What is a key limitation regarding the use of trim air?

The key limitation regarding the use of trim air is that it should not be used on the ground. Trim air is used to manage cabin temperature by allowing for a more precise control of airflow, contributing to passenger comfort in flight. However, using trim air while the aircraft is stationary can lead to inefficiencies and potentially overcooling or overheating the cabin, as the environmental conditions may not be conducive for efficient trim air operation.

Moreover, on the ground, other systems are managing the environment, typically air conditioning or ground power systems, which are designed for such situations. Additionally, during ground operations, there may be safety protocols and operational procedures that discourage the use of certain systems to prevent any added complications or risks.

This understanding helps in ensuring that cabin comfort is managed correctly and safely according to the operational environment of the aircraft.