On a busy day there’s atleast 1x B752 and 1x B738 spare.Jet 2 never seem to reach to movement levels of Ryanair and easyjet despite the higher number of based a/c. Their schedules are never as tight as the other 2 carriers and the A330's will require longer turn-round times. Also, I'm not sure if they have 1 or more spare a/c based.