Airframe Electrical 1 Practice Test

What frequency do most aircraft power systems use, and what is a common AC voltage level?

50 Hz AC; 230 VAC 400 Hz AC; commonly 115V or 115/200 VAC 60 Hz AC; 120 VAC 800 Hz AC; 208 VAC

Correct Answer:

400 Hz AC; commonly 115V or 115/200 VAC

Explanation:

High-frequency AC power is used because it lets generators and transformers be much smaller and lighter, which is crucial for aircraft. The standard operating frequency in most aircraft power systems is 400 Hz. For voltage, the common level is about 115 V AC, with some installations using 115/200 VAC in a three‑phase setup. This combination keeps the power hardware compact while supplying sufficient power for avionics and other systems. Frequencies like 50 Hz or 60 Hz would require larger, heavier equipment, and 800 Hz isn’t the normal standard today; 208 VAC is more typical of building power than aircraft.

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