efficiency.

Engine mounts transmit thrust and loads to the airframe; they include thrust links and shear pins with defined load paths.

FADEC units are dual-channel with cross-monitoring; a single-channel failure usually allows continued operation with degraded redundancy.

Firewalls and fire detection loops protect the engine compartment; the fire handle shuts off fuel, bleed air and hydraulics.

Oil system components: tank, pressure pump, filter, pressure regulator, cooler, scavenge pumps, chip detector and indicating system.

Oil quantity is checked after shutdown and settling; low quantity with normal pressure may indicate a gauge or dipstick error, not a leak.

Fuel is filtered at the LP stage and again at the HP stage; a blocked HP filter can cause low fuel flow and a hung start.

Fuel control acceleration schedule prevents over-fuelling during acceleration; a misrigged control causes hot starts or slow acceleration.

Igniter plugs are removed, inspected and gapped per the manual; a fouled or worn plug causes weak or intermittent spark.

Fuel nozzles are flow-checked and spray-pattern inspected; uneven flow causes EGT spread and hot-section distress.

Fuel system leak checks and pressure checks are done after any component replacement; record results against manual limits.

Water in fuel is drained from sumps before flight; microbial contamination is treated per the fuel supplier's procedure.

Start sequence is normally automatic on FADEC engines: the FADEC controls fuel scheduling and ignition timing within the start envelope.

Start envelope limits (N2, EGT, time) are published in the manual; exceeding them requires an inspection or a report.

Ground idle and flight idle settings differ; flight idle is higher to allow rapid acceleration and to keep bleed air available.

EGT indication lag and thermocouple drift are checked during run-up; a sudden step change suggests a probe or harness fault.

N1 and N2 are measured by tachometer generators or magnetic speed pickups; a failed pickup can cause an overspeed trip or a false indication.

Torque indication on turboprops is cross-checked against fuel flow and N1 to detect a faulty torquemeter.

Engine trend monitoring records N1/N2, EGT, fuel flow and oil data over time; a trend shift triggers maintenance action.

Overspeed and overtemperature protection are tested during scheduled maintenance; a failed test grounds the engine.

Take-off thrust/power is certified at a defined sea-level static condition; corrections apply for altitude and temperature.

Maximum climb and maximum cruise ratings are lower than take-off and are time-unrestricted within limits.

EGT limit is a hard limit; exceeding it requires a hot-section inspection per the manual.

N1 and N2 limits protect the rotating assemblies; overspeed requires an inspection and a report.

Oil pressure and temperature limits are published for idle, take-off and cruise; operating outside them requires action.

Ratings are affected by bleed air and power extraction; the manual gives corrections for both.

Deterioration trends are compared against a baseline established at entry into service or after overhaul.

The type certificate data sheet lists the approved ratings and operating limitations for the engine type.

Approved data means the current manual, service bulletin or AD; unapproved data cannot be used for a maintenance release.

Work cards are signed off as each task is completed; incomplete sign-off means the task is not released.

Life-limited parts are tracked in the engine logbook and the operator's LLP records; a part without traceable history cannot be installed.

Borescope findings are recorded with stage, location and description; a crack or burn requires an engineering assessment.

Torque and clearance limits are taken from the current manual revision; a superseded revision is not approved data.

After maintenance, a ground run or test cell run verifies parameters against the manual; results are recorded.

Configuration control records part numbers, serial numbers and modification status for traceability.

An engine returned to service requires a maintenance release signed by authorized personnel.

High EGT with normal thrust/power suggests compressor fouling or hot-section deterioration; a compressor wash or borescope confirms.

High fuel flow with low EGT and poor acceleration suggests a fuel control or nozzle fault, or a bleed leak.

Vibration rising with N1 or N2 indicates imbalance, bearing wear, blade damage or FOD; trend against speed to isolate the spool.

Low oil pressure with high oil temperature suggests pump wear, a blockage or excessive bearing clearance; stop the engine below the limit.

