What is the purpose of the box heater in a BAK-14 support system?

The correct answer identifies the purpose of the box heater in a BAK-14 support system, which is to protect the air cylinder from freezing moisture. This is essential in ensuring that the air cylinder operates effectively regardless of ambient temperatures. Cold weather can lead to moisture freezing within the air cylinder, which could impede its functionality and performance.

By including a heating mechanism, the system ensures that any moisture is kept in a liquid state, thus preventing the formation of ice. This is particularly important in maintaining the reliability of equipment used in outdoor environments where temperature fluctuations can occur.

The other options, while they may involve related concepts of support systems, do not accurately describe the specific function of the box heater in this context. For instance, ventilation and runway drying pertain to entirely different processes, and heating hydraulic fluid is a separate concern that is not the primary function of the box heater in this specific application.