Gear down, 316 tonnes, three miles out. The runway is already doing the math.
Most people look at the six-wheel main landing gear bogie and see a bigger aircraft needing more rubber. The real reason runs deeper — literally into the pavement beneath the runway.
Airports are rated for load-bearing capacity using the ACN/PCN system, a framework developed by ICAO that governs which aircraft can legally operate on which surfaces. ACN — Aircraft Classification Number — measures the load a specific aircraft imposes on a given pavement type. PCN — Pavement Classification Number — is the airport's published limit. Exceed it, and you're accelerating pavement deterioration. Breach it repeatedly, and you lose access entirely.
More wheels don't reduce the aircraft's weight. They redistribute it. Spread the same mass across six contact points instead of four, and each point presses less hard into the surface. The A350-900 manages fine on four wheels at its 280-tonne MTOW. At 316 tonnes, the -1000 needed a sixth wheel per bogie to keep its ACN within the PCN limits of airports that weren't engineered for jets this heavy.
The engineering trade-off is real — six-wheel bogies add mechanical complexity and weight. But Airbus wasn't just solving a physics problem. It was solving a network economics problem.
The A350-900 and -1000 share a common type rating. Airlines bought the -1000 precisely because crews trained on the -900 could fly it without recertification, and routes could flex between variants overnight. That commonality only holds its commercial value if both aircraft can serve the same airports — not just the reinforced mega-hubs, but the secondary cities with aging tarmac and tighter pavement ratings.
Six wheels made that possible. Without them, the -1000 would have been a premium jet stranded at premium airports.