[Milsurplus] Aircraft Electrical Question

[Jack Antonio]

This is concerning an aircraft using 120V 400 cycle
power. And I realize it may vary between aircraft,
so I'm wondering if there is "standard practice"
concerning this.

Is one side of the AC line grounded? Is the 120V
floating, or balanced with respect to ground?

If one side is grounded, do they use a single point
ground, or use the airframe as a return conductor?

Looking at some gear here in the shack that uses
400 cycle, which is what got me wondering.

Thanks

Jack Antonio WA7DIA/4