Apparatus indicated generally at 26 is incorporated within an aircraft. The apparatus 26 includes an electric motor 28, a first drive train 30 and a second drive train 32. The first drive train 30 provides drive from the electric motor 28 for one or more of the wheels 20, allowing the electric motor 28 to propel the aircraft when taxiing. The second drive train 32 provides drive from the electric motor 28 for an aircraft system which is operational at least when the aircraft is in flight. In this example, the electric motor 28 is illustrated using the second drive train 32 for driving a compressor 34 of the ECS 24, the compressor 34 being responsible for cabin pressurization during flight. A clutch 36 allows the drive train 30 to be connected or disconnected from the electric motor 28, thereby connecting or disconnecting the drive from the electric motor 28 to the wheels 20. The clutch 36 is controlled to disconnect the first drive train 30 when the aircraft is in flight. Thus, when the aircraft is in flight, the full output of the motor 28 is available for driving the compressor 34; when the aircraft is on the ground, the compressor 34 is not required or is less demanding, and surplus output of the motor 28 can be used for driving the wheels 20.