When designing the Airbus A350-900, Airbus did a great job of focusing on creating a plane that is both fuel efficient and comfortable for passengers. The aircraft is powered by two Rolls-Royce Trent XWB engines, making it one of the most fuel-efficient medium- to long-haul planes in operation today. The plane also boasts a spacious cabin with many amenities, including wide seats, the latest in-flight entertainment systems, and improved air quality thanks to the aircraft's carbon-fiber construction.

Airbus also did well in making the plane as lightweight as possible. By utilizing advanced materials such as carbon-fiber reinforced plastic and titanium alloys, the company was able to reduce the aircraft's weight significantly, resulting in better fuel economy and improved performance.

Where Airbus could do better is in the design of the engines. While the Trent XWB engines are powerful and efficient, they are also quite expensive, making the aircraft more expensive to purchase and operate. Additionally, the aircraft is relatively loud, especially during takeoff and landing, which can be uncomfortable for those in the vicinity of the aircraft.

Overall, the Airbus A350-900 is a well-designed aircraft that offers great fuel efficiency, a comfortable cabin, and improved performance. With a few modifications, Airbus could make the aircraft even better by reducing engine cost and noise levels.