spare aircraft
Don't forget JET2 own there planes so don't have lease payments to make so they don't have to fly the planes in winter months if they are going to make a loss
Unlike thomson or thomas cook who send about 6-8 aircraft each on lease to skyservice during the winter months as these aircraft are leased and they need to make money during the quiet months.
Come august u won't find jet2 with a spare aircraft sitting around.
TOM and TCX may have a back up aircraft but only one.
I'm sure that last summer tcx had to charter other airlines when they had tech aircraft!