Earthing of Electrical Equipment in an Aeroplane

It usually won't be a grounding chain hanging down to earth....

Obviously not !!!! Thats why curious about the alternate solution !!!

I might be totally all wet about this, but I would guess that the skin and entire structural frame should be continuously bonded, if they aren't already on account of being riveted together.

Are you sure about that?

It usually won't be a grounding chain hanging down to earth....

Might be if on the ground and fueling. It also won't be a wet kite string with a key in the middle and Ben Franklin on the far end, but he doesn't want to know what it isn't.

All electronic equipments have a common node in the circuit called earth.

heard about IT system of earthing. No connection of neutral to earth. (Any way which is not present)

As previously stated, the metal structure is bonded together. This requires special attention to components such as Ailerons, Rudder, and elevator and is usually done via a braided strap. If lightning strikes the airplane it must have a path through and then out of the structure.

Now consider an airplane with a fiberglass or composit structure. Usually there is a metal mesh made into the structure to provide that conductivity.

Antennas need a ground plane to prevent reflected power.

Some older aircraft I see sometimes have lighting that is failing due to corrosion preventing a return path to the battery.

Aircraft and cars are the same "earth" is chassis.

Though generally the fuselage (chassis) in a modern aircraft is not used as a "battery negative" current return.

I don't understand what you mean by "alternate arrangement".

What problems are you having? Or why are you asking?

Please down load a copy of Advisory Circular AC 21-99 Aircraft Wiring & Bonding.