Engine and System Monitoring
Domain 9 covers engine and system indication: which parameters are displayed, what they mean, what the limits are, and how FADEC and the monitoring systems use them. The exam tests parameter definitions, start limits and system-page interpretation.
Engine parameters
- N1 - fan or LP spool speed, the usual thrust-setting parameter on turbofans; EPR - engine pressure ratio, used instead on some types.
- N2 - HP spool speed as a percentage of rpm; governs starting and accessory drive.
- EGT / TGT / ITT - exhaust gas, turbine gas and inter-turbine temperature; the naming depends on the manufacturer. All are thermocouple-based and have a start limit and a continuous limit, often time-limited in between.
- Fuel flow (mass flow), oil pressure and temperature, vibration (N1/N2 and airframe), and on some types EGT margin.
FADEC/EEC schedules fuel, controls variable stators and bleed valves, protects against overspeed and over-temperature, and reports faults to the maintenance system.
Start monitoring
A hot start (EGT rising towards or past the limit), a hung start (N2 stagnates below idle) or a failure to light up requires closing the fuel and continuing to motor. Start limits are short - seconds - because the turbine is not yet cooled by fuel flow.
System monitoring
Fuel quantity by capacitance probes with dielectric-constant compensation; fuel temperature for cold-soak limits. Fire and overheat detection by resistance or thermocouple loops; a dual-loop system can survive one loop failure with degraded detection. EICAS/ECAM pages show synoptics, and status messages flag dispatch-relevant faults.
Worked example
On start, EGT approaches the start limit while N2 stays flat at 25 %. That is a hung start with rising temperature: close the fuel, continue motoring to clear fuel and cool the turbine, then investigate. Do not simply wait for light-up.
Traps that cost marks
- Confusing N1 and N2, or EPR and N1 as thrust parameters.
- Treating the continuous EGT limit as valid during start.
- Forgetting that a single fire-loop failure leaves degraded, not necessarily lost, detection.
- Reading a synoptic value without checking the associated status message.