How fast does the boeing 747 fly?

Every 747, from the -100 of 1970 to the 747-8 of 2011, carries essentially the same high-speed wing, swept 37.5 degrees at the quarter chord. Boeing sized it for a long-range cruise near Mach 0.85, about 900 km/h (490 kn) true airspeed at 35,000 ft (10,700 m), and the figure hardly moved across four decades of new engines and stretched fuselages. The 747-8, the last passenger and freighter variant, is quoted at a typical cruise of Mach 0.855, while the maximum operating limit sits at Mach 0.90 to 0.92 depending on the model.

Above roughly 8,000 m crews stop watching indicated airspeed and start watching Mach number, because what limits the aeroplane is how close the airflow accelerating over the upper wing comes to the speed of sound. Push past the design point and local shock waves form, drag climbs steeply and fuel burn rises far faster than the gain in speed. The speed of sound also falls with temperature: at the roughly -55 °C of the cruise levels, Mach 0.85 is near 900 km/h, whereas the same Mach number at sea level would be close to 1,040 km/h.

Passengers experience ground speed, which is true airspeed plus or minus the wind, and over the North Atlantic the jet stream can add or subtract well over 100 km/h. That is why an eastbound crossing is routinely an hour shorter than the westbound leg on the same route. Block times also absorb taxi, a climb of twenty minutes or more, air traffic control speed restrictions below 10,000 ft and a descent flown well under cruise speed, so the average speed gate to gate is always lower than the cruise figure quoted for the type.