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 a ratio of a length, L, of the internal and external sliding surfaces to a diameter, D, of the journal bearing is between around 1.1 and 1.4 and,
• wherein the journal bearing has a diametral clearance that is between 0.1% and 0.3%.