How high does a Boeing 737 fly?

A 737-800 or 737 MAX 8 on a two-hour flight typically cruises between 10,000 and 11,900 m (FL330-FL390), a level it reaches about 20 to 25 minutes after takeoff. The flight management computer proposes the optimal altitude based on weight and forecast conditions, and air traffic control confirms or adjusts it to maintain separation from other aircraft. On routes of less than an hour, many airlines plan cruise levels of 8,000-9,500 m: climbing to a higher level would consume almost the entire flight time without saving fuel.

When Boeing redesigned the 737 in the 1990s, the Next Generation series (-600, -700, -800 and -900) received a new, larger wing with greater fuel capacity, and more powerful CFM56-7 engines. That combination raised the certified maximum altitude from 37,000 ft (11,300 m) to 41,000 ft (12,500 m), a figure the 737 MAX retains with its LEAP-1B engines. The limit is set by cabin pressurization, which is maintained at an equivalent altitude of about 2,400 m (8,000 ft), and by aerodynamic margins: at higher altitudes, stall speed and maximum speed converge, and the aircraft has less spare thrust available for maneuvering.

With a light load, for example on a positioning flight or near the end of a long leg, a 737 may request FL410 to climb above turbulence or traffic. With the aircraft full and tanks loaded, however, the maximum level attainable on the first leg of the flight is usually closer to FL350. Storms are flown around, not over, since their tops can exceed 15,000 m.