What ensures the turbine is protected from overheating during the start process in the APU fuel system?

The correct answer highlights the specific design features that are integrated into the APU (Auxiliary Power Unit) fuel system to prevent overheating of the turbine during the startup process. Provisions for over temperature protection are critical safety measures that monitor the temperature of the turbine and activate countermeasures if it begins to exceed safe operating levels.

These provisions typically include sensors that provide real-time temperature data, and automated systems that adjust fuel flow or implement other cooling measures as necessary. By having such mechanisms in place, the system can automatically react to potential overheating situations, maintaining operational integrity and preventing damage to the turbine.

In contrast, while pressure sensors and temperature regulation mechanisms play important roles in the overall operation of the APU, they do not specifically address the proactive measures needed for overheating protection as robustly as dedicated over temperature protection mechanisms do. Manual fuel valve adjustments also do not provide the same level of automation or reliability as systems designed specifically for temperature safeguarding.