Final answer:
To prevent an APU from exceeding its max EGT, a control unit with a fuel control system is used to regulate fuel, and an EGT limiter or overtemperature protection system may also be in place.
Step-by-step explanation:
The question refers to how the Exhaust Gas Temperature (EGT) of an Auxiliary Power Unit (APU) is regulated to prevent it from exceeding its maximum temperature during heavy loads. An APU is an engine used on aircraft to provide energy for various functions while the main engines are shut down.
To prevent the APU from overheating, a control unit is used, which typically includes a fuel control system that regulates the amount of fuel entering the combustion chamber, and thus, controls the EGT.
In addition, some systems may also have an EGT limiter or overtemperature protection that provides an additional layer of safety by automatically reducing fuel flow or shutting down the APU to prevent damage from excessive temperatures.