The primary source of AC electrical power is the ___.

• A. Engine Driven Integrated Drive Generator
• B. APU Generator
• C. External Power Source
• D. DC Generator

Answer: (A)

Engine-driven integrated drive generators provide the primary AC power because they are connected to the engines and deliver regulated three-phase 400 Hz AC throughout flight. As long as the engines are running, these generators supply power to the aircraft’s electrical buses, keeping voltage and frequency stable even as engine speed varies. The integrated drive generator is designed specifically for this role, combining the generator with a drive mechanism that maintains consistent frequency.

The other sources serve as backups or alternatives rather than the normal supply. The APU generator can supply power when the engines are not running or when additional capacity is needed, but it’s not the standard primary source during flight. An external power source is used on the ground when plugged into ground power, not in normal airborne operation. A DC generator provides direct current, which then must be converted to AC if needed, so it isn’t the primary source of AC power.