Originally Posted by
cperciva
Most trivially, if the plane is swapped out for a smaller one due to mechanical problems, lots of people with selected seats are likely to get bumped.
I remember this happening at NRT a few years back when the scheduled A330 to YVR was replaced by a 767 - AFTER check-in had commenced.
Utter chaos at the gate as many seats had to be reallocated!!!
This is one reason to research what metal is used on a specific route and ensure that your seat selection exists on both
Another thing is to check-in as early as possible on intercontinental longhauls.