Can Air Act As "Ground" For Electrical Circuits?
In airplanes, the wings have these small outlets that act as 'ground'. Ideally used when the lightening strikes (from what I've read). So when flying, airplanes do use Air as 'ground'. Does it only hold true when the potentials are *VERY HIGH* - tens of thousands of volts? What are the other conditions in which air can be used as electrical 'ground'?