Geared gas turbine engine

An aircraft comprising a gas turbine engine, the gas turbine engine 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 diameter of the fan being ϕfan (m);
• and
• a gearbox that receives input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, wherein:
• a minimum number of rotor blades in any single rotor stage of the turbine is NTURBmin, NTURBmin being in a range of from 80 to 140;
• a lateral full-power reference noise measurement point is defined as a point on a line parallel to and 450 m from a runway centre line where an Effective Perceived Noise Level (EPNL) is a maximum during take-off of the aircraft to which the gas turbine engine is attached;
• the turbine comprises at least two axially separated rotor stages and has a rotational speed at the lateral full-power reference noise measurement point of WIrp rpm, WIrp being in a range of from 8000 rpm to 9500 rpm;
• and
• a low speed system parameter (LSS) is defined as:
• LSS=WIrp×NTURBmin×ϕfan
• where:
• 1.3×106 m·rpm≤LSS≤2.9×106 m·rpm.