The starter must not be engaged if indicated N2 RPM exceeds what percentage?

• A. 45%
• B. 40%
• C. 50%
• D. 55%

Answer: (A)

During a turbine engine start, the starter spins the core up to a speed where ignition can take over. There’s a limit to how fast the core can be driven by the starter while it’s still engaged. The indication of N2 should not exceed 45 percent with the starter connected, because that point allows the engine to be energized to ignition safely and then continue accelerating on its own. If the starter stayed engaged beyond that, and ignition hadn’t occurred, the starter or drive train could be overstressed or damaged by overspeed, especially if the engine fights to light off. So 45 percent is the chosen threshold to protect the starter while ensuring a reliable light-off when ignition is introduced. Exceeding 40% but not yet reaching 45% can delay the light-off, while going to 50% or 55% risks overstressing the starter if light-off hasn’t happened.