Method and system for reducing hot soakback

A method for cooling an auxiliary power unit, the method comprising:

• discontinuing fuel delivery to a combustor of the auxiliary power unit;
• supplying power to a starter to rotate a starter shaft;
• and
• translating rotational motion of the starter shaft to a shaft of the auxiliary power unit to rotate a compressor stage and a turbine stage of the auxiliary power unit to circulate air within the auxiliary power unit until a temperature of the auxiliary power unit is below a low limit temperature threshold.

A system for preventing hot soakback in an auxiliary power unit, the system comprising:

• a starter motor;
• a compressor having at least one stage;
• a turbine having at least one stage;
• a shaft connected to the at least one stage of the compressor and the at least one stage of the turbine;
• a gearbox for connecting the starter motor to the shaft;
• a temperature sensor;
• and
• a controller for:
• receiving information from the temperature sensor;
• and
• instructing the starter motor to rotate when the temperature sensor senses a temperature above a low limit temperature threshold;
• wherein the gearbox translates rotation of the starter motor to the shaft to rotate the at least one stage of the compressor and the at least one stage of the turbine to circulate air within the auxiliary power unit in response to the controller when the temperature sensor senses the temperature above the low limit temperature threshold in order to reduce hot soakback.