Abstract: An emergency power system may provide hydraulic and electrical power to an aircraft in the event of a failure of the aircraft's primary control power system. The system may be constructed as a ram air turbine in which a single ram air fan may drive both a hydraulic pump and an electrical generator. A unique gearbox may incorporate compound gearing to permit the pump and the generator to be driven at different speeds. Thus the pump and the generator may be driven at their respective optimum speeds. The pump and the generator may be detachably mounted on a gearbox that supports the ram air fan. The detachable mounting of the pump and generator may accommodate ease of maintenance of these items. The gearbox may be provided with a ground testing port through which rotational testing force may be introduced to a shaft that supports the ram air fan. This may permit ground level testing of the system. Ground level testing may reduce a need to perform periodic in-flight testing of the system.