Overboooking probably accounts for most of these incidents, but in this particular case they had to switch to a slightly smaller plane due to mechanical issues.

Overboooking probably accounts for most of these incidents, but in this particular case they had to switch to a slightly smaller plane due to mechanical issues. So eliminating overbooking won't fix this problem completely. However, having a policy of not forcing passengers to relinquish seats they've already sat down in would...