Starting and Ignition Systems
What this domain tests
Starting and Ignition tests the sequence from motoring to idle, ignition sources, and abnormal starts. Expect light-off, hung start, hot start, wet start, and EGT limits.
Core rules
- Start sequence: starter motoring, ignition on, fuel on, light-off, acceleration to idle, starter cutout. FADEC may automate the sequence.
- Ignition systems use exciters and igniters; some engines have intermittent or continuous ignition for icing, turbulence, or relight.
- A hung start is a failure to accelerate; a hot start is excessive EGT; a wet start is fuel without light-off. All require fuel shutoff and dry motoring.
- Starter types include air turbine and electric. Air starters need a ground cart or cross-bleed.
Worked example
During start, EGT rises to 950 C against a limit of 900 C and N2 stagnates at 35%. The start is abnormal. The reasoning: N2 stagnation indicates insufficient starter or fuel scheduling, while high EGT indicates fuel is burning without enough airflow. The correct action is to shut off fuel, continue motoring to clear fuel, and investigate. Do not continue to idle.
Traps
Confusing hung and hot starts; assuming ignition is always continuous; ignoring starter duty cycle; treating a wet start as a minor event; forgetting that EGT limits apply during start.