United Flight 233, change to 747

So, I’m on this flight tomorrow(10/5) from IAD-SFO and I noticed today it was changed from a 777 to a 747. Can anyone tell me why they did this? Also are they doing this on my flight tomorrow? If so, what happens to our current seat assignments, since there is a different layout?

It can be done for a number of reasons.

For example, they may need an extra 747 in IAD as one may have gone out of service there or the 747 is coming from heavy maintenance in SFO. Or there may have been a major cancellation earlier in the day and the 747 swap was done to accommodate the passengers off the canceled flight.

Usually these swaps are 1-day only and don’t roll to the next day.

In general, your seat assignment will stay the same unless your seat no longer exists, at which point you will be reseated. I suggest you check-in online to confirm and possibly change your seats as early as possible.