I did a search and only found older info on a few airlines. What I'm wonder is how many and of what kind of airplanes do airlines keep in back up for active use and also in "cottonballed" status as a FA referred to them once.

For example how many usable aircraft and and what kind do UA and CO individually have on call. Also if known how many in long term storage. I've been curious about this for awhile. I figure within the US CO has a few spare 737s but probably not a half dozen 777s hanging out and IAH and EWR. Not looking for speculation rather looking for some hard numbers.