How does the ignition system remain energized?

How does the ignition system remain energized?

• A. For 5 seconds after start.
• B. Until N2 rpm is 54% or greater or throttle is retarded below idle.
• C. Until MIL power is reached.
• D. Only during initial start.

Answer: (B)

Ignition stays energized through start and into transient operation until the engine reaches a self-sustaining state, indicated by N2 reaching 54% or greater, or if the throttle is moved below idle. Reaching about 54% N2 means the compressor, combustor, and fuel system are producing enough throughput for stable combustion that doesn’t rely on continual ignition sparks. If you pull the throttle back below idle, the risk of flameout increases during that transient, so keeping ignition energized allows an immediate relight if needed. Once the engine is past that speed threshold or throttle position is stable above idle, the system no longer needs continuous ignition. The other options don’t reflect how ignition is managed during start and transient operation: it isn’t a fixed 5-second window, isn’t tied to MIL power, and isn’t limited to just the initial start.

Ignition stays energized through start and into transient operation until the engine reaches a self-sustaining state, indicated by N2 reaching 54% or greater, or if the throttle is moved below idle. Reaching about 54% N2 means the compressor, combustor, and fuel system are producing enough throughput for stable combustion that doesn’t rely on continual ignition sparks. If you pull the throttle back below idle, the risk of flameout increases during that transient, so keeping ignition energized allows an immediate relight if needed. Once the engine is past that speed threshold or throttle position is stable above idle, the system no longer needs continuous ignition. The other options don’t reflect how ignition is managed during start and transient operation: it isn’t a fixed 5-second window, isn’t tied to MIL power, and isn’t limited to just the initial start.