August 2003, Iberia, MAD-JFK. A340-300, EC-GGS.
Boarded the plane (they were boarding in zones, and I was one of the last to go through in my zone - and got upgraded to biz as a consequence
) normally. 60 minutes later we're still sitting on the tarmac and the jetway is still connected and (speculating, not sure how the system works) the A/C was being fed from the ground. The captain finally announces why we're still waiting - seems that Iberia somehow made a mistake (in his words "In the 25 years I've been flying with Iberia this is the first time this has happened") and the F/O allocated to the flight arrived JFK-MAD the same morning and couldn't possibly be flying with us. Well - 20 minutes later we got our spare F/O
D.