The design cruising speed is Mach 2.35 (2,500 km/h) with partial afterburner in operation. The maximum speed of Mach 2.83 (3,000 km/h) is allowed to maintain no more than 5 minutes due to the danger of overheating of the airframe and fuel in the tanks. When the airframe temperature reaches 290 °C, the warning lamp lights up, and the pilot must reduce airspeed. The use of a partial afterburner and a cruising flight altitude 19,000–21,000 m makes it possible to have a range only 230 km less than when flying Mach 0.9 at altitudes 9,000–10,000 m. The maximum altitude of flight without an afterburner in operation is 12,000 m. The poor fuel consumption in the subsonic regime, and hence range, is due to the engines having extremely low pressure ratio of just 4.75 at subsonic speeds. The specific fuel consumption (SFC) of the engines is 1.12 in cruise and 2.45 with afterburners. For comparison purposes, this is 50% worse in cruise than the first generation of F100 engines from the F-15 Eagle, but the SFC with afterburners is actually nearly equal, despite the F100 being a far newer engine design.