Rolls-Royce is pioneering the UltraFan engine family architecture containing a planetary gearbox in a power range of 15 to 80 megawatts. To increase the efficiency of the UltraFan, a planetary gearbox is introduced between fan and intermediate pressure compressor. This enables running the turbine to rotate faster and allows a reduced fan speed.

The load carrying capacity of spur gears may be calculated by ISO 6336 using influence factors. The face load factor considers the impact of the non-uniform load distribution over the face width. Even if the gears had perfect geometry, the load would not distribute uniformly along the contact lines. The face load factor depends on deformations of all parts of the containing gearbox and mainly of the teeth, gears and shafts as well as on manufacturing and assembly deviations.