Ignition, Starting and Engine Control
Domain 7 - Ignition, Starting and Engine Control
The exam tests ignition systems, start sequences, start faults and FADEC or hydro-mechanical control.
Core rules
- Ignition consists of an exciter and high-energy igniter plugs, usually two with one selectable as backup. Light-off occurs at a defined N2 during the start sequence. Ignition may be continuous in rain, icing or low-power approach.
- Starter types are air turbine starter using bleed air, electric starter/generator and cartridge. The sequence is crank, ignition on, fuel on at scheduled N2, light-off, acceleration to idle, starter cut-out.
- Start faults: hung start, where acceleration stalls below idle because of low starter torque, low bleed pressure or fuel scheduling; hot start, where excess fuel drives EGT over the limit and the crew must close the fuel and motor the engine; wet start, where fuel passes without light-off and exhaust fire is a risk; and no-light.
- Control: a hydro-mechanical fuel control with FADEC supervision, or full-authority digital control. The FADEC schedules fuel, variable geometry, bleeds and ignition, and protects against overspeed and over-temperature. It has dual channels and fault codes.
- Thrust is set by N1 or EPR and limited by EGT, N2 and torque.
Worked example
During start, EGT climbs quickly towards the limit and N2 stalls at 42%. Fuel is being scheduled but acceleration is poor. A hung start with rising EGT means the fuel/air ratio is too rich for the available airflow, often from low starter bleed pressure or a stuck bleed valve. Abort the start, motor the engine to clear fuel, then investigate the starter and bleed system.
Traps
- Continuing a hot start to see whether it recovers.
- Assuming a FADEC fault always grounds the aircraft instead of using the MEL and fault codes.
- Confusing an ignition exciter failure with a fuel scheduling problem; check the igniter first.