A system for supplying compressed air to a main engine starter motor, comprising: an auxiliary power unit including a compressor section and a turbine section, the compressor section including adjustable inlet guide vanes that are moveable to a plurality of inlet guide vane positions; a main engine start conduit coupled to receive compressed air from the compressor section and supply the compressed air to the main engine starter motor; a surge control valve in fluid communication with the main engine start conduit, the surge control valve responsive to valve position commands to move between a fully-closed position and a plurality of open positions between the fully-closed and a fully-open position; and an APU control unit in operable communication with the APU and the surge control valve and configured to control the APU, the inlet guide vanes, and the surge control valve, the APU control unit configured to selectively control at least the inlet guide vanes and surge control valve using first or second inlet guide vane control logic (302, 304) and first or second surge control valve control logic (306, 308), respectively, wherein: when the first inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand signal, when the second inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand schedule, when the first surge control valve logic is used, the surge control valve is commanded to repeatedly move to only a fully-closed position and a fully-open position, and when the second surge control valve logic is used, the surge control valve is commanded to one of the plurality of open positions between the fully-open position and a minimum open position, wherein the minimum open position is a position between the fully-closed position and the fully-open position and is commanded to the fully-closed position only when maximum flow to the main engine starter motor is commanded. an auxiliary power unit including a compressor section and a turbine section, the compressor section including adjustable inlet guide vanes that are moveable to a plurality of inlet guide vane positions; a main engine start conduit coupled to receive compressed air from the compressor section and supply the compressed air to the main engine starter motor; a surge control valve in fluid communication with the main engine start conduit, the surge control valve responsive to valve position commands to move between a fully-closed position and a plurality of open positions between the fully-closed and a fully-open position; and an APU control unit in operable communication with the APU and the surge control valve and configured to control the APU, the inlet guide vanes, and the surge control valve, the APU control unit configured to selectively control at least the inlet guide vanes and surge control valve using first or second inlet guide vane control logic (302, 304) and first or second surge control valve control logic (306, 308), respectively, wherein: when the first inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand signal, when the second inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand schedule, when the first surge control valve logic is used, the surge control valve is commanded to repeatedly move to only a fully-closed position and a fully-open position, and when the second surge control valve logic is used, the surge control valve is commanded to one of the plurality of open positions between the fully-open position and a minimum open position, wherein the minimum open position is a position between the fully-closed position and the fully-open position and is commanded to the fully-closed position only when maximum flow to the main engine starter motor is commanded. when the first inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand signal, when the second inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand schedule, when the first surge control valve logic is used, the surge control valve is commanded to repeatedly move to only a fully-closed position and a fully-open position, and when the second surge control valve logic is used, the surge control valve is commanded to one of the plurality of open positions between the fully-open position and a minimum open position, wherein the minimum open position is a position between the fully-closed position and the fully-open position and is commanded to the fully-closed position only when maximum flow to the main engine starter motor is commanded.