During ground operations, IDG loads in excess of 41% require advancing thrust to a minimum of what N1 percentage?

• A. 25%
• B. 28%
• C. 30%
• D. 32%

Answer: (D)

When electrical demand is high on the ground, the engine must supply enough shaft power to drive the generator. The IDG pulls torque from the engine through the accessory gearbox, so as the load climbs beyond about 41%, idle-level engine speed isn’t enough to keep the generator up to speed and stable. Advancing thrust to a minimum N1 of 32% provides the necessary engine power to meet that electrical demand without risking a drop in generator output or engine instability. Values lower than that don’t give sufficient RPM to sustain the high IDG load, while 32% hits the practical threshold where the engine can comfortably support the generator.