United Airlines is reconsidering the cabin design for its 167 Boeing 737 Max 10 aircraft after years of certification delays left hundreds of planned lie-flat premium seats in storage. CEO Scott Kirby told CNBC that the seats do not fit other airplanes, while the airline has shifted its premium-cabin investment to a subfleet of Airbus A321neo narrow-body aircraft. United expects to receive its first Max 10s in summer 2027, but has not disclosed their final layout or routes.