Earthing, in the traditional sense, refers to connecting a device to a path of low electrical resistance, such as the earth. This is often called grounding but there is a subtle difference depending on the type of connection used (the earth wire and the neutral are two different wires).
& Grounding is a method of giving electricity the most effect way to return to ground via the service panel. You see current flows from the panel to the outlet or device to power it up. The neutral wire is the return path for unused current. The ground wire is an additional path for electrical current to return safely to the ground without danger to anyone in the event of a short circuit. In that instant, the short would cause the current to flow through the ground wire, causing a fuse to blow or a circuit breaker to trip.
Don't mistake the electrical ground to be 'mother earth ground' which is used for protection for humans against lethal shocks from the body metal of the equipment. The ground on electronic circuits mean just a ' Common return path" just like the common return path for the water used in your house in the kitchen sink, bathroom, toilets etc.
For most commercial jets, whilst in the air:
There's a main generator (and possibly backup generator) attached to each engine, one attached to the auxiliary power unit in the tail, and a battery and possibly an emergency battery. There's also a Ram Air Turbine, which is a small emergency air-powered generator which drops into the airflow when the main power sources fail.
On the ground, power can be supplied by the battery, the auxiliary power unit, or from an external ground power unit, or hookup to the airport's fixed ground power supply network.
common return isn't the same as an earth ground. But aircraft also have wicks that function as a static discharger to drain charge from them as they fly. Look for them on the trailing edges of wings and control surfaces. This doesn't reduce the potential to zero, but it keeps it from building up as far as it might..
I hope this article will help you..