What is the N2 idle speed percentage range?

What is the N2 idle speed percentage range?

• A. 40-50%
• B. 50-60%
• C. 55-65%
• D. 60-70%

Answer: (C)

N2 idle speed is the high‑pressure spool speed the engine sits at when you’re idling. The FADEC or engine control holds N2 in a narrow band so the core stays stable and enough bleed air is available for systems, while still keeping fuel flow low and the engine ready to respond to throttle input. For the CRJ‑550’s engine, that idle window is centered around the mid‑50s to mid‑60s percent of maximum N2. The range 55–65 percent best reflects the typical operating band under varying conditions (temperature, altitude, bleed load). If N2 were allowed much lower, you risk instability or flameout; if it were much higher, idle would waste fuel and reduce efficiency. So 55–65 percent is the most representative idle range for this aircraft.

N2 idle speed is the high‑pressure spool speed the engine sits at when you’re idling. The FADEC or engine control holds N2 in a narrow band so the core stays stable and enough bleed air is available for systems, while still keeping fuel flow low and the engine ready to respond to throttle input.

For the CRJ‑550’s engine, that idle window is centered around the mid‑50s to mid‑60s percent of maximum N2. The range 55–65 percent best reflects the typical operating band under varying conditions (temperature, altitude, bleed load). If N2 were allowed much lower, you risk instability or flameout; if it were much higher, idle would waste fuel and reduce efficiency. So 55–65 percent is the most representative idle range for this aircraft.