Metallic particles in the oil filter or chip detector indicate bearing or gear wear; the debris type and quantity guide the inspection.

Slow acceleration or a hung start is typically low starter power, low fuel flow or a misrigged fuel control.

No light-off with fuel flow present: check igniter, exciter output and nozzle spray; verify the fuel grade.

Troubleshooting follows a logical sequence: confirm the indication, isolate the system, then verify the fix by run-up and trend data.

Danger zones: intake suction and exhaust blast; never stand in the intake or exhaust plane, and secure loose items before start.

Before start: confirm fire extinguishing equipment, chocks, intake/exhaust area clear, and personnel clear of the propeller/rotor disc.

No fuel or ignition source near the engine during maintenance; bond/ground the aircraft before refuelling.

Human factors: fatigue, complacency, distraction and dispatch pressure are common causes of maintenance error; use checklists and independent inspection.

The engine is approved as part of the aircraft type certificate or as a separate engine type certificate; ICAO Annex 8 and national regulations apply.

Maintenance error reporting and a just culture encourage reporting; the aim is to fix the system, not to blame the individual.

Hearing protection is mandatory near running engines; noise levels exceed safe exposure limits within the ground-running area.

Fire drill: know the location of fire bottles, the fuel shut-off and fire handle; the fire handle closes the fuel and bleed valves and arms the extinguisher.

Brayton cycle efficiency rises with pressure ratio and turbine inlet temperature; specific work peaks at an intermediate pressure ratio.

Compressor work is a significant fraction of turbine work; a small compressor efficiency loss has a large effect on net output.

Isentropic efficiency of compression and expansion is typically 85–90% for well-designed components.

Combustor pressure loss is kept to a few percent; any loss reduces turbine work and net output.

Mass flow is set by compressor and turbine nozzle areas; a restriction raises back pressure and reduces surge margin.

Overall efficiency = thermal efficiency × propulsive efficiency; high-bypass turbofans improve propulsive efficiency.

Engine deterioration shows as reduced EGT margin, higher SFC and lower thrust/power at a given N1 or torque setting.

Surge and choke bound the compressor map; surge is low-flow/high-pressure-ratio instability, choke is sonic throat flow.

Fan blades are wide-chord titanium or composite; they are the first line of defence against bird strike and FOD.

Variable stator vanes (VSVs) and bleed valves modulate airflow at low speed to maintain surge margin.

Combustor liners use film cooling and thermal barrier coatings; hot spots appear as local discolouration or cracking.

Turbine nozzle guide vanes (NGVs) turn and accelerate gas onto the rotor blades; they are usually the hottest static parts.

Active clearance control uses cooling air on the casing to shrink tip clearance at cruise for better efficiency.

Engine mounts transmit thrust and loads to the airframe; they include thrust links and shear pins with defined load paths.

FADEC units are dual-channel with cross-monitoring; a single-channel failure usually allows continued operation with degraded redundancy.

Firewalls and fire detection loops protect the engine compartment; the fire handle shuts off fuel, bleed air and hydraulics.

Oil system components: tank, pressure pump, filter, pressure regulator, cooler, scavenge pumps, chip detector and indicating system.

Oil quantity is checked after shutdown and settling; low quantity with normal pressure may indicate a gauge or dipstick error, not a leak.

Fuel is filtered at the LP stage and again at the HP stage; a blocked HP filter can cause low fuel flow and a hung start.

The fuel control acceleration schedule prevents over-fuelling during acceleration; a misrigged control causes hot starts or slow acceleration.

Igniter plugs are removed, inspected and gapped per the manual; a fouled or worn plug causes weak or intermittent spark.

Fuel nozzles are flow-checked and spray-pattern inspected; uneven flow causes EGT spread and hot-section distress.

Fuel system leak checks and pressure checks are done after any component replacement; record results against manual limits.

Water in fuel is drained from sumps before flight; microbial contamination is treated per the fuel supplier's procedure.

The start sequence is normally automatic on FADEC engines: the FADEC controls fuel scheduling and ignition timing within the start envelope.

Start envelope limits (N2, EGT, time) are published in the manual; exceeding them requires an inspection or a report.

Ground idle and flight idle settings differ; flight idle is higher to allow rapid acceleration and to keep bleed air available.

EGT indication lag and thermocouple drift are checked during run-up; a sudden step change suggests a probe or harness fault.

N1 and N2 are measured by tachometer generators or magnetic speed pickups; a failed pickup can cause an overspeed trip or a false indication.

Torque indication on turboprops is cross-checked against fuel flow and N1 to detect a faulty torquemeter.

Engine trend monitoring records N1/N2, EGT, fuel flow and oil data over time; a trend shift triggers maintenance action.

Overspeed and overtemperature protection are tested during scheduled maintenance; a failed test grounds the engine.

Take-off thrust/power is certified at a defined sea-level static condition; corrections apply for altitude and temperature.

Maximum climb and maximum cruise ratings are lower than take-off and are time-unrestricted within limits.

EGT limit is a hard limit; exceeding it requires a hot-section inspection per the manual.

N1 and N2 limits protect the rotating assemblies; overspeed requires an inspection and a report.

Oil pressure and temperature limits are published for idle, take-off and cruise; operating outside them requires action.

Ratings are affected by bleed air and power extraction; the manual gives corrections for both.

Deterioration trends are compared against a baseline established at entry into service or after overhaul.

The type certificate data sheet lists the approved ratings and operating limitations for the engine type.

Approved data means the current manual, service bulletin or AD; unapproved data cannot be used for a maintenance release.

Work cards are signed off as each task is completed; incomplete sign-off means the task is not released.

Life-limited parts are tracked in the engine logbook and the operator's LLP records; a part without traceable history cannot be installed.

Borescope findings are recorded with stage, location and description; a crack or burn requires an engineering assessment.

Torque and clearance limits are taken from the current manual revision; a superseded revision is not approved data.

After maintenance, a ground run or test cell run verifies parameters against the manual; results are recorded.

Configuration control records part numbers, serial numbers and modification status for traceability.

An engine returned to service requires a maintenance release signed by authorized personnel.

High EGT with normal thrust/power suggests compressor fouling or hot-section deterioration; a compressor wash or borescope confirms.

High fuel flow with low EGT and poor acceleration suggests a fuel control or nozzle fault, or a bleed leak.

Vibration rising with N1 or N2 indicates imbalance, bearing wear, blade damage or FOD; trend against speed to isolate the spool.

Low oil pressure with high oil temperature suggests pump wear, a blockage or excessive bearing clearance; stop the engine below the limit.

Metallic particles in the oil filter or chip detector indicate bearing or gear wear; the debris type and quantity guide the inspection.

Slow acceleration or a hung start is typically low starter power, low fuel flow or a misrigged fuel control.

No light-off with fuel flow present: check igniter, exciter output and nozzle spray; verify the fuel grade.

Troubleshooting follows a logical sequence: confirm the indication, isolate the system, then verify the fix by run-up and trend data.

Danger zones: intake suction and exhaust blast; never stand in the intake or exhaust plane, and secure loose items before start.

Before start: confirm fire extinguishing equipment, chocks, intake/exhaust area clear, and personnel clear of the propeller/rotor disc.

No fuel or ignition source near the engine during maintenance; bond/ground the aircraft before refuelling.

Human factors: fatigue, complacency, distraction and dispatch pressure are common causes of maintenance error; use checklists and independent inspection.

The engine is approved as part of the aircraft type certificate or as a separate engine type certificate; ICAO Annex 8 and national regulations apply.

Maintenance error reporting and a just culture encourage reporting; the aim is to fix the system, not to blame the individual.

Hearing protection is mandatory near running engines; noise levels exceed safe exposure limits within the ground-running area.

Fire drill: know the location of fire bottles, the fuel shut-off and fire handle; the fire handle closes the fuel and bleed valves and arms the extinguisher.