The Airbus A321XLR doesn't have unlimited range. It has a cliff.
At around 5,000km with a full passenger load, the payload-range curve turns sharply against you. Fuel mass crowds out payload mass — and on a narrowbody, there's nowhere to hide. Montreal to Dublin sits at approximately 5,110km great-circle. Air Canada has chosen to operate that route with an A321XLR starting May 2027, which means departing YUL with tanks near capacity and cabin revenue doing most of the heavy lifting.
The physics are unforgiving. The XLR's published maximum range is 8,700km, but that number assumes a light load. Push toward a full 180-seat configuration on a transatlantic sector and the usable range compresses fast. Crew, catering, and passenger bags all count. At YUL-DUB distances, the aircraft is operating close to its structural payload limit — not its range limit. The margin between those two constraints is where the business case either works or doesn't.
The economics only hold because the alternative is worse. Air Canada already serves Montreal-Dublin seasonally, historically with widebody equipment. A 787-9 burns roughly 30% more fuel per seat on medium-haul Atlantic sectors than the XLR. On a thin origin-and-destination market that never filled a widebody consistently, that unit cost gap was always the problem. Montreal-Dublin has largely survived on connecting traffic through London and Paris — demand that doesn't reward frequency or capacity.
Gauge down, and the math changes. A smaller aircraft needs fewer passengers to hit breakeven. Yield can soften without destroying the P&L. Seasonal flying becomes less of a gamble when you're not ferrying 250 empty seats across the ocean.
Air Canada isn't pioneering a concept here — it's executing one that Iberia, Norse, and others are stress-testing simultaneously. The narrowbody Atlantic isn't a theory anymore. It's a schedule.
The XLR was built to make thin routes viable; Montreal to Dublin will find out exactly how thin is too thin.