What is the primary source of power in large commercial aircraft?

• A. DC power
• B. AC power is the primary form of power
• C. Battery power
• D. Solar power

Answer: (B)

The main idea is that large commercial aircraft are designed around generating and distributing alternating current. Engine-driven generators (and the APU) produce three-phase AC power, typically at 400 Hz, which is then distributed to the aircraft’s electrical buses and essential systems. This AC power is used directly by many loads and is also converted to DC where needed for some avionics and other equipment. Batteries provide backup and start power, but they are not the primary source.

AC is preferred as the primary form because at 400 Hz the electrical equipment and transformers can be smaller and lighter, which is crucial for an aircraft. DC power has its role, but it is derived from the AC system via converters and used for certain subsystems or as backup. Solar power isn’t part of the standard aircraft power architecture.