Unlike a reciprocating engine's dual continuous ignition system, a turbine engine's ignition exciter typically operates on what duty cycle during normal flight operations?
- AContinuous duty, energized throughout every flight from engine start to shutdown
- BIntermittent duty, energized only during starting and selectively during conditions such as icing or turbulence
- CContinuous duty, but only on the number two igniter while the number one igniter remains off at all times
- DIntermittent duty, energized only after the engine reaches idle and shut off immediately after light-off
Show answer & explanationAnswer & explanation
Correct answer: B. Intermittent duty, energized only during starting and selectively during conditions such as icing or turbulence
Turbine ignition systems are designed for intermittent duty. Once the engine achieves stable combustion (light-off and acceleration to idle), the igniters are normally switched off to conserve exciter life, and are re-energized manually or automatically only during starts, airstarts, or conditions with a risk of flameout such as heavy precipitation, icing, or turbulence.
Why the other options are wrong
- A. Continuous operation throughout flight would rapidly wear the igniter plugs and exciter, contrary to design intent.
- C. Both igniters are typically capable of use, not permanently restricted to only one.
- D. Turning off immediately at light-off, before reaching idle, would risk flameout during the acceleration; ignition is normally kept on through stabilized idle.
Turbine Ignition Duty Cycle
Turbine ignition exciters are designed for intermittent operation, used mainly for starting and during conditions with flameout risk, not continuously throughout flight.
- Energized during ground/air starts until stable combustion is achieved.
- Re-energized during icing, heavy rain, or turbulence to guard against flameout.
- Continuous use would shorten igniter plug and exciter service life.
Memory trick: Ignite to start, rest at cruise, ignite again if the sky gets rough.