Gearboxes for aircraft gas turbine engines

A method of operating a gas turbine engine for an aircraft, 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 gearbox that is configured to receive an input from the core shaft and provide an output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox comprising:
• a sun gear;
• a plurality of planet gears surrounding and engaged with the sun gear;
• and
• a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin,
• wherein the internal or external sliding surface of the journal bearing has a surface coating,
• wherein a fan tip loading is defined as dH/Utip2, where dH is an enthalpy rise across the fan and Utip is a velocity of the fan tip, and the fan tip loading at cruise conditions is in a range of from 0.28 J kg−1/((m s−1)2) to 0.37 J kg−1/(m s−1)2),
• wherein the method comprises operating the engine at maximum take-off conditions such that a specific loading multiplied by a sliding speed for each journal bearing is greater than around 240 MPa m/s,
• and wherein the specific loading at maximum take-off conditions is greater than 5 MPa.