Patent ID: 8424280

Claim:
A gas turbine engine arrangement comprising a first gas turbine engine, a power unit, a differential gearbox and at least one electrical generator, the differential gearbox having a first input drive, a second input drive and an output drive, wherein the differential gearbox comprises a sun gear, a plurality of planet gears, and an annulus gear, wherein the planet gears mesh with the sun gear and the annulus gear and the planet gears are rotatably mounted on a carrier, wherein the first input drive is affixed to one of the sun gear, the annulus gear, or the carrier, wherein the second input drive is affixed to one of either the sun gear or the annulus gear and is not affixed to the same structure as the first input drive, wherein the output is affixed to the carrier or the annulus gear and is not affixed to the same structure as either the first input drive or the second input drive the first gas turbine engine being an aircraft gas turbine engine, the power unit comprising a second gas turbine engine, the second gas turbine engine being an auxiliary power unit, the output drive of the differential gearbox being arranged to drive the at least one electrical generator, the first gas turbine engine being arranged to supply power to the first input drive of the differential gearbox, the power unit being arranged to supply power to, or remove power from, the second input drive of the differential gearbox, a first brake is provided between the first input drive and the first gas turbine engine, the first brake being operable to prevent rotation of the first input drive if the first gas turbine engine and/or the first input drive fails, a second brake is provided between the second input drive and the second gas turbine engine, the second brake being operable to prevent rotation of the second input drive if the second gas turbine engine and/or the second input drive fails, a clutch or a fluid coupling is operable to allow the second gas turbine engine to start the first gas turbine engine, the clutch or the fluid coupling being provided between the first input drive and the first gas turbine engine or between the second input drive and the second gas turbine engine, and the output drive has a brake operable to prevent rotation of the output drive to allow the second gas turbine engine to start the first gas turbine engine.