It's not just the airplane that needs earthing; If you are wearing a woollen jumper over a nylon shirt, you might just be at 10,000v relative to earth with the static build-up.
You can earth yourself when you grab hold of the nozzle, as I think the hose contains conductive material.
The size of the spark is largely dependant upon the size of the object which is charged. So you would have less Coulombs than the airplane, and the airplane would have less than the hangar doors (if they are insulated from ground.)
When I worked in Telecoms, we used to test the underground cable from Chester to Manchester, with a 500v Mega. It took an age to charge the cable up, and several minutes for the charge to decay.. Indicating that there was no fault or breakdown of its insulation.