I understand that 400Hz, 26Vrms power is found in a lot of aviation equipment. But how common is it? Is it in every plane and every instrument or is it restricted to certain sectors, like military, commercial, or private planes?

Is it used a lot in ground applications to power aviation equipment, like in a workshop/lab setting?

The reason I ask is that I'm trying to gauge interest in a small 400Hz, 26Vrms power supply for the benchtop (plug it into regular 60Hz 120V power). From what I can see, these are hard to find below a few thousand dollars.


2 Answers 2


In modern military and commercial aviation, aircraft power is 3-phase 115V at 400Hz (AC), and 28V DC. This is standard just about everywhere.

AC power is 3-phase 115V AC at 400Hz (alternating current). When the engines are spinning, this power is produced by onboard generators (alternators) feeding redundant power buses. On the ground, this is typically sourced from a ground power unit (GPU). During emergencies, AC power may be produced by an auxiliary power unit (APU).

DC power is provided by converting a portion of the 115V AC power to 28 volts DC for powering many of the avionics systems and charging the aircraft battery.

EDIT: My apologies, contrary to my original answer (I was thinking powering the cockpit displays/indicators mostly), a lot of navigation and pitch/attitude sensors take 26vac/400Hz input power. Rate gyros, compass, flux valve, etc. See, e.g. this section from a Cessna Citation.

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One example of 26VAC in aircraft is in old analog avionics (think DC10-era autopilot or navigation instruments), where it is used as a reference voltage for the signals transmitted using synchro. I think these days it is fairly uncommon.


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