Reliable gearbox for gas turbine engine

A gas turbine engine for an aircraft comprising:

• an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor;
• a fan located upstream of the engine core, the fan comprising a plurality of fan blades;
• and
• a gearbox arranged to receive an input from the core shaft and to output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox comprising a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the planet gears are mounted, the planet carrier having an effective linear torsional stiffness and the gearbox having a gear mesh stiffness between the planet gears and the ring gear and a gear mesh stiffness between the planet gears and the sun gear, and wherein:
• a gear mesh stiffness between the planet gears and the sun gear is in the range from 1.20×109 N/m to 1.60×1010 N/m;
• and
• the gear mesh stiffness between the planet gears and the ring gear multiplied by the gear mesh stiffness between the planet gears and the sun gear is less than 1.5×1019 N2m−2.