Aviation has high standards. This applies also to Aircraft maintenance practices, which includes testing safety systems. Air driven generator test machine powers plane air driven back up generator. Minimum requirements for powering the generator are 8000 rpm and 13,5 kW. The electricity produced powers planes essential systems in case of primary source failure. In work we manage to calculate the test machine for flow, pressure and efficiency. We compared two types of hydraulic pumps, constant flow and variable flow pump on the same test machine.