Airbus has gone on record saying that there should be a minimum standard for seat width on international flights and that width should be 18″.
Notice that Airbus has no opinion on seat pitch (think legroom) whatsoever.
The reason Airbus wants an 18″ standard is that it downgrades Boeing aircraft without impacting Airbus aircraft. Airbus tends to build its airplanes a touch wider than Boeing but not wide enough for another seat row. This means that Airbus is perceived as being a little bit more comfortable.
This comes at a cost, however. Airbus aircraft is typically heavier and has more drag on a per seat basis than Boeing aircraft which are really designed around a 17″ to 17.5″ seat width.
Boeing can claim a 10 abreast seating configuration for its 777 airplanes whereas Airbus has just a 9 abreast configuration for its A350 aircraft. If 18″ is the new standard, Airbus will remain 9 abreast but Boeing would have to downgrade its claims to 9 abreast.
The truth is that many airlines do operate the 777 in a 9 abreast configuration today. Some have gone to a 10 abreast configuration (and are largely despised for it.)
I can’t say that I disagree that an 18″ wide seat is far more appropriate for an international flight. Hey, let’s go whole hog and ask for 18″ wide seats with a minimum seat pitch of 32″ for an international flight.
It’s all academic anyway because there is zero enforcement authority for this anywhere.
It’s Airbus being an upstart and getting attention again. Positive attention that cost them not a single penny.