Originally Posted by
Catusa
I have never heard an airline say that the seatback couldn't support the extra-weight only the problem with seat space.
I have actually had to deal with a similar problem in the past. A passenger weighing ~300kg could not be accommodated on one of our flights due to the seat loading limits (which were in the 250kg range). That passenger was also physically unable to pass through either the aisle of the aircraft or an overwing type III exit, making them a serious liability in the case of an emergency.
We eventually required that the passenger provide a doctor's note confirming that they had sufficient mobility (either with or without assistance of an attendant) to be able to evacuate the aircraft in an emergency. They were unable to provide this.