Which statement best defines an Integrated Drive Generator (IDG) and its key function?

• A. A generator with built-in regulation that maintains constant voltage and frequency despite engine speed variations and load changes
• B. A standalone generator without regulation that follows engine RPM
• C. A device that converts DC to AC for load balancing
• D. A backup battery used during generator faults

Answer: (A)

An Integrated Drive Generator provides stable aircraft electrical power by combining a generator with internal regulation and a constant-speed drive. The built‑in regulator adjusts excitation to keep the output voltage steady as load changes, while the constant‑speed drive keeps the generator spinning at a set speed so the frequency remains constant even when engine RPM varies. This combination is what lets the system deliver reliable 400 Hz power regardless of how the engine speed or electrical load fluctuates.

A description of a standalone generator without regulation would permit voltage and frequency to drift with engine speed and load, which IDGs are specifically designed to avoid. A device that converts DC to AC describes an inverter, not an IDG. A backup battery is not a generator at all.