Air Transat squeezes the seat width to 16.5" while AC is closer to 18". It makes a difference. Taking 1.3 inches off 8 seats still doesn't leave enough for a full seat, so the aisles are narrower too because Air Transat has 3-3-3 seating in most of the cabin while other airlines, including Air Canada, have 2-4-2. The 2-4-2 arrangement is tight and adding one more seat to every aisle makes for about as bad as it gets. The 31 inch spacing is beat by Ryanair with a 30 inch spaceing. I was on a Delta 2-4-2 in a middle seat for a long flight. It was not pleasant. Making it narrower would have meant that the fat guy on the aisle would have take up even more of my space.