What is idle Ng speed for the PT6E-67XP?

• A. 64.5%
• B. 60%
• C. 66%
• D. 68%

Answer: (A)

Idle Ng speed is the engine’s gas generator speed when the engine is idling but still providing enough power to drive accessories and bleed air. For the PT6E-67XP used on the PC-12 NGX, the engine control system (FADEC) targets a precise idle Ng to keep the core spinning just enough to stay stable and ready for any load, while keeping fuel burn and temperatures reasonable.

The value of 64.5% Ng is the specification chosen by the engine designers as the optimum idle point. It’s high enough to ensure stable compressor operation and to supply the electrical and pneumatic loads at idle without risking flameout or excessive fuel flow. Values like 60% would generally be too low to reliably support idle electrical/bleed demands and could invite unstable idle, while higher values like 66% or 68% would increase fuel burn and temperatures without providing additional necessary stability at idle. Therefore, 64.5% is the correct target because it represents the calibrated balance for this engine at idle.