For me it depends on the image, if there is a decent cloudscape or the aircraft is in a particularly dynamic angle then I will crop looser. However if it is just blue sky sky behind and the aircraft is in a standard angle etc. I see no reason to show much sky as you loose that lovely close detail and you don't particularly get any benefit from it. In short, I only do if it I feel it is worth doing it.
I have plenty of loose crops though around my gallery.