The Boeing 737 sits unusually close to the aircraft apron, a design choice that traces its origins back to the 1960s, when many airports lacked jet bridges, high-loaders, and large amounts of ground service equipment. Keeping the jet’s fuselage low made boarding via the stairs easier, sped up baggage handling, and simplified maintenance on the aircraft. It also locked the aircraft into short landing gear and a tight space under the wing. Decades later, that constraint collided with a very modern demand for lower fuel burn. High-bypass turbofans deliver big efficiency gains, and their fans continue to grow in diameter.