score:9
Did a contract at a major Australian airline, where I was required to fly on specific planes on specific days.
Even up to 30 min before, our own internal systems might show one plane, and then engineering or Ops would switch them.
So the first point, is especially on busy routes, you can't always guarantee which plane you'll be on.
As for the seat plan - correct, you can't fit x passengers on a plane with less than x seats. Those passengers might be bumped to a later flight. That's assuming it was a full plane though - might just be fewer empty seats.
We used to use flightradar24 and flightaware if we didn't have access to our own internal applications.
But even when I had those, and knew which plane I wanted, there wasn't a guarantee. Even had a 737 switched out for a 330. Happens :/
Upvote:2
Delta's Dublin to JFK flight changes from a 767 to an A330 starting next Friday, the 31st of January. This change was announced back in May of 2019.
Whilst looking at the flight history is often a good indication of the type of plane that will fly future flights, they do change over time, however in general these changes will be reflected on the carriers website well in advance (generally months ahead of time) to avoid any issues like those you've stated around different numbers of seats being available/different seat numbering/etc.
It is always possible that the aircraft type will change very close to the flight, especially when there is bad weather as the airline shuffles flights to use which aircraft are available, but this is rare.