Originally Posted by
Back_of_the_Bus
I can understand the regulations but at the same time it sure seems crazy for that to be the policy for checking a carry-on at the gate. There's no change in total weight when a bag that was intended as a carry-on get checked.
But the average weight for (pax + carry-on) is calculated on the assumption that the carry-ons all fit. The size of the bins limits the average carry-on that can be brought on board. Moving a carry-on to the hold increases the "carry-on" capacity and the average calculation is no longer valid.