General Authority of Civil Aviation (GACA) Aeronautical Information Publication (AIP) Practice Exam

What can cause the trim air valve to be commanded closed?

1. Excessive humidity in the cabin

2. Overheating of ducts

3. Faulty temperature gauges

4. High cabin altitude

The correct answer is: Overheating of ducts

The trim air valve is an essential component in aircraft environmental control systems, as it regulates the temperature of the air distributed to the cabin. When considering the situation under which the trim air valve might be commanded to close, overheating of the ducts is a crucial factor. If the ducts carrying the air become too hot, this could indicate a potential hazard that might compromise the safety and comfort of the cabin environment. In this context, the system would respond by closing the trim air valve to prevent the distribution of excessively hot air, thus protecting passengers from uncomfortable or dangerous conditions. This proactive measure helps maintain a safe operating environment within the aircraft. The other scenarios presented—excessive humidity in the cabin, faulty temperature gauges, and high cabin altitude—are significant operational issues but do not directly invoke a command to close the trim air valve in the same immediate manner as duct overheating. Instead, they might lead to other corrective actions or system adjustments but would not automatically result in the closure of the trim air valve.