Turbine engine gearbox

A method of designing a gas turbine engine comprising:

• providing a fan;
• providing a fan drive turbine rotor to drive the fan through a gear reduction;
• and
• the gear reduction including at least two double helical gears in meshed engagement, each of the at least two double helical gears disposed to rotate about respective axes, and each of the at least two double helical gears having a first plurality of gear teeth axially spaced from a second plurality of gear teeth by a spacer, wherein each of the first plurality of gear teeth has a first end facing the spacer and each of the second plurality of gear teeth has a first end facing the spacer, with each first end of the first plurality of gear teeth being circumferentially offset from each first end of the second plurality of gear teeth.