Gearboxes for aircraft gas turbine engines

A gearbox for an aircraft gas turbine engine, 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, with the aircraft gas turbine engine operating at maximum take-off conditions, an eccentricity ratio, E, of each journal bearing is a function of a temperature T of oil flowing into the journal bearing, such that E>AT+B where A is 0.0015/° C. and B is 0.69, the eccentricity ratio being defined as 1-2Hmin/c, where Hmin is a minimum oil film thickness between the internal and external sliding surfaces and c is the diametral clearance of the journal bearing.