A turboprop's power lever divides into three ranges:
Alpha range — the flight range: the lever sets power and the propeller governor holds rpm by adjusting pitch, the constant-speed arrangement of the piston module.
Beta range — behind the flight idle gate, the ground range: the governor stands aside and the lever commands blade pitch directly, giving the fine control of thrust around zero that taxiing needs.
Reverse — the beta range's continuation: negative pitch with power, for the landing roll.
Inadvertent beta selection in flight is dangerous out of proportion to the lever movement that causes it: the blades run to flat pitch, drag rises enormously and asymmetrically on a twin, the propeller can overspeed as the airflow drives it, and the aeroplane can depart controlled flight — which is why the gate, and on modern types additional locks, stand between flight and beta.
Trending, and the EGT's special place
Engine trending is the habit of recording the engine's parameters, EGT margin above all, at a fixed condition every flight and watching their drift over weeks: a healthy engine's numbers wander slowly, and a bearing, seal or blade beginning to fail bends the trend long before any single flight's readings leave limits. The purpose is to catch deterioration on the ground, scheduled, instead of in the air, unscheduled.
EGT is the turbine's stress gauge by proxy: the temperature that actually matters, at the turbine's inlet, is too hot to measure reliably, so probes read the gas further back, and the certified EGT limits are calibrated stand-ins for the turbine stress upstream. Acceleration raises the EGT (fuel leads airflow up the acceleration schedule) and deceleration drops it, so transient peaks accompany every big lever movement. Exceeding EGT limits attacks the hot section directly: creep accelerates, blades and NGVs distort, coatings and in the extreme the blades themselves melt or crack, and life is consumed silently. That silence is why every exceedance must be reported: the damage is inside the engine, invisible from the flight deck and often symptomless for many flights, and only a report triggers the inspection that finds it before it matters.
Reverse at low speed, revisited
The previous lesson's rule gets its operational numbers here: reverse thrust is reduced to idle reverse by a specified low forward speed, typically in the region of 60 to 80 kt, because below it the reversed air outruns the aircraft, kicking debris ahead of the intakes and offering the engine its own exhaust and disturbed air to swallow — ingestion and FOD in exchange for very little further deceleration.
Seizure, leaks and blockages
Engine seizure is rotation stopping because rotating and static parts have locked together. Its causes and preventions:
Bearing failure — from oil starvation or contamination; prevented by the oil system's monitoring, the chip detectors' early warnings, and respect for oil limits.
Heavy rubbing — after an overtemperature or a surge; prevented by the limits discipline above.
Thermal distortion — the still-hot rotor bowing or the casing shrinking onto it after shutdown; prevented by cool-down running before shutdown and care on quick turnarounds.
Fuel-oil heat exchanger leak, oil pressure the higher — oil leaks into the fuel system: the fuel arrives at the nozzles contaminated, and combustion and the engine's running can be affected.
Fuel-oil heat exchanger leak, fuel pressure the higher — fuel leaks into the oil system and is carried to warm parts of the engine that should never see fuel: the risk is fire.
Oil-filter clogging — the filter's bypass opens (usually with a cockpit or maintenance indication) and the bearings receive unfiltered oil: the engine keeps running, but whatever clogged the filter is now circulating, and the lubrication system's protection is degraded until the cause is found.
Instruments, and reading damage from them
The monitoring instruments: the spool speeds (N1, N2 and N3 where fitted), EGT, fuel flow, oil pressure, temperature and quantity, and engine vibration. Damage is identified by reading them together: vibration rising with an EGT shift and a spool-speed mismatch points at blade damage; oil pressure falling as oil temperature rises is the piston module's quantity triangle, here meaning bearing or oil-system trouble; EGT rising over weeks at the same N1 is the trend of deterioration; and a bang with EGT rise and rpm stagnation is the surge picture of the compressor lesson. One needle alone is a suspicion; a coherent pattern across several is a diagnosis.
Starting malfunctions
False start, dry — the engine motors but never lights because no (or too little) fuel was delivered: rpm normal for the starter, EGT never rises.
False start, wet — fuel flows but ignition never comes: no light-off, no EGT rise, and unburned fuel pooling in the engine, to be drained and ventilated by dry motoring before another attempt.
Tailpipe fire (torching) — pooled fuel ignites in the jet pipe (the tailpipe of the name), flames visible at the exhaust: fuel off and keep motoring, blowing the fire out through the engine, usually without any extinguisher.
Hot start — light-off happens but EGT races toward or past the start limit while airflow lags: fuel off, motor to cool.
Abortive (hung) start — light-off happens but rpm stagnates below self-sustaining, EGT high-ish and steady: the engine will not finish the start; fuel off, investigate starter air and bleed configuration.
No N1 rotation — the starter turns the HP spool but the fan never moves: possible rotor lock or ice; no start may be attempted on a rotor that cannot turn.
No FADEC indications — the control's screens or data are dead before the attempt: without its full-authority computer alive, there is no start to attempt at all.
The relight envelope
A flamed-out engine can be restarted in flight only inside the relight envelope, the region of airspeed and altitude the manufacturer has demonstrated: at higher airspeeds, windmilling alone spins the engine fast enough for a starter-less relight; at lower speeds the starter must assist; and outside the envelope, too high (air too thin for the flame) or too slow (rotation insufficient), attempts are not approved and the drill is to reach the envelope first, typically by descending and accelerating.