Normally several "risers" of charge ascend, at the same time the main charge descends , or several threads of charge coalesce and descend. One lucky riser gets to meet the charge coming down first, and so gets the full current. The "Lightning strikes" that don't do much damage or that people walk away from I am pretty sure are un-fulfilled risers. Getting the main discharge is so much energy it's not going to just burn your bum.
A dirty great alloy fin (tailplane) sticking the air is a good start to a riser (much like a lightning rod). Given the plane is wearing rubber shoes, I too am not sure of the wisdom of connecting the (anti static) earth with a storm overhead. It certainly wouldn't be me connecting it.
Maybe some meteorologist will be along with the full sp shortly.