Service ceiling
Service ceiling is the maximum altitude at which an aircraft can still climb at a small, defined rate, in practice the highest cruising level it is certified to use. Most business jets are certified to 41,000–45,000 ft and the Gulfstream, Global, Falcon and Citation X families to 51,000 ft, well above the 35,000–41,000 ft where airliners cruise. Flying higher puts business jets above most weather and airline traffic, gives a smoother ride and more direct routings, and improves fuel efficiency. The trade-off is a stronger pressurisation system, which is why high-ceiling aircraft often also offer a lower cabin altitude.