Abstract: A multifunction integrated power unit (MIPU) (10) for use aboard aircraft provides the functions both of an auxiliary power unit and of an emergency power unit while being smaller, lighter, and less expensive than the two units it replaces. Additionally, the integration of both functions in a single unit allows elimination of duplicated service devices and a further reduction in size, cost, and weight in the aircraft itself. The MIPU (10) includes two turbine engines (12, 22) operable under differing conditions, an integrating gear box (34) receiving power from the two engines (12, 22) selectively, and a plurality of accessory devices (36, 38) receiving shaft power from either of the two engines (12, 22) via the gear box (34). The gear box (34) includes a power transfer unit (PTU) apparatus (108) which selectively delivers shaft power from one of the engines (12, 22) to the accessory devices (36, 38).