An earth for a lightning protector doesn't have to be just a stake in the ground. For buildings they are sometimes an underground mesh or ring around the building to help dissipate the charge so as not to cause damage to building foundations.
What I've noticed is that the easiest path to ground is usually someone touching (or wearing a headset attached to) an aircraft. Surely an earth cable would help, given the only other path to ground is through thick rubber tyres.