A gearbox 104 for an auxiliary power unit (APU) 100 includes a front side defining a generator interface 120 configured to be coupled to a generator 108, the front side further defining an oil pump and fuel control component interface 176 configured to be coupled to an oil pump 112 and fuel control component 160, and a starter interface 122 configured to be coupled to a starter 122. The gearbox 104 further includes a back side on an opposite side to the front side and configured to house a gear train 128; a bottom side defining an oil tank interface 126 configured to be coupled to an oil tank 114; and a debris conduit 148 extending from the generator interface 120 to the oil tank interface 126.