A gas turbine engine for an aircraft. The engine including: an engine core with a turbine, a compressor, a fan located upstream of the compressor and including a plurality of fan blades, and a core shaft connecting the turbine to the compressor; a gearbox which receives an input from the core shaft and outputs drive, via a driveshaft, to the fan so as to drive the fan at a lower rotational speed than the turbine, the drive shaft and core shaft forming a shaft system.