How high does a Boeing 747 fly?

A 747 in regular service climbs after takeoff to an initial cruise level usually between 9,000 and 11,000 m (FL290-FL360), and as it burns fuel and loses weight it requests higher levels in 600 m (2,000 ft) steps, a procedure known as a step climb. On long flights, the final hours are often spent between 11,500 and 12,500 m (FL380-FL410). The service ceiling, the maximum altitude at which the aircraft retains a useful rate of climb, is around 13,700 m (45,100 ft) on the 747-400 and 13,100 m (43,100 ft) on the 747-8, though it's rarely reached with a commercial load.

At high altitude the air is less dense, which reduces aerodynamic drag and improves engine fuel burn, but it also limits available lift and thrust. For a given weight, every 747 has an optimal altitude at which the margin between stall speed and maximum operating speed, known as the coffin corner, remains safe. The cabin is also pressurized to an equivalent altitude of about 2,400 m (8,000 ft), and the fuselage structure is certified for a specific pressure differential that sets the upper limit.

The final altitude also depends on air traffic control, which assigns odd or even levels based on heading, and on the jet stream: eastbound routes try to catch it, westbound routes try to avoid it. A typical London-New York flight, for instance, crosses the Atlantic at levels between FL330 and FL390. Convective storms can top 15,000 m, so the 747, like any commercial jet, flies around them rather than over them.