Welcome onboard
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Aircraft changes do happen from time to time unfortunately. You don't say what dates you are flying, which departure airport and on which flight (number) so I can't check (there are several flights per week from the UK to Varadero), but if you've been notified of a change then is has been. You'll find lots of aircraft information on our What Aircraft? guide (link below). I know last Thursdays flight from Manchester to Varadero was changed to a 76W as I was at MAN on Friday morning when it landed so I assume it's the TCX051K/L you're on?
Darren