Running and maintaining turbines

Starting

The starter spins the engine. At the speed the manual gives, ignition comes on and fuel is introduced; light-off shows as a rise in exhaust gas temperature. The engine accelerates, the starter cuts out once it can sustain itself, and it settles at idle. Watch for:

• Hot start: the engine lights but exhaust temperature rises past the limit, from too much fuel or too little air. Shut down; the manual says what inspection follows.
• Hung start: it lights but won't accelerate to idle, often because the starter or air supply is weak.
• No light (wet start): fuel but no ignition. Shut off fuel and ignition and motor the engine with the starter to blow the fuel out before trying again.

Reading the engine

Thrust is set by EPR (engine pressure ratio, turbine discharge pressure divided by compressor inlet pressure) or by N1. Temperature is watched as EGT, ITT or TIT, depending on where the engine measures it. Operators also trend monitor: small changes in temperature, fuel flow and vibration over weeks show an engine wearing out before it fails.

Maintenance

• Foreign object damage (FOD): check the inlet and first fan or compressor stages for nicks; keep the ramp clean.
• Borescope: look at blades, vanes and the combustor through ports without taking the engine apart.
• Blending: nicks in blades within the manual's limits are filed or ground to smooth curves to remove stress raisers.
• Compressor wash: washing out dirt and salt restores airflow and lowers operating temperatures.
• Hot section inspection: combustor and turbine parts are checked for cracks, burning and creep (blades slowly stretching under heat and spinning loads).

Stay out of the inlet and exhaust danger zones of a running engine; the inlet can pull a person in. Wear hearing protection.