Seldom is the 738 swapped in favour of the 733 - its more the other way round. The only time the 733 will take the place of a 738 is always dependant on the load factor. For example, If 60 people are due to fly, and 2 of those have booked extra legroom on a 738, it might be worth swapping in such case. Most of the time, aircraft swaps are in advance, and as mentioned, its usually an increase rather than a decrease. If there is high demand from Jet2holidays on a route operating a 733, then, in advance, the likelihood is that Jet2 are going to, if possible, unlock another 41 seats, if the demand is there.
