Airframe Electrical 2 Practice Test 2026

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Explain the difference between direct current (DC) and alternating current (AC) in aircraft electrical systems and where each is typically used.

DC is used for fixed-voltage power distribution (e.g., 28V) for most aircraft systems; AC may be used for specific loads or converted by power conversion equipment; many GA aircraft operate primarily on DC

Direct current provides a stable, fixed-voltage power supply that is ideal for the avionics and most loads on smaller aircraft. In general aviation, the standard is a 28-volt DC distribution system, with the battery and the generator feeding the DC bus directly or via rectification. This simple, robust arrangement keeps wiring and electronics reliable and uncomplicated.

Alternating current shows up where higher power is needed or where aircraft are designed around AC power. In larger airplanes, for example, power is distributed as AC (common values include 115 VAC at 400 Hz) to drive motors, environmental systems, and other heavy loads. On aircraft that do use AC, any loads not natively designed for AC are powered through inverters or other power conversion equipment that create the needed DC or AC form.

So, most GA aircraft operate primarily on DC (fixed voltage like 28V) with AC used only for specific loads or when power conversion equipment is employed to supply AC.

DC is used for high-power lighting; AC is used for all other systems

AC is used for fixed-voltage distribution (e.g., 28V) for most aircraft systems; DC may be used for specific loads

There is no distinction; DC and AC are interchangeable in aircraft