The cruising speed of a Boeing 737, one of the world's most common commercial aircraft, is typically around Mach 0.78 to 0.79, which translates to approximately 530 mph (850 km/h) or 460 knots at a standard cruising altitude of 35,000 feet. This speed can vary slightly depending on the specific model—for instance, the newer 737 MAX series is designed for slightly better aerodynamic efficiency compared to the older 737 Next Generation (NG) models like the -800. It is important to note that "ground speed" (how fast the plane moves relative to the earth) can be significantly higher or lower than this "airspeed" due to the influence of the jet stream; a strong tailwind can push a 737's ground speed over 600 mph, while a headwind can slow it down considerably. Pilots adjust the "cost index" in the flight computer to balance speed with fuel efficiency, meaning the plane may fly slightly slower on a short-haul route to save fuel or faster if the flight is running behind schedule.