Why are turbine engines operated during maintenance?
Fault confirmation, post-maintenance checks, performance investigation, control wear checks, taxi checks, aircraft movement.
Which engine types do ground operation procedures apply to?
Turbofan, turboprop, turboshaft engines and APUs.
What does advancing the thrust lever do?
Increases engine speed and commands increased fuel flow.
Key pre-start inlet inspection requirement
Ensure compressor/turbine rotate freely and no FOD is present.
Common sources of engine starting air
Ground air unit, APU, or bleed air from another engine.
Key parameters monitored during engine start
RPM (N1/N2/N3), oil pressure, and EGT.
What is a hot start?
Excessive EGT during engine start.
What is a hung start?
Insufficient engine acceleration during start.
Aircraft positioning requirement for engine run
Aircraft positioned into wind with chocks fitted and brakes applied.
Minimum intake clearance during engine run
Approximately 10 m (30 ft) in front of intakes.
Why is engine cool-down at idle required before shutdown?
Prevents rotor distortion, bearing damage, and rotor seizure.
Purpose of engine performance indications
Allow monitoring of engine operation and limits during start, ground operation, and flight.
Main engine monitoring parameters
EPR, N1/N2/N3, fuel flow, and EGT.
Define Engine Pressure Ratio (EPR)
Ratio of turbine discharge pressure to compressor inlet pressure.
Advantage of EPR as a thrust indication
Largely independent of ambient temperature and accurate for axial-flow engines.
What does N1 indicate?
Low-pressure spool speed driving the fan and LP compressor.
Why is N2 important during engine start?
Confirms starter cut-out speed and detects hung starts.
Purpose of fuel flow indication
Flight planning, trend monitoring, and detecting abnormal fuel usage.
Why is EGT critical?
Indicates thermal condition and prevents engine overheating.
Primary power indication on turboprop engines
Engine torque.
Torque is proportional to what?
Shaft horsepower.
Common torque sensing methods
Hydro-mechanical, electronic shaft twist, and phase displacement systems.
Purpose of engine trend monitoring
Detect abnormal deterioration early and support on-condition maintenance.
Main benefit of trend monitoring
Prevents failures and reduces operating costs.